C H A P T E R
II
Phase Transfer Assisted Permanganate Oxidations
DONALD
G. LEE
I. Introduction
II. The Phase Transfer Process
A. Phase Transfers from Aqueous Permanganate
B. Phase Transfer Utilizing Solid Permanganate
C. Phase Transfer Mechanisms
D. Use of Solid Supports for Permanganate Oxidations
E. Reactions in Micelles
III. Oxidation of Alkenes
A. Terminal Alkenes
B. Nonterminal Alkenes
IV. Oxidation of Alkynes
A. Nonterminal Alkynes
B. Terminal Alkynes
V. Oxidation of Arenes
VI. Oxidation of Alkanes
VII. Oxidation of Polycyclic Aromatic Hydrocarbons
VIII. Oxidation of Alcohols
IX. Oxidations of Phenols
X. Oxidation of Ethers
XI. Oxidation of Aldehydes
XII. Oxidation of Sulfur Compounds
XIII. Oxidation of Halides
XIV. Oxidation of Amines
1 4 7
1 5 2
152
162
166
167
167
1 6 8
1 6 8
I
7 3
1 8 2
1 8 2
1 8 5
16
8
1 9 0
192
1 9 3
1 9 6
1 9 9
2 0 1
2
01
2 0 3
2 0 4
I. Introduction
T h e use of p e r m a n g a n a t e as an oxidant for organic transformations has a
long a n d extensive h i s t o r y . It h a s been used b o t h as a selective oxidant a n d
as a scavenger to remove small a m o u n t s of organic material present as
c o n t a m i n a n t s in either water or air.
1
1
J. W. Ladbury and C. F. Cullis, Chem. Rev. 58, 403 (1958), and references therein.
147
Oxidation in Organic Chemistry, Part D
Copyright © 1982 by A c a d e m i c Press, Inc.
All rights of reproduction in any form reserved
I S B N 0-12-697253-2
148
DONALD G. LEE
The use of permanganate as a selective oxidant for a variety of reactions
has been reviewed by Stewart in a previous volume in this series. Other
reviews include those by A r n d t , F r e e m a n , W a t e r s , and L e e .
The purification of water by treatment with permanganate has been
discussed by a number of a u t h o r s and Posselt and Reidies have described
the removal of malodorus c o m p o u n d s from factory off-gases by use of a
permanganate scrubber.
The use of aqueous permanganate in syntheses is limited to the oxidation
of organic c o m p o u n d s that are at least partially soluble in water. If the
solubility is too low there is not sufficient contact between the oxidant and
the reductant at the interface and the rate of reaction is drastically reduced.
This problem has been illustrated by the work of Eastman and Q u i n n . They
showed that the alkane, 2,2,4-trimethylpentane, did not undergo an a p ­
preciable a m o u n t of oxidation at the tertiary hydrogen over a period of
several months in contact with aqueous permanganate, while the correspond­
ing alcohol, 2,4-dimethylpentan-2-ol, which contains a similar tertiary
hydrogen, was oxidized with a half-life of a b o u t 5 days under similar con­
ditions. The alcohol, because of its ability to hydrogen-bond with water, has
greater solubility in the aqueous phase and therefore came into more intimate
contact with the oxidant.
Consequently aqueous permanganate has found its greatest application
in the oxidation of organic c o m p o u n d s containing polar groups that provide
them with at least partial solubility in water. Stewart has tabulated these
reactions and described the mechanisms involved.
The classical way of overcoming the solubility problem has been by use
of polar organic solvent systems that will dissolve both reactants. Examples
of solvents that have been used include ethanol, tert-butyl alcohol, acetone,
pyridine, acetic acid, acetic anhydride, and trifluoroacetic acid. Some
representative reactions have been summarized in Table I.
2
3
4
5
6
7
8
9
2
2
3
4
5
6
7
8
9
R. Stewart, in "Oxidation in Organic Chemistry" (Κ. B. Wiberg, ed.), Part A, pp. 1-68.
Academic Press, New York, 1965.
D. Arndt, in "Methoden der Organischen Chemie, Houben-Weyl" (E. Muller, ed.). Thieme,
Stuttgart, 1975; D. Arndt, "Manganese Compounds as Oxidizing Agents in Organic
Chemistry." Open Court, La Salle, 1981.
F. Freeman, Rev. React. Species Chem. React. 2, 179 (1973).
W. A. Waters, "Mechanisms of Oxidation of Organic Compounds." Methuen, London, 1964.
D. G. Lee, "Oxidation of Organic Compounds by Permanganate Ion and Hexavalent
Chromium." Open Court, La Salle, 1980.
R. G. Spicher and R. T. Skrinde, J. Am. Water Works Assoc. 57, 472 (1965), and references
therein.
H. S. Posselt and A. H. Reidies, I ά EC Prod. Res. Dev. 4, 48 (1965).
R. H. Eastman and R. A. Quinn, J. Am. Chem. Soc. 82, 4249 (1960).
//. Phase Transfer Assisted Permanganate Oxidations
149
TABLE I
USE OF ORGANIC SOLVENT SYSTEMS FOR PERMANGANATE OXIDATIONS
Reactant
Solvent system
1,4-Cyclohexadiene
Cyclohexene
Methyl cinnamate
2,5-Dimethoxy-2,5-dihydrofuran
Aq.
Aq.
Aq.
Aq.
ewfo-Dicyclopentadiene
Aq. ethanol
Norbornene
Norbornene
4-Oxo-4-(2-xanthenyl)butyric acid
2-(4-Methoxyphenyl)cyclohexanone
Aq. /-butyl
alcohol
Aq. /-butyl
alcohol
Aq. acetone
Aq. acetone
Aq. acetone
3-Methyl-5-carbomethoxypentanal
Aq. acetone
2-Amino-2,4,4-trimethylpentane
1,2-Dimethylcyclopentene
Aq. acetone
Aq. acetone
(Z,Z)-2,6-Octadiene
Aq. acetone
3/?-Acetoxy-20-ketopregna5,16-diene
Methyl levopimarate
Aq. acetone
Butylamine
ethanol
ethanol
ethanol
ethanol
Aq. acetone
Product (% yield)
Ref.
4,5-Dihydroxycyclohexene (7)
cis-\,2-Dihydroxycyclohexane (33)
Phenylglyceric acid (67)
2,5-Dimethoxy-3,4-dihydroxytetrahydrofuran (37)
5-exo,6-e;c0-Dihydroxy-£Yii/0-3a,4,5,6,7,7ahexahydro-4,7-methanoindene (28)
2,3-e-*0,c7s-Dihydroxynorbornane (40)
10
11
12
13
Butanol (46)
15
1,3-Diformylcyclopentane (54-66)
4-Oxo-4-(2-xanthonyl)butyric acid (93)
6-Oxo-6-(4-methoxyphenyl)hexanoic acid
(70)
3-Methyl-5-carbomethoxypentanoic
acid (65)
2-Nitro-2,4,4-trimethylpentane (77)
c«-l,2-Dimethyl-l,2dihydroxycyclopentane (45)
m-2,5-Bis(hydroxyethyl)
tetrahydrofuran (32)
16α, 17a-Dihydroxy-3i?-acetoxy-20ketopregn-5-ene (40)
Methyl dehydroabietate (76)
14
16
17
13a
14
18
19
20
20a
21
22
(Continued)
1 0
1 1
1 2
1 3
1 3 a
1 4
1 5
1 6
1 7
1 8
1 9
2 0
2 0 a
2 1
2 2
K. A. Powell, A. L. Hughes, H. Katchian, J. F. Jerauld, and Η. Z. Sable, Tetrahedron 28,
2019 (1972).
M. F. Clarke and L. N. Owen, / . Chem. Soc., 315 (1949).
C. N. Ruber, Chem. Ber. 48, 823 (1915).
J. C. Sheehan and Β. M. Bloom, J. Am. Chem. Soc. 74, 3825 (1952).
D. Brewster, M. Myers, J. Ormerod, P. Otter, A. C. B. Smith, Μ. E. Spinner, and S. Turner,
J. Chem. Soc. Perkin 1, 2796 (1973).
K. Wiberg and K. A. Saegebarth, J. Am. Chem. Soc. 79, 2822 (1957).
S. S. Rawalay and H. Shechter, J. Org. Chem. 32, 3129 (1967).
A. M. El-Abbady, S. Ayoub, and F. G. Baddar, J. Chem. Soc, 2556 (1960).
E. R. Clark and J. G. B. Howes, J. Chem. Soc, 1152 (1956).
V. R. Mandapur, P. P. Pai, Κ. K. Chakravarti, U. G. Nayak, and S. C. Bhattacharyya,
Tetrahedron 20, 2601 (1964).
N. Kornblum, R. J. Clutter, and W. J. Jones, J. Am. Chem. Soc. 78, 4003 (1956).
P. D. Bartlett and A. Bavley, J. Am. Chem. Soc. 60, 2416 (1938).
D. M. Walba, M. D. Wand, and M. C. Wilkes, J. Am. Chem. Soc. 101, 4396 (1979).
G. Cooley, B. Ellis, F. Hartley and V. Petrow, J. Chem. Soc, 4373 (1955).
B. Marchand, Chem. Ber. 91, 405 (1958).
150
DONALD G. LEE
TABLE I (cont.)
Reactant
Solvent system
Heptafluoroisoquinoline
Aq. acetone
Phenylmethanesulfinamide
2,5-Dihydro-5-methyl-3,6-diphenyl1,2,4-triazine
4-Methyl-1 -(4-nitrophenyl)-5morphoHno-4,5-dihydro-v-triazole
8-Hexadecyne
5-Decene
3-Phenoxytoluene
2,5-Dimethylbiphenyl
2-Acetylbiphenylene
4-(2-Phenylvinyl)-6quinolinecarboxylic acid
2,8-Dimethyl-10-acetylphenoxazine
Aq. acetone
Aq. acetone
Aq. acetone
Aq.
Aq.
Aq.
Aq.
Aq.
Aq.
acetone
acetone
pyridine
pyridine
pyridine
pyridine
Aq. pyridine
Pregnenolone acetate
Aq. pyridine
3,5-Di-i-butyltoluene
1 -Phenyl-2-methyl-1 -propanol
1,2-Diphenyl-1,2bis(3,4-diethoxyphenyl)ethylene
2-Chloromethyl 4-methylphenyl
sulfide
Bis(2-keto-2-phenylethyl) sulfide
4-Aminophenyl 4-nitrophenyl sulfide
Oleic acid
Aq. pyridine
Acetic acid
Acetic acid
Cyclohexane
2 3
2 4
2 5
2 6
2 7
2 8
2 9
3 0
3 1
3 2
3 3
3 4
Acetic acid
Acetic acid
Acetic acid
Acetic
anhydride
Trifluoroacetic
acid
Product (% yield)
Ref.
2,5,6-Trifluoropyridine-3,4dicarboxylic acid (52)
Phenylmethanesulfonamide
5-Methyl-3,6-diphenyl-l,2,4-triazine (73)
23
4-Methyl-1 -(4-nitrophenyl)-5-(2-oxomorpholino)-4,5-dihydro-v-triazole (40)
8,9-Hexadecanedione (81)
5-Hydroxy-6-decanone (73)
3-Phenoxybenzoic acid (71)
2,5-Biphenyldicarboxylic acid (75)
2-Biphenylenylglyoxylic acid (49)
4,6-Quinolinedicarboxylic acid (76)
26
10-Acetylphenoxazine-2,8-dicarboxylic
acid (75)
Pregnane-3/?,5,6-triol-7,20-dione
3-acetate (26)
3,5-Di-/-butylbenzoic acid (73)
Phenyl isopropyl ketone (71)
2,3,6,7-Tetraethoxy-9,10diphenylphenanthrene (65)
2-Chloromethyl 4-methylphenyl
sulfone (83)
Bis(2-keto-2-phenylethyl) sulfone
4-Aminophenyl 4-nitrophenyl sulfone
9,10-Diketostearic acid (46)
33
39
40
41
Adipic acid (75)
42
R. D. Chambers, M. Hole, W. K. R. Musgrave, A. A. Storey, and B. Iddon, J. Chem. Soc. C,
2331 (1966).
H. Seiler and H. Erlenmeyer, Helv. Chim. Acta 40, 88 (1957).
C. M. Atkinson and H. D. Cossey, J. Chem. Soc, 1805 (1962).
L. M. Rossi and P. Trimarco, Synthesis, 743 (1978).
N. S. Srinivasan and D. G. Lee, J. Org. Chem. 44, 1574 (1979).
N. S. Srinivasan and D. G. Lee, Synthesis, 520 (1979).
French Pat. 1398558 (1964), The British Petrolium Co. Ltd., C. F. Forster.
Ε. K. Weisburger and J. H. Weisburger, J. Org. Chem. 23, 1193 (1958).
J. F. W. McOmie and S. D. Thatte, J. Chem. Soc, 5298 (1962).
A. P. Shroff, H. Jaleel, and F. M. Miller, J. Pharm. Sci. 55, 844 (1966).
R. Hazard, J. Cheymol, P. Chabrier, A. Sekera, and J. De Antoni, Compt. Rend. 252, 4166
(1961).
H. R. Nace and A. L. Rieger, J. Org. Chem. 35, 3846 (1970).
24
25
27
28
29
30
31
32
34
35
36
37
38
//. Phase Transfer Assisted Permanganate
Oxidations
151
Obviously, the use of organic solvent systems is limited to the oxidation
of those c o m p o u n d s that react m u c h more readily with permanganate than
does the solvent itself.
Another more recent a p p r o a c h involves the use of salts such as tetrabutyla m m o n i u m p e r m a n g a n a t e or benzyltriethylammonium p e r m a n g a n a t e
which, because of the organophilicity of the quaternary a m m o n i u m cations,
are soluble in nonpolar solvents. These salts may be prepared by adding a
solution of the corresponding quaternary a m m o n i u m halide to a solution
of potassium permanganate. However, caution should be exercised because
there have been reports of explosions associated with their u s e . Above a
certain temperature most quaternary a m m o n i u m permanganates spon­
taneously i g n i t e .
It is unnecessary, however, to prepare and isolate the quaternary am­
m o n i u m permanganates. They can be prepared in situ (without danger of
ignition) by reacting a quaternary a m m o n i u m halide ( Q X ~ ) with potassium
permanganate. Anion exchange [Eq. (1)] then produces a quaternary
a m m o n i u m ion pair that is soluble in n o n p o l a r solvents.
43
44
4 5
45a
+
Q X" + K M n 0 " ^ Q Mn0 " + K X"
+
+
+
4
+
4
(1)
This exchange usually takes place with a change of phase by the per­
manganate ion. Typically, the quaternary a m m o n i u m halide dissolved in an
organic solvent such as methylene chloride, is added to either solid K M n 0
or an aqueous solution of potassium permanganate. During the exchange,
the permanganate ion migrates to the organic phase and exists there as an
ion pair.
Quaternary p h o s p h o n i u m and arsonium salts can also be used as phase
transfer agents, as can both cyclic and acyclic polyethers. In the latter cases,
the polyether complexes the potassium ion causing it to become organophilic
4
3 5
3 6
3 7
3 8
3 9
4 0
4 1
4 2
4 3
4 4
4 5
4 5 a
M. G. J. Beets, W. Meerburg, and H. van Essen, Rec. Trav. Chim. Pays-Bas 78, 570 (1959).
H. A. Neidig, D. L. Funck, R. Uhrich, R. Baker, and W. Kreiser, J. Am. Chem. Soc. 72,
4617 (1950).
J. Gardent, Bull. Soc. Chim. Fr., 1049 (1962).
D. Klamann and H. Bertsch, Chem. Ber. 88, 201 (1955).
J. D. Loudon and L. B. Young, J. Chem. Soc, 5496 (1963).
T. Naito, S. Nakagawa, and K. Takahashi, Chem. Pharm. Bull. 16, 148 (1968).
H. P. Jensen and Κ. B. Sharpless, J. Org. Chem. 39, 2314 (1974).
R. Stewart and U. A. Spitzer, Can. J. Chem. 56, 1273 (1978).
T. Sala and Μ. V. Sargent, J. Chem. Soc. Chem. Comm., 253 (1978).
H. J. Schmidt and H. J. Schafer, Angew. Chem. Int. Ed. Engl. 18, 68 (1979).
J. A. Morris and D. C . Mills, Chem. Ind. 446 (1978); H. Jager, L. Lutolf, and M. W. Meyer,
Angew. Chem. Int. Ed. Engl. 18, 786 (1979); H. J. Schmidt and H. J. Schafer, Angew.
Chem. Int. Ed. Engl. 18, 787 (1979).
H. Karaman and D. G. Lee, unpublished results.
152
DONALD G. LEE
and thereby produces an ion pair that is soluble in organic solvents [Eqs.
(2) and (3)].
This phase transfer technique has been applied extensively to a variety of
synthetic procedures in addition to oxidation reactions. N u m e r o u s review
a r t i c l e s and three b o o k s on the subject are available. In the next section
we will examine the actual phase transfer process, with particular attention
to permanganate. In succeeding sections the use of permanganate ion
(dissolved in organic solvents) as an oxidant for a variety of organic com­
pounds will be considered.
46
4 7
II. The Phase Transfer Process
A. PHASE TRANSFERS FROM AQUEOUS PERMANGANATE
The effectiveness of any particular phase transfer system will be dependent
on the ability of that system to bring the permanganate ion into solution in
the organic phase. (It should be noted that, whereas most reactions will
probably be more efficient when the concentration of permanganate in the
nonaqueous phase is high, some selective oxidations may require a low, but
constant concentration of oxidant.)
4 6
4 7
Ε. V. Dehmlow, Chem. Technol. 5, 210 (1975); Angew. Chem. Int. Ed. Engl. 13, 170 (1974),
ibid. 16, 493 (1977); R. A. Jones, Aldrichimica Acta 9, 35 (1976); G. W. Gokel and H. D.
Durst, Synthesis, 168 (1976); G. W. Gokel and W. P. Weber, J. Chem. Ed. 55, 350, 429
(1978).
W. P. Weber and G. W. Gokel, "Phase Transfer Catalysis in Organic Synthesis." SpringerVerlag, New York, 1977; C. M. Starks and C. Liotta, "Phase Transfer Catalysis, Principles
and Techniques." Academic Press, New York, 1978. Ε. V. Dehmlow and S. S. Dehmlow,
"Phase Transfer Catalysis." Verlag Chemie, Weinheim, West Germany, 1980.
//. Phase Transfer Assisted Permanganate
Oxidations
153
It is well k n o w n that potassium permanganate exists in an ionic form when
dissolved in water. However, when a quaternary a m m o n i u m permanganate
salt dissolves in an organic solvent it exists predominantly as an ion pair.
This can be seen from the calculations described in B r a n d s t r o m . H e has
shown that for two spherical ions, Q a n d X " , situated in a large sphere of
solvent with dielectric constant Z>, the probability (P) of finding Q a n d X "
separated by a distance between r a n d r + dr is given by Eq. (4), where R
is the radius of the solvent sphere, k is the Boltzmann constant, a n d Τ is
the t e m p e r a t u r e .
48
+
+
49
(4)
Assuming that the sphere is large enough to give ideal behavior even
when the concentration of ions is increased, the total probability (dH) of
finding the center of an ion, X " , at a distance between r a n d r + dr from the
center of a n ion Q when m o r e ions are present is given by Eq. (5).
+
(5)
A plot of dH/dr against r passes through a minimum at r = e /2DkT
(Fig. 1). The significance of this figure can be understood in the following way:
if the ions can approach each other sufficiently close so that the distance
between their centers is less than e /2DkT, the attractive forces will be strong
enough t o cause ion pair formation. If the ions cannot approach each other
sufficiently close, the attractive forces will be smaller a n d solvation (resulting
in the formation of individual ions) will occur. T h e fact that the point at
which ion pair formation occurs is inversely dependent o n the dielectric
constant of the solvent means that ion pairing is much more likely t o occur
in nonpolar solvents with low dielectric constants. T h e values of e /2DkT
for several solvents have been collected in Table II.
F r o m this table one can determine if a particular quaternary a m m o n i u m
permanganate will exist in a particular solvent as an ion pair or as free ions.
F o r example, since the ionic radii of tetramethyl and tetraoctyl a m m o n i u m
ions have been found to be a b o u t 3 A a n d 6 A , respectively, it can be seen
that the value of r for the a m m o n i u m permanganates will be substantially
2
2
2
50
4 8
4 9
5 0
A. Brandstrom, Adv. Phys. Org. Chem. 15, 267 (1977).
N. Bjerrum, K. Dan. Vibensk. Selsk. Mat.-Fys. Medd. 7, 1 (1926); C. A. 22, 1263 (1928);
see also, M. Szwarc, in "Ions and Ion Pairs in Organic Reactions" (M. Szwarc, ed.), Vol. 1.
pp. 1-26. Wiley (Interscience), New York, 1972.
S. R. C. Hughes and D. H. Price, J. Chem. Soc. A, 1093 (1967); B. S. Krumgal'z, Russ. J.
Phys. Chem. 45, 1448(1971).
154
DONALD G. LEE
FIG. 1. Plot of dH/dr against r where dH is the probability of finding the center of an ion,
X", at a distance between r and r + dr from the center of an ion, Q . (Reprinted with permission from Brandstrom . Copyright by Academic Press, London.)
+
48
less than e /DkT in solvents with low dielectric constants (accepting the
value of about 2.5 A for the ionic radius of the permanganate i o n ) . Consequently, it can be assumed that when permanganate ion is transferred into
an organic solvent with the aid of a phase transfer agent, it exists for all
practical purposes as an ion pair.
The concentration of permanganate ion pair that can be obtained in the
nonaqueous phase will be dependent on at least three factors: (1) the structure
of the organic cation; (2) the polarity of the organic phase; and (3) the
nature of the anions involved.
2
5 1
5 1
G. J. Palenik, Inorg. Chem. 6, 503 (1967).
//. Phase Transfer Assisted Permanganate
Oxidations
155
TABLE II
SOLVENT PARAMETERS"
Solvent
Dielectric
constant
Water
Methanol
Ethanol
Acetone
1,2-Dichloroethane
Methylene chloride
Chloroform
Diethyl ether
Benzene
Carbon tetrachloride
78.5
32.5
24.3
20.5
10.17
8.9
4.7
4.2
2.27
2.22
e /2DkT
2
(A)
3.57
6.8
11.5
13.7
27.6
31.5
60
67
123
126
Reprinted with permission from Brandstrom. Copy­
right by Academic Press, London.
a
48
1. STRUCTURE OF THE CATIONS
A high concentration of anion in the organic phase is promoted by use of
a phase transfer agent which provides a highly organophilic cation. This was
illustrated clearly by the work by Gibson and W e a t h e r b u r n when they
studied the distribution of a number of quaternary salts between water and
four different organic solvents (chloroform, methylene chloride, 1,2-dichloroethane, and 2,2'-dichlorodiethyl ether). The concentrations of quater­
nary salt in each phase was measured spectrophotometrically and expressed
as a ratio (a) of the concentration in the organic phase over the concentration
in the aqueous phase, i.e., α = [ Q X ] r g / [ Q X ] a q - Some of the results which
they obtained using methylene chloride as the solvent have been sum­
marized in Table III.
An examination of these distribution ratios indicates that they increase
with the length of the alkyl chain. Eq. (6), where η is the number of methylene
groups in the alkyl chain and α' is the ratio for the methyl c o m p o u n d , was
found to correlate the data.
52
0
log α = 0.5« + log a'
(6)
Somewhat similar studies on the effectiveness of various phase transfer
agents with potassium permanganate have also been reported. O k i m o t o and
S w e r n have published data from which the ratios summarized in Table
53
5 2
5 3
N. A. Gibson and D. C. Weatherburn, Anal. Chim. Acta 58, 149, 159 (1972).
T. Okimoto and D. Swern, J. Am. Oil Chem. Soc. 54, 862A (1977).
156
DONALD G. LEE
T A B L E III
DISTRIBUTION RATIOS FOR VARIOUS QUATERNARY SALTS
BETWEEN METHYLENE CHLORIDE AND WATER
0,6
a-Values
Cation
Ph PCH
Ph AsCH
Ph PCH CH
Ph PCH CH CH
Ph PCH CH CH CH CH
+
3
3
+
3
3
+
3
2
3
3
2
2
3
3
2
2
2
+
2
+
3
c
CI"
C10 "
C10 "
Br"
Br0 "
I~
0.02
0.02
0.01
0.03
0.22
0.40
0.53
0.90
2.1
5.6
9.5
11.0
40
60
70
0.08
0.24
0.25
0.68
2.3
0.04
0.04
0.08
0.22
1.0
1.7
1.9
4.9
4.3
8.5
3
4
3
Data from Gibson and Weatherburn.
Temp. = 25°C, ionic strength = 0.1, initial concentration of quaternary salt in aqueous
phase = 5 χ 10" Μ.
a = [QX] /[QX] .
a
52
b
3
c
org
aq
TABLE I V
EXTRACTION OF PERMANGANATE ION FROM WATER INTO BENZENE
OR METHYLENE CHLORIDE USING PHASE TRANSFER AGENTS"
Phase transfer agent
[QMn0 ]
4
Tetrabutylphosphonium chloride
Hexadecyltrimethylammonium
bromide
Tetrabutylammonium bromide
Propyltrioctylammonium bromide
Benzyltriethylammonium chloride
Tetraethylammonium bromide
a
b
c
C6H6
/[Mn0 -]
4
aq
[QMn0 ]
4
CH2
ci /[Mn0 -]
2
99
0.03*
252
105
14
96
0.02"
0
100
43
9.4
0.26
4
aq
c
From Okimoto and Swern.
A precipitate formed in the aqueous phase; 40-80% of the permanganate unaccounted for.
About 20% of the permanganate unaccounted for.
53
IV m a y be calculated. Their a p p r o a c h was to extract 25 ml of 0.02M a q u e o u s
K M n 0 with 25 ml of a 0.03M solution of phase transfer agent in benzene
or methylene chloride, and to estimate the concentration in each phase
iodometrically.
4
Herriott and P i c k e r have also reported results obtained when solutions
of water containing 1.00 m m o l of K M n 0 were extracted with an equal
volume of benzene containing 1.5 m m o l of various phase transfer agents.
Their results are summarized in Table V.
5 4
4
5 4
A. W . Herriott and D. Picker, Tetrahedron Lett., 1511 (1974).
//. Phase Transfer Assisted Permanganate
Oxidations
157
TABLE V
EXTRACTION OF WATER CONTAINING 1.00 MMOL OF PERMANGANATE ION WITH AN
EQUAL VOLUME OF BENZENE CONTAINING VARIOUS PHASE TRANSFER AGENTS"
a
b
Phase transfer agent (mmol)
Amount of permanganate
transferred (mmol)
Tetramethylammonium chloride (1.51)
Triethylbenzylammonium chloride (1.63)
Tetrabutylammonium bromide (1.54)
Tetrabutylphosphonium chloride (1.54)
Cetyltrimethylammonium bromide (1.53)
Aliquat 336" (1.52)
Sodium dodecyl sulfate (1.50)
0.00
0.84
0.95
0.96
0.86
0.93
0.00
From Herriott and Picker.
Trioctylmethylammonium chloride (General Mills).
54
In a somewhat more thorough study of the distribution constants associated with permanganate phase transfer reactions, K a r a m a n prepared
solutions of permanganate salts in various organic solvents by stirring a
solution of phase transfer agent over finely powdered potassium permanganate, removed an aliquot and extracted it with an equal volume of
water. The equilibrium involved in this process would be defined by Eqs.
(7) and (8).
5 5
Q\
q
+ Mn0
^Q Mn0
[Q MnQ -]
+
4
D
or8
[Q ]a [Mn0 -]
=
+
q
(7)
+
4 a q
4
aq
4 o r g
[Q+MnQ -]
4
[Mn0 -]
4
or8
2
1
a q
'
The values of K (Table VI) were then obtained by plotting [Q M n 0 " ]
against [ M n 0 " ]
for several concentrations of phase transfer agents; both
concentrations were determined spectrophotometrically.
The results obtained from all of these studies indicate that to a first
approximation the most important factor is the size of the quaternary ion.
In fact, there is a rough correlation between the total number of carbons in
the quaternary ion and the corresponding equilibrium constant.
It may also be noted that the two most readily available, and inexpensive,
commercial phase transfer agents, Adogen 464 (Ashland Chemicals) and
Aliquat 336 (General Mills) exhibited excellent transferability with respect
to permanganate. Both of these agents are quaternary a m m o n i u m chlorides
containing three large alkyl groups (8 to 10 carbons) and a methyl group.
+
D
4
2
4
5 5
a q
H. Karaman, M. S. Thesis, Univ. of Regina, Regina, Canada, 1979.
o r g
158
DONALD G. LEE
TABLE VI
EQUILIBRIUM CONSTANTS FOR THE DISTRIBUTION OF QUATERNARY AMMONIUM
PERMANGANATES BETWEEN WATER AND METHYLENE CHLORIDE.
Phase transfer agent
Number
of carbons
Tetramethylammonium chloride
Tetraethylammonium bromide
Phenyltrimethylammonium bromide
Benzyltrimethylammonium bromide
Benzyltriethylammonium bromide
Tetrabutylammonium bromide
Benzyltributylammonium chloride
Cetyltrimethylammonium bromide
Adogen 464
Aliquat 336
4
8
9
10
13
16
19
19
25-31
25-31
K
0
b
D
0
54
24
66
957
oo
1489
00
00
00
° From Karaman.
K = [ Q M n 0 ] / [ M n 0 ~ ] , 0 indicates that all of the permanganate
was in the aqueous phase while oo indicates that it was all in the organic phase.
55
b
+
-
D
4
2
o r g
4
a q
It is possible that their effectiveness is due to the high organophilicity imparted by the three long alkyl chains combined with the small methyl group
which would allow the permanganate ion to be closely associated with the
positive n i t r o g e n .
K a r a m a n also examined the distribution of permanganate ion between
aqueous and organic phases in the presence of polyethers. His results
(Table VII) indicate that crown ethers are substantially more effective than
the corresponding linear polyethers in promoting phase transfers. This is
likely true because the energy requirement associated with the process
would be decreased by use of a preformed cyclic ether. Such an assumption
is consistent with the results reported by C r a m and his co-workers; they
found that preorganization of the binding sites in 18-crown-6 caused it to
form a stronger complex with cations than the corresponding acyclic polyether, dimethylhexaethylene glycol. With the ter/-butylammonium cation,
the difference in free energy was found to be about 6 keal/mol.
Although the linear polyethers in Table VII contain three different types
of terminal groups ( C H 0 — , H O — and ( C H ) S i — ) , the most important
factor appears to be the length of the chain. F r o m Fig. 2, where a plot of
48
5 5
5 6
3
5 6
3
3
E. P. Kyba, R. C. Helgeson, K. Madan, G. W. Gokel, T. L. Tarnowski, S. S. Moore, and
D. J. Cram, J. Am. Chem. Soc. 99, 2564 (1977). J. M. Timko, S. S. Moore, D. M. Walba,
P. C. Hiberty, and D. J. Cram, J. Am. Chem. Soc. 99, 4207 (1977).
//. Phase Transfer Assisted Permanganate
Oxidations
159
TABLE VII
EQUILIBRIUM CONSTANTS FOR THE DISTRIBUTION OF POTASSIUM
PERMANGANATE BETWEEN WATER AND METHYLENE CHLORIDE
IN THE PRESENCE OF POLYETHERS"
Polyether
Average
molecular
weight
15-Crown-5
18-Crown-6
CH (OCH CH ) OCH
CH (OCH CH ) OCH
CH (OCH CH )„OH
CH (OCH CH )„OH
CH (OCH CH )„OH
(CH ) Si(OCH CH )„OSi(CH )
(CH ) Si(OCH CH ) OSi(CH )
(CH ) Si(OCH CH ) OSi(CH )
220
264
178
397
350
550
750
462
487
662
3
2
2
M
3
3
2
2
n
3
3
2
2
3
2
2
3
2
2
3
3
3
3
3
3
2
2
2
n
3
3
3
3
2
2
w
3
3
From Karaman.
= [Q Mn0 "]
sium cation complex.
a
2
47
128
0.77
1.46
1.63
2.71
4.10
1.46
1.45
2.48
55
b
+
4
org
/[Mn0 "]
4
2
aq
, where Q is a polyether-potas+
5 h
4
8
12
Average
16
20
η
FIG. 2. Plot of K against chain length for various polyethers. Key: A, CH (OCH CH )„: H ; · , CH (OCH CH ) OH;
(CH ) Si(OCH CH OSi(CH ) .
55
D
3
3
3
2
2
n
3
3
2
2
3
3
2
2
160
DONALD G. LEE
K against η (the number of ethylene glycol units) has been reproduced, it
can be seen that there is a direct relationship between the two parameters.
Hence it would seem that greater organophilicity or stronger binding is
associated with longer chains.
D
2.
SOLVENT POLARITY
F r o m a study of the distribution ratios for a number of phase transfer
agents in four solvents (chloroform, methylene chloride, 1,2-dichloroethane
and 2,2 -dichlorodiethyl ether) Gibson and W e a t h e r b u r n concluded, in
part, that
/
52
. . . the effect of the solvent on the extraction is quite small, very much smaller than the
effects of the cation discussed above, and the anion discussed below. However, definite
solvent effects on the extraction may be seen, although there is little correlation between
extracting ability and bulk properties such as dielectric constant.
On the other hand, B r a n d s t r o m has reported constants for the ex­
traction of tetrabutylammonium bromide into 41 different solvents and
noted that they vary by factors of greater than 10 . H e also noted that the
magnitudes of these constants do not correlate with the dielectric constants
of the solvents, but that the best solvents were those containing two or
more d o n o r groups on the same or adjacent carbons (e.g., C 1 C H C N ,
C 1 C H C H C N , C H N 0 , and C H C 1 C H C 1 ) . It was assumed that the
d o n o r groups would solvate the cations, while the acidic hydrogens adjacent
to these groups would accommodate the anion and that tetrabutylammonium
bromide would consequently be extracted as a solvent-separated ion pair.
Okimoto and S w e r n have examined the extraction of permanganate ion
from water into either benzene or methylene chloride with six different phase
transfer agents. Their results (Table IV) indicated that permanganate ion was
more readily extracted into methylene chloride than benzene in almost
every case.
This conclusion was also confirmed by K a r a m a n when he examined the
distribution coefficients for a variety of phase transfer agents in five different
solvents: methylene chloride, chloroform, benzene, carbon tetrachloride,
and pentane. His results (some of which have been summarized in Table
VIII) indicate that methylene chloride is the most satisfactory solvent and
that the distribution coefficients are, in general, lower in solvents with low
dielectric constants.
In many cases he found that the permanganate ion did not distribute
between two phases; it either remained completely in the aqueous phase
or extracted completely into the organic phase (within detectable limits, at
least). Again, the practical observation was made that Adogen 464 and
48
6
2
2
2
3
2
2
2
53
5 5
//. Phase Transfer Assisted Permanganate
Oxidations
161
T A B L E VIII
EQUILIBRIUM CONSTANTS FOR THE DISTRIBUTION OF PERMANGANATE SALTS
BETWEEN WATER AND VARIOUS ORGANIC SOLVENTS '*'
0
Carbon
tetraBenzene chloride Pentane
Phase transfer agents
Methylene
chloride
Tetramethylammonium chloride
Tetraethylammonium bromide
Tetrabutylammonium bromide
Phenyltrimethylammonium bromide
Benzyltrimethylammonium bromide
Benzyltriethylammonium bromide
Methyltriphenylphosphonium bromide
Dodecyltriphenylphosphonium bromide
18-Crown-6
Dimethylpolyethylene glycol 178
Dimethylpolyethylene glycol 397
Methoxypolyethylene glycol 350
Methoxypolyethylene glycol 550
Methoxypolyethylene glycol 750
Adogen 464
Aliquat 336
d
d
d
d
54
00
24
63
960
00
00
128
0.77
1.46
1.63
2.71
4.10
00
00
0
00
0
28
132
00
00
116
0
0.54
0.41
0.76
0.88
00
00
d
d
d
0
0
d
d
d
d
d
d
d
d
d
d
d
d
d
00
0
0
0
0
0
0
00
00
00
0
0
0
0
0
0
00
00
0
0
0
0
0
0
00
00
c
c
c
c
c
Chloroform
d
d
From Karaman.
Equilibrium constant = [ Q M n 0 ~ ] / [ M n 0 ~ ] . 0 indicates all of the oxidant was in
the aqueous phase, oo that it was all in the organic phase.
This number indicates the average molecular weight.
Phase transfer agent insoluble.
a
55
b
+
2
4
org
4
aq
c
d
Aliquat 336 were both effective phase transfer agents for all solvents
investigated.
In summary, all evidence indicates that methylene chloride is generally
the most useful solvent. Besides the fact that it solvates permanganate salts
well, it is resistant to oxidation and, because of its low boiling point, it can
be easily removed by vacuum distillation from the reaction products.
3. N A T U R E OF THE A N I O N
Gibson and W e a t h e r b u r n have reported that anions are extracted from
aqueous solutions into organic solvents with the aid of phase transfer
catalysts in the following general order:
52
M n 0 " > C10 ~ > S C N " > I" > C10 " > N 0 " > Br~ > B r 0 " > C P
4
4
3
3
3
This order has also been confirmed by other w o r k e r s and indicates that
permanganate will be extracted in preference to almost all other anions. Its
47
162
DONALD G. LEE
ease of extraction is probably associated with the fact that it has a low
charge to volume ratio and that the charge is extensively delocalized. This
would decrease the extent of hydration and thus reduce the energy required
to transfer it from an aqueous solution into an organic solvent.
B. PHASE TRANSFERS UTILIZING SOLID PERMANGANATE
Permanganate can also be brought into solution in organic solvents by
adding solvent containing a phase transfer agent to finely ground potassium
p e r m a n g a n a t e . An exchange takes place [Eq. (9)] and permanganate dis­
solves in the form of an ion pair.
57
KMn0
+ Q X
+
4(s)
( o r g )
-
Q Mn0
+
4
(org)
+ KX
(S)
(9)
This procedure has advantages in certain cases where it is important to
maintain anhydrous conditions. F o r example, it is known that nonterminal
alkynes undergo a cleavage reaction if the organic solvent is wet from being
in contact with aqueous permanganate. However, under anhydrous con­
ditions the cleavage is suppressed and good yields of diketones may be
obtained.
It has also been observed that some phase transfer agents function better
in the absence of water. For example, dimethyloctaethylene glycol does not
extract potassium permanganate from an aqueous solution into benzene,
but it will solubilize solid anhydrous potassium permanganate in the same
solvent.
M a n y of the same factors which control the effectiveness of transfers from
aqueous solutions also influence the solid to solution transfers.
58
59
1. STRUCTURE OF THE PHASE TRANSFER AGENTS
K a r a m a n has observed that b o t h quaternary a m m o n i u m and phosphonium salts as well as polyethers can be used to solubilize anhydrous
permanganate in organic solvents. He measured the concentration of
permanganate that could be obtained from the treatment of finely ground
potassium permanganate with limited a m o u n t s of phase transfer agent in
various solvents, and calculated ratios [Eq. (10)] which indicate the effective­
ness of the phase transfer agents in solubilizing permanganate.
5 5
_ [Q MnO -]
+
4
K
5 7
5 8
5 9
0 r g
* ~ [crx-iLau,
( 1 0 )
A finely ground (3μ) form of potassium permanganate is available from the Carus Chemical
Company under the trade name "Cairox M."
D. G. Lee and V. S. Chang, J. Org. Chem. 44, 2726 (1979).
D. G. Lee and V. S. Chang, J. Org. Chem. 43, 1532 (1978).
//. Phase Transfer Assisted Permanganate
Oxidations
163
TABLE IX
SOLUBILITY RATIOS FOR PERMANGANATE
IN METHYLENE CHLORIDE SOLUTIONS"
a
5
Phase transfer agents
K?
Methyltriphenylphosphonium bromide
Ethyltriphenylphosphonium bromide
H-Propyltriphenylphosphonium bromide
/i-Butyltriphenylphosphonium bromide
Dodecyltriphenylphosphonium bromide
0.86
0.97
0.91
0.89
0.85
From Karaman.
A = [Q Mn0 -] /[Q X-]
55
+
r
+
4
elI
IIIIIi
..
l
His results indicated, a m o n g other things, that there is a certain specificity
of phase transfer agents for each solvent. F o r example, Table IX shows that
the magnitude of K passes through a m a x i m u m as the alkyl group in
alkyltriphenylphosphonium bromides is varied from methyl to dodecyl.
The K values for polyethers in methylene chloride are quite interesting.
Crowns which contain 6 oxygens and 12 carbons in the ring were found to
have K values close to unity, thus indicating their capacity to solubilize
approximately one mol of K M n 0 per mol of crown in solution. In the
case of acyclic polyethers, the K values were found to vary from 0.007 to
5.84 depending on the chain lengths (Fig. 3). Values greater than unity suggest
that these c o m p o u n d s are capable of complexing m o r e than one potassium
ion per mol of phase transfer agent as depicted in Fig. 4. O t h e r polyethers
are also k n o w n to be capable of complexing more than one mol of potassium
ion per mol of phase transfer a g e n t .
r
r
r
4
r
60
2. SOLVENT EFFECTS
The effectiveness of phase transfer agents under these conditions was
found to be markedly dependent on the nature of the s o l v e n t . F o r example,
it was noted that whereas methyltriphenylphosphonium bromide was a
satisfactory phase transfer agent with methylene chloride and chloroform,
dodecyltriphenylphosphonium bromide was far more effective for use in the
less polar solvents such as benzene and carbon tetrachloride (Table X).
55
F. Vogtle and V. Heiman, Chem. Ber. I l l , 2757 (1978); G. Weber and W. Saenger, Angew.
Chem. Int. Ed. Engl. 18, 227 (1979); F. Vogtle and E. Weber, Angew. Chem. Int. Ed. Engl.
18, 753 (1979).
164
DONALD G. LEE
6
5
4
3
2
20
40
60
80
Average
100
120
η
FIG. 3. Plot of K against chain length for various polyethers. Key: A , CH (OCH CH )„OCH ; · , CH (OCH CH )„OH; • , (CH ) Si(OCH CH ) OSi(CH3)3.
55
r
3
3
3
2
2
3
3
2
2
2
2
n
Tetrabutylammonium bromide is also quite effective for solubilizing
permanganate in dichloromethane, chloroform and benzene, but less satis­
factory in carbon tetrachloride and pentane. Adogen 464 and Aliquat 336
were found to be quite good phase transfer agents, although the concentra­
tions produced in pentane were rather low.
3. IDENTITY OF THE A N I O N
Equation (9) involves an exchange of anions between a solid phase and a
solution. Hence it is not surprising that the identity of the anion in the phase
Mn04
FIG. 4. Complexation of two moles of K M n 0 by a single acyclic polyether.
4
//. Phase Transfer Assisted Permanganate
Oxidations
165
TABLE X
SOLVENT EFFECTS ON PERMANGANATE SOLUBILITY RATIOS"
Phase transfer agents
Methylene Chlorochloride
form
Methyltriphenylphosphonium
bromide
Dodecyltriphenylphosphonium
bromide
Tetrabutylammonium bromide
Aliquat 336
Adogen 464"
d
" From Karaman.
Benzene
Carbon
tetrachloride
Pentane
c
0.86
0.74
c
c
0.85
0.58
1.03
0.89
c
1.04
0.82
0.82
0.58
0.84
0.88
1.04
0.84
0.90
0.11
0.88
0.91
c
0.07
0.08
55
K = [Q Mn0 -L /[Q X-]i„iua..
b
+
+
t
c
d
4
G
The phase transfer agent is insoluble.
Methyltrialkyl ( C - C ) ammonium chloride.
8
10
transfer agent can effect the magnitude of the K values. Table X I contains
some examples that illustrate this phenomena. Although the n u m b e r of
examples in this table is too small to reach any general conclusions, it appears
that the greatest effects are present when chloroform is used as the solvent.
On the basis of the available evidence, it seems that quaternary a m m o n i u m
chlorides are substantially more effective phase transfer agents in chloroform
than are the corresponding bromides.
r
TABLE XI
THE EFFECT OF ANIONS ON PERMANGANATE SOLUBILITY RATIOS"
Phase transfer agents
Tetrabutylammonium chloride
Tetrabutylammonium bromide
Benzyltriethylammonium chloride
Benzyltriethylammonium bromide
° From Karaman.
55
"/ς = [Q Mn0 -L,/[Q X-]i„m..+
+
4
c
The phase transfer agent is insoluble.
Methylene Chloro­
form
chloride
0.92
1.04
0.97
0.93
0.97
0.58
0.96
0.45
Benzene
0.78
1.04
c
c
Carbon
tetra­
chloride
Pen­
tane
0.11
0.11
<
c
c
c
c
c
166
DONALD G. LEE
C. PHASE TRANSFER MECHANISMS
In the earliest descriptions of phase transfer reactions it was assumed that
the exchange of anions took place in the aqueous phase as d e p i c t e d :
47
R—Y + Q X "
R—X + Q Y " organic phase
+
+
i-
Y" + Q X " «
+
f
X~ + Q Y " aqueous phase
+
Alternatively, the exchange of anions could take place across the interface
without migration of the phase transfer agent into the aqueous phase.
R
Y(org) +
Q
+
X
( o r g ) ~** R
X(org) +
Q
+
Y
(org)
Q Y (org) + X ( a q ) ~ ' Q X (org) + Y ( a q )
+
>
+
The possibility that the latter mechanism may be important in many
reactions has been demonstrated by Landini, Maia, and M o n t a n a r i .
Using liquid membranes, they showed that the transport of anions from one
phase into another did not require the simultaneous transfer of a quaternary
a m m o n i u m or phosphonium ion.
The experiments were carried out in a " U " system in which two organic
phases (A) and (B) were separated by an aqueous solution of sodium bro­
mide. When quaternary cations such as tetrabutylphosphonium bromide
and tetrapropylammonium bromide, which are partly soluble in water, were
dissolved in solution A and the system stirred, partitioning between A a n d
Β was observed. However, if more organophilic cations such as hexadecyltributylphosphonium bromide or tetraoctylammonium bromide were used, n o
transfer from A to Β could be detected. Hence, it would appear that these
two cations lack sufficient solubility in water to be transferred. They were
found, however, to be effective phase transfer agents for the following
reaction:
61
C H OS0 CH
8
17
2
3
+ KYpj^C H
8
l
7
Y + CH S0 K
3
3
The importance of this observation was further emphasized by the fact
that the largest pseudo-first-order rate constants were obtained for those
cations that had the least solubility in water. In fact, it was found that the
greater rates obtained with these agents could be attributed almost entirely
to their insolubility in water. A n analysis of the kinetic data showed that the
rates were directly dependent on the concentration of the phase transfer
agent in the organic p h a s e .
62
6 1
6 2
D. Landini, A. Maia and F. Montanari, J. Chem. Soc. Chem. Comm., 112 (1977).
D. Landini, A. Maia and F. Montanari, J. Am. Chem. Soc. 100, 2796 (1978).
//. Phase Transfer Assisted Permanganate
Oxidations
167
Detailed mechanisms for phase transfers associated with alkylation and
dihalocarbene reactions have been considered by D e h m l o w .
46
D. USE OF SOLID SUPPORTS FOR PERMANGANATE OXIDATIONS
It has been observed that the attachment of reagents to solid supports can
be used effectively in several synthetic p r o c e d u r e s . F o r example, Regen
and his co-workers have reported that both molecular sieves and alumina
coated with potassium permanganate may be used to oxidize alcohols in
benzene or toluene solutions. Yields varying from 26 to 100% were
obtained.
Menger and Lee have subsequently shown that moisture is essential for
these r e a c t i o n s .
F o r example, they found that drying of the molecular
sieve/permanganate reagent over phosphorous pentoxide greatly reduced
its ability to oxidize secondary alcohols. Furthermore they showed that the
solid hydrate, C u S 0 · 5 H 0 , also acted as an excellent support for the
oxidation of secondary alcohols by potassium permanganate in b e n z e n e .
63
64
643
4
2
643
E. REACTIONS IN MICELLES
Certain quaternary cations act as phase transfer agents by forming micelles
that bring organic substrates into the aqueous phase where they can react
with water-soluble reagents. Micelles are usually formed with quaternary
cations that contain one large and three small alkyl groups. Aggregates
( 1 0 - 5 0 molecules) of these c o m p o u n d s form with the large alkyl groups
providing an hydrophobic center in which organophilic substrates also
dissolve. The polar exterior of this droplet promotes its dispersion into the
aqueous phase. In this way the organic substrates are brought into contact
with reagents dissolved in the aqueous p h a s e .
Certain oxidation reactions are believed to proceed in this way. F o r
example, piperonal has been oxidized to piperonylic acid in 65% yield by
treatment with aqueous potassium permanganate containing a small a m o u n t
of cetyltrimethylammonium b r o m i d e . (In the absence of the phase transfer
agent, the yield was reduced to about 35%.)
It has also been demonstrated that the rate of oxidation of 1-octene by
aqueous potassium permanganate is accelerated by addition of emulsifying
agents including sodium stearate and sodium l a u r a t e .
65
65
66
6 3
6 4
6 4 a
6 5
6 6
C. C. Leznoff, Chem. Soc. Rev. 3, 65 (1974).
S. L. Regen and C. Koteel, J. Am. Chem. Soc. 99, 3837 (1977); S. Quid and S. L. Regen,
J. Org. Chem. 44, 3437 (1979).
F. M. Menger and C. Lee, J. Org. Chem. 44, 3446 (1979).
F. M. Menger, J. U. Rhee, and Η. K. Rhee, J. Org. Chem. 40, 3803 (1975); F. M. Menger,
Acc. Chem. Res. 12, 111 (1979).
F. Yamashita, A. Atsumi, and H. Inoue, C. A. 83, 113378 (1975).
168
DONALD G. LEE
III. Oxidation of Alkenes
A. TERMINAL ALKENES
One of the first examples of the use of phase transfer assisted permanganate
oxidations involved the conversion of 1-decene into nonanoic a c i d . The
reaction of terminal alkenes was subsequently investigated thoroughly by
K r a p c h o , Larson, and E l d r i d g e and has now become a standard procedure
for the oxidation of long-chain terminal alkenes that lack solubility in
w a t e r . As the results summarized in Table XII indicate, a variety of phase
transfer agents and solvents have been successfully used with Adogen 464
(or Aliquat 336) in methylene chloride the most economical and generally
convenient combination.
When terminal alkenes are oxidized a certain a m o u n t of over oxidation
occurs; e.g., the oxidation of 1-octene gives about 10% hexanoic acid in
addition to the main product, heptanoic acid. This problem has been
investigated extensively by K r a p c h o et al. with the conclusion that over
oxidation is promoted by hydroxide ions which are produced during the
reduction of permanganate. They found, for example, that the over oxidation
of allylbenzene could be greatly increased by adding base, but substantially
reduced by adding acetic acid. In fact, the addition of acetic acid to the
reaction mixture was found to almost completely eliminate over oxidation
in most cases. As a consequence, most synthetic preparations are now carried
out in solvents containing 5 - 1 0 % acetic acid. Table XIII contains some
examples that illustrate the control of over oxidation reactions.
Whereas it is clear that hydroxide ion promotes over oxidation, the
mechanism of the reaction is still somewhat obscure. K r a p c h o et al.
observed that the product carboxylic acids were subject to further oxidation
under reaction conditions particularly in the presence of base. Phenylacetic
acid, for example, was oxidized to benzoic acid with yields higher (65%) in
0.1 Μ K O H than in the presence of acetic acid. Similarly, the treatment of
heptanoic acid (0.03 mol) with K M n 0 (0.12 mol in 0.1 Μ K O H ) for 6
hr gave a 4% yield of hexanoic acid.
It is possible that the presence of base promotes the formation of enolates
that would be readily cleaved by permanganate [Eq. (11)]. Such an explana­
tion is consistent with the greater ease of oxidation of phenylacetic acid where
67
68
69
68
68
4
6 7
6 8
6 9
C. M. Starks, J. Am. Chem. Soc. 93, 195 (1971).
A. P. Krapcho, J. R. Larson, and J. M. Eldridge, / . Org. Chem. 42, 3749 (1977).
D. G. Lee, S. E. Lamb, and V. S. Chang, Org. Synth., 60, 11 (1981).
//. Phase Transfer Assisted Permanganate
Oxidations
169
TABLE XII
PHASE TRANSFER ASSISTED OXIDATION OF TERMINAL ALKENES BY AQUEOUS PERMANGANATE
Substrate
1-Octene
1-Octene
1-Octene
1-Decene
1-Decene
1-Decene
1-Undecene
1-Dodecene
1-Tetradecene
1-Tetradecene
1-Hexadecene
1-Hexadecene
1-Octadecene
1-Octadecene
Phase transfer agent
Tetrabutylammonium
bromide
Benzylhexadecyldimethylammonium chloride
Adogen 464
b
Aliquat 336
Benzylhexyldimethyl
ammonium chloride
Dimethyloctaethylene
glycol
Benzylhexyldimethyl
ammonium chloride
Benzylhexyldimethyl
ammonium chloride
Benzylhexyldimethyl
ammonium chloride
Adogen 464*
c
Benzylhexyldimethyl
ammonium chloride
Adogen 464
b
Benzylhexyldimethylammonium chloride
Adogen 464*
1-Eicosene
Benzylhexyldimethylammonium chloride
Adogen 464*
1-Docosene
Adogen 464
Styrene
Adogen 464*
Allylbenzene
Benzylhexyldimethylammonium chloride
1-Eicosene
a
b
c
d
b
Solvent"
Products (% yield)
Benzene
Heptanoic acid (81)
Benzene
Heptanoic acid (97)
Hexanoic acid (3)
Heptanoic acid (73)
Methylene
chloride
Benzene
Benzene
Methylene
chloride
Benzene
68
8
1 0
0
70
d
67
68
d
59
68
d
d
68
Tridecanoic acid (83)
d
68
Methylene
chloride
Benzene
Tridecanoic acid (83)
d
69
Pentadecanoic acid (84)
d
68
Methylene
chloride
Benzene
Pentadecanoic acid (84)
d
69
Heptadecanoic acid (80)
d
68
Methylene
chloride
Benzene
Heptadecanoic acid (81)
d
69
Nonadecanoic acid (90)
d
68
Methylene
chloride
Methylene
chloride
Methylene
chloride
Benzene
Nonadecanoic acid (80)
d
69
Benzene
Undecanoic acid (90)
Benzene
Heneicosanoic acid (84)
Benzoic acid (96)
d
Phenylacetic acid (80)
Benzoic acid (20)
With the exception of the first and fourth entries 5-10% acetic acid was added.
Methyltrialkyl ( C - C ) ammonium chloride (Ashland Chemicals).
Methyltrialkyl ( C - C j ) ammonium chloride (General Mills).
Isolated yield.
8
54
d
d
Nonanoic acid (90)
Nonanoic acid (87)
Octanoic acid (3)
Nonanoic acid (95)
Decanoic aqjd (86)
Ref.
d
69
69
68
170
DONALD G. LEE
TABLE XIII
EXAMPLES OF OVER OXIDATION"
Substrate
Phase transfer agent
Additives
Products (% yield)
1-Octene
Aliquat 336*
none
1 -Octene
Aliquat 336
Acetic acid
1-Decene
Benzylhexadecyldimethylammonium chloride
Benzylhexadecyldimethylammonium chloride
Benzylhexadecyldimethylammonium chloride
Benzylhexadecyldimethylammonium chloride
Benzylhexadecyldimethylammonium chloride
Benzylhexadecyldimethylammonium chloride
1-Decene
1-Decene
Allylbenzene
Allylbenzene
Allylbenzene
b
Heptanoic acid (90)
Hexanoic acid (10)
Heptanoic acid (97)
Hexanoic acid (3)
Nonanoic acid (77)
Octanoic acid (8)
Nonanoic acid (82)
Octanoic acid (14)
Nonanoic acid (87)
Octanoic acid (3)
Phenylacetic acid (50)
Benzoic acid (50)
Phenylacetic acid (5)
Benzoic acid (95)
Phenylacetic acid (80)
Benzoic acid (20)
none
KOH
Acetic acid
none
KOH
Acetic acid
The solvent used in these experiments was benzene. The oxidant was aqueous potassium
permanganate. See ref. 68 for details.
Methyltrialkyl ( C - C ) ammonium chloride (General Mills).
α
b
8
1 0
formation of an intermediate enolate would be aided by conjugation of the
double bond with the ring.
Ο
RCH CO" + OH" ^
2
ORCH=C
+ H 0
2
(11)
O"
G o o d yields are obtained when the oxidant is introduced either as a solid
anhydrous powder or as an aqueous solution. Table XIV compares the
results obtained for the oxidation of 1-decene using a variety of different
phase transfer agents and conditions. Since the yields are quite good under
all conditions, it appears that in most cases practical considerations such as
the cost and availability of the phase transfer agent will determine the best
method to be used.
Some comments concerning the use of acyclic polyethers are appropriate
at this p o i n t . As the results in Table XIV indicate, acyclic polyethers
[ R O ( C H C H 0 ) R ] function fairly well as phase transfer agents for this
reaction regardless of the nature of the terminal (R and R') groups. It was
noted, however, that terminal hydroxyl groups were gradually oxidized to
59
/
2
2
n
//. Phase Transfer Assisted Permanganate
Oxidations
171
TABLE XIV
OXIDATION OF 1-DECENE USING DIFFERENT PHASE TRANSFER AGENTS AND CONDITIONS
Phase transfer agent
Solvent*
Oxidant
phase
Adogen 464
c
Benzene
Solid
Adogen 464
c
Methylene chloride
Aq.
a
Benzene
Solid
d
Methylene chloride
Aq.
Methylene
Methylene
Benzene
Methylene
Methylene
Benzene
Aq.
Solid
Solid
Aq.
Aq.
Solid
CH (OCH CH ) OCH
3
CH (OCH CH ) OCH
3
3
2
3
2
2
2
8
8
CH (OCH CH ) OH
CH (OCH CH ) OH
CH (OCH CH ) OCH
CH (OCH CH ) OCH
(CH ) Si(OCH CH ) OSi(CH )
Dicyclohexano-18-erown-6
e
3
2
2
7
3
2
2
7
3
2
2
3
3
3
2
2
3
3
e
c
/
3
3
2
2
7
3
fl
3
chloride
chloride
chloride
chloride
0
Products (% yield)
Nonanoic acid (91)
Octanoic acid (3)
Nonanoic acid (94)
Octanoic acid (1)
Nonanoic acid (70)
Octanoic acid (4)
Nonanoic acid (92)
Octanoic acid (2)
Nonanoic acid (88)
Nonanoic acid (84)
Nonanoic acid (93)
Nonanoic acid (93)
Nonanoic acid (85)
Nonanoic acid (86)
Octanoic acid (5)
From Chang and Lee.
* Acetic acid (5-10%) was added to the solvent.
Methyltrialkyl ( C - C ) ammonium chloride (Ashland Chemicals).
H. Lehmkuhl, F. Rabet and K. Hauschild, Synthesis, 184 (1977).
Carbowax methoxy polyethylene glycol (Union Carbide).
Ansul E-181 (Ansul Company).
Obtained as a gift from Dr. Gerd Rossmy (Goldschmidt).
a
70
c
8
10
d
e
f
9
carboxyl groups. Although this process consumed some oxidant it did not
appear to decrease the effectiveness of these c o m p o u n d s as phase transfer
agents.
Because it is known (Fig. 2) that the ability of polyethers to act as
phase transfer agents for potassium permanganate decreases with the
number of ethylene glycol units in the chain, it is surprising (but convenient)
that dimethyl triethylene glycol proved to be as effective as most of the other
phase transfer agents for these purposes. (The fact that the concentration of
permanganate in the organic solvent was not high did not prevent the reaction
from going to completion.)
It was also noted in Table VIII that dimethyl octaethylene glycol could not
be used to transfer potassium permanganate from water to benzene, however
it does bring solid permanganate into a benzene solution. This observation
can sometimes be used advantageously in the following way: If the reaction
7 0
V. S. Chang and D. G. Lee, unpublished results.
172
DONALD G. LEE
LO
2.0
3.0
TIME
4.0
(HR)
FIG. 5. Comparison of the use finely powdered (O) and reagent grade ( # ) K M n 0 for the
phase transfer assisted oxidation of 1-decene.
4
is carried out using solid K M n 0 , solubilized by dimethyl octaethylene
glycol in benzene, the phase transfer agent can be removed easily from the
final product by a simple aqueous extraction. Evaporization of the solvent
then leaves a product that can be used for many purposes without further
purification.
It should also be noted that when solid oxidant is employed, it is advantageous to use a finely divided f o r m . This is illustrated by Fig. 5 where it is
apparent that the reaction in which powdered permanganate was used
proceeded at a faster rate.
4
57
A TYPICAL PROCEDURE
Preparation of Tridecanoic Acid by Oxidation of l-Tetradecene*
Al-1
round-bottomed flask was charged with K M n 0 (32 g, 0.20 mol) and 300 ml
4
* Reprinted with permission from Krapcho et al., J. Org. Chem. 42, 3749. Copyright (1977)
American Chemical Society.
//. Phase Transfer Assisted Permanganate
173
Oxidations
of water. The flask was immersed in an ice bath and stirred vigorously with
an egg-shaped magnet (1 in.). A solution of 1-tetradecene (11.8 g, 0.06 mol),
300 ml of benzene (or toluene), 60 ml of glacial acetic acid, and benzylhexadecyldimethylammonium chloride (0.2 g, 0.5 mmol) was added in one
portion. Stirring was continued without any further addition of ice to the
bath for a b o u t 4 hr. A total of 35 g of N a S 0 was added to the cooled
reaction mixture followed by the slow addition of a solution of 35 ml of
concentrated H C l in 35 ml of water. T w o clear layers resulted. The layers
were separated and the benzene layer washed once with a 100-ml portion of
cold water. The benzene layer was dried over anhydrous sodium sulfate, the
drying agent removed by filtration, and the bulk of the benzene removed by
distillation. The residual benzene was removed on a rotary evaporator to
yield 12.7 g (99%) of crude solid. The crude acid was dissolved in pentane
(60 ml), filtered to remove traces of insoluble material, and placed in the
freezer overnight. Filtration yielded 10.6 g (83%) of tridecanoic acid of m p
4 3 ° - 4 4 ° C . Treatment of a sample of the crude or crystallized acid with
C H N followed by G L C analysis showed about 2% contamination of
dodecanoic acid and a trace a m o u n t of a short retention time impurity.
2
2
3
2
B. NONTERMINAL ALKENES
In aqueous solutions permanganate readily oxidizes water-soluble al­
k e n e s . The nature of the products is, however, dependent on the reaction
conditions: in acidic solutions, cleavage reactions p r e d o m i n a t e ;
under
basic conditions, dihydroxylation is the main r e a c t i o n ; and in a neutral
medium, ketols are formed as the major p r o d u c t s . Unfortunately the
conditions under which these reactions take place are not sharply defined
and mixtures of products are often obtained. However, it is generally possible
to predict what will be the major product of a reaction under a particular
set of conditions.
There appears to be general a g r e e m e n t
' with a suggestion m a d e
nearly a century a g o that the initial reaction between alkene and per2
71
72
27
2 , 7 1 , 7 3
7 4
7 5
7 1
7 2
7 3
7 4
7 5
D. G. Lee and J. R. Brownridge, J. Am. Chem. Soc. 96, 5517 (1974).
A. Lapworth and Ε. N. Mottram, J. Chem. Soc. 1628 (1925).
F. Freeman, Rev. React. Species Chem. React. 2, 179 (1973); F. Freeman, C. O. Fuselier,
and Ε. M. Karachefski, Tetrahedron Lett., 2133 (1975); F. Freeman and Ε. M. Karchefski,
Biochim. Biophys. Acta 447, 238 (1976).
M. Jaky and L. I. Simandi, React. Kinet. Catal. Lett. 3, 397 (1975); K. Polgar, M. Jaky, and
L. I. Simandi, React. Kinet. Catal. Lett. 5, 489 (1976); L. I. Simandi and M. Jaky, J. Am.
Chem. Soc. 98, 1995 (1976).
G. Wagner, Zh. Russ. Fiz Khim. Ova 27, 219 (1895).
174
DONALD G. LEE
manganate results in the formation of a cyclic manganate(V) diester
[Eq. (12)].
Η
R — C H = C H — R ' + Mn0 "
R'
• R-
4
(12)
Η
O
\
/
Mn
//
\
Ο
o
oU n d e r acidic conditions the I manganate (V) diester apparently undergoes
an oxidative decomposition that results in cleavage products plus manganate
(III) [ E q . ( 1 3 ) ] .
71
Η
R'
R—Vt—I"—Η
(
X
Q
Ο
Ο
• RCH + RCH + MnO,"
Q
</ V
Ο
II
ο
II
MnO."
RCH + RCH
4
> RCOOH + R'COOH
On the other hand, under basic conditions the intermediate would be
hydrolyzed to a cis-a\o\ [Eq. (14)]
2
C
Η
R'
R—)
Ο
Ο
χ
Η
-^r+R-J
J\
R'
— g , —
Η
OH
An
o
Η
OMn0 H-
(14)
3
oH
R ^
OH
R'
H
+
H 2 M n
° "
4
OH
Convincing evidence for these mechanisms has been provided by the work
of Ogino and M o c h i z u k i . They have reported the preparation of stable
solutions of several manganate(V) diesters by reacting alkenes with per­
manganate in cold (0°-3°C) methylene chloride solutions while using
76
7 6
T. Ogino and K. Mochizuki, Chem. Lett., 443 (1979).
//. Phase Transfer Assisted Permanganate
Oxidations
175
benzyltriethylammonium chloride as a phase transfer agent. The h o m o ­
geneous dark brown solution of manganate(V) diester that formed was then
treated with an aqueous solution to produce products. If the aqueous
solution was basic, diols were formed; if it was acidic, dialdehydes were
produced:
+ Q Mn(V
+
CH C1
2
2
y
Η
R
Ο
\
/
Ο
Μη
//
\
Ο
Η,Ο
OQ
\
+
H /H «
+
2
2RCH
OH
OH
It is probable that the intermediate manganate(V) diester could be more
stable under these conditions because it would be complexed with the
quaternary a m m o n i u m ion a n d because the hydrolysis reaction would
be suppressed in the absence of water.
This procedure has provided a simple route to a n u m b e r of diols a n d
dialdehydes that are difficult to prepare by other methods (see Tables XV
and XVI). In particular it m a y be noted that it is possible to prepare 1,2-diols
from terminal alkenes by use of this procedure.
α-Diols are also obtained from phase transfer assisted p e r m a n g a n a t e
oxidations if the reactions are carried out in contact with an aqueous solution
of sodium h y d r o x i d e .
'
In fact, the yields of diols are often better
than for the corresponding reaction in w a t e r , and because one is not
limited to the use of water-soluble alkenes, a greater range of products is
available.
In order for the reaction to be effective, it is probably necessary to use a
phase transfer agent that is capable of transferring both the hydroxide ion
and the permanganate ion into the organic phase. Several examples of such
dihydroxylation reactions have been summarized in Table XV.
5 9 , 7 7
7 8 , 7 9
79
7 7
7 8
7 9
T. Okimoto and D. Swern, J. Am. Oil Chem. Soc. 54, 867A (1977).
T. A. Foglia, P. A. Barr, and A. J. Malloy, / . Am. Oil Chem. Soc. 54, 858A (1977).
W. P. Weber and J. P. Shepherd, Tetrahedron Lett., 4907 (1972).
Tetrabutylammonium bromide
Tetrabutylammonium bromide
Dicyclohexano-18-crown-6
Dicyclohexano-18-crown-6
Benzyltriethylammonium chloride
Benzyltriethylammonium chloride
Benzyltriethylammonium chloride
Adogen 464
Triethylbenzylammonium chloride
Triethylbenzylammonium chloride
Triethylbenzylammonium chloride
Triethylbenzylammonium chloride
Oleyl alcohol (c/s-9-Octadecen-l-ol)
Elaidyl alcohol (iraws-9-Octadecen-l-ol)
9-Octadecene
Methyl oleate
c/s-Cyclooctene
/ra,w-Cyclododecene
Cyclohexene
/ra«s-5-Decene
ewi/o-Dicyclopentadiene
Norbornene
/raHs-Stilbene
1-Octene
3% NaOH"
3% NaOH"
3% NaOH*
15-20% NaOH
15-20% NaOH
40% NaOH
40% NaOH
40% NaOH
40% NaOH
40% NaOH
15% NaOH
3% NaOH*
Aqueous phase
fl
erythro-l,9,10-Octadecanetriol (60-80)
threo-1,9,10-Octadecanetriol (40-50)
9,10-Octadecanediol (80)
Methyl 9,10-dihydroxyoctadeconate (25)
cis- 1,2-Cyclooctanediol (50, 70)
frans-1,2-Cyclooctanediol (50)
c/s-l,2-Cyclohexanediol (15)
5,6-Decanediol (20)
5-ex0,6-e*0-Dihydroxy-e/w/0-3a,4,5,6,7,7ahexahydro-4,7-methanoindene (83)
ejc0-d.r-Bicyclo[2.2. l]heptane-2,3-diol (69)
Hydrobenzoin (26)
1,2-Octanediol (80)
Products (% yield)
76
76
76
b
83
76
77
77
78
78
79, 76
79
79
59
76
Ref.
° The higher yield (80%) was obtained when the reaction intermediate was allowed to form under anhydrous conditions and then hydrolyzed with water.
The reaction was carried out under anhydrous conditions and then treated with 3% N a O H .
Phase transfer agent
Substrate
PHASE TRANSFER ASSISTED DIHYDROXYLATION OF ALKENES IN METHYLENE CHLORIDE
TABLE XV
//. Phase Transfer Assisted Permanganate
Oxidations
177
U n d e r neutral aqueous conditions, the intermediate manganate(V)
diesters are hydrolyzed to the corresponding acyclic manganate(V) esters
which undergo an oxidative decomposition giving the observed ketols
[Eq. ( 1 5 ) ] .
71
Η
R'
Η
R'
. - ) - ( - . - » - - . - f - ^
Ο
\
Μη
/
Ο
Ο
OH
•
Ο)
Ο
\
Ο"
Μη
Γ//
ΟΗ
Ο"
Η
R
\
l D
)
R'
)
^
ΟΗ
+ Η Μη0 "
2
3
Ο
Alternatively the intermediate cyclic manganate(V) diester could be
oxidized prior to hydrolysis and oxidative decomposition [Eq. (16)].
Η
R
R'
)
ό
Ο
(
\
//
/
Μη
\
Η
Η
ό
Ο"
R'
R
Mn0~
4
*
ο
)
{
\
/
//
Ο
Η
ο
Μη.
Χ
Ο
Η
Hio^R-y
OH
^ - v S
θ)
\
ΗΟ
/
(16)
Ο
Γ//
Μη^
%
Ο
Η
R-Λ
ΟΗ
10
11
12
3
R'
ί
+ Η Μη0
2
3
Ο
Ν. S. Srinivasan and D. G. Lee, unpublished results.
Κ. B. Sharpless, R. F. Lauer, O. Repic, A. Y. Teranishi, and D. R. Williams, J. Am. Chem.
Soc. 93, 3303 (1971); H. P. Jensen and Κ. B. Sharpless, J. Org. Chem. 39, 2314 (1974).
D. J. Sam and Η. E. Simmons, J. Am. Chem. Soc. 94, 4024 (1972).
W. Rennie and D. G. Lee, unpublished results.
178
D O N A L D G . LEE
TABLE
XVI
PREPARATION OF DIALDEHYDES FROM THE OXIDATION OF NONTERMINAL ALKENES"
Substrate
Quenching solution
Products (% yield)
ewifo-Dicyclopentadiene
Acetate buffer*
Norbornene
ds-Cyclooctene
/rajis-Stilbene
Acetate buffer
1 Μ HC10
Acetate buffer
lj3,50-Bicyclo[3.3.O]oct6-ene-2a,4a-dicarboxaldehyde (81)
1,3-Diformylcyclopentane (63)
Octanedial (74)
Benzaldehyde (79)
a
b
c
b
4
c
From Ogino and Mochizuki.
pH = 3.
pH = 5.
76
Experiments in which the products obtained from the oxidation of £ - 5 decene in aqueous acetone were monitored by G L C , indicated that the
diones were more rapidly formed from the oxidation of the ketols when the
water content of the solvent was d e c r e a s e d .
Thus it is found that in the
absence of water (e.g., in acetic anhydride solutions) diones are observed as
the major p r o d u c t s .
It has also been found that diones can be obtained in good yield from
the phase transfer assisted oxidation of nonterminal alkenes. F o r example,
5,6-decanedione and 1,2-cyclodecanedione have been obtained in 5 3 % and
69% yields, respectively, from the oxidation of the corresponding alkenes
under specific c o n d i t i o n s . If sufficient oxidant is used, oxidative cleavages
accompany these reactions (Table XVII).
Phase transfer assisted permanganate reactions have also been used to
oxidize polymers with unsaturated side chains. These c o m p o u n d s , formed
from the copolymerization of terminal alkenes and nonconjugated dienes,
are readily oxidized to oil-soluble polymers with polar pendent g r o u p s .
F o r example:
77,80
81
59
8 4
RCH=CH + CH =CHCH CH CH=CH
2
2
2
2
polymerize
:
R
I
-eCHCH CH CHi2
2
CH
Q+MnQ4
" > -eCHCH CH CH^CH
2
I
2
I
CH
2
I
CH
COOH
II
CH
2
I
2
I
CH
2
2
U.S. Patent, 4,152,276 (1979). P. F. Jackisch, Ethyl Crop., Richmond, Virginia.
Dimethylpolyethylene glycol
Dimethylpolyethylene glycol
Tetrabutylammonium bromide
Dicyclohexano-18-crown-6
Adogen 464
Dicyclohexano-18-crown-6
Dicyclohexano-18-crown-6
Tetrabutylammonium bromide
Tetrabutylammonium bromide
Dicyclohexano-18-crown-6
Adogen 464
/ra«s-5-Decene
fra«s-2-Heptene
Methyl oleate
Cyclohexene
Cyclododecene
a-Pinene
/raws-Stilbene
/ra/w-Stilbene
ds-Stilbene
Triphenylethylene
Benzene
Benzene
Benzene
Benzene
Pyridine
Benzene
Benzene
Methylene chloride
Benzene
Methylene chloride
Benzene
Methylene chloride
Benzene
Solvent
Solid
Solid
Solid
Aqueous
Solid
Aqueous
Solid
Solid
Solid
Aqueous
Solid
Aqueous
Aqueous
Oxidant
phase
Acetic acid
Acetic acid
Acetic acid
Additives
Nonanoic acid (80)
Nonanoic acid (50)
9,10-Diketooctadecane (27)
9-Hydroxy-10-octadecanone (5)
Valeric acid (69)
5,6-Decanedione (28)
Valeric acid (67)
Nonanoic acid (67)
Monomethyl azelate (72)
Adipic acid (100)
Dodecanedioic acid (27-83)
1,2-Cyclododeanedione (7-19)
2-Hydroxycyclododecanone (6-7)
Pinonic acid (90)
Benzoic acid (100)
Benzoic acid (95)
Benzoic acid (98)
Benzoic acid (92)
Benzaldehyde (7)
Benzophenone(50)
Benzoic acid (17)
Products (% yield)
83
82
82
54
43
83
82
59
70
78
59
78
78
Ref.
a
Tetrabutylamonium permanganate, prepared from the reaction of aqueous permanganate with tetrabutylammonium bromide, was used in a pyridene
solution.
iraw5-Stilbene
0
Tetrabutylammonium bromide
Cetyltrimethylammonium bromide
Phase transfer agent
9-Octadecene
9-Octadecene
Substrate
OXIDATIVE CLEAVAGES OF NONTERMINAL ALKENES
TABLE XVII
180
DONALD G. LEE
If the diene is cyclic, oxidation gives two alkanoic acid groups on adjacent
carbons, i.e.,
RCH=CH
2
+
CH=CH
/
CH
\
CH
2
I
CH
\
POLYMERIZE
>
2
I
2
CH=CH
CH
/
2
R
R
-eCHCH -H:H—CHt-
Q+Mn
2
CH
CH
2
I
2
2
\
CH
2
/
CH=CH
CH
2
CH
2
I I
I
CH
° " > -eCHCH CH—CH^4
2
CH
2
CH
2
I I
C0 H C0 H
2
2
These products may be used as ashless dispersants and viscosity lift additives
for lubricating o i l s .
84
TYPICAL PROCEDURES
Oxidation of Nonterminal Alkenes by Solid Potassium Permanganate *
Alkene (0.054 mol) was dissolved in 130 ml of solvent (methylene chloride
or benzene) and 25 ml of acetic acid in a 500-ml, three-necked, roundbottomed flask equipped with a mechanical stirrer. A b o u t 3 g of phase
transfer agent (Adogen 464, dicyclohexano-18-crown-6, or dimethyl poly­
ethylene glycol) dissolved in 20 ml of solvent was added, followed by addition
of powdered potassium permanganate (0.177 mol) in small portions for a
period of 2 hr. A n ice bath was used to maintain the temperature below
20°C. The mixture was then stirred vigorously overnight, cooled, and treated
with 100 ml of water and 5 g of sodium bisulfite to reduce any excess oxidant.
After 20 min the solution was acidified (concentrated HC1) and the manga­
nese dioxide was reduced by addition of the required a m o u n t of sodium
bisulfite in small portions. Any solid carboxylic acids that precipitated were
collected by filtration, and the nonaqueous layer was separated. The aqueous
layer was saturated with sodium chloride and extracted with 2 χ 50 ml of
ether. The combined organic layers were extracted with 2 χ 100 ml of 5%
sodium hydroxide solution to remove any additional carboxylic acids, dried
over anhydrous magnesium sulfate, and concentrated by rotary evaporation.
The resulting yellow oil could then be analyzed directly by G L C (when
benzene and dimethylpolyethylene glycol had been used as solvent and phase
transfer agent) or distilled under vacuum and then analyzed.
* Reprinted with permission from Lee and Chang, J. Org. Chem. 43, 1532. Copyright (1978)
American Chemical Society.
//. Phase Transfer Assisted Permanganate
Oxidations
181
The precipitated carboxylic acids were dissolved in a 5% sodium hydroxide
solution and combined with the basic solutions from previous extractions.
The solution was filtered to remove any residual manganese dioxide, acidified
with concentrated hydrochloric acid, and extracted with 2 χ 250 ml of
ether. This solution was dried over magnesium sulfate and evaporated to
give purified carboxylic acids.
Oxidation of Nonterminal Alkenes by Aqueous Potassium
Permanganate^
Alkene (0.054 mol) was dissolved in a mixture of methylene chloride (130 ml),
acetic acid (25 ml), and water (100 ml) in a 500-ml, three-necked, roundbottomed flask equipped with a mechanical stirrer. A b o u t 3.5 g of phase
transfer agent (Adogen 464 or dimethyl polyethylene glycol) dissolved in
20 ml of methylene chloride was added. The mixture was cooled in an ice
bath and powdered potassium p e r m a n g a n a t e (0.177 mol) was added in
small portions over a 1-hr period. The mixture was stirred vigorously for
another 6 hr, cooled, and treated with 5 g of sodium bisulfite to reduce any
excess oxidant. After 20 min the solution was acidified (concentrated HC1)
and the manganese dioxide reduced by addition, in small portions, of the
required a m o u n t of sodium bisulfite. The products were then isolated as
described above.
Oxidation of endo-Dicyclopentadiene**
The oxidant solution was prepared
by treating pulverized potassium permanganate (3.41 mmol) with triethylbenzylammonium chloride (3.41 mmol) in methylene chloride (40 ml) and
added dropwise to a stirred solution of ewtfo-dicyclopentadiene (2.27 mol) in
methylene chloride (20 ml) at such a rate that the temperature was main­
tained at 0 ° - 3 ° C under cooling with an ice bath (40-50 min). After addition
was complete, stirring was continued until the permanganate ion was
completely consumed (30-40 min). The homogeneous dark brown mixture
was then treated with either acidic or basic aqueous solutions.
W h e n the reaction mixture was treated with 3 % N a O H solution (30 ml)
under a nitrogen atmosphere at r o o m temperature for 18 hr, a crystalline
product, m p 47°-52°C, was obtained in 8 3 % yield from the organic layer
u p o n usual work-up. This product was identified as the exo,cis-dio\ from I R
and N M R data. N o other products were detected on T L C and G L C . On
the other hand, when the reaction mixture was treated with an acetate
solution (30 ml) at p H 3, the dialdehyde, m p 42°-44°C, was obtained in 8 1 %
yield as the single product (TLC, G L C ) .
7 6
t Reprinted with permission from Lee and Chang, J. Org. Chem. 43, 1532. Copyright (1978)
American Chemical Society.
** Reprinted with permission from Ogino and Mochizuki, courtesy of The Chemical
Society of Japan.
76
182
DONALD G. LEE
IV. Oxidation of Alkynes
A. N O N T E R M I N A L A L K Y N E S
C a r b o n - c a r b o n triple bonds are also succeptable to oxidation by permanganate although the rate of reaction is somewhat slower when compared
to the corresponding alkenes. Nonterminal alkynes containing substituents
that impart some solubility in water are oxidized to diketones by neutral
aqueous permanganate. A well-known example is the oxidation of stearolic
acid which has been described by K h a n and N e w m a n [Eq. (17)].
8 5
CH (CH ) C^C(CH ) C0 H
3
2
7
2
7
CH (CH ) COCO(CH ) C0 H
2
3
2
7
2
7
2
(17)
On the other hand, nonsubstituted low molecular weight alkynes are
cleaved by aqueous permanganate, whereas the higher molecular weight
c o m p o u n d s are insoluble in water and thus unreactive. This is illustrated by
the results summarized in Table X V I I I .
The use of phase transfer agents overcomes the solubility problems
encountered with large alkynes and permits the preparation of diones in
good y i e l d s . Some examples are found in Table X I X .
It is of interest to note that the results presented in Table X I X indicate that
alkynes undergo a nonsymmetrical cleavage when oxidized in organic
solvents. F o r example, 8-hexadecyne, when it is cleaved, gives approximately equal amounts of octanoic and heptanoic acids rather than the
expected two moles of octanoic a c i d . This observation has been rationalized by assuming cleavage takes place by reaction of the intermediate dione
5 8
58
58
T A B L E XVIII
THE OXIDATION OF ALKYNES BY AQUEOUS POTASSIUM PERMANGANATE
0
Recovered
substrate
a
5
Alkyne
(%)
8-Hexadecyne
7-Tetradecyne
1 -Phenyl-1 -pentyne
94
91
90
5-Decyne
56
4-Octyne
6
From Lee and Chang.
Products (% yield)
—
Benzoic acid (8)
1 -Phenyl-1,2-pentanedione (trace)
Valeric acid (19)
5,6-Decanedione (trace)
Butyric acid (73)
Propionic acid (6)
5
N. A. Khan and M . S. Newman, J. Org. Chem. 17, 1063 (1952).
//.
Phase Transfer Assisted
Permanganate
Oxidations
183
TABLE X I X
THE PHASE TRANSFER ASSISTED OXIDATION OF ALKYNES
BY PERMANGANATE ION IN METHYLENE CHLORIDE
a
b
Alkyne
Oxidant*
phase
Diphenylacetylene
Aqueous
1 -Phenyl-1 -pentyne
1-Phenyl-1-hexyne
Solid
Aqueous
7-Tetradecyne
Aqueous
8-Hexadecyne
Solid
0
Products (% yield)
Benzil (93)
Benzoic acid (2)
l-Phenyl-l,2-pentanedione (81)
1 -Phenyl-1,2-hexanedione (41)
Benzoic acid (32)
Butyric acid (27)
7,8-Tetradecanedione (54)
Heptanoic acid (25)
Hexanoic acid (17)
8,9-Hexadecanedione (80)
Octanoic acid (5)
Heptanoic acid (trace)
From Lee and Chang.
The phase transfer agent used was Adogen 464.
58
in its enol form [Eq. (18)]. Such a suggestion is not u n r e a s o n a b l e since
p e r m a n g a n a t e is k n o w n to react readily with c a r b o n - c a r b o n double b o n d s
a n d it has been established that diones are intermediates in the cleavage
reaction.
58
οο
RCH C=CCH R
2
RCH C—CCH R
2
HO
Ο
I
H
2
Λ
Ο
2
HO
M
RCHT-C-CCH R
/-J
2
n0 -
I
4
<
4
O
υ
RCH=C—CCH R
2
( Ο
y
v >
Μη
o^
\ r
(18)
i
ο
ο
II
II
RCH +
RCH CCOOH
2
Ο
R C H ^ - R C O O H
Ο
RCH CCOOH
2
RCH COOH +
2
C0
2
184
DONALD G. LEE
TYPICAL EXPERIMENTAL PROCEDURES
Preparation of 1-Phenyl-1,2-pentanedione
by Oxidation of
1-Phenyl-lpentyne.^
A 200-ml Erlenmeyer flask, equipped with a reflux condenser,
was charged with dichloromethane (100 ml), acetic acid (5 ml), and 1-phenyl1-pentyne (2.0 g, 0.014 mol). The solution was stirred magnetically and
heated to reflux temperature before powdered potassium p e r m a n g a n a t e
(5.85 g, 0.037 mol) and the phase transfer agent (Adogen 464, 1.6 g) were
added. After being stirred vigorously for 4 hr the precipitated manganese
dioxide was collected and washed with dichloromethane (2 χ 50 ml).
Residual manganese dioxide was reduced by addition (to the combined
filtrates) of 20% hydrochloric acid (40 ml) followed by small portions of
sodium hydrogen sulfite until all of the brown color had disappeared. T h e
organic phase was separated, washed with water, and dried with a n h y d r o u s
magnesium sulfate. Most of the solvent was removed using a rotary evapo­
rator and the remaining yellow oil distilled under va cuum to give unreacted
starting material (0.14 g) and 1 -phenyl-1,2-pentanedione; yield: 1.98 g
(81%); b p 108°-110°C/5.5 torr.
57
Preparation of 8,9-Hexadecanedione
by Oxidation of
8-Hexadecyne*
Potassium permanganate (5.85 g, 0.037 mol) was dissolved in water (100 ml)
in a 500-ml Erlenmeyer flask and a solution consisting of 8-hexadecyne
(2.0 g, 0.009 mol), dichloromethane (100 ml), acetic acid (5 ml), and phase
transfer agent (Adogen 464, 1.5 g) was added. The solution was stirred
magnetically and heated under reflux for 6 hr. After cooling, sodium hy­
drogen sulfite (2 g) was added to reduce any unreacted permanganate.
After 15 min the solution was acidified (cone, hydrochloric acid) and the
precipitated manganese dioxide reduced by addition, in small portions, of
the required a m o u n t of sodium hydrogen sulfite. T h e aqueous phase was
separated, saturated with sodium chloride, and extracted with dichloro­
methane (3 χ 75 ml). The organic layers were combined and extracted with
5% aqueous sodium hydroxide (3 χ 75 ml), dried over anhydrous mag­
nesium sulfate, and concentrated by rotary evaporation to give a yellow
liquid which solidified on cooling. This yellow solid was recrystallized from
methanol (15 ml) to give 8,9-hexadecanedione; yield: 1.55 g (68%); m p
51°-52°C.
ft Reprinted with permission from Lee and Chang , courtesy of Thieme, Stuttgart.
* Reprinted with permission from Lee and Chang , courtesy of Thieme, Stuttgart.
D. G. Lee and V. S. Chang, Synthesis, 462 (1978).
86
86
//. Phase Transfer Assisted Permanganate
Oxidations
185
B. T E R M I N A L A L K Y N E S
Terminal alkynes are smoothly oxidized to the corresponding carboxylic
acids under phase transfer conditions. The yield is slightly reduced by over
o x i d a t i o n , which probably arises from the oxidation of enols as described
in the previous section. The reaction seems most applicable for high molecular weight alkynes that are not soluble in water. K r a p c h o et a / .
have
shown that 1-hexyne reacts quantitatively with aqueous p e r m a n g a n a t e ;
however, the yield d r o p s off progressively with 1-octyne and 1-decyne,
presumably because of their decreased solubilities in water.
Some examples of the phase transfer assisted reaction are presented in
Table X X .
68
68
A TYPICAL EXPERIMENTAL PROCEDURE
Preparation of Heptanoic Acid from Oxidation of 1-Octyne* Potassium
permanganate (28 g, 0.18 mol) and 200 ml of t a p water were placed into a
1-1 round-bottomed flask fitted with a 1-in. egg-shaped spinbar. The mixture
was stirred and immersed in an ice bath. A solution of 1-octyne (5.0 g,
0.045 mol), 120 ml of pentane, 60 ml of acetic acid, and 0.2 g of Aliquat
336 was added in one portion. T h e mixture is stirred for 5 hr without replenishing the ice. The b l a c k - b r o w n mixture was cooled in an ice bath a n d
TABLE
xx
PHASE TRANSFER ASSISTED OXIDATION OF TERMINAL ALKYNES BY PERMANGANATE"-*
Alkyne
Phase transfer agent
Solvent
Oxidant
phase
1-Hexyne
Aliquat 336
Pentane
Aqueous
1-Octyne
Aliquat 336
Pentane
Aqueous
1-Decyne
Aliquat 336
Pentane
Aqueous
Phenylacetylene
Dimethylpolyethylene
glycol
Methylene
chloride
Solid
° From Lee and Chang.
From Krapcho et al.
b
Products (% yield)
Pentanoic acid (99)
Butanoic acid (1)
Heptanoic acid (88)
Hexanoic acid (2)
Nonanoic acid (76)
Octanoic acid (3)
Benzoic acid (91)
58
68
* Reprinted with permission from Krapcho et al, J. Org. Chem. 42, 3749. Copyright (1977)
American Chemical Society.
186
DONALD G. LEE
N a S 0 (30 g) was added in several portions. A solution of 60 ml of concentrated HC1 in 60 ml of water was then cautiously added. The t o p pentane
layer was separated and extracted once with 50 ml of cold water, dried over
N a S 0 , decanted from the drying agent, and concentrated on a rotary
evaporator to yield 5.4 g of crude product (90% recovery). Vacuum distillation yielded 4.1 g (70%) of heptanoic acid (98% pure by G L C of the methyl
esters). Trace a m o u n t s of short retention-time impurities were also present.
2
3
2
4
V. Oxidation of Arenes
There are numerous examples in the literature of the use of aqueous
permanganate for the oxidation of toluene derivatives to the corresponding
benzoic a c i d s . The evidence indicating that these reactions are likely
initiated by hydrogen a t o m abstraction at the benzylic position has been
reviewed in a previous volume in this series.
U n d e r phase transfer conditions it has been observed that it is possible
to oxidize toluene and xylene when they are used as solvents for the rea c t i o n . However, the phase transfer assisted oxidation of toluene dissolved in methylene chloride gave a very low yield of benzoic a c i d . Similarly it was observed that 1,2-diphenylethane and acenaphthene were not
oxidized when treated in a methylene chloride solution with potassium
permanganate and Adogen 4 6 4 .
On the other hand, Sala and S a r g e n t have reported that /?-nitrotoluene
is oxidized to /?-nitrobenzoic acid by tetrabutylammonium permanganate in
pyridine at 65°C. In this procedure, tetrabutylammonium permanganate was
first prepared and isolated by reacting tetrabutylammonium bromide with
aqueous potassium permanganate. The resulting precipitate was collected
and purified by crystallization from a dichloromethane-benzene solution
before being used as an oxidant. This process, which has also been applied
to the oxidation of alkenes, alcohols and aldehydes provides an important
new oxidation procedure. It should be noted, however, that some caution must be exercised when handling solid quaternary a m m o n i u m permanganates; on at least one occasion tetrabutylammonium permanganate
was observed to undergo a violent spontaneous ignition while being transferred from a bottle to weighing p a p e r .
In a similar series of experiments Schmidt and S c h a f e r have described
the preparation of benzyltriethylammonium permanganate and its use for
the oxidation of arenes in either methylene chloride or glacial acetic acid.
Their results may be summarized by the following equations where the
6
2
82
70
7 0
43
45
44
//. Phase Transfer Assisted Permanganate
Oxidations
187
yields given are based on the a m o u n t of arene consumed. (The extent of
conversion, based on the a m o u n t of arene initially present, was approximately 29%, 16%, 49%, and 70%, respectively, for these four reactions.)
98%
4%
37%
These products suggest that the reaction proceeds initially to the corresponding benzyl alcohol. If the initial product is a secondary alcohol, it
188
DONALD G. LEE
may be further oxidized to the corresponding phenyl ketone or react with
acetic acid to give a n ester as in the following reaction.
/
(C^^
\
/
CH CH CH CH
2
2
2
M
3
\
OH
° ° " »·
CHCH2CH CH
4
rzr\
2
3
QAc
-CHCH CH CH
2
CCH,CH,CH
2
3
If the initial product is a tertiary alcohol, it may undergo dehydration
followed by oxidative cleavage of the c a r b o n - c a r b o n double b o n d as well
as ester formation. F o r example, the products obtained from sec-butylbenzene may be formed as in the following reaction sequence.
CCH CH
2
3
Sangaiah a n d Krishna R a o
have used a modification of the procedure
developed by Schmidt a n d S c h a f e r to oxidize the side chains of arenes
bearing alkoxy and acetoxy substituents. W h e n c o m p o u n d s such as 4-acetoxytoluene were treated with a suspension of benzyltriethylammonium
permanganate (1 part) a n d potassium permanganate (10 parts) in glacial
acetic acid the corresponding acetoxybenzoic acids were obtained in moderate yields (25-50%). U n d e r similar conditions benzylic methylene groups
8 6 a
44
R. Sangaiah and G. S. Krishna Rao, Synthesis, 1018 (1980).
//. Phase Transfer Assisted Permanganate
Oxidations
189
were converted into carbonyl groups as in the syntheses of espeleton shown
below.
CH O
3
ο
CH O
3
ο
CH O
ο
3
26%
9%
The formation of a benzyl acetate as a side product suggests that this
reaction (as well as those reported by Schmidt and Schafer) may proceed via
a benzyl carbonium ion intermediate. However, Sangaiah and Krishna R a o
also reported that the reaction of thymol acetate (below) under similar
conditions results in oxidation at the primary rather than the tertiary benzyl
carbon (which would be expected to give a more stable carbonium ion). The
results are unfortunately inconclusive because of the lack of a mass balance
for the reaction; i.e., 72% of the starting material was unaccounted for.
CH
3
COOH
28%
Phase transfer assisted oxidations (not involving prior preparation a n d
isolation of quaternary a m m o n i u m permanganates) were found to be
useful for the preparation of diaryl ketones from the corresponding diarylm e t h a n e s . As the examples summarized in Table X X I indicate this reaction
is particularly appropriate for the oxidation of a n u m b e r of c o m p o u n d s that
are not readily soluble in aqueous solutions.
70
TYPICAL EXPERIMENTAL PROCEDURE
Preparation of 1-Tetralone by Oxidation of
1,2,3,4-Tetrahydronaphthalene.
A 500-ml Erlenmeyer flask, equipped with a reflux condenser, was
charged with methylene chloride (150 ml), acetic acid (10 ml), sulfuric acid
(10 ml), water (100 ml), 1,2,3,4-tetrahydronaphthalene (10.0 g, 0.076 mol),
and Adogen 464 (2.0 g). The solution was stirred magnetically and heated
at reflux temperature for 2 hr while potassium permanganate (25.0 g,
0.16 mol) was added in small portions. After cooling, sufficient sodium
10
190
DONALD G. LEE
TABLE
XXI
PHASE TRANSFER ASSISTED OXIDATION OF DIARYLMETHANES
BY AQUEOUS POTASSIUM PERMANGANATE
0
Substrate*
Products (% yield)
Diphenylmethane
4-Benzylpyridine
Fluorene
9,10-Dihydroanthracene
Tetralin
Indane
Benzophenone (80-85%)
4-Benzoylpyridine (70-80%)
9-Fluorenone (80-82%)
Anthraquinone (96%)
Tetralone (70-75%)
Indanone(70-75%)
"From Chang and Lee.
The phase transfer agent was Adogen 464, the solvent was methylene
chloride containing 5% acetic acid, the oxidant was used as an aqueous
solution containing 10% H S 0 .
70
b
2
4
hydrogen sulfite to reduce the precipitated manganese dioxide was gradually
added. The aqueous phase was separated, saturated with sodium chloride,
and extracted with methylene chloride (3 χ 50 ml). The organic layer was
extracted with a 5% sodium hydroxide solution (2 χ 50 ml). The organic
layers were combined, dried over anhydrous magnesium sulfate, and con­
centrated by rotary evaporation to give a yellow liquid. Distillation of this
product under vacuum (6 torr) gave unreacted starting material (1.0 g) and
1-tetralone (7.7 g, 0.053 mol, 70%), bp 113 -116°C.
0
VI. Oxidation of Alkanes
Schmidt and S c h a f e r have reported the products obtained from the
oxidation of several alkanes by benzyltriethylammonium permanganate in
glacial acetic acid at 30°-60°C. The results are summarized in the following
reactions. (The yields given here are based on the a m o u n t of alkane con­
sumed; conversions based on the a m o u n t of alkane used were 25-40%.)
44
I
CH CH CHCH CH
3
2
2
ο
ο
CH CH
II
II
I
2
3
"g£wc°'~' CH CH CCH CH + CH C—CHCH CH +
nC
3
3
2
2
3
3
2
25%
3
25%
CH CH
2
CH CH
3
2
3
CH CH CCH CH + CH CH CCH CH
3
2
OH
24%
2
3
3
2
2
OAc
10%
3
//. Phase Transfer Assisted Permanganate
/
(
\
^
^
r
-
PhCH Et NMnQ ~
H
^
2
3
A
c
O
3
/
4
H
\
^
O
\ _ / ^ C H
,60«C*
Oxidations
, /
H
\
191
Γ
Η
V V ^
+
3
72%
9%
OH
PhCH Et NMnQ A c O H , 60°C
2
3
4
37%
10%
OH
PhCH Et NMnQ ~
A c O H , 30°C
2
3
4
These results clearly indicate that tertiary c a r b o n - h y d r o g e n bonds are
more easily cleaved than secondary c a r b o n - h y d r o g e n bonds. When statisti­
cal factors are taken into account, the former appear to be 15-25 times as
reactive under these conditions.
The initial products in each of these reactions appear to be either secondary
or tertiary alcohols. F o r example, the products obtained from 3-ethylpentane
may be produced in the following sequence of reactions.
CH CH
2
I
CH CH
3
CH CH CHCH CH
3
2
2
4
OHCH CH
3
2
I I
3
* CH CH CCH CH + CH CHCHCH CH
3
3
2
I
MnO" ,
2
2
3
3
2
3
>\
OH
Ο
CHCH
II
2
3
CH CH
2
I
2
3
4
2
2
OAc
Ο
II
3
2
3
CH CH CCH CH
Mn0 "
CH CH CCH CH
2
I
2
3
CH C—CHCH CH
3
CH CH CCH CH
3
CH CH
3
3
2
3
192
DONALD G. LEE
Leddy, McKervey and M c S w e e n e y have noted that the stability of
quaternary a m m o n i u m permanganates can be increased by adsorbing them
on alumina. F o r example, they have reported the hydroxylation of dia m a n t a n e and triamantane by benzyltriethylammonium permanganate dispersed on alumina. As illustrated by the following reaction, oxidation was
observed to take place preferentially at the tertiary positions.
87
OH
VII. Oxidation of Polycyclic Aromatic Hydrocarbons
Although the yield of phthalic acid that may be obtained from the oxidation of naphthalene under phase transfer conditions is only 20%, anthracene and phenanthracene are converted to the corresponding quinones in
about 75% y i e l d s .
70
o
TYPICAL EXPERIMENTAL PROCEDURE
Preparation of 9,10-Phenanthraquinone by Oxidation of
Phenanthrene.
A 500-ml Erlenmeyer flask, equipped with a reflux condenser, was charged
with methylene chloride (150 ml), acetic acid (5 ml), sulfuric acid (10 ml),
water (100 ml), phenanthrene (5.0 g, 0.27 mol), and Adogen 464 (1.5 g).
10
8 7
B. P. Leddy, M. A. McKervey, and P. McSweeney, Tetrahedron Lett., 2261 (1980).
//. Phase Transfer Assisted Permanganate
Oxidations
193
Powdered potassium permanganate (28.0 g, 0.18 mol) was added slowly
with stirring and the solution was gently refluxed for 4 hr. The solution was
cooled in an ice bath and the precipitated manganese dioxide was reduced by
addition of the required a m o u n t of sodium hydrogen sulfite in small portions.
The aqueous phase was separated, saturated with sodium chloride, and
extracted with ether (2 χ 40 ml). The organic layers were combined, dried
over anhydrous magnesium sulfate, and concentrated by rotary evaporation
to give a pale yellow liquid which solidified on cooling. It was further purified
by recrystallization from a w a t e r - a c e t o n e solution to give 9,10-phenanthraquinone (4.2 g, 0.02 mol, 75%) m p 206°-208°C.
VIII. Oxidation of Alcohols
Alcohols are readily oxidized by permanganate ion in both aqueous and
n o n a q u e o u s solutions. The use of phase transfer agents to solubilize the
oxidant in n o n p o l a r solvents is particularly useful for high molecular weight
c o m p o u n d s . The employment of volatile organic solvents also simplifies
product isolation somewhat.
Table X X I I contains several examples of the oxidation of both primary
and secondary alcohols. As in the corresponding aqueous reactions, primary
alcohols were found to yield carboxylic acids whereas ketones were obtained
from secondary alcohols.
Solid supports have also been used to assist the oxidation of alcohols by
permanganate. The supports include molecular s i e v e , a l u m i n a ,
and
hydrated copper s u l f a t e .
There is good evidence that the presence of
moisture on the solid supports is essential if a high yield of product is to be
realized. W h e n the solid supports were carefully dried over p h o s p h o r o u s
pentoxide before use, the yields decreased m a r k e d l y .
F u r t h e r m o r e , it was shown that the low yields obtained from the oxidation
of primary alcohols is due to a retardation of the reaction by carboxylic
acids (which are formed from the oxidation of primary a l c o h o l s ) .
Table X X I I I contains several examples of the use of this procedure.
64
64
643
643
643
TYPICAL EXPERIMENTAL PROCEDURE
Preparation of Hexadecanoic Acid by Oxidation of
l-Hexadecanol.
A 500-ml Erlenmeyer flask equipped with a reflux condenser was charged
with methylene chloride (150 ml), acetic acid (5 ml), 1-hexadecanol (4.0 g,
0.017 mol), water (100 ml), and Adogen 464 (1.0 g). Powdered potassium
permanganate (5.0 g, 0.032 mol) was added in small portions and the
solution stirred under gentle reflux for 4 hr. The solution was cooled and
10
194
Triphenylmethylarsonium chloride
Adogen 464
Adogen 464
5-Decanol
/-Menthol
Tetrabutylammonium
bromide
Tetrabutylammonium
bromide
Dicyclohexano-18crown-6
Dicyclohexano-18crown-6
Tetrabutylammonium
bromide
Adogen 464
Adogen 464
Adogen 464
Adogen 464
Adogen 464
Phase transfer agent
2-Propanol
Secondary alcohols
1-Decanol
1-Dodecanol
1-Tridecanol
1-Hexadecanol
1-Docosanol
1-Octanol
1-Heptanol
Benzyl alcohol
Benzyl alcohol
Benzyl alcohol
Primary alcohols
Substrate
chloride
chloride
chloride
chloride
chloride
Methylene chloride
Methylene chloride
Chloroform
Aqueous
Aqueous
Aqueous
Aqueous
Aqueous
Aqueous
Aqueous
Aqueous
Aqueous
Benzene
Methylene
Methylene
Methylene
Methylene
Methylene
Solid
Solid
Solid
Aqueous
Oxidant
phase
Benzene
Benzene
Pyridine
Benzene
Solvent
acid
acid
acid
acid
acid
Acetic acid
Acetic acid
Acetic
Acetic
Acetic
Acetic
Acetic
Additives
THE PHASE TRANSFER ASSISTED OXIDATION OF ALCOHOLS
T A B L E XXII
5-Decanone
Menthone (92)
Acetone (100)
Decanoic acid
D o d e c a n o i c acid (92)
Tridecanoic acid (92)
Hexadecanoic acid (95)
D o c o s a n o i c acid (87)
Octanoic acid (47)
Heptanoic acid (70)
Benzoic acid (100)
Benzoic acid (98)
Benzoic acid (92)
Products (% yield)
80
70
88
70
70
70
70
70
54
82
82
43
54
Ref.
195
7
2
2
2
2
2
8
I
7
S
2
|
OH
2
OL
X "
2
8
8
2
2
2
7
CH (CH ) CH(CH ) CH=CH(CH ) CH
3
3
CH (CH ) =C(CH ) OH
5
6
3
5
6
Benzhydrol
Unsaturated
alcohols
C H CH=CHCH OH
C H =CCH CH OH
CH (CH ) CH=CH(CH ) OH
Benzhydrol
Benzhydrol
3
Methylene chloride
A d o g e n 464
A d o g e n 464
Methylene chloride
Methylene chloride
Methylene chloride
Methylene chloride
Methylene chloride
A d o g e n 464
A d o g e n 464
A d o g e n 464
A d o g e n 464
Methylene chloride
Benzene
Pyridine
permanganate
Dicyclohexano-18crown-6
A d o g e n 464
Tetrabutylammonium
Solid
Aqueous
Solid
Solid
Aqueous
Aqueous
Aqueous
Solid
Solid
Acetic acid
Acetic acid
Acetic acid
Acetic acid
Acetic acid
Acetic acid
Acetic acid
6
3
3
5
5
2
2
2
2
7
2
7
(53)
II
Ο
2
2
2
8
8
1
II
2
Ο
II
OH
Ο
3
2
2
2
7
CH (CH ) C(CH ) CH—C(CH ) CH
3
CH (CH ) C(CH ) COOH
7
L1
7
7
C H ( C H ) C O O H (19)
6
C H C O O H (72)
C H C O O H (79)
C H ( C H ) C O O H (62)
H O O C ( C H ) C O O H (66)
C H ( C H ) C = C ( C H ) C O O H (73)
Benzophenone (93)
Benzophenone (100)
Benzophenone (97)
3
(50)
70
70
70
70
70
70
70
82
43
196
DONALD G. LEE
TABLE XXIII
OXIDATION OF ALCOHOLS USING SOLID SUPPORTS
Substrate
Solid support
Product (% yield)
2-Octanol
2-Octanol
2-Octanol
2-Hexadecanol
1 -Cyclohexylethanol
3-Methylcyclohexanol
Cycloheptanol
Cyclooctanol
Cyclododecanol
Cyclododecanol
Cholestanol
Cholestanol
Benzhydrol
Benzhydrol
Ethyl lactate
Benzyl alcohol
Cinnamyl alcohol
1-Hexanol
1-Octanol
1 -Octanol
1-Decanol
1 -Dodecanol
Molecular sieve
Alumina
CuS0 5 H 0
CuS0 5 H 0
CuS0 5 H 0
CuS0 5 H 0
Molecular sieve
Molecular sieve
Molecular sieve
Alumina
Molecular sieve
CuS0 -5H 0
Molecular sieve
CuS0 5 H 0
CuS0 5 H 0
Molecular sieve
Molecular sieve
Molecular sieve
CuS0 5 H 0
Molecular sieve
Molecular sieve
Molecular sieve
2-Octanone (82)
2-Octanone(100)
2-Octanone (96)
2-Hexadecanone (84)
Methyl cyclohexyl ketone (96)
3-Methylcyclohexanone (97)
Cycloheptanone (94)
Cyclooctanone (87)
Cyclododecanone (90)
Cyclododecanone (95)
Cholestanone (9\)
Cholestanone (91)
Benzophenone (100)
Benzophenone (100)
Ethyl pyruvate (73)
Benzaldehyde (80)
Cinnamaldehyde (94)
Hexanal (29)
Octanal (20)
Octanal (26)
Decanal (26)
Dodecanal (34)
a
b
4
2
4
2
4
2
4
2
4
2
4
2
4
2
4
2
b
b
b
b
b
b
ft
b
0
Ref.
64
64
64a
64a
64a
64a
64
64
64
64
64
64a
64
64a
64a
64
64
64
64a
64
64
64
Yield determined by GLC unless indicated otherwise.
Isolated yield.
the precipitated manganese dioxide was reduced by addition of the required
a m o u n t of sodium hydrogen sulfite. T h e a q u e o u s phase was separated,
saturated with sodium chloride, a n d extracted with ether (2 χ 40 ml). T h e
organic layers were combined, dried over a n h y d r o u s magnesium sulfate,
a n d concentrated by rotary evaporation to give a solid residue. T h e p r o d u c t
was purified by recrystallization from a q u e o u s ethanol (2 χ 50 ml) to give
hexadecanoic acid (4.0 g, 0.016 m o l , 95%) m p 6 2 ° - 6 3 ° C .
IX. Oxidation of Phenols
Phenols readily reduce p e r m a n g a n a t e in b o t h a q u e o u s a n d n o n a q u e o u s
solutions. A l t h o u g h this is an i m p o r t a n t reaction in some water purification
p r o c e s s e s , its application to organic syntheses is n o t extensive.
89
18
19
N. A. Gibson and J. W. Hosking, Aust. J. Chem. 18, 123 (1965).
J. T. O'Connor and Κ. Y. Baliga, J. Sanit Eng. Div. Am. Soc. Civ. Eng. 96 (SA6), 1377 (1970).
//. Phase Transfer Assisted Permanganate
Oxidations
197
The products obtained appear to be formed in oxidative polymerizations
a n d / o r coupling reactions. As the following reactions indicate, the a m o u n t s
of coupling and polymerization obtained from 2,6-dialkylphenols is controlled by the size of the alkyl g r o u p s .
70
198
DONALD G. LEE
3,5-Di-ter/-butylcatechol can be converted into 3,5-di-teri-butyl-0-quinone
in excellent yields in methylene chloride using either 18-crown-6 or Adogen
464 as c a t a l y s t s . '
70
90
OH
Ο
97%
In aqueous solutions it has been found that the reaction of phenolates with
permanganate ion proceeds by a mechanism in which the first step involves
electron transfer with formation of a phenoxy free r a d i c a l .
9 1 , 9 2
Although mechanism studies have not been reported for the phase transfer
assisted oxidations, the products obtained may be accounted for if formation
of a phenoxy free radical is assumed to be the initial reaction in nonpolar
solvents as well. F o r example, the oxidation of 2,6-dimethylphenol may be
visualized as proceeding as follows:
Polymer
//. Phase Transfer Assisted Permanganate
Oxidations
199
X. Oxidation of Ethers
Schmidt and S c h a f e r have reported that aliphatic ethers can be oxidized
by benzyltrimethylammonium permanganate in methylene chloride solu­
tions. The reaction, which involves conversion of an α-methylene into a
carbonyl group, results in formation of an ester. In many respects the
reaction is similar to the oxidation of ethers by ruthenium t e t r o x i d e .
However, this procedure has an advantage over the use of ruthenium
tetroxide because aromatic rings are not as readily degraded by benzyltriethylammonium p e r m a n g a n a t e . The results reported by Schmidt and
Schafer have been summarized in Table XXIV.
Although it has been shown that ether oxidation by ruthenium tetroxide
involves hydride a b s t r a c t i o n , the products summarized in Table X X I V
93
94
93
95
9 0
9 1
9 2
9 3
9 4
9 5
G. W. Gokel and H. D. Durst, Synthesis, 168 (1976).
M. Dore, B. Legube and N. Merlet, / . Fr. Hydrol. 18, 53 (1975).
C. Sebastian, M.S. Thesis, Univ. of Regina, Canada, 1979.
H. J. Schmidt and H. J. Schafer, Angew. Chem. Int. Ed. Engl. 18, 69 (1979).
D. G. Lee and M. van den Engh, in "Oxidation in Organic Chemistry (W. S. Trahanovsky,
ed.), Part B, pp. 222-225. Academic Press, New York, 1973.
D. G. Lee and M. van den Engh, Can. J. Chem. 50, 3129 (1972).
TABLE
XXIV
OXIDATION OF ETHERS BY BENZYLTRIETHYLAMMONIUM PERMANGANATE IN METHYLENE CHLORIDE"
Time Temperature
(days)
(°Q
Ether
ConYield version
(%)*
(%)
Product
c
Ο
CH (CH ) 0(CH )3CH3
3
2
3
2
C6H CH OCH C H
5
2
2
6
5
14
30
6
- 5 to 20
CH (CH ) OC(CH ) CH
Ο
3
2
3
2
2
3
||
C H CH OCC H
Ο
Ο
6
5
2
6
II
C H CH 0(CH ) CH
6
5
2
2
3
CH 0(CH ) CH
3
2
3
CH 0(CH ) CH
3
2
7
3
3
3
C H CH OCH(CH CH )
6
5
2
2
C H CH OCH
6
5
2
3
2
3
8
0
10
42
14
42
7
-5
7
-5
5
3
2
3
2
3
14
2
30-42
6
2
3
80
3
2
2
3
3
2
6
3
5
8
5
3
||
CH OC(CH ) CH
Ο
||
CH OC(CH
) CH
Ο
||
C H COCH(CH CH )
Ο
2
3
2
||
C H COCH
Ο
||
CH (CH ) COCH(CH CH )
Ο
6
CH (CH ) OCH(CH CH )
ο
5
6
84
II
2
C H CO(CH
II
) CH
Ο
6
58
5
C H C—OCH 0—CC H
6
80
5
99
90
40
23
79
41
85
84
84
83
73
45
3
3
2
2
2
3
2
II
CH CH CCH CH
Ο
3
C H CH OCHCH
6
5
2
9
3
5
2
2
3
3
II
C H COCHCH
6
5
83
71
3
Ο
II
CgH CCH
Ο
5
C H CH OC H
6
5
2
6
5
CH (CH ) OCHCH
3
2
3
3
9
0
8
25
II
C H COC H
Ο
II
II
CeH CCH
6
5
6
5
C H
6
6
3
5
94
42
67
38
3
5
Ο
II
3
CH (CH ) COCHCH
3
2
2
3
Ο
2
II
CH (CH ) OC H
3
a
b
c
2
3
6
14
5
42
CH (CH ) OCC H
CH (CH ) COC
H
Ο
||
3
2
3
6
5
3
2
2
6
5
From Schmidt and Schafer.
Yield is based on the amount of ether consumed as determined by gas chromatography.
Conversion is based on the amount of ether initially present.
93
92
11
//. Phase Transfer Assisted Permanganate
Oxidations
201
could also result from a hydrogen a t o m transfer mechanism which would
be more likely in a n o n p o l a r solvent.
R
O—R' + Q M n < V
• R
+
C
Η
/ \
O—R' + Q HMnO"
+
.C
Η
R
\
C
/
Ο—R'
\
Η
R
2
/
O—R'
Ο
+
+
\
A H
II
ο
Q H MnO
4
/\
_
3
HO
0"Q
+
XI. Oxidation of Aldehydes
Aldehydes are easily oxidized to the corresponding carboxylic acids under
phase transfer conditions. Several examples are summarized in Table XXV.
The reactions proceed in good yield to give a single product. It should be
noted, however, that the oxidation of cinnamaldehyde and phenylpropargyl
aldehyde resulted in cleavage of the c a r b o n - c a r b o n double and triple bonds
respectively. Hence, it is apparent that formyl groups cannot be selectively
oxidized in the presence of double b o n d s .
XII. Oxidation of Sulfur Compounds
Sulfides and sulfoxides are oxidized by permanganate to the corresponding
sulfones in both aqueous and organic solvents. The phase transfer assisted
reaction has also been found to produce pure products in good y i e l d s .
Table X X V I contains several examples.
U n d e r similar conditions alkyl sulfides are converted to sulfonic a c i d s .
2
7 0 , 8 0
70
General Procedure for Phase Transfer Assisted Permanganate
Oxidations
of Sulfides
Potassium permanganate (45.5 mmol), dissolved in 40 ml of
water and Adogen 464 (1 g) dissolved in 10 ml of methylene chloride were
placed in an Erlenmeyer flask fitted with a condenser and immersed in a
water bath at r o o m temperature.
80
permanganate
permanganate
permanganate
permanganate
Tetrabutylammonium permanganate
Cetyltrimethylammonium bromide
Dicyclohexano-18-crown-6
Adogen 464
Adogen 464
Tetrabutylammonium
Tetrabutylammonium
Tetrabutylammonium
Tetrabutylammonium
Phase transfer agent
° Acetic acid (5%) was added to the solvent.
m-Nitrobenzaldehyde
/7-Chlorobenzaldehyde
/7-Anisaldehyde
4-Acetoxy-2-methoxybenzaldehyde
Piperonal
Piperonal
Benzaldehyde
Cinnamaldehyde
Phenylpropargyl aldehyde
Substrate
Pyridine
Water
Benzene
Methylene chloride
Methylene chloride
Pyridine
Pyridine
Pyridine
Pyridine
Solvent
THE OXIDATION OF ALDEHYDES
TABLE XXV
0
0
Solid
Aqueous
Solid
Aqueous
Aqueous
Solid
Solid
Solid
Solid
Oxidant phase
ra-Nitrobenzoic acid (95)
p-Chlorobenzoic acid (99)
/7-Anisic acid (94)
4-Acetoxy-2-methoxybenzoic acid (85)
Piperonylic acid (99)
Piperonylic acid (64-74)
Benzoic acid
Benzoic acid (83)
Benzoic acid (81)
Products (% yield)
43
65
82
70
70
43
43
43
43
Ref.
//. Phase Transfer Assisted Permanganate
Oxidations
203
T A B L E XXVI
PHASE TRANSFER ASSISTED OXIDATION OF ORGANIC SULFUR COMPOUNDS
BY AQUEOUS POTASSIUM PERMANGANATE
0
Substrate
Product (% yield)
Phenyl sulfide
w-Butyl sulfide
«-Octyl sulfide
/-Butyl sulfide
Dibenzothiophene
Phenyl sulfoxide
fl-Butyl sulfoxide
1-Dodecanethiol
Phenyl sulfone (98)
«-Butyl sulfone (95)
«-Octyl sulfone (94)
/-Butyl sulfone (82)
Dibenzothiophene sulfone (93)
Phenyl sulfone (95)
,i-Butyl sulfone (86)
1-Dodecane sulfonic acid (87)
The phase transfer agent was Adogen 464, the solvent was methylene
chloride containing 5-10% acetic a c i d .
a
70,80
The mixture was stirred for a b o u t 2 hr with a magnetic stirrer and the
manganese dioxide that formed was reduced with sodium bisulfite and
dilute sulfuric acid. The organic phase was separated and the aqueous phase
was extracted with ether (3 χ 40 ml). The combined organic solvents were
dried (anhydrous M g S 0 ) and the volatiles removed using a rotary evapo­
rator. The product was purified by crystallization or distillation.
4
XIII. Oxidation of Halides
The oxidation of hydrocarbons can sometimes be facilitated by prior
halogenation of the oxidation site. U n d e r reaction conditions, the halide
presumably undergoes hydrolysis to the corresponding alcohol which is
then oxidized. The following reaction illustrates this a p p r o a c h .
96
I. L. Finar, "Organic Chemistry," Vol. 1, 5th ed., p. 720. Longmans, Green, 1967.
204
DONALD G. LEE
It has been observed that benzhydryl chloride can also be oxidized under
phase transfer conditions. Benzophenone was obtained in 82% yield when
benzhydryl chloride and tetraethylammonium bromide were dissolved in
methylene chloride and treated with aqueous p e r m a n g a n a t e .
80
TYPICAL EXPERIMENTAL PROCEDURE
Preparation of Benzophenone by Oxidation of Benzhydryl
Chloride
A 500-ml Erlenmeyer flask equipped with a condenser was charged with
methylene chloride (120 ml), benzhydryl chloride (3.0, 0.015 mol), water
(20 ml), tetraethylammonium bromide (1.0 g), sodium hydroxide (2.2 g)
and potassium permanganate (2.5 g, 0.16 mol). The mixture was stirred
with a magnetic stirrer and refluxed for 2 days. The precipitated M n 0 was
reduced using sodium bisulfite and dilute sulfuric acid. The organic phase
was separated and the aqueous phase extracted with ether (3 χ 50 ml).
The combined organic solvents were dried (anhydrous M g S 0 ) and the
volatiles removed using a rotary evaporator. The crude mixture obtained
was analysed by G L C .
80
2
4
XIV. Oxidation of Amines
The oxidation of amines under phase transfer conditions results in the
formation of products similar to those found during oxidations by neutral
aqueous permanganate. F o r example, the oxidation of dibenzylamine in a
methylene chloride solution containing Adogen 464 as a phase transfer
agent gave 7V-(a-dibenzylaminobenzyl)benzamide and b e n z a l d e h y d e :
70
PhCH NHCH Ph " ^ Q ^
C
2
2
/
d
n
en
464
Q
> PhCONHCH(CH Ph) + PhCHO
I
28%
Ph
46%
2
2
A similar reaction was observed when Shechter and R a w a l a y oxidized
dibenzylamine with potassium permanganate in a neutral solution of water
and ter/-butyl alcohol. They obtained 7V-(a-dibenzylaminobenzyl)benzamide
as the sole product (62% yield) but noted that benzaldehyde was one of the
hydrolysis products. They also described a possible reaction mechanism that
leads to the formation of this rather complex product.
97
9 7
H. Shechter and S. S. Rawalay, J. Am. Chem. Soc. 86, 1706 (1964).
//. Phase Transfer Assisted Permanganate
Oxidations
205
Rossi and T r i m a r c o also found that similar products were obtained when
1 -aryl-5-morpholino-4,5-dihydro-v-triazoles and 1 -aryl-5-dimethylamino4,5-dihydro-v-triazoles were oxidized by potassium permanganate either in
acetone or in benzene containing cetyltrimethylammonium bromide as the
phase transfer agent.
The products were the corresponding 2-oxomorpholino or 7V-formylamino
compounds:
26
Ar
The observed products suggest that these reactions may be initiated by
oxidative attack on a hydrogen adjacent to a nitrogen. However, the report
did not contain any mechanistic considerations.
TYPICAL EXPERIMENTAL PROCEDURE
Preparation of
l-(4-Fluorophenyl)-4-methyl-5-(2-oxomorpholino)-4,5-dihydro-v-triazole*
To a 250-ml round-bottomed flask fitted with a dropping
funnel and an efficient mechanical stirrer was added cetyltrimethylamm o n i u m bromide (36.4 mg, 0.1 mmol), benzene (25 ml), and a solution of
potassium permanganate (0.553 g, 3.5 mmol) in water (40 ml). A solution
of l-(4-fluorophenyl)-4-methyl-5-morpholino-4,5-dihydro-v-triazole (0.53 g,
2 mmol) in benzene (40 ml) was dropped into the flask and stirring was
continued until no more starting c o m p o u n d could be detected by T L C . The
* Reprinted with permission from Rossi and Trimarco , courtesy of Thieme, Stuttgart.
26
206
DONALD G. LEE
reaction mixture was filtered and the organic layer separated. After concentration, the product was precipitated by adding pentane to the benzene
solution and purified by chromatography over silica gel with benzene/ethyl
acetate (4:1). The product was recrystallized from benzene/pentane;
yield, 4 5 % .
ACKNOWLEDGMENT
The author wishes to acknowledge the assistance and encouragement of several co-workers
who participated in some of the work reported herein. In particular, use of previously unpublished results obtained by Dr. Victor S. Chang, Dr. N. S. Srinivasan, Mr. Hasan Karaman and
Mr. William Rennie is noted with gratitude.