L
'
produCt of the microscale technique.
The a proach outlined in this and the followingpaper is not
intend to be a subtitute for adequate laboratory ventilation
or for carryingout certain manipulationsin properly operating
hoods, We do feel that the concept offers the potential for
increasing laboratory safety while lowering capital investment,
energy use, materia1costs and indicatesan avenue which other
.chemistry departments may wish to explore.
J
Acknowiedgmenl
The authors would like to acknowledge the assistance of
Bowdoin College undergraduate Chemistry Majors Marcia
Meredith and Gregory Merklin in carrying out the measurements of emissions and concentrations. We also wish to express our thanks to A. H. Fuchs, Dean of the Faculty, for his
constant encouragement of this program from its inception
Financial support for the prejiminary work described here
-_-
has been provided by Bowdoin College and a grant to the
Department by the du Pont Corporation.
Literature Ciled
(1) Bmyer. R E.. J. CHLM.EDW, 57. A287 (1980).
(2) Mclnikmv, J.. Keefe, J. R. and Ber-Uin. R L,1.W
w
t Euuc. 58. A11 (1982).
(3) Hertlein. F, 111. J. C H W EDUC.. 67. A199 (1979).
(4) Bayer. FL. J. CHBM. EDUC 69.4385 (1982).
(5) F d . Reg..ZS.Ch. 17.1910.1000.
(6) P e d wmmuniucion with m wietyol(7) Turk. A.. ASHRAE Joumul, U(1963).
(8) Emen. N. A., Enu. Sci. Technol.. I t , 331 (1978).
(9) Wdden. R A. and Scheff, P. A.,"Indmr Air Pollution." Wiley. New York 1985
Narirml Aadcmy h m ,W;rhinglaq
(10) NaLionrl Rasurh coune*'Indam Pdu-"
Dc 1981.
(11) %vu. P.J,Simynd* P.G, md S L u ,F. H..Enu. Sei. Tlchnol.. 6,609 (1972).
(12) Ishuu,Y..€nu. &I. Tcchnol., 14.1254 (1980).
(13) Butcher, S S. and tyccU.6. J. Submiuad for publiitioo.
(14) Hawr, T.Rand Cummim, R L.AML Chrm., 36,679 (1964).
(15) Butcber. S. S. and Ellenbecksr. M.J.. J. Air Poll. Control A m . . 32,380(1981).
(16) Committee m I n d d VenliL(i0a '1ndUwi.l Ven(iLtion." Amcriun ConfdCovcmmeatdIndumtkl HyLi.nkl* Laming, Mf. 1980.
Microscale Organic Laboratory
+ e
II: The Benefits Derived from Conversion to the Program
and Representative Experiments
Dana W. Mayo, Samuel S. Butcher, Ronald All. Pike',
Caroline M. Foote, Janet R. Hotham, and David S. Page
Bowdoin College. Brunswick, ME 04011
:-. ..
3 from
Part I presented apreliminary study of the emissions
selected processes and the mixing of these emissions within
t h e laboratory atmosphere (I).?'hi.. paper describes the redsztion to practice of microscale laboratory prkedures and
outlines benefits derived from this approach to improving
laboratory air quality. In order to illustrate the style and scale
of &e laboratory experiments which may be incorporated into
such a program two representativeexamples are given in detail
in the discussion,
We are currently in the procesa of developing and testing
a wide variety of experiments a t the microscale level. These
exercises will eventually provide the core of a laboratory texfi
Wa are also in tbe process of evaluating the reduction of
harmful emissions from these microexperiments (1).The resulb of this latter work and an illustrated discussion of the
microtechniques involved will be incorporated inan iiwtcuctar's manual to accompany the new student text.
MIcroscale bcganic Laboratory Experiments
Two r e a w n sequences which have been reduced to practice in our laboratory program are described. These experiments represent a variety of introductory transformations
ranging from the classical to the rarely performed. In all cases
the quactity of starting material does not exceed 150 mg.
The compelling arguments for undertaking the microapP w c h are as follows: (1)reduction of the scale of starting
material by 100-fold (nearly 1000-fold in certain cases) leads
to a parallel reduction in organic soluents required for these
experiments. This contraction from the usual level (50-500
9) of solventJstudent/experimentreduces the demands on the
L
4
Resentad at the 187th Mationat ACS Meeting. St. Louis, MO, April
1984.
' k m a n e n t address: Memmack College. North Andover. MA
01845,
...I
laboratory ventilation system (I); (2) regardlessof the quality
of a laboratory atmosphere, microscale reactions simply reduce student contact with toxic materials of all types; (3) the
threat to laboratory safety from explosion or fire is largely
eliminated; (4) the cost of chemicals parallels the 100- to
1000-fold reduction in use; (5)conversely, the very large reduction in chemical costs presents on opportunity to expand
the available variety of experiments. Until the introduction
of the microscalereactions,elimination of experiments based
on cost has been a recurring theme over the past few years in
this laboratory, and it appears that the complete elimination
of the undergraduate introductoryorganic laboratory at many
institutions is a likely response to advancing budgets; (6) the
option of being able locally to synthesize adequate supplies
of reagents and starting materials, not commerciallyavailable,
for use in a particular experiment, is an additional bonus of
the microapproach If a relatively simple synthesis of the
materials is available in the literature, a multiple year supply
can usually be obtained from a single synthetic preparation
(seeexperiment B: Preparation of an Aromatic Nitrile); (7)
in our experience microglassware (Ace Glass,Inc) (2) is considerably more. durable than macro- or semimicro-ground
glass equipment.This stability translatesinto lower laboratory
breakage costs and, thus, is welcome news to students, whose
costs for organicchemistry are already very high. It should be
emphasized that, while commerciallyavailablemicroglassware
kits (2)are attractive for programs underthking full conversion
to this scale of experimentation, many of the microscale experiments can be carried out utilizing ordinary organic laboratory equipment. For example, the Cannizzaro reaction described below can be run quite satisfactorily employing two
10 X 75-mm test tubes and one 12-mLcentrifuge tube plus a
Pasteur pipet (which can function both as a &paratory funnel
and as a means to transfer solutions); and finally, (8)we perceive a significant pedagogic advantage in this laboratow
concept at the sophomore level. For example, the close relationship of the techniques required to those of analytical
chemistry reinforces parallel laboratory programs a t thisstage
.I
.
--
.
in the student's development. Related to this point is our
observation that students quickly recognize that small accidental losses of material cannot be tolerated when working
with milligram quantities.
The following are two experiments currently being carried
out by a volunteer section in our sophomore laboratory program:
Cannizzaro Reaction
The Cannizzaro reaction of p-chlorobenzaldehyde, (I),
represents an interesting example of a classical oxidationreduction reactionhot often carried out in the introductory
organic laboratory program. The procedure represents a
particularly difficult experimental challenge as the quantity
of starting aldehyde has been reduced 100-fold from the
conventional (3)quantity and ultimately becomes divided into
two products which are both isolated and characterized.
1
I1
III
micro-scaleexperiments. First, the Pasteur Nter pipet h
extensivelyfor the transfer of smaU quantities of liquids
PFP is an essential means of successfully carrying OUI
nipulations of small quantities of liquids required in tll
actions undertaken a t this scale and ita use should be ii
duced early in the program. Second, the separation of u
from neutral products is effectively deinonstrated. Thim
technique of recrystallization is demonstrated by purifia
of the alcohol.
Preparation of an Aromatic Nitrile
This is a conversion usually requiring the use of an arolr
amine (o-toluidine. 11g), diazotization (CuS04-5H20,
NaN02,7.3 g) and cyanide (NaCN, 16 g) in a Sandmeya
action (6).
We start with an aldehyde, (for example, piperonal,
a known flavoring material, 30 mg) which is converted 11
0-phenylated oxime, (V).This crystalline inkmedim
isolated,characterized, and then treated with alcoholic:
to yield the nitrile, (VI) (10 mg) by an elimination react1
This approach is based on the work of Miller and I,OH
(7).
C!@uaro Reaction: Student Preparation of p-chlorobenzyl
Alcohol (ll) and p-Chknvbenzoic Acid (Ill)
AuK.edure: In a 1-mL vial is placed p-chlorobenzaldehyde (I) (150
mg, 1.07 mmol) followed by methanol (0.4 mL). In a 5-mL micro-
reaction cone vial is dissolved potassium hydroxide (0.24 g, 4.3 mmol)
in distilled water (0.4 mL). This alkaline solution is then cooled to
mom temperature. The aldehyde solution is transferred by Pasteur
pipet to the gently swirled reaction vial containing the base. A
micro-reflux condenser is attached to the flask and the reactants are
maintained
by use of a hot water bath. After cooling,
VI
2 mL of distilledwater are G e d and the aqueous methanolic solution
extracted with methylene chloride (three 0.5-mL portions). [Note:
The reagent 0-(2,4dinitrophcnyI)hydroxylt1mine, (3
The alkaline phase is saved for further workup.] %e methylene
not commercially available, but the synthesis from e t h j
chloride layers are transferred by Pasteur filter pipet (PFP)2 to a
is straightforward (8,9).A slh
3 - m L v i a l T h ~ c o m b i n e d e ~ a r e w a s h ~ w i t h s a ~ ~ s o d i u mhydpxyecetimidate (vm)
mocyfied and reliable route is included below:
bicarbonate solution (two 0.25-mL portions). The aqueous upper
e
-4
phase is removed and discarded (a PFP is used in this operation). The
methylene chloride solution is dried over granularanhydroussodium
adfate (150 mg). The dried solution is then transferred by a PFP to
a tared 5-mL micro-reaction cone vial. The sodium sulfate drying
agent is r i dwith fresh methylene chloride (0.3 mL) and the wash
combined with the dried organic phase. The solvent is then evaporated usingp stream of dry nitrogen gas under the hood to yield the
crude alcohol product, II. After weighing, this crude product is recryatallid from a solution of 4% acetone and hexane ( 4 . 2 5 mL).
Collection of recryatallid I1 by use of a Hinch filter (11.5-mm plate
diameter) followed by washing with hexane (0.2 mL) yields p-chlorobenzyl alcohol, (II), m.p. 6 8 - 6 9 O (lit. value 75O) (4).
The alkaline aqueous phase (28mL) remaining from the original
extraction procedure is acidified with concentrated hydmchloric acid
(0.4 mL). The voluminouswhits precipitate iscollected under reduced
X
pmsure on the Hinch filter and rinsed with distilled water (2 mL).
Air drying yields para-chlorobenzoic acid, (111). m.p. 237-239' (lit.
Preparation
of Nitrile Reagent: Instructor preparationof u
value 243O) (5). The product may be recrystallized from methanol.
(2,4-dinitmphenyl)+jxfro<y1amine,( x )
Characterization of the reaction produds, I1 and 111, is carried out
by comparison of their IR spectra with a reference standard.
This preparation illustrates the synthesis of a reagent;
Typical product yields for the alcohol, 11. are in the range of 48 mg
in the reaction sequence that is not commerciallyavail]
'(63%). Fbr the acid, 111, typical yields around 62 mg (75%) are obOn the scale described below, the amount of product I3
tained.
tained would be sufficient for appoximately 150 stud1
-
The above experiment involves the utilization of a number
of techniques which will be useful to the student carrying out
Since the intermediate M stores easily for long periods off
sufficient material for several years can be readily prodl
in one preparation.
*The Pasteur filter pipet is a very useful means of efficiently transferring small quantities of solution. These pipets are easily assembled
from standard PasteV gkss pipets (availablefrom Fisher Scientific &.)
by shorteming the capillary tip (from 125 to 50 mm) and inserting a
prewash4 cotton plug (3-5mm)into the tip end.
Procedw: Ethyl 0-(2,4-dinitmphenyl)a~etohydro*amate
((
In a 250-mLthree-necked round-bottomed flask fitted w
condenser protected by a calcium chloride drying tube, mail
stirrer and addition funnel is placed ethyl N-hydroxyacetimi
(VIII), (3.1 g, 0.03 mol) dissolved in absolute ethanol (40m L
tasaium hydroxide (pellets, 1.7 g, 0.03 mol) is suspended in tkl
lution. A solution of 2&dinitrochlo~benzene,(VII). (6.1g, 0.01:
-
'l'he above reaction sequence thus demonstrates the c h i c
fdrmation of an oxime derivative of an aldehyde carbonyl
followed by a recently described example of a base catalyzed
precipitation of the light yellow hydromate. After *-m.ng for an
elimination reaction. The intermediate product 2 purified by
additional45 min at 10'. the mixture is filtered undu reduced presrecrystallization and the nitrile isolated in the pure state folsure to yield the product, IX.Recrystallization of thismaterial from
absolute ethanol gives ethyl O-(~,edinitrophenyl)a~y~o~etohydro.amab, lowing column chromatography.
.-."p".Js
\LU
U U l l WIUl
surriw whrle mrunta~~~ing
the reaction mixture at &1W by aid of an
ice bath. The solution rapidly becomes bomogewoue followed by
(E),
us light yellow, flat plates, m.p. 111-112' (lit, value 211-112')
(8).
Stored in the freezer under nitrogen t
hismaterial is stable for a long
period of time. Typical crude yields average 6.7 g (83%)and recrystallized yields are in the range 6.0 g (75%).
Procedure: 0-(2,4-dinitrophenyl)hydroxylamine,
(X).
In a 50-mL three-necked round-bottomed flask fitted with a
magnetic stirrer, addition funnel and condenser is placed IX (2.9 g,
0.01 mol). Dissolution of IX is then accomplished by dropwise addition of 70% perchloric acid (10 mL) a t 0' (icebath) with stirring. After
the addition of the acid the reaction mixtpre is held at 0' for an additional 60 m i a The temperature of the solution is then allowed to
rise to ambient values and stirring'continued for an additional 24 h.
Filtration of the precipitate under reduced pressure yields crude X.
Recrystallization from hot ethanol gives 0-(2,4-dinitrophenyl)hydroxylamine, (XI.m-p. 111-112' (lit. value lll-112°) (7.9). mid
crude yields average 1.8 g (8946). RecrystaUiied yields range in the
vicinity of 1.6 g (80%).
Aromatic Nitrile: Student Preparation of Piperonylonitrile (VI).
In a &XI&micro-reaction flask fitted with a reflux candenser and
drying tube, is placed 0 - ( 2 , 4 a i n i t r o p h e n y I ) h ~ (X).
~ ~ ~(40
i~,
mg, 0.20 mmol). Dissolution of X occurs on the addition of absolute
ethanol (3 mL) with gentle warming. The condenser isremoved and
is added to the reaction mixture.
p i p e r o d , (IV),(30mg, 0.02"01)
Following dissolution of the aldehyde, 12M HCI (two dmps)is added
through the refluxcondenser (Pasteurpipet). Complete precipitation
of the oxime, (VI,is accomplished by swirling the reaction flask in an
ioebath. Callectionof the precipitate by use of a Hi& filter (1l.5-mm
plate diameter), followed-bywashing with cold absolute ehnol(O.5
mL, saw filtrate) &d air drying gives piperonal O-(2,4ainitrophenyl)oxime, (VI,(lit. value, m.p. 194-195O) (7). Refrigerhion of
the filtrate for at least 24 h produces a second crop of oxime crystals.
This second crop, co1lected by the same technique, may be combined
with the initial product if its m.p. is above leOo. Overall oxime yields
in excess of90% are generally obtained.
Characterization of the oxime, (V), is carried out through comparison of its infrared spectrum to a refereuce standard. Provided
there is R close spectral match and the m.p. is in the range (>187O),
proceed to the second step in the reactiou sequence (a m i n i u m of
50 mg or a 75% yield of V is m"ry to continue).
In a M-mL micro-reaction h k fitted with reflux condenser is
plpced the oxime, V. (50mg,0.15 mmol) suspended in 95% ethanol
(S mL). Ethanolic KOH (0.2 N,2 mL) is then added. The reaction
mixture is slowly heated to reflux temperature by use of a hot water
bath. During this warming period the solution rapidly kunr a deep
yellow. The reaction mixture is maintained a t miid r d l a for a period
of 1 h. Following the reflux period, the condenser ia removed, nnd the
rcwt.im mixture concentrated b approximately a 0.5-mL volume
employing a gentle stream of nitrogen gas. An extraction mlution is
pspandby diluting !j%
NaOH (1.5 mL) with distilled water (7.5 mL).
This b i c solution (three3-mL portions) is used to transfer the above
rariction qes-idue (0.5 mL) to a 12-mL capped centrifuge tube. This
wpchsion is extract4 with methylene chloride (four 2-mL portions).
Thc organic fractions are combined and dried over granular anhylnws sodium sulfate (-70 mg). By use of a PFP the dried solution
s transferred into a IO-mL micro-reaction flask. The drying agent
s rinsed with methylene chloride (two 1-mL portions) and these
innings combined with those from the initial extraction. The solvent
I evaporated (in the hood) under a stream of N2 gas to obtain the
rude piperonylonitrile, (VI). This residue is dissolved in methylene
hloridelbexane 1:1(50.25 mi.). The solution is applied to the head
f a micro-chromatographic column (neutral alumina, activity 1.0.3
1. The column is eluted with the CH&lz/hexane (1:1) solvent mixture
-1.0 mL). On evaporation under a stream of N 2 gas the single colc t d fraction yields the desired piperonylunitrile. (W),
a~white, thin
ctdles. &.p. 92-93' (lit. value 92-93")(7).
Characterization of th@produd is carried out by comparison of its
frored spectrum with a reference standard and a mixed m.p. dermination with a reference standard. Typical crude yields of VI are
the range of 16 mg, (73%). Those of purified material are in the
nge of 10 mg (45%).
Discussion
One factor leading to the choice of the above experiments
for inclusion in this microprogram is that they produce readily
crystallizablecompounds.Solid products in the 5-15 mg range
can be dealt with by beginning students in a reasonably easy
manner. Furthermore, as micro-sampling techniques have
been developed for routine characterization of solid materials
by infrared spectroscopy,heavy use of this type of data is incorporated in product determinations.
A series of parallel experimentsand techniques for handling
liquids a t the mg level is now in progress. In thisgroup of reactions, gas chromatography will play a significant role in
product purification and analysis. This work will be reported
in future publications. The reduction to practice of a number
of microscale experiments by a volunteer test section of our
organic laboratory course has established the feasibility of the
microlaboratoryconcept. These results have convinced us that
conversion of organic laboratory programs to the milligram
level can be achieved. .
We have pointed out a number of advahtages which
prompted consideration of this curricular change. There
clearly are further advantagesto be gained in adoption of this
program by other institutions facing major ventilation modernization or new construction costs. Also,it should be mentioned that additional savings in operational costs should
result from reduced waste chemical disposal problems.
In summary, it is felt that the concept offers the potential
for increasinglaboratory safety and at the same time lowering
capital investment, energy use, and material costs. Carefully
developed7it can introduce students to an exciting range of
organic reactions, some of which would not be accessiblewith
standard procedures. Finally, the m i c r d e laboratory approach offers the pedagogical challenge of placing a greater
demand on the development of laboratory skills and the
benefits derived therefrom.
Acknowledgment
The authors would like to acknowledge Marcia Meredith
and Gregory Merklin for their efforts and suggestionsduring
the development of the initial set of experiments for thb instructional laboratory and for their help in carrying out the
measurement of emissionsand concentxations. The enthusiasm of the 19 sophomore organic students who volunteered
for the microscale pilot section during its fvst two yeam of
operation at Bowdoin played a key role in encouraging us to
continue these efforts. We also wish to express OUT thanks to
A. H.Fuchs, Dean of the Faculty, for his constant encouragement of this program from its inception.
Financial support for the preliminary work described here
end in Part I has been provided by Bowdoin College and a
grant to the Department by the du Pont Corporation.
Liferature Cited
f
(1) Butcher. 5.S.. Mayo. D.W., Pike. R. M..Fou(c. C. M.. Hochun. J. R.. urd P 4 e . D.S.,
J. CHEM. EOW.,(1984).
(2) Ace Clara, Inc., Vineland. NJ 08360.
(3) DunL H. D.and Cokel. G. W.. "EsperimenlllOWMU Chemistry." McGnw-HiU. lnc..
Ncw York. NY. 1980. p. 331.
(4)
Wrrut.R.C..(editor),"HandhookofChemiaty.nd
Phylia."S2nd Edition,Chemiul
Rubber Publishing '3..Cleveland, OH, 1972, p. C-516.
(5) See rel. 4, p. C-181.
(6)
l
Appkbn-Cen. . Swinehart. J. S.. "Oiaanic Chcmirtw An E r p r i m e n ~ Approach."
tu+.hltR.
New Y k . NY. 1969. p. 399.
(7) Miller. M. J. and Lwd0n.G. M.. J. Ora. Chem., 40.126 (1975).
(8) Il~erW.
A. 0.and Mmer. A.. H e l c C h h Acio. 46. xu4 (1963). The imidate is . d a b l e
from the Aldrich Chcmicsl Co.
(91 Tamara. Y.. Minsmikawa. J., Sumoto. K.. Fujii. S., and Ikeda. M.,J. Or& Chrm.. 3%
1'239 (1973).
Volume 62 Number 2
February 1985
151
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