SD 433 „
190 S7
REACTIGNS GF LIGNIN WITH HYDR.C•C{'
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVIC E
FOREST PRODUCTS LABORATOR Y
Madison, Wisconsi n
In Cooperation with the University of Wisconsi n
November 1938
By E . E . HARRIS, Chemis t
Forest Products Laborator y
and HOMER ADKINS, Professor of Chemistr y
University of Wisconsi n
Abstract
Lignin isolated by methanol and hydrochloric aci3,, ., alkali lig iin ,
and sulphuric-acid lignin have been subjected to teruperatires x~f 2°50 t o
260° C . in the presence of hydrogen at 170 to 400 atmospleres . .Fou r
products have been separated and identified ; methanol ;-n--propyieyclohexanol-l ; 14--n-propylcyclohexaned .iol-1 ; 2 ; and 7(4-laydroxycpclohexyl)-propanol-1 . The properties of the high-boiling resit
. e show tha t
there are units in lignin containing 18 or more carbon atoms .
Soluble lignin was converted into a mixture of colorless p`r .adiuct s
when it was heated with hydrogen under pressure in the pr .esernce of
copper chromium oxide . One mole of hydrogen was taken up for •eae i 25 .
to 35 grams of lignin used, depending on the type of lignin and th e
method of isolation . The reaction took place in dioxane solaitlom at
250 to 2 60°
6
C . under 150 to 250 atmospheres of hydrogen during a periMd .
of 18 to 24 hours .
Lignin was converted by this reaction into methanol,, a fraetiorx boiling at 70 to 129° C . at 1 mm ., and a residue boiling above 130° a t
1 mm . The fraction boiling at 70 to 129° was fractionated into thre e
derivatives of propylcyclohexane, namely, an alcohol boiling at 69 t o
70° at 1 mm., which has been identified as 4-n-propylcyclohexano1- l
(formula I) ; a glycol boiling at 107 to 110° at 1 mm,, which has heed .
identified as 14--n-propylcyclohexanediol.-1, 2 (formula II) ; and a'giyco l
boiling at 125 to 129° at 1 mm ., which has been identified a s
30_hydroxycyclohexyl)-propanol-l (formula III) .
1
Presented at the fall meeting of the Technical Association of the PuOfp. ,
and Paper Industry, Green Bay, Wis ., September 8-10, 1938 . Pu.blis
,;
in the Paper Trade Journal, November 17, . 1938 .
.p
it
OH
OH
OH
OH
S
C3 H7
Formula I
Formula II
CH2 CH2 CH2 O H
Formula II I
The amounts of these fractions were found to vary, depending o n
the source of the lignin and the manner of isolation . These are shown i n
Table 1 .
The identification of the products of hydrogenation of lignin hav e
been described in a former publication by Harris, D'Ianni, and Adkins (6) .
The material boiling above 130° C . at 1 mm, was a nixture
-cadre
less compounds having the general formula (C5 H 11 0 ) r . .• The •residue from the.
hydrogenation of hardwood lignins contained no methoxyl, t :Yifa:t fron',0hit e
spruce contained 10 .0 percent methoxyl . The residues boiled _D-Toef -wid e
Th e
range, but practically all the material distilled below 300° at I min .
boiling range and the composition corresponded to compou ;cis having th e
formula, 0 18 H32 0 3 or
024H%+204 for the hardwood lignin,. while that from
spruce containing methoxyl corresponded to the formula 0 19 1138 0. -,
The products boiling above 130° C . at 1 mm,, were deYydrate!d. b
1
heating at 430° over alumina deposited on Italian pumace and then :, hydr o
genated over Raney nickel . A mixture of a hydrocarbon and an `alc ;oar l
were obtained that boiled at 80 to l40° at 1 mm . The alcohol-was .re
moved by treatment with metallic sodium, which made . the alcohol•imseaub e. .
in ether . The hydrocarbon was extracted with ether and distill-ed . The!
hydrocarbon boiled at 92 to 95° at -1 mm. and had the general formul a
Cn H2n-2 .
The boiling range suggested that the hydrocarbon hadl• o r
more carbon atoms .
A preliminary investigation of the properties of the produet :s o f
hydrogenation-revealed that compound I (n-propylcyclohexanol-l) was a
good solvent for lignin, resins, and oils . It was insoluble -in water . .'- ~
y
It had possibilities, because of its stability, as a solvent for 'the .r dgenation of lignin, . Tests made at the Forest Products Laboratory-showed
t a1
-1
that it was a very good plasticizer for lignin plastics and also' that it .
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S
Table Jam ,-Yield of hydrogenated products from various lignin s
Source of lignin and
method of isolation
Products isolated fro m
:Part of : Methoxyl :
hydrogenated lignin
total :content of :
: lignin: isolated :
III :Residu e
:in wood : lignin :Methanol : I : II
:Percent : Percent
Aspen lignin by methanol and :
hydrochloric acid
Aspen lignin by sulphuric
.
acid method (alcohol
soluble)
Aspen lignin soda pulping
:°
liquor (precipitated by
.
acid)
White spruce lignin b y
methanol and hydrochloric :
acid
:
Black gum lignin (soda pulp- :
ing liquor precipitated) . . :
60
: Percent :
Percent
27 .0
26 .5
:11 .C : 3 .2 :24 .0 : 22 . 0
30
:
20 .6
. r
. 19 .0
: 6 .o : 2 .0 :15 .0 : 48 . 0
60
.
11 .6
: 10 .5
. 4 .0 : 1 .4 : 9 .0 : 66 . 0
25
23 .0
: 15 .0
: 7 .0 : 2 .0 :12 .0 : 52 . 0
60
11 .8
11.0
: 5 .0 : 1 .0 :14 .0 : 604 0
was a preservative of about the same value as creosote against wood-destroy ing organisms . Compounds II and III were very viscous and had the propert y
of delaying the evaporation of low boiling organic solvents . The high-boiling residue was instlub1e in water and melted high enough to be satisfac 'to,wr for use in bonding plywood .
The conditions under which hy dr ogen was taken up and the product s
formed are of significance in a study of the structure of lignin . The be havior of a great number of organic compounds toward hydrogen in th e
presence of copper-chromium oxide on Raney nickel at elevated temperature s
has been studied by Adkins and his coworkers . The results have been pub lished in a .monograph (1) and in the Journal of the American Chemica l
Society . These may be summarized as follows : a cleavage betwe$n oxyge n
(1) and carbon .(2) occurs in the presence of hydrogen over copper-chromiu m
oxide at 250° C . in the Following groupings and in the order given :
S
and between carbon (1) and carbon (2) in the following groupings :
1
2
H
(e ) Ph3 C . . . C - P112
2
1
(f) R . . . CH2OH
2 OH
1 OH
- R2
(g) R2 - C' . . . . C'
1
0
(h) RCS
2
1 0
CH2 . . . . C~ - R
If lignin consisted of units of p-propyl phenol groups as shown i n
formula IV or V
jOCH
i 3
CH0
3\
-0 . . . c.
c c
C- C -
Formula IV
H2
C ---O C
/
CH3
CH
c
I,
0
1C
-C
0_
HC---O
H
Formula V
as proposed by Freudenberg or of units of metasacchronic a%p 4f which
Hall (5) has proposed as an intermediate compound that ma
ise .4am
.in•plants,
sugars and may be the source of the aromatic substances
OH
H2
G
C
/
_-T
0 . . .Ho
H H
,0
C= C- C . . . 0---
\ /
C s,
OH
H2
H2
Formula V I
it would give the nine carbon alcohols and glycols reported above fro m
either formula IV or VI, but would require cleavage of a carbon-to-carbo n
linkag e- in formula V . The boiling range of the high-boiling product ob tained from the hydrogenation of lignin would indicate that lignin als o
contained units of 18 or more carbon atoms . The presence of such unit s
has- been suggested by Freudenberg (formula V) and by Hibbert (7), bu t
thus far the only known unit containing more than nine carbon isolate d
from lignin is dehydrodiveratrtc acid and that would not be Thrmed excep t
by rearrangement of the groupings in the proposed formulas .
Hydrogen was taken up very slowly by lignin ; very little being
taken up until after heating for about 4 hours at 250° C . This tempera ture is above that at which lignin begins to decompose, so that th e
products obtained are not indicative of the preexistence of such unit s
in the lignin molecule, but merely of the presence of certain groups tha t
may form them on cleavage . For example, the aromatic compound ,
4-n-propyl phenol, was hydrogenated to n-propylcyclohexanol-1 ver y
readily with Raney nickel and hydrogen at 200° C ., whereas lignin too k
up very little hydrogen under these conditions . The work of other investigators involving the cleavage of lignin by heat, which gave aromati c
compounds with propyl side chains and hydroxyl groups, was by destructiv e
distillation (8) and by alkali fusion (3) . These products led Freuden berg (4) to postulate aromatic formulas for lignin . The low yields o f
these products and the fact that destructive distillation and alkal i
fusion of lignin were exothermic reactions suggests that the aromati c
products were the result of cleavage of the lignin molecule and th e
recombination of the residues into aromatic substances .
The lignins subjected to hydrogenation correspond to the formulas :
Methanol aspen lignin [Ci2H320g(OC H3 )g(OH )2] x
Aspen lignin by eulphuric acid
`C 2H30 0g(0C H3 )6(0H)4] x
Aspen and black gum lignin by
soda pulping
Methanol white spruce lignin -
[C 42H340 8 (OC H3 ) 3 (OH ) 3]
.] x
: . . [C H3306(OC H3 )6(OH)L
One oxygen in each of the foregoing lignins appears too be a carbony l
group . This leaves severaloxygens that are not accounted for in hydroxy l
groups, methoxyl groups, and in joining the nine carbon units together .
The presence of units of more than, nine carbons indicates that some o f
the oxygens exist as cyclic ethers .
Experimental Par t
Preparation of Ligni n
Methanol lignin.--Coarse sawdust, 20 to 4o mesh, was extracte d
first with cold ethyl alcohol and then with an ethanol-benzene mixtur e
(1 :2) in a Lloyd extractor . The extracted wood (450 g .) was refluxe d
for three days with 4. 5 liters of methanol (99 percent) containing 3 per cent hydrogen chloride . The solution was removed, concentrated to abou t
2 liters, 'and poured into 10 liters of cold water . The precipitate d
lignin was filtered from the solution, air dried, again dissolved in 750
cc . of methanol, and precipitated by pouring into 10 liters of water, ai r
dried and then dissolved in 300 cc . of glacial acetic acid . Insolubl e
fractions were discarded . The acetic acid solution was poured into 2 0
liters of water and after filtering, was washed free of acetic acid . I t
was air dried . and then dried at 35° (5 mm .) overnight . The yield fro m
aspen was about 60 percent and from white spruce 25 percent of theory .
The yi/eld could be increased by further treatments to 90 and 40 percent ,
respectively .
Soda liquor lignin,--Soda liquor obtained from the pulping of woo d
(12 pounds) with 2 .4 pounds of caustic soda dissolved to make a 4 percent
solution was acidified with 10 percent sulphuric acid and the precipitate d
lignin removed by filtration . The product was air dried and dissolved . i n
6 liters of alcohol after which it was again precipitated by pouring int o
water containing a small amount of acetic acid, Under these condition s
' the lignin was a granular material which filtered easily . After air drying the lignin was dissolved in 1 liter of glacial acetic acid, filtered ,
and then poured into 20 liters of water . The lignin, which was a ligh t
tan color, was filtered from the solution and washed until colorless . The
yield of dried material was 60 percent of the theoretical yield .
The soluble fraction of the sulphuric acid lignin was obtained b y
extracting the lignin prepared by methods (9) described formerly .
Reaction of hydrogen with lignin .--Seventy-five grams of drie d
lignin were dissolved in 700 cc . of dry dioxane and placed in a 1300 cc .
bomb with 25 grams of copper-chromium oxide (2) . Hydrogen was introduced .
at a pressure of 170 atmospheres . The bomb was heated to 250° for 2 4
hours while shaking . Luring this time the pressure dropped 50 to 100
atmospheres, depending on the lignin used .
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Isolation of products .--The catalyst was removed. The methanoldioxane-water fraction was distilled through aWidmer column and the n
dried over anhydrous potassium carbonate to remove the water . The
methanol and dioxane were fractionated in a 30-cm . Widmer column .
.
I
.
A fraction boiling at 65 to 150° C . at 1 mm . was removed from the
material remaining without the use of a distilling column . That remaining is designated as residue in Table 1 . The fraction boiling at 65 t o
150° was carefully distilled and redistilled in a modified 7idmer colum n
(10) into the three fractions shown in Table 1 .
Literature Cite d
(1) Adkins, H ., Reactions of hydrogen with organic compounds ove r
copper-chromium oxide and nickel catalysts . Univ .
of Wis . Press . Madison, Wis ., 1937 .
(2) Connor, R ., Folkers, K., and Adkins, H . J . Am . Chem . Soc . 54 :
1138 (1932) .
(3) Freudenberg, K ., Ber . 70 :50 (1937) .
(4)
Papierfabr . 36 :34 (193 g ) .
(5) Hall, J . A., Chemical Reviews 20 :305-344 ( 1 937) .
(6) Harris, E . E ., E'Ianni, J ., and Adkins, H ., J . Am . Chem . Soc .
6o :i467 ( 193 g ) -
(7) Leger, F ., and Hibbert, H ., J . Am . Chem . Soc . 60 :565 (1938) .
(5) Phillips, Max, and Goss, M . J ., J . Am . Chem . Soc . 54 :1518 (1932) .
(9) Sherrard, E . C ., and Harris, E . E ., Ind . Eng . Chem . 24 :103 (1932)
(10) Smith, M . E ., and Adkins, H . J . Am . Chem . Soc . 60 :657 (1935) .
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