Lignin Hydrogenation Products ELWIN E. HARRIS, JEROME F. SAEMAN, AND CLARENCE B. BERGSTROM Forest Products Laboratory, U.S. Department of Agriculture, Madison, Wis.
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1
Two samples of lignin recovered from the soda-process pulping liquors were hydrogenated in continuous equipment, one at about 325" C. with copper chromite catalyst, and the other at about 400' C. with tin sulfide and iodoform. In both cases about 70qo of the lignin was converted into volatile products, including gas, water, hydrocarbons, methyl alcohol, ketones, cyclic alcohols, and phenolic compounds. The 325' C. hydrogenation produced 14% water, 8oJ, methanol, 894 tar acids, 13.3% oxygen compounds, 21.8% unsaturated and 2% saturated hydrocarbons, 4qo gas, and 28qo heavy oil. Catechols were removed from tar acids with lead acetate and appeared in about equal amounts as catechol, 4-methylcatechol, 4-ethyl-
catechol, and 4-propylcatechol; they represented 12% of the tar acids. The noncatechol fraction contained phenol, guaiacol,p-cresol, 4-allcyl-2-methoxyphenols,and xylenols beside several unidentified phenolic substances. Neutral oxygen compounds were removed from the neutral oils remaining from alkaline extraction by treatment with anhydrous magnesium chloride. The oxygen compound was recovered by decomposing tho oxygen compound with water. These products represent 30 to 40% of the neutral oils or10 to 1557oofthc lignin. Acetone,methyl ethylketone, cyclopentsinone, and other ketones were among the products isolated. The higher-temperature hydrogenation produced similar products but in different amounts.
T
iodide catalyst removed a greater amount of oxygen. T h l e compares the amounts of products in runs 102 and 103. The light oil was distilled with the following results:
WO samples of crude hardwood lignin were recovered by precipitation from commercial soda pulping liquors, p r e pared by a method described b y Plunguian (14). The methoxyl content of the lignin was 15.8%; 75% of the lignin dissolved in acetone, and the acetone-soluble fraction contained 21.4% methoxyl. Both samples of lignin were hydrogenated in equipment of the U. 8.Bureau of Mines a t Pittsburgh (16); the procedures, except for temperature and catalyst, were similar to those previously used for coal. Hydrogen absorption was about 5% of the weight of the lignin. Run 102 was made a t 300" to 327' C., with 1% copper chromium oxide ( 1 ) and a small amount of nickel (8, 9) as catalyst. The primary products were a volatile fraction (69%) and a heavy oil fraction (28%). The volatile fraction was separated into a water layer (22%) and a n oil layer (47%) of the lignin. Run 103 utilized 170 pounds of lignin containing 15.870 methoxyl, with tin iodide catalyst similar to that used for work on coal at the Bureau of Mines (16), at approximately 400' C. The products were volatile fraction (65%) and heavy oil (29%); the volatile oils were separated into water layer (18%) and oil layer (47%). PRELIMINARY CHARACTERIZATION O F PRODUCTS 0
9
Examination of the total volatile oil layers after removal of the water from the two runs showed that approximately 35% of the oil in both runs waa soluble in 10% alkali. This alkalisoluble material was assumed t o be mixtures of tar acids, cyclic alcohols, higher aliphatic alcohols, ketones, and possibly glycols. Extraction of the alkali-extracted oil with 20% sulfuric acid removed 1 to 3% material classified as tar bases and water-soluble material not removed by the alkali. The alkaliextracted oil from each was tested for solubility in 85% sulfuric acid and found t o be 20 to 30% soluble. This fraction was probably a mixture of olefins and oxygen-containing compounds. The oils extracted with 85% sulfuric acid were also treated with 98% sulfuric acid. The oil produced with the copper chromite catalyst was about 95% soluble; that produced a t the higher temperature with tin iodide catalyst was about 75% soluble. The material soluble in 98% acid and not soluble in 85% acid was assumed to be largely aromatic and partially hydrogenated hydrocarbons; the product not soluble in 9873 acid was assumed to be saturated hydrocarbons. The use of higher temperatures and the tin
Copper Chromite, Run 102 Temp., O C. % 20-200 16.6 200-270 42.4 270-300 13.4 300-330 9.0
I
Tin Iodide, Run 103 Temp., O C. % 20-200 41 200-270 36.8 270-300 10 300-330 8.2
FRACTIONATION O F LIGHT OILS
The light oil, after removal of water from run 102, was Rubsequently fractioned into sixteen equal cuts in the Bureau of Mines pilot plant. Fractions 1 t o 9 were distilled a t atmospheric pressure and boiled up t o 210 O C. Fractions 10 t o 16 were distilled at 2 mm. pressure and boiled from 100" to 180'. Oil from run 103 was fractioned into seventeen equal cuts. Fractions 1 to 10 were distilled at atmospheric pressure and boiled u p to 185'. Fractions 11 t o 17 were distilled at 2 mm. and boiled at 60" t o 160". The various water layers, fractions of light oil, and heavy oil were taken t o the Forest Products Laboratory for further characterization. REMOVAL O F PRODUCTS FROM WATER LAYER
The water layers that had been separated from the light oils in runs 102 and 103 were extracted continuously with ether until nothing further was removed and then distilled to remove products not extracted. The combined extract and distillate from the aqueous layer was distilled after being made alkaline to hold back the organic acids and prevent ester formation. The water layer from run 102, representing 22% of the lignin, contained about 40% of volatile water-soluble organic products; that from run 103, representing 18% of the lignin, contained 21.2% of volatile products. EXTRACTION O F TAR ACIDS FROM OIL LAYERS
Each fraction of the volatile light-oil layer from runs 102 and 103 was extracted several times with 10% alkali. The tar acids were recovered from each by acidification with the alkaline solution and extraction with ether. The acidified alkaline solutions, after removal of phenols, were combined and distilled to recover
2063
INDUSTRIAL AND ENGINEERING CHEMISTRY
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TABLE I. LIGNINHYDROGENATION PRODUCTS Run 102 a t 325' C. Product
%
R u n 103 at 400' C.,
%
Vol. 41, No. 9
alkaline solution with ether. This scparation was made more difficult by low acidity of certain substituted tar acids and the solubility of their sodium derivatives in neutral oils and ether (10).
A test with lead acetate gave a precipitate indicating tht: presence of catechols. Freudenberg and Adam (6) showed that 2 Water-sol. catechols are precipitated by lead acetate. The tar acids were 11 .O .8 3.5 Sol. in 10% alkali Sol. in 85% I+QOI 7.8 9.3 dissolved in alcohol, and an alcoholic solution of lead acetate was T a r acids, volatile 10 2 8.0 added. The acetic acid produced in the reaction was neuUnsatd. and aromatic hydrocarbons (sol. in 957" acid) 21.8 tralized with sodium hydroxide. Lead catecholates were re12.7 11 0 Satd. hydrocarbons 2.0 Gas 4.0 6.0 moved by centrifuging the solutions, and freed from other tar Heavy oil, nonvolatile a t temp. of acids by washing several t i m e expt. 28.0 29.0 with alcohol. To recover the catechol, the TABLE 11. T ~ ACIDS R EXTRACTED IN 10% ALKALI (RUN102) lead salt was suspended in Crude ether, and hydrogen chloride Boiling Refractive Densitv 801. in T a r Acid Density of Can No. Range, C. Index, n%o 60' F." ' hlkali, % Recovered, Washed Oil gas was introduced t o convert 1 40-90a 1.430gb 0.820b 32 0.0 b the salt,s t o lead chloride and 2 90-125 1.4490 0,894 6.5 1 0.883 free catechol. The lead chlo3 125-150 1.4880 0.946 15.0 14.8 0.917 4 150-158 1,4912 0.Y72 17.0 16.9 0.943 ride was removed by filtering 5 156-1 66 1.4875 0.972 12.8 12.6 0.953 6 156-160 1 , .ip 0,972 12.7 12.5 0.957 and tmhecatechol recovered by 7 160-175 0.971 5.8 5.8 0.952 evaporation of the ether. 8 175-190 1.4985 0,972 12.2 12.0 0,974 9 100-210 1.5310 0,983 18.0 15.0 0.957 About 1470 of the total tar 10 100-120d 1,5330 1,004 47.5 47.4 0.964 11 120-130d 1 ,5480 1.020 31.5 31.5 0.986 acid fraction was obtained as 1.2 130-135d 1.5660 1,029 29.6 29.6 01.013 ,998 a catechol fraction. Thc prod13 135-145d 1.3630 1.031 19.8 19.8 14 145-146" 1.5690 1.034 26.8 26.8 1,023 uct was separated into the 1.j 146-155" 1 ,5780 1.035 30.0 30.0 1,028 16 165-180d 1.5780 1.034 23.3 23.3 1.021 various catechols for identification by distillation in a 5Contains 940 0 0 . of a water layer and 285 cc. of oil boiling above 130° C Refractive index, density, and alkali solubility made on water-free sample. loot column packed wit'h lisN O satisfactory reading. d A t 2 mm. inch glass helices. The column iacket was heated in three sections with s p a r a t e water-soluble products, and the products combined with volatilc control to provide adiabatic distillation conditions. The cfficiproducts froin the water layer separated from the original light ency of this type of column vias described by Fenslre et nl ( . 5 ) . oil. Tables I1 and I11 show the alliali solubility. tar acid recovered, and change, in density when extracted. Comparison of CHARACTERIZATION OF CATECHOLS the tables indicates that more low-boiling nonphenolic products CATWHOL. The first fraccion of the catechol series (boiling were present in the oil layer of run 102 than in that of run 103. point 131-137" C. at 15-mm. pressure) was crystalline. ReThe presence of these products had caused some of the tar acids to crystallization of a port'ioii gave a product with a melting point distill at temperatures below their boiling point. of 103-104". Mixed nielting point with an authentic sample of The light oils from run 102 yielded 19% tar acids, or 8% of the catechol showed no depression. lignin; run 103 yielded 22% tar acids or 10.2% of the lignin. ~-METHYLCATECHOL. The fraction boiling a t 142-152 C. a t 15-mm. pressure was conveited to the 3,5-dinitrobenzoate, VOLATILE WATER-SOLUBLE PRODUCTS melt'ing a t 168-170'. This x a s compared with synthetic 4methylcatechol, which boiled at 143-145' C. a t 15-mm. pressure Organic products from t,he water layer and from the 10% and gave a 3,5-dinitrobenzoate which melted at, 171-172'. A alkali-soluble material, after removal of tar acids, were fracmixcd melting point gave no depression. tionally distilled in a &foot distilling column having an efficiency ~-ETHYLCA.TECHOL, A fourth fraction boiling a i 152-15Go C. of about fift,y p1at)es. Table IV gives the products from the t v a at 15-mm. pressure was converted to the carbanilate by pheiiyl hydrogenation runs. isocyanate and a trace of triethylamine. The product was crystalFraction 2 was identified as acetone by the formation of the lized from carbon tetrachloride and melted at 157-159'. The hydrazone; fraction 3, as methanol by density and refractive carbanilate prepared from synthetic 4-ethylcatechol melted at index; and fract,ion 4,as methyl ethyl ketone by the formation 157-159" and gave no depression in melting point \-,-hen mixed of the 2,4-djnitrophenglhydrazone. wvith the sample. Methanol from run 102 represented 87" of the lignin. The P PROPYL CATECHOL. h fifth fraction boiling at 160-lii2 C. at saniple of lignin used for this study contained 15,8YGnitthoxyl. 15-nim. pressure was conrerted to the 3,5-dinitrobenzoate arid Therefore, slightly over half of the methoxyl was recovered as crystallized from alcohol. The product melted at 78-81 '. .In methanol. Lower t>emperatures and longer periods of hydroauthentic iamp!e, boiling at 160-161 a t 15-nim. pressure, progenation gave almost quantitative cleavage of the methoxyl to duced a 3,5-diiiitroheiizoa~emelting at 78-51 ' and, when mixed methanol (7'). The higher temperature and tin iodide catalyst wit,h the derivative of the sample, did not lower the melting point. used in run 103 resulted in the formation of more lorn-boiling hgHigher-boiling produc,ts precipitable n-ith lead were obtained drocarbons at t,he expense of t8heoxygen compounds. The fracbut, n o t identified. tions boiling a t 100" C. and above were principally tar acids and were added to the tar acid fraction, Water Methanol Nonphenolio oxygen compounds
14 8
16 2
'
CHARACTERIZATIOK OF NOYCATECHOL TAR ACIDS SEPARATION AND IDENTIFICATION OF T.4R ACIDS
The tar acids from run 102, removed from the light-oil fractions by extraction with alkali, were combined, The tar acids were freed of neutral oil by dissolving in alkali and extracting the
The tar acids not precipitated by the lead acetate n-ere subjected t o fract,ional distillation. PHENOL. Fraction I (boiling point, 105-108" C . at 50 mm.) consisted of phenol that crystallized. This showed a melting
September 1949
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INDUSTRIAL AND ENGINEERING CHEMISTRY
point of 38' and was converted to phenyl benzoate (melting a t 68.5-69.5 ') by the Schotten-Bauman reaction. 0-CRESOL. Fraction I1 (boiling a t 108-118" C. a t 50 mm.) contained small amounts of o-cresol that was identified by the formation of the 3,5-dinitrobenzoate (melting at 138"). CRESOL. Fraction I11 (boiling at 118-123" C. a t 50 mm.) was a mixture of guaiacol and p-cresol. The first of the fraction contained more of the p-cresol, but it was not possible to obtain good separation in a distilling column with a rated hundred-plate efficiency. p-Cresol was separated by dissolving a portion of the fraction in ether and extracting several times with a small amount of 5% sodium hydroxide to separate the phenols on the basis of their acidity. The less acidic fraction remaining in the ether solution was recovered and converted to a 3,5-dinitrobeneoate by a modification of the Schotten-Bauman reaction proposed by Lipscomb and Baker (11 ). The p-cresyl 3,5-dinitrobenzoate melted at 185-186.5' C. and gave no depression in melting point when mixed with the derivative of an authentic sample of p-cresol. GUAIACOL.The more acidic portion of fraction I11 was converted to the picrate and N-phenyl carbamate. The picrate melted at 87-89' C., and the N-phenyl carbamate after several recrystallizations melted a t 149-150.5'. These values agree with those from derivatives of authentic guaiacol. Mixed melting points showed no depression. Analysis of fraction 111 for methoxyl gave a value of 15,2%, an indication that about 60% of the fraction was guaiacol. 2,4-DIMETHYLPHENOL. Fraction I v (boiling point 129-134' c. at 50 mm.), consisting of 2,4-dimethylphenol and 2-methoxyCmethylphenol, had a methoxyl content of 9.55%. The methoxy1 content of 2-methoxy-4-methylphenol is 22.42%. To separate the less acidic phenol from the guaiacol, fraction IV was dissolved in ether and extracted several times with small amounts of 5% sodium hydroxide. The ether solution was evaporated and found to contain about 30% of the original fraction, which had a methoxyl content of less than 0.15%. The product was converted to the 3,5-dinitrobenzoate (melting a t 164.6 ") and compared with a similar derivative of authentic 2,4dimethylphenol for identification. 2-METHOXY-4METHYLPHENOL. The more acidic material was recovered from the alkali-soluble portion of fraction IV and converted to the picrate, which melted at 110-111" C., and the Synthetic 23,5-dinitrobenzoate, which melted at 91.5-92.5 methoxy-4-methylphenol was produced by hydrogenation of vanillin over Raney nickel in ethanol at about 100" C. for 4 hours. The product boiled a t 132-134.5' a t 50 mm., and formed a picrate melting a t 110-111 ' and a 3,5-dinitrobenzoate melting a t 90.592.5'. Mixed melting points of the picrates and of the 3,5-dinitrobenzoates gave no depression. Assuming only two constituents in this fraction, the methoxy content of the mixture would indicate the presence of 60.5% 2,4dimethylphenol and 39.570 2-methoxy-4methylphenol. This fraction represented 8% of the phenolic fraction of run 102. 2-METHOXY-4-ETHYLPHENOL. Fraction v boiled a t 143-146 a t 50 mm. and was found to contain 13.6% methoxyl. Dissolving the fraction in ether and extracting with 5% sodium hydroxide separated the products into a compound with no methoxyl and one with 20.4% methoxyl. The latter was recovered from the alkali and converted to the picrate (melting a t 73-75" C.), the 3,5-dinitrobenzoate (122-123.5"), and the aryloxy acetic acid (67.5-69.9 "). Synthetic 2-methoxy-4-ethylphenol was prepared by converting guaiacol acetate t o acetovanillone by the Fries rearrangement, according to the method of Coulthard, Marshall, and Pyman ( d ) , and hydrogenating in 95% ethanol over Raney -nickel, first at room temperature and then a t 150" C. The solvent was removed, and the product dissolved in alkali and extracted with ether to remove neutral material. The phenol was recovered from the alkali and distilled a t 50-mm. pressure. The product boiled a t 144" C. The picrates, 3,5-dinitrobenzoate, and
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e
c.
~
2065
IN 10% ALKALI(RUN 103) TABLE111. TARACIDSEXTRACTED
Can No.
1 2 3 4 5 6 7 8 Sand 10 11 12 13 14 15 16 17 a b c
Boiling Rtnge,
Refractive Index,
C. 40-70 70-100 100-110 110-120 120-130 130-165 165-170 170-180 180-185
n "Do
Density, 60' F.
1.4127 1,4220 1.4342 1,4435 1.4532 1.4753 1.5035 1.5180 1.5248 1.5280 1.5125 1.4990 1.5160 1.5230 1.5300 1.5420
0.756 0.790 0.819 0,854 0.874 0.909 0.946 0.960 0.963 0.955 0.947 0.955 0.965 0.977 0 I990 0.995
50-60"
60-75C 75-7SC 78-800 80-100c 100-1300 130-1500
Removed by Alkali,
% 0 D 0 (1
4.7 10.0 23.0 21.7 19.7 18.6 27.8 40.2 45.0 42.5 39.1 35.1
Density of Washed Oil
0.755' 0.788 0.818 0.852 0.860 0.890 0.914 0.938 0.948 0.945 0.920 0.920 0.920 0.939 0.956 0.972
Nothing removed. Refractive index and density taken on water-free sample. At 2 mm.
TABLEIV. WATER- AND ALKALI-SOLUBLE PRODUCTS FROM HYDROGENATION OF SODA LIGNIN Fraction No.
Boiling Point, 20-50 50-60
C.
60-69
70-80 80-100 100 andabove
Product Recovered. %" Run 103 0.04 0.03 0.70 1.4 2.5 8.0 0.6 1.9 0.1 0.3 0.1 0.3
Run 102
Expressed as per cent of lignin.
aryloxy acetic acid were prepared, The values corresponded to those of the unknown. Mixed melting points of the derivatives of the known and unknown showed no depression in melting point. This fraction was 12% of the phenolic fraction. The less acidic part of the fraction was not identified. 2-METHOXY-4-PROPYLPHENOL. FractionVX boiledat 124-129 c. a t 15 mm. It was treated like fraction V to separate less acidic substances and gave a product with 18.5%methoxyl. The latter was converted to the 3,5-dinitrobenzoate, melting a t 114.5-116' C. A known sample of 2-methoxy-4-propylphenol was prepared by hydrogenating 99 grams of eugenol in alcohol over Raney nickel at room temperature. The product distilled a t 128" C. a t 15 mm. It contained 18.6% methoxyl and formed a 3,5-dinitrobenzoate (melting a t 115-116' C,). Mixed melting point of the derivatives of the known and unknown showed no depression. About 85% of fraction VI consisted of 2-methoxy-4propylphenol. Fraction VI represented 12% of the tar acids. HIGHER-BOILING TARACIDS. Phenolic fractions, boiling above 129" C. at 15 mm. and representing 40% of the phenolic material, proved difficult to idcntify because of the complexity of the mixtures. Attempts to make preliminary chemical fractionations resulted in the production of intensely colored compounds that decomposed when distilled. Because of the sensitivity of the materials, separation and identification of higher boiling products has not been completed. Methoxyl analyses were made on representative samples of the remaining materials, and i t was evident that phenolic ethers were present: B.P. of Fraction, C. 144-150 at 15 m m . 150-160 at 15 m m . 160 at 15 m m . to 140 at 5 m m . 140-160 at 5 m m .
Methoxyl, % 9.8
7.2 4.2 3.5
The tar acids from run 103 that had been produced a t higher temperatures were treated and fractionally distilled in a manner similar to those from run 102. The types of products were the same but differed in amount.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2066
EXTRACTION O F OXYGEN COMPOUNDS FROM NEUTRAL OIL
The neutral oils remaining after the removal of the tar acids by alkaline extraction contained oxygen compounds, unsaturated hydrocarbons, and aromatic, hydroaromatic, and paraffin hydrocarbons. Fractionation of these oils into their components by distillation was not possible, and hence it was necessary t o employ chemical ineans for the separation. It is known that neutral oxygen compounds form complexes with acids and certain neutral salts. The use of sulfuric acid was discarded as an extracting agent, owing to the possibility of structural changes. Osokin ( l a , 13) showed that magnesium chloride extracts various types of organic oxygen compounds from mixtures with hydrocarbons. Alcohols, aldehydes, ketones, esters, lactones, anhydrides, and acids are known to form complexes, whereas phenol ethers, pyran, furan, and their alkyl dorivatives do not. Since the oxygen compounds were already mixed with hydrocarbons, a modification of the Osokin method was used. Technical-grade anhydrous magnesium chloride was ground to apowder. Portions of 250 ml. of the oil were extracted in a 500-ml. flask with 25 t o 50 grams of the chloride in a mechanical shaker as long as the chloride remained loose. The solid tends t o become sticky after reaction with oxygen compounds. The magnesium chloride complex was removed, and the oil treated with fresh magnesium chloride until no further reaction was shown. The complex was washed with petroleum ether and combined. Table V shows the amounts removed from the neutral oils that boiled in the various ranges. To recover the oxygen compounds, the complex was placed in flasks, water was added to decompose the complex, and then the oil was removed from the water by steam distillation. The oil recovered from the complex was dried over anhydrous potassium carbonate and fractionally distilled in a 5 - f O O t column filled with Pyrex helices. The fractions were principally mixtures of ketones because they formed phenyl hydrazones readily, but were such mixtures that it was difficult to obtain pure derivatives or t o fractionate the derivatives into pure compounds. The following were identified: ACETONE. Fraction boiling a$ 33-56 O C.; 2,Pdinitrophenyl hydrazone, melting point 128 ; semicarbazone, 190"; nf$' 1.3569. Corresponding derivatives from known acetone gave same.melting points, and mixed melting points did not show depression. METHYLETHYL KETOKE. Fraction boiling a t 56.5-75.5' C: n v 1.3785; 2,4-dinitr;phenyl hydrazone, melting point 116 semicarbazone, 136.5 Corresponding derivatives of known methyl ethyl ketone gave same melting points and, when mixed with derivatives of the unknown, gave no depression. METHYL %-PROPYL KETONE.Fraction 95-102" C.I nZ," 1.390; 2,4-dinitrophenyi hydrazone, melting point 140-144 ; semicarbazone, 110-112 . Corresponding derivatives gave same melting points and mixed melting points. CYCLOPEKTANONE. Fraction 120-130 O C.; nf$' 1.438; 2,P dinitrophenyl hydrazone crystallized from alcohol, meJting point 142-143 "; semicarbazone, melting point 203-204 . Known derivatives gave same melting points and mixed melting points. Data on cyclohexanones follow:
'i
.
Fraction 140-155' C. Cyclohexanone Mixed m.p. 158-165' C. 5-Methglcyclohexanone Mixed m.p.
'%n 1.449 1.452
1.'4491 1,4483 ,
,
.
Melting Point, C. 2.4-Dinitrosemioarhydrazone bazone 160-162 157-160 166-167 162 160-162 165-167 125-130 195 135 133-135
197 196-197
.4nalysis, % C H 73.40 10.14 73.48 10.18 74:91
10:s
75.00
10.71
.. .
...
Derivatives of higher boiling ketones were prepared but were mixtures that did not resolve into definite compounds on repeated recrystallization. Analysis of the ketones and of their derivatives indicated the presence of ethylcyclohexane (CsHlaO) and pro-
Vol. 41, No. 9
pylcyclohexane (CeHlaO), but satisfactory derivatives were not prepared. Methyl ethyl ketone and cyclohexanone were t'he largest fractions identified. HYDROCARBONS
Hydrocarbons remaining after the extraction of the neutral oils with anhydrous magnesium chloride were still found to contain ketones that formed derivatives with 2,4-dinitrophenyl
TABLEv. OXYGEN COMPOUNDS REMOVEDFROM NEUTRAL HYDROGENATION LIGHTOIL Boiling Range of Neutral Oil, C. 38-88 at atm. 88-158 at atm. 62-107 at 50 mm. 107-141 a t 50 mm. 141 a t 50 mm. to 119 a t 2 mm.
Compound Removed, % 11.5 35 75 35 11.4
Compound Recovered, % 9.2 33.1
66.5
28.5
11.4
hydrazine. No satisfactory way of removing them has been found. Their presence caused abnormal distillation of the hydrocarbons, so that satisfactory fractionation was difficult. The residues from the magnesium chloride extraction distilled at temperatures ranging from 39" to 400' C. The greateat portion boiled a t 150" t o 250". Work on these hydrocarbons is being continued. DISCUSSION
The results of the hydrogenation of soda-pulping lignin are of interest for two reasons. They show that, by continuous hydrogenation, 8 to 10% volatile phenols, 12 t o 13% ketones, and up to 8% methanol may be obtained from lignin by hydrogenolysis. This indicates that lignin may be considered a potential source of these products. The results are also of interest because they add t o our knowledge of the chemistry of lignin. If the oxygen recovered as methanol and methoxy compounds is taken into consideration, and if it is assumed that methoxyl not recovered produced water and methane, about one third of the oxygen in lignin reacted readily with hydrogen or split out hydroxyl and hydrogen to produce water. This would indicate oxygen linkages more easily attacked than either phenol hydroxyl or methoxy oxygen. As in previous hydrogenation studies (2, Y, 8, M), i t was found that some methoxy groups were converted to methanol and some to methane and water. High temperatures favor the latter. The yield of phenolic substances (8 to lo%), as Table VI shows, was low, based on building units of
or
for lignin. However, most of the phenolic substances-phenols, methoxyphenols, and catechols-isolated could be accounted for on the basis of such building units. High temperature caused the cleavage of the propyl side chain t o ethyl or methyl or its removal entirely. It is not believed that o-cresol or 2,4dimethylphenol may be accounted for on the basis of such a building unit. It is possible, however, that some rearrangement, catalyzed by heat, was responsible for the production of these substances because the amount present was greater in the oil from the run made a t higher temperature. The unidentified high-boiling phenolic substances hold considerable promise in throwing new light on the structure of the building unit, but unfortunately their complexity increases as the boiling point goes up. Work on these is being continued.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
September 1949
2067
ACKNOWLEDGMENT
TABLE VI. PHENOLIC SUBSTANCES FROM HYDROGENATION OF LIGNIN
Substance Phenols Phenol o-Cresol w-Cresol Guaiacol 2 4-Dimethylphenol 2~Methoxy-4-methylphenol 2-Methoxy-4-ethylphenol 2-Methoxy-4-propyl phenol Higher-boiling phenol8 and methoxyphenols
Hydrogenation, % At 325O C. A t 400' C.
1010 6.0 9.0
-
-
2.8 1.4 2.2 2.3 5.3
5.1 1.8 3.0
40
81.6
Catechols Catechol 4-Methylcatechol 4-Ethylcatecbol 4-Propylcatechol Higher-boiling products
4.0 2.7
1.2 0.2 3.2 4.8 4.9 3.3 12.0 12.0
-14.0
The authors wish to express their appreciation to the U. S. Bureau of Mines Pittsburgh, for the use of hydrogenation equipment, t o H. H. &orch, L. L. Hirst, and co-workers for carr ing out the hydrogenation, and to A. Eisner for a preliminary anaf sis of the products. They also wish t o thank John Traquair, $he Mead Corporation, for supplying the lignin for this work.
5.5
15.0 9.1
28.6
84.9
2.5
4.1 18.6
The nonphenolic oxygen compounds, consisting principally of ketones, appear t o be accounted for as products that resulted from the pyrolysis of 2-methoxy-4propylphenol derivatives. The hydrocarbons represent the products of greater degradation. It is possible that a knowledge of the hydrocarbons produced at the lower temperature will be of value in the determination of structure but not to the extent that the phenolic compounds are. The high-boiling heavy tar obtained in this work is similar in amount and in properties to that obtained in the hydrogenation of other lignin preparations. Further hydrogenolysis at long periods of time converts this product to cyclohexane and cyclohexanol derivatives, which are in keeping with the proposed building unit.
LITERATURE CITED
(1) Adkins, H., "Reactions of Hydrogen," p. 12,Madison, University of Wisconain Press, 1937. (2) Adkins, H., Frank, R. L., and Bloom, E. S., J. Am. Chem. SOC., 63,549-55 (1941). (3) Corson, B.B., and Ipatieff, V. N., J . Phye. Chem., 45,431(1941). (4) Coulthard, C. E.,Marshall, J., and Pyman, F. L., J . Chem. Soc., 34,280(1930). (5) Fenske, M. R., Tongberg, C. O., and Quiggle, D., IND.ENG. CHEM., 26,1169 (1934). (6) Freudenberg, K., and Adam, K., Ber., 74B, 387-98 (1941). (7) Harris, E. E., D'Ianni, J., and Adkins, H., J . Am. Chem. SOC., 60,1467(1938). (8) Harris, E. E., Saeman, J. F., and Sherrard, E. C., IND. ENG. CHEM.,32,440(1940). (9) Ipatieff, V. N., Corson, B. B., and Kurbatov, J. D., J . Phgs. Chem., 44,670(1940). (10) Kester, E. B., IND. ENO. CHEM.,24, 1121 (1932); 25, 1148 (1933). (11) Lipscomb, W. N.,and Baker, R. H., J . Am. Chem. SOC.,64,179 (1942). (12) Osokin, A. S., J . Gen. Chem. (U.S.S.R.), 8, 583-7 (1938). (13)Ibid., 9,1315-25(1939). (14) Plunguian, Mark, IND. ENG.CHEM., 32, 1399 (1940). (15) Saeman, J. F., and Harris, E. E., J . Am. Chem. SOC.,68,2507 (1946). (16) Storoh H. H., Hirst, L. L., Fisher, C. H., and Sprunk, G. C., U.8. Bur. Mines, Tech. Papar 622 (1941). RECEIVWD September 10, 1948. Presented before the Divieion of Cellulose Chemistry at the 114th Meeting of the AMERICAN CHEMICAL SOCIETY, Portland, Ore. A portion of the work on the isolation and fractionation of the oxygen-containing aompounds in the neutral oil fraction was conducted by C. B. Bergstrom, and the report is presented a8 fulfilling a part of the requirements for a master's thesis a t the University of Wisconsin.
Viscosity of Normal Paraffins near -the Freezing Point J
E. B. GILLER AND H. G . DRICKAMER University of Illinois, Urbana, I l l . m
3
T h e viscosities of a series of normal paraffin hydrocarbons have been measured over a temperature range down to the freezing point and into the supercooled region. The results show that the free energy of activation per unit volume is substantially independent of temperature except at the freezing point and below, where an increase is noted, probably due to increased molecular orientation. A relation i s shown between freezingpoints of compounds and freezingpoint viscosities.
T
HE purpose of this work was t o investigate the viscosity-
temperature relations of a homologous series of paraffin hydrocarbons down t o the freezing point, as a possible contribution to the establishment of a kinetic theory of liquids.
The cryostat used was a slight modification of the one described by Egerton and Ubbelohde (6),capable of holding + 0 . 0 5 O in the range 0" to -50' C. and *0.lo in the range -50" to -140'.C. The bath liquid was low-boiling petroleum ether, cooled with li uid air (6). %he Cannon-Fenske modified Ostwald viscometer was used.
Flow time generally was well above 200 seconds as recommended which gave an err& of *0.2% for relative viscosities and *0.5$ for absolute viscosities; the exceptions were pentane and hexane at 20" C . Flow time was measured with a stop watch, checked against the international time signal for an error of less than 0.2%. Pure grade n-pentane and n-heptane were supplied by Phillips Petroleum Company; n-hexane n-octane, n-decane, n-dodecane, and n-tetradecane were obtained from the Connecticut Hard Rubber Company. The normal paraffins were tested with potassium permanganate for a color reaction. n-Pentane and n-heptane showed no reaction, but the other paraffins gave a positive test. n-Hexane, n-octane, n-decane, n-dodecane, and n-tetradecane were shaken with concentrated sulfuric acid until no color formed in the acid layer. They were then washed five times with distilled water and dried over calcium chloride for several days. No chemical treatment was given to n-pentane and n-heptane. All compounds were distilled in a 2-foot column filled with small glass helices. The middle cut boiling over a 0.1 O C. range was retained for use in the investigation. All samples were dried over sodium wire for several weeks before being tested in the viscometer. The measured properties are compared with the best available data from the literature in Table I.
