November 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY LITERATURE CITED
(1) Allegheny-Ludlum Steel Ccrp., privata communication. (2) Hadfield, R., Elliott, T. G., and Sargent, R. J., J . Soc. Chem. Ind. (London),49, 41 (1930). (3) Kosting, P. R., and Reins, Conrad, Jr., IND. ENQ.CHIM.,23, 140 (1931). (4) Monypenny, J. H. G., “Stainleee Iron and Steel,” 2nd ed., New York, John Wiley & Sow, 1931. (6)Poe, C. F., and Nyholm, Elizabeth, Unio. C o h . StwEies, Ser. D, 2, 307 (1947). (6) Poe, C. F., and Van Vleet, E. M., IND.ENQ.CHEM.,41, 208 (1949).
2575
(7) Priestly, W. J., Zbid.. 28, 1381 (1936). Snell, F. D., and Snell, C. T., “Colorimetric Methoda of Analysis,” pp. 275,299,315, New York,D. Van Noatrand Co.,1936. (9) Strausa, B., Am. SOC.Testing Muterialr, Proc., 24, 208 (1924). (10)Strausa, B., Krupp Momlsh., 6, 149 (1926). (11) Wallin, W. C., and Grove, C. S., J . ElQha Mitchell Xci. SOC..51, 214 (1935). (12) Wright, E. C., and Lugar, K.E.,Chem. & Met. Eng., 39, 494 (1932). (8)
R ~ C ~ I VDecember ED 15, 1948.
Trifluoroacetic Acid as an Esterification Catalvst J
PAUL W . MORGAN Pioneering Research Section, Technical Division, Rayon De artment, E. I. du Pont de Nemours & Co., Wilmington,
DJ
T h i s study was undertaken to determine the usefulness of trifluoroacetic acid as an esterification catalyst and to find any characteristics distinguishing its behavior from that of other halogenated organic acids. Trifluoroacetic acid was used to catalyze the esterification of amyl alcohol, ethylene glyml, glycerol, and activated celluloses with acetic anhydride. It was also used in the direct esteri6cationof amyl alcohol with acetic acid. While trihoroacetic acid is not as effective as some mineral acids, it possesses much greater catalytic activity than chlorinated acetic acids and is much more hydrolytically stable. One of the principal advantages of the use of trifluoroacetic acid in esterifications is the ready and complete removal of the catalyst and its lack of combining power with alcohols in the presence of other carboxylic acids. Cellulose esters prepared in this way need no special washing or beat-stabilizing treatments and yet possess good stability to heat and storage.
T
RIFLUOROACETIC acid has been recognized as an extremely powerful and corrosive acid since its discovery (8). It has an equivalent conductance (A 0.001) of 392 at 27’ C. (3). Until recently it has not been readily available and very few reports on its we have been made. Newman ( 6 ) reported uaing trifluoroacetic acid as a condeneation catalyst for the preparation of gmethoxyacetophenone from anisole and acetic anhydride but it does not seem t o have been considered as a n esterification catalyst in place of strong mineral acids. Block ( 1 ) used aqueoua trifluoroacetic acid for the hydrolysis of proteins. Since the present work was completed, papera by Stacey and coworkers (7) have appeared describing the uee of trifluoroacetic anhydride with organic acids as a method of esterification. This reaction proceeds under mild conditions and probably depends more on the formation of a mixed acid anhydride than on the catalytic activity of the trifluoroacetic acid formed as a by-product. In a recent paper (6)the author has shown that trifluoroacetic acid catalyzes the acetylation of polyvinyl alcohol by acetic acid. The present paper describes a broader application of this acid as an esterification catalyst. In a number of ewes trifluoroacetic acid possesses special advantages over most mineral acids and, where it suffers because of low boiling point, it can be replaced by some of the higher fluorinated homologs, such as pentafluoropropionic or heptafluorobutyric acid, which are also strong acids.
Triauoroacetic acid was used to catalyze the esterification of amyl alcohol, ethylene glycol, glycerol, and activated celluloaee with acetic anhydride. It was also used in the direct esterification of amyl alcohol with acetic acid. One of the principal advantages of its use in such caws is the ready and complete removal of catalyst, and in many caws where the product is the highest boiling fraction there is no need for a complete distillation or other purification step. This is of interest in preparing high boiling plasticizers. The catalyst may be recovered by extraction or distillation procedures. Acetylation of cellulose by conventional methods, using sulfuric acid, produces derivatives with chemically bound acid sulfate groups. Because thew groups have a degrading effect on the cellulose acetate, they must be inactivated by treatment with hard water or removed by steaming (8). When trifluoroacetic acid is used in the preparation of cellulose acetate, practically none of it reacts with the cellulose and therefore the products may be isolated a t any time with only the washing neceseary to remove the acids. The hardness of the water is unimportant. The products washed only with distilled water are thermally stable and do not show appreciable hydrolytic cleavage of acetyl groups or acetal linkages after 4 years of normal laboratory storage. Trifluoroacetic acid did not catalyze the acetylation of alkaliactivated cellulose or hyaroxyethylcellulose t o an appreciable extent under the usual industrial acetylation conditions, which UBB sulfuric acid and temperatures below 50” C. It also did not produce highly acetylated derivatives from air-dry cellulose at higher temperatures. Stacey et u2. (7)obtained cellulose acetates, propionates, and benzoates of high substitution a t low temperatures by using relatively large amounts of trifluoroacetic anhydride with the respective acid. Trifluoroacetic acid did catalyze the acetylation of alkaliactivated cotton linters and hydroxyebhylcelluloe at temperatures from 80’ t o 120’ C. The reaction proceeded more rapidly as the temperature was raised or the activation of the cellulose increased by pretreatment, hydroxyethyl substitution, eta. The high temperatures appeared t o produce no marked degradation effects on the product. The speed of the reaction was proportional to the amount of catdyst preeant as shown in Table I. Chlorinated aliphatic acids were ineffective or much less effective in catalyzing the acetylation of hydroxyethylcelluloee; data are presented in Table 11.
2576
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEI. EFFECTOF QUANTITY OF TRIFLUOROACETIC ACID ON ACETYLATION O F HYDROXYETHYLCELLULOSE 1 part hydroxycthylcellulose (0.3 mole hydroxyethyl group per anhydro. Jucoae unit), 5.7 parts acetic acid, 3.8 parts acetic anhydride, reaction 1 hour at loOD C. Acetyl Groups per Trifluoroacetic Acid, Anhydroglucose Unit Part in Product Remarks None 0.26 Fibrous 0.075 2.08 Fibrous, swollen mass 0.15 2.56 Nearly clear solution, some fibers 2.69 Clear solution in 46 min0.30 Utes, a few fibers in 60 minutes 0.60 2.76 Solution in 30 minutes, no fibers in 60 minutes
EXPERIMENTAL
ETHYLENE GLYCOLDIACETATE. Ten milliliters of pure
ethylene glycol were mixed with 40 ml. of acet,ic anhydride in a 100-ml. round-bottomed flask equipped with reflux condenser. The temperature of the mixture dropped 3' C. and the liquids were incompletely miscible. One-tenth milliliter of trifluoroacetic acid waa added and the mixture became homogcneous in 5 minutes. After 1 hour while the temperature slowly rose a rapid reaction took place and the temperature reached 100' d, Total reaction time was about 2 hours. The mixture was carefully distilled under 40-mm. mercury pressure and an 87% yield of pure ethylene glycol diacetate was obtained. It was checked by saponification equivalent. A similar reaction was produced by 0.2 ml. of heptafluorobutyric acid. GLYCEROL TRIACETATE. Five grams of pure glycerol were mixed with 30 grams of acetic anhydride a t 30' C. and 0.1 ml. of trifluoroacetic acid was added. The temperature spontaneously rose to 40" C. in 15 minutes while the mixture was stirred; a t this point the liquids became miscible. The temperature continued to rise but was held between 45' and 50' C. by outward cooling. After a total of 90 minutes the evolution of heat subsided and the acetic acid, acetic anhydride, and trifluoroacetic acid were distilled from the mixture under 50-mm. pressure, leaving a nearly quantitative yield of colorless glycerol triacetate-checked by saponification equivalent. A control mixture without the trifluoroacetic acid evolved no heat and remained as two immiscible liquid phases for 24 hours. Heatin this mixture to 50' C. did not brin about miscibility. The afdition of .a few drops of acetic acif made the liquids miscible but rapid esterification did not take place without a catalyst. When the temperature was allowed to rise spontaneously with a catalyst, it reached 100' C. in 25 minutes and dropped slowly after a few minutes a t that temperature. Two-tenths milliliter of heptafluorobutyric acid and 0.2 ml. of trifluoroacetic anhydride produced similar reactions. Trichloroacetic acid produced only a very slight reaction as judged by the rate of evolution of heat. n-AMYL ACETATE.n-Amyl alcohol (44.04 grams, 0.5 mole) lacial acetic acid (30 grams, 0.5 mole), and trifluoroacetic acid t3.75 grams) were heated a t reflux for 1 hour and the mixture was distilled throu h an 8-inch Vigreux column. Twenty-nine g r a m e 4 3 % tkeoretical yield-of ester, boiling at 145' to 148.5Oc., weroobtained. When theby-productwaterwasremoved from such an esterification mixture by azeotropic distillation with 50 ml. of benzene added after 1 hour at reflux, 46 grams of ester, which was a 69.2% yield, were obtained. The benzene-water azeotrope boils at 69.2' C., while trifluoroacetic acid boils at 72.5' to 73.0' C. When acetic anhydride was used in place of acetic acid, a nearly quantitative yield of ester was obtained and the azeotropic distillafion was unnecessary. CELLULOSE ACETATE. One part of cotton linters, activated by soaking for 1 hour in 18% aqueous sodium hydroside, was washed free of alkali and then dried by rinsing in acetic acid until the melting point of the acid was 16.2" C. The cellulose was centrifuged to contain 1 part acid and was then added to a mixture of 5 parts of acetic acid, 4 parts of acetic anhydride, and 0.2 part of trifluoroacetic acid in a round-bottomed flask equipped with a reflux condenser connected by a standard taper joint. An all-glass stirrer was driven by a shaft through the condenser column. The reaction mixture was rainy and hazy after 1 hour of stirring and heating a t 110" in an oil bath. A t 90 minutes a a m p l e was isolated from the nearly fiber-free solution by coagulation and washing in water. I t was insoluble in acetone and con-
8
Vol. 43, No. 11
tained 2.23 acetyl groups per anhydroglucose unit. At the end of 3 hours a second sample was withdrawn from the reaction mixture, and after precipitation and washing, the cellulose acetate contained 2.92 acetyl groups per anhydroglucose unit. This was also insoluble in acetone. At this point 15 parts of 75% aqueous acetic acid were added to the acetylation miuture. T h o ansuin hydrolysis was allowed to proceed for 3 hours at 80' C. The fin8 product contained 2.61 acetyl groups per anhydroglucose unit and was soluble in acetone, from which it formed clear tou h films. The specific viscosity in glacial acetic acid a t 25' C. a n f a concentration of 1,000 gram per liter wai 0.204. Heat stability of these and following esters were judged by noting the coloration and degradation by dry heat up to 200' C. and by the degree of coloration of a solution of 2 grama in 25 ml. of dimethyl phthalate a t 200' C. for 1 hour as compared to similar tests on commercial yarn-type cellulose acetate flakes. In nearly all cases both the primary and secondary esters prepared with trifluoroacetic acid as the catalyst, and which had received no s ecial heat-stabilizing treatments, were equal in heat and color stagility to commercial stabilized cellulose esters prepared in the presence of sulfuric acid. HYDROXYETHYLCELLULOSE ACETATE. One part of hydroxyethylcellulose, containing 0.3 mole of hydroxyethyl group per glucose unit, was dried directly after its preparation ( 4 )by solvent exchange from water to acetic acid until the freezing point of the acid was 16.3' C. This required three to four washings in acetic acid for 30 minutes with intermediate centrifuging. The cellulose was centrifuged to contain 1 part of acetic acid and then added to a mixture of 5 parts of acetic acid, 4 parts of acetic anhydride, and 0.3 part of trifluoroacetic acid in a reaction vessel equipped for stirring and for refluxing the liquids. The mixture was heated and stirred for 90 minutes a t 80' C.; a clear, fiber-free viscous solution was then obtained. A sample taken a t this point was precipitated and washed with water. It contained 2.73 acetyl groups per glucose unit, was soluble in 98% a ueous acetone or chloroform-methanol azeotrope, and formed c?etrr, tough, heatstable films from these solvents. Ten parts of 50% aqueous acetic acid were added to the reaction mixture and heating and stirring a t 80' C. were continued for 3 hours. A t this time the solution was diluted further, precipitated in soft water, washed, and dried. The product contained 2.39 acetyl groups per glucose unit and formed clear, tough, heatstable films from 98% a y e o u s acetone. The specific viscosity in glacial acetic acid a t 25 C. and a concentration of 1.000 gram per liter was 0.194. Neither the primary or secondary acetates contained any fluorine. Another preparation was made in which higher substitution was obtained in the primary ester. One part (10 grams) of hydroxyethylcellulose wet with 1.64 parts of lacial acetic acid, 4.5 parts of additional acetic acid, 4.0 parts acetic anhydride, and 0.3 part of trifluoroacetic acid were mixed and reacted according to the following schedule:
07
Houk 0.25
Condition of Mixture Fihrousmush Rapid reaction and solution in 6 minutes Clear dope with fea*lumps Cleardope Cleardope
Tep8:*
0.33
80 90
0.50
80
1.0 1.6 1.6
75 75 80
4.6
80
Remarks
Product Acetyls per anhydroglucose unit
Sample
2.62
0.256
Sample Added 13 parts 50% acetio acid Coagulated
a.oi
0.216
2.38
0.186
-
Specifio viscosities were determined in glacial acetio acid a t 25' C.: conoentration 1.000 g./l. a
Properties of the products were similar to those of preceding samples. The viscosity values were practically unchanged after storage in sample bottles for 4 years. HYDROXYETHYLCELLULOSE PROPIONATE. One part of hydroxyethylcellulose was prepared as described for the acetate using anhydrous propionic acid. Eaterification W L B carried out with a total of 5 parts of propionic acid, 5 parts of propionic anhydride, and 0.2 part of trifluoroacetic acid, After the mixture was heated for 45 minutes a t 100' C., the hydroxyethylcellulose was highly swollen. The temperature was raised to 130' C. for 15 minutes, during which time the fiber dissolved quickly to form a clear, viscous solution. The solution was heated an additional 30 minutes a t 100' C. before coagulation and washing with distilled
November 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE 11. ACETYLATION OF HYDROXYETHYLCELLULOSE USINQ HALOGENATED ORQANIC ACIDSAS CATALYSTS 1 part hydrosyethylcellulose (0 3 mole hydroxyethyl grou per slucoae unit), 5.7 parts acetic &id, 3.8 parts acetic anhyjride
Temperature, C.
Time,
Hours
110 110 110
2 2
110
2
110
1.5
80
1.5
2
Acetyl Groups per AnhydrogluParts of Catalyst cole Unit in Product None 0.94 0.3 Chloroacetic acid 0.88 0.3 Trichloroacetic 1.46 acid 0.43 Trichloroacetic 1.92 acid 0.56 Heptafluorobutyric 2 71 acid 0.3 Trifluoroacetic acid 2 73
RemarLs Fibrous Swollen fibrods Swollen
fibrods
Grainy solution Clear solution
water. Analysis of the product revealed that it contained 2.72 propionyl groups per anhydroglucose unit. It was soluble in acetone as were the primary acetates of hydroxyethylcellulose.
25111
The specific viscosity in glacial acetic acid a t 25' C. and a concentration of 1.00o gram Per liter 0.180. LITERATURE CITED
(1) Block, R. J., Anal. Chem., 22, 1327 (1950). (2)Farquhar, B. s.,and Schulze, F., U. s. Patent 2,365,258(Dec. 19, 1944).
Minnesota Mining and Manufacturing Co., St. Paul, Minn., Technical Bulletin on Trifluoroacetic Acid, 1949. (4) Morgan, P. W.,IND.ENG.CHDM.,ANAL.ED.,18, 500 (1946). (5) Morgan, P.W.,J. Am. Chem. Soo., 73,860 (1951). (8) Newman, M.S., J . Am. Chem. Soc., 67,345 (1945). (7) Stacey, M., Bourne, E. J., Tatlow, J. C., and Tedder, J. N.. Nature, 164, 705 (1949); J. Chem. SOC.,1949,2976. (8) Swarts, F., Bull. sei. acad. roy. B d g . , 8, 343-70 (1922). (3)
RECEIVED October 26, 1950.. Presented a t the Chemical Symposium of the Delaware Seotion of the AMERICAN CHWICALSOCIETY a t Newark. Del. January 13, 1951.
Nitrogen Content of Crude JOHN S. BALL, M. L. WHISMAN, AND W. J. WENGER Petrolsum and Oil-Shule Experiment Station, Bureau of Mines, Laramie, Wyo.
Petroleums o
In order to make Bureau of Mines analyses
h
of crude oils more useful, the value of including a determination of nitrogen content was investigated. Nitrogen contents of 153 crude petroleums from all parts of the United States were investigated. In general, the more asphaltic crude oils contained the higher nitrogen contents and the bulk of the nitrogen was in the high molecular weight portion of the oils. Correlations were developed between the Conradeon carbon residue of the oil and the nitrogen content for oils from particular geological periods. The nitrogen content of petroleum fractions is assuming considerable importance because of its adverse effect on cracking eatalysts and on stability of finished products. Consequently, generalizations as to the amount of nitrogen in the crude oil, and information as to its boiling-range distribution are important in the selection of crude stocks for particular operations. Correlations of nitrogen content with geologic age may give clues as to the origin and process of conversion of petroleum.
HILE the presence of nitrogen in crude petroleums has been well known for many years, attention has recently been directed toward it because of its adverse effect on cracking catalysts (7, 8). Some evidence is also accumulating (6, 10) to indicate that it may contribute to formation of gum in refined
0
0
2.0
CALIFORNIA LOUISIANA TEXAS FOREIGN
4.0 6.0 8.0 10.0 12.0 CARBON RESIDUE OF CRUDE OIL, PERCENT
I4.0
Figure 1. Crude Oils Produced from Formations of Tertiary Period
