February, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
(8) Brancker, A. V., Hunter, T. G., and Nash, A. W., IND. ENO. CHEM.,Ax.4~.ED., 12, 35 (1940). (9) Coull, J., and Hope, H. B.,J . Phgis. Chem., 39,967(1936). (10) Evans, T.W., IND. ENO.CHEM.,ANAL.ED., 6,408(1934). (11) Evans, T.W.,J . Chem. Education, 14,408 (1937). (12) Gibbs, J. W., Trans. Conn. Acad., 3, 176 (1876). (13) Gibby, C. W.,J . Chem. SOC.,1932,1540. (14) Zbid., 1934,9. (15) Hand, D.B.,J. Phys. Chem., 34, 1961 (1930). (16) Horiba, S.,Mem. Coll. Ew. Kyoto I m p . Univ., 3, 63 (1911). (17) International Critical Tables, Vol. 111,pp. 398 et seq., New York, McGraw-Hill Book Co., 1929. (18) Kono, M., J. Chem. SOC. Japan, 44,406(1923). (19) Lloyd, B. A., Thompson, 8. O., and Ferguson, J. B., Can. J . Research, 15B,98 (1937). (20) McDonald, H.J., J. Am. C h m . SOC.,62,3183 (1940). (21) Mason, L. S.,and Washburn, E. R., Ibid., 59,2076 (1937). (22) Mertslin, R. V., and Zhuravlev, E. F., J . Gen. C h m . (U.9. S. R.), 8, 635 (1938). (23) Meurs, G.J. van, 2.physik. Chem., 91,313(1916). (24) Miller, W.L., and McPherson, R. H., J . Phys. Chem., 12, 706 (1908). (25) Mochalov, I., Bull. inst. recherches biol. Perm, 11, 25 (1937). (26) Mochalov, I., J . Gen. C h m . (U. 9. S . R.)8,529(1938). (27) Mueller’ Pugs’ey* I.* and Ferguson’ J’ ” phys* Chem., 35, 1313 (1931). (28) Perel’man, F.,Bull. acad. sci. U . R. S. S., 1936, 379. (29) Pound, J. R.,and Wilson, A. M., J . Phys. Chem., 39,709 (1935). (30) Reburn! W.T.9 and Shearer, w*N.1 J * Am. Chem*SOC.9 5511774 (1933). (31) Roozeboom, H. E. W., 2. physik. Chem., 15,984 (1894).
**
237
(32) Saal, N. J., and Van Dyck, W. J. D., T o d d Petroleum Congr., London, 198.9, PTOC.,2, 352. (33) Schreinemakers, F. A. H., 2.physik. Chem., 11, 76 (1893). (34) Schreinemakers, F. A. H., and Bos,J. L. M. van der H. van den, Ibid., 79,551 (1912). (35) Sherwood, T. K., “Absorption and Extraction”, 1st ed., New York, McGraw-Hill Book Co., 1937. (36) Stokes, G., Proc. Roy. SOC.(London), 49,174 (1891). (37) Tarasenkov, D. N., and Paulsen, I. A,, Acta Phisicochem. U . E . S. S., 11, 75 (1939). (38) Tarasenkov, D. N., and Paulsen, I. A,, J . Gen. Chem. (U. S. 8. R.), 7,2143 (1937). (39) Ibid., 8,76 (1938). (40) Taylor, S. F.,J . Phys. Chsm., 1,461 (1897). (41) Trimble, H. M.,and Frazer, G. E., IND.ENQ.CHE)M.,21, 1063 (1929). (42) Varteressian, K.A.,and Fenske, M. R., Ibid., 28, 928 (1936). (43) Ibid.9 291 270 (1937)* (44)Vold, R. D., and Washburn, E. R., J . Am. Chem. SOC., 54,4217 (1932).
~~~~~~; ~ .
~ : , a ~ ~ ~ ~ n ~ ~ ~ ~ : , E a
61, 1694 (1939). (47) Washburn, E. R., Graham, C. L., Arnold, G. B., and Transue, L. F.,Ibid., 62,1454 (1940). (48) Washburn, E. R.,Hnizda, V., and Vold, R. D., Zbid., 53, 3237 (1931). (49) Washburn, E. R., and Spencer, H. C., Ibid., 56, 361 (1934). (50) Woodman, R.M., Chem. N ~140,~1 (1930). ~ , (61) Woodman, R. M., and Corbet, A. S., J . Chem. SOC.,1925,2461. (62) Wright, C. R. A., Proc. Roy. SOC.(London), 49,174 (1891). (53) Zbid., 50,372 (1892).
DRYING OILS AND RESINS Alkali-Induced Isomerization of Drying Oils and Fatty Acids’ THEODORE F. BRADLEY AND DAVID RICHARDSON American Cyanamid Company, Stamford, Conn.
The isomerizing action of alkali metal hydroxides on unconjugated fatty acids and oils is reviewed, and data are presented which show that the isomerizations proceed in water as well as in alcohols, provided the temperatures are sufficiently high. A commercially feasible process is described which has enabled the formation of from 30 to 50 per cent of conjugated acids from soybean and linseed oils. Such acids have been found to be useful for the production of improved drying oils and resins.
1 This paper is the tenth in the series on “Drying Oils and Resins”. Others appeared in 1937, 1938, 1939, 1940, and 1941.
H E recognized benefits of conjugated unsaturation in drying oils and the continued shortage and high price level of conjugated oils have focused the attention of chemists and industrialists alike upon ways and means of providing adequate supplies a t more reasonable cost. It is not desired to review the numerous attempts which have been made to solve this problem or to detail many of the advances which have been effected within the past few years and which appear to offer so much promise. Attention is therefore directed solely to certain means of converting some of our domestic drying oils such as those of linseed, cottonseed, corn, soybean, and the fish oils into conjugated isomers of enhanced value. It has been recognized in biochemical circles since 1933, at least, that during the saponification of drying and semidrying oils with caustic alkalies in alcoholic solvents the unsaturated linkages tended to undergo a permanent shift of position. This became evidenced by a substantial increase of absorption in certain regions of the ultraviolet spectrum (3, 6, 7, IO). Edisbury, Morton, and Lovern (6) considered this to be due to cyclization. Moore (IO),on the other hand, attributed the increased absorption to the formation of conjugated isomers and reported the isolation of an eleostearic acid isomer from
T
238
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
FIGURE1.
hIEDIUhf
QUARTZ-PRISM SPECTROGRAPH
WITH HILGCR SPEKICER P H O T O X E T E R AXD DISCHlRGE TUBE
alkali-isomerized linseed acids. Noore's conclusions 1~ax-e since been amply confirmed by Kass, Miller, and Burr (2, 7 ) It appears probable, however, that cyclized isomers are formed to some extent from acids containing three or more double bonds, after these bonds have become conjugated. I n fact, certain of the present data, particularly those concerning the tung oil acids (Table IV), appear to support this idea, while our prior work (1) showed that the thermal treatment of drying oils results in the formation of both monomeric and polymeric cyclized derivatives from the aliphatic, conjugated intermediates. In an endeavor to develop an economical commercial process for the isomerization of domestic drying and semidrying oils, the authors and their associates undertook investigations which were based upon the thought that, although contrary t o more recent intimations (8), the desired isomerizations might be effected in aqueous rather than in nonaqueous media. Satisfactory results were shortly achieved and are believed to warrant the attention of the oil refining and consuming industries. Inasmuch as the Dresent investiaat,ions reauired the detection and estimation of the several forms of conjugation with a certainty and precision not previously attained by the widely used maleic anhydride or diene value methods, and as it was found necessary to employ the ultraviolet spectrophotometer to this end, an adequate description of this analytical method is included as an essential feature of this work. (We report no diene values for comparison; our experience has been that such values frequently are abnormally low and are too unreliable to justify inclusion. Reports from many other laboratories confirm this.)
Vol. 34, No. 2
HYDROGEN
in cyclohexane solutions contained in an adjustable micrometer absorption cell TTith quartz end plates. The interpretation of the curves depends on the wellestablished fact that fatty acids, either free or combined, which have no conjugated unsaturation show very little absorption in the near ultraviolet region of the spectrum, while those with two, three, four, or more conjugated double bonds do absorb strongly in particular regions of the spectrum. The position of an observed absorption band indicates the number of conjugated double bonds in the acid, and the intensity of the band gives the proportion of that acid in the sample. Thus it is possible to report results of spectrographic conjugation assays in terms of acids with tn-o three, four, and more conju-
Detection and Estimation of Conjugate Unsaturation The basis for the ultraviolet absorption method for conjugation assays of oils and their fatty acids has already been given by several workers in this field (1, /r , 8, 9). The absorption spectra of the oils are plotted from data obtained mith a medium Hilger, type E-498, quartz-prism spectrograph equipped with a Hilger Spekker photometer (Figure 1). Automatic operation is secured by a suitable system of electric motors and relays (1 1 ) . The oil or fatty acid is examined
WAVENU MBER (M MTI)
FIGURE 2. STANDARDS FOR ULTRAVIOLET CONJUGATIOK ASSAYS
(1) 9,ll-Linoleic acid (6), CHa-(CHz)n-(CH=CH)z-(CHz) 7-COOH (2) a-Eleostearic acid ( 4 ) , CHa-(CH2ls-(CH=CH)a-(CHz) 7-COOH (3) Parinario acid (8),CHaCHz-(CH=CH)n-(CHd7-COOH
February, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. STANDARDS USEDFOR CONJUGATION ASSAYSOF 18-
K4a00 =
CARBON ACIDS
1.63 o m m -- 44.3
Acids with 2 conjugated double bonds
NO.
Conjugated Double Bonds
Absorption Bands"
References
Remarks Miller and Kass (9) accept this figure after independent checks. These values are lower t h a n those of Hulst (6) a n d Miller and Kass (91, b u t give consistent results for tung a n d oiticica oils. These, the only published values found are based on measurements) on parinaric acid.
a Specific extinction, K , equals d / L C where d = log IdI L is length of cell, in om., containing C grams per liter of sample. Bknd osition is expressed a8 wave number in mm.-1 (the reciprocal of wave lengtx in mm.).
gated double bonds, a result not yet attainable by chemical methods. The question of suitable standards for this type of work was recently discussed by Miller and Kass (9). We have made no measurements on highly purified acids with a constant number of conjugated double bonds; the standards used (Table I and Figure 2) have seemed best in the light of our experience with many oils for which some independent data are available. If the selected values for the absorption standards are too low, the results in terms of the estimated concentrations of conjugated acids will be correspondingly high. To measure the proportion of acids with a given number of conjugated double bonds in a sample, all that is necessary is to measure the specific extinction, K , of the sample at the wave length of the band for that number of conjugated double bonds and divide by the standard value of K given in Table I. For example, a sample of isomerized soy acids is made up to 0.16 per cent in cyclohexane and found to have d = 1.63 a t 4300 mm.-1 when examined in a cell 0.23 mm. long. I n this case:
239
= 44.3
loo = 36.9%
120
I n a similar manner the amounts of triple-conjugated acids can be determined using the measured values of K a t 3565 and 3700 mm.-l. It was thought to be of interest to list the results of conjugation assays for series of common oils. The figures in Table I1 apply only to raw oils which have not been subject to heat treatment or aeration. The errors inherent in these conjugation assays may total as much as 5 per cent of the amounts reported. Consequently, when results are given with three significant figures, there is no certainty in the third figure. For the purpose of comparing the results on two similar samples run on the same day by the same operator, the third figure has some justification as the systematic errors will not affect the comparison. The marked change in the itbsorption spectrum of fatty acids which is observed upon alkali treatment is illustrated in Figure 3. Curve 1is for linseed acids before treatment and indicates less than 1 per cent of acids with two, three, or four conjugated double bonds. Curve 2 represents the same acids after 3 hours a t 225' C. with an equal weight of sodium hydroxide. The proportions of double- and triple-conjugated acids for this sample are, respectively, 41.0 and 8.2 per cent. A distillation of this isomerized product yielded a cut illustrated by curve 3 which contains 43.1, 18.8, and 0.4 per cent, respectively, of acids with two, three, and four conjugated double bonds.
TABLE11. TYPICALCONJUGATION ASSAYSOF THIRTEENRAW OILS^ ?% Acids with Conjugated Double Two
'
Bonds Three
Four
-
Castor Chia Corn Cottonseed Dehydrated c Linseed Oiticica Olive Peanut Perilla Sardine Soybean Tung
These figures are based upon the assumption t h a t all the observed absorption for each oil is due t o conjugation.
Preparation of Conjugated Fatty Acids from Domestic Oils and Fatty Acids The various oils and fatty acids employed in the present investigations were typical commercial grades, chiefly of domestic origin. Unless otherwise noted, they were found upon examination by the ultraviolet absorption method to contain no more than traces of the conjugated forms of those acids which are characteristic of the oils. Typical of the initial experiments were the runs listed in WAV EN UM BER 4.(l M7I) Table 111. The materials were charged in a 300-cc. stainless steel hydrogenation bomb which was placed in a MicromaxFIGCRE 3. ULTRAVIOLET ABSORPTION OF ISOMERIZED controlled, electrically heated, jacket mounted on the standLINSEEDACIDS ard rocking device. After the stipulated time of reaction, the (1) Linseed acids before alkali treatment, n v = 1.4690 bomb was cooled and the soaps were hydrolyzed a t 90-96O C. (2) Linseed aoids isomerized by sodium hydroxide for 3 hours a t with an excess of 40 per cent hydrochloric or sulfuric 225O C., n v = 1.4746 acid. After separation of the aqueous acid solution from the (3) Distillation fraction from isomerized IinseedIacids, 180-90' C. a t I mm., n y = 1.4850 supernatant fatty acid layer, the latter was washed free from
INDUSTRIAL AND ENGINEERING CHEMISTRY
240
Vol. 34, No. 2
crease the net amount of conjugated unsaturation. Nevertheless, isomerizations occur and the more highly conjugated and therefore Analyses of Recovered acids % Conjugation more active systems of three and four conF a t t y Acids Alkali Water, Heating 2 double 3 double jugated bonds are decreased. Name Grams Name Grams Grams H r . C. ng5 bonds bonds One notes, however, that this decrease is Linseed 75 XOH 76 100 2 225 1.4782 34.6 7.66 3 225 1.4808 41.0 8.20 compensated by the appearance of a substanLinseed 75 NaOH 75 125 SOY 100 XOH 75 110 2.5 225 1.4676 20.20 1.33 tial amount of an acid with two conjugated Sardinea 75 LiOH 100 100 3.5 225 1.4906 23.2 8.00 Dehydrated double bonds plus a substantial increase in the castorb 75 LiOH 76 100 3 225 1.4734 41.7 0.75 amount of nonvolatile residue (polymer). This Isomerization also produced 2.3% of a n acid containing four conjugated double bonds. is thought to result from both intra- and interb T h e original acids, typical of those commercially made from dehydrated castor oil, had an n y of 1.4706 and contained 26.0% of two double-bonded and 0 27% of three doublemolecular cyclizations (addition reactions) of bonded conjugated acids. these most highly conjugated systems and to a ~ b value i ~was doubled in succeeding experiments (Table VI). suggest a logical reason why larger amounts of the eleostearic acid isomer are not formed or isolated from the alkali-isomerized acids of linseed and perilla oils. mineral acids by four to five successive 500-cc. portions of Oil chemists and industrialists have long appreciated the boiling water, separated from the excess of water, and dehydifficulty of distilling tung oil acids on a commercial scale drated over anhydrous calcium chloride or by heating in a without excessive loss by polymerization. Although laborastream of carbon dioxide to 120" C. until free from water. tory distillations a t 1-2 mm. are more effective, we have noted As the work progressed, other and larger sized types of standthat even such distillations of 1500-2000 gram lots of linseed ard industrial pressure equipment were utilized as reaction acids result in reactions quite analogous to those of the tung vessels for the isomerizations. acids, including loss through polymerization: It thus became evident that sodium, potassium, and lithium hydroxides in aqueous solution were capable of isomerizing % Conjugated Acids substantial proportions of the polyene acids of drying oils to 2 double 3 double bonds bonds conjugated forms and, moreover, that even the fair percentage Crude isomerized linseed acids 25.9 8.4 of conjugated unsaturation which is characteristic of the deAfter distn. a t 1-2 mm. from 170-200° C. 30.5 6.8 hydrated castor oils could be materially increased by this means. On the other ha.nd, vacuum distillations of isomerized soy acids, because of the relatively greater heat stability of the Effect on Tung Oil Acids conjugated octadecadienoic acid and the negligible proportion of more highly conjugated acids, involves less loss by polyThe effect of the aqueous, alkali isomerization process on merization and less alteration of the structure: the acids of tung oil was determined since they were known to be more highly conjugated than any of the synthetic, isomer% Conjugated Acids ized fatty acid mixtures. 2 double 3 double bonds bonds Seventy-five grams of tung oil acids, 75 grams of potassium Crude isomerized BOY acids 38.5 1.60 hydroxide, and 100 grams of water were admixed and proAfter distn. a t 1-2 mm. from 170-190' C. 39.8 1.55 cessed at 225' C. for 21/4 hours, cooled, hydrolyzed, washed, and dried in the usual manner. The refractive index (n") Flash or molecular distillations may be advised t o minimize of 1.5042 decreased to 1.4952, which indicated a loss of consuch changes as have been noted during thermal treatments of jugation. Samples (40-50 grams) of the original tung acids the more highly conjugated acids. and of the isomerized tung acids were each fractionated from a Claisen flask which was heated on an oil bath a t 250-300' C. Combined Saponification and Isomerization a t 1mm. mercury pressure (Table IV). Twenty-five pounds of linseed oil, 3.87 pounds of sodium These experiments showed that, in the case of mixtures hydroxide, and 25 pounds of water were processed in a mewhich initially contained a major proportion of an acid such chanically agitated autoclave during 4 hours at 265-230" C. as eleostearic with three conjugated double bonds, the isomand thereafter hydrolyzed with 40 per cent sulfuric acid, erization process would reverse its normal course and deTABLE 111. INITIAL ISOMERIZATION EXPERIMENTS
1
~~
OF TUNG ACIDS TABLE IV. FRACTIONATION
TABLEV.
FRACTIONATION OF ISOMERIZED LINSEED AND SOY ACIDS
71Conjugated Acids Fraction No.
1 2 3 4 Nonvolatile residue
9%
Yield 16.0 42.0 22.0 6.0 14.0
ng
2 double bonds
Original Acids 1.4916 1.9 0.1 1.5008 1.5105 0.0 1.5063 0.0
....
..
Isomerized Acids 1.4845 12.0 1.4946 9.9 1.5006 7.5 1.5029 6.3
3 double bonds
4 double bonds4
Fraction NO.
54.0 73.0 83.7 70.5
0.33 0.41 0.70 1.57
..
..
38.5 0.20 1 12.5 50.4 0.33 2 27.5 61.2 0.43 3 12.5 59.7 0.37 4 10.0 Konvolatile residue 37.5 1.5071 12.0 2.86 0.19 a T h e occurrence in tung oil of a n acid cpntaining four conjugated double bonds and in this percentage has not prevlously been reported.
% Yield (by Wt.)
ny
% Conjugation 2 double 3 double bonds bonds
Linseed Acids 1 2 3 4 Sonvolatile reaidue
...
2.2
1.4680 1.4723 1.4810 1.4846
34. .' 1 44.9 33.6
3.45 8.70 17.45
20.0
1.5013
..
...
26.4 42.4 44.9
0.85 2.12 7.78
0.6 51.1 26.1
Soy Acids
1
2 3 Nonvolatile residue
48.0 35.0 1.6 16.4
1.4640 1.4720 1.4780
....
..
February, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
washed, and dehydrated in the usual manner.
241
This yielded
22 pounds of isomerized acids of n2z = 1.4802, which were found to contain 33.6 per cent of double-conjugated and 5.55 per cent of triple-conjugated acids. Fractionation of a 1700gram charge of these acids a t 170-210' C. and 1-2 mm. mer-
cury pressure yielded the fractions shown in Table V. Upon substituting soybean oil for the linseed oil of the preceding example, the fatty acids recovered were found to have a n n2: value of 1.4708 and to contain 35.1 per cent of doubleconjugated and 1.45 per cent of triple-conjugated acids. Fractionation of a 1300-gram charge a t 170-200' C. and 1-2 mm. mercury pressure yielded the fractions shown in Table V. It may be concluded from these experiments that linseed and soybean oils are isomerized during their saponification under these conditions fully as well as the fatty acids, since the isomerizations actually occur in the soaps and the presence of glycerol does not interfere with the reaction. The use of the oils is normally most economical. This work has also shown that a substantial amount of fractionation is possible during careful distillations a t 1-2 mm. mercury pressure; the result is the effective concentration of the conjugated components, including also the eleostearic acid isomers in the higher boiling fractions.
Influence of Time and Temperature upon Isomerization Duplicate runs were made with 500 grams of soybean oil, 75 grams of sodium hydroxide, and 500 grams of water; only the time and temperature of autoclaving were varied. Corresponding runs were made with linseed oil. The results are given in Table VI. TABLEVI. ISOMERIZATION OF SOYBEANAND LINSEED OILS Hr. at Max. Temp. 48 48 36 24 18 4 3.5 2.5 0.5 5 min.
Max. Temp.,
c.
165 185 185 185 185 225 225 225 250 280
Analysis of Recovered Acids yo Conjugated Acids 2 double 3 double n bonds bonds
FIGURE 4. A FROSTED FILMOF ISOMERIZED LINSEEDESTER
Isomerization in Alcohol Solutions Typical of the isomerizations which may be effected in alcohol solutions were the following experiments : Metallic sodium (10grams) was dissolved in 600 grams of anhydrous n-butanol, and after addition of 30 rams of anhydrous linseed fatty acids, the mixture was refluxej under nitrogen at 110-120' C. for a number of hours. Samples withdrawn, hydrolyzed, and purified in the usual manner analyzed as follows:
s5
Soybean Oil 1.4690 1.4713 1.4711 1.4692 1.4689 1.4708 1.4701 1.4676 1,4720 1.4714
17.8 39.2 37.5 32.5 26.8 35.1 39.8 20.2 43.8 40.2
1.66 1.75 1.90 2.08 2.13 1.45 1.55 1.33 2.2 1.3
Linseed Oil
Hr. Refluxed 0 10 20
Analyses of Recovered Acids % Conjugated Acids 2 double 3 double bonds bonds 1.4685 0.28 0.12 1.4706 4.11 0.78 1.4751 16.3 5.5
Linseed oil (500 grams), sodium hydroxide (75 grams), and ethylene glycol (500 grams) were heated under a reflux condenser at 180-185° C,and in the presence of nitrogen, and samples were taken at suitable intervals for hydrolysis, purification, and analysis: Analyses of Recovered Acids Conjugated Acids 2 double 3 double ny bonds bonds 1.4767 27.4 10.0 1,4787 33.2 11.8 1.4787 34.2 11.6 1.4800 34.8 8.9 1.4800 34.7 8.6 1.4795 30.5 3.3
r0
Hr. Refluxed 0.5 2 4 18 24 92
So long as the soap solutions contained sufficient alkali metal to remain distinctly alkaline, numerous experiments had shown that the isomerizations proceed satisfactorily over a wide range of alkali concentrations. A large excess of alkali was not required, although it tended to increase the velocity of isomerization. The use of larger amounts of water than are here recorded was similarly observed to be of little benefit. On the other hand, as Table VI clearly shows, the rate and and degree of the isomerizations vary materially with the temperature. The effect of temperature upon the rate of isomerization of fatty acids or oils during saponification in alcohols was first reported by Edisbury, Morton, and Lovern (6). This has since been confirmed by Burr (a) and Kass et al, (7).
Repetition of the fore oing example but with replacement of ethylene lycol with dietfylene lycol to permit of a higher temperature f2OO0 C.) provided the following results:
Hr. Refluxed
Analyses of Recovered Acids 70Conjugated Acids 2 double 3 double bonds bonds
These experiments show that rapid processing at the highest practicable temperature provides the optimum degree and
242
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
type of isomerization. Although the rate of isomerization at any given temperature is substantially greater in alcohol solutions than in aqueous solutions, this can be compensated by operation a t higher temperatures in the case of the latter. It is instructive also to observe that an optimum time of reaction exists for each temperature beyond which the degree of conjugation falls. Furthermore this loss of conjugation involves mainly the more highly conjugated and therefore least thermally stable component.
Utilization of Isomerized Acids It seems obvious that the successful re-esterification of isoinerized fatty acids with glycerol or pentaerythritol should yield useful drying oils, since the corresponding esters of linseed, soybean, dehydrated castor, and tung oil acids have long been known and their relative values fully appreciated. As in the case of tung, oiticica, and dehydrated castor oils, the glycerol and pentaerythritol esters of the alkali-isomerized fatty acids should be expected to heat-body faster than the corresponding unconjugated esters, and t o exhibit other special characteristics by reason of their conjugated unsaturation. Improved drying and water resistance but some tendency t o frost (Figure 4), gas check, or wrinkle might be expected. Our investigations have confirmed most of these anticipated cliaracteristics of the re-esterified isomerized acids, yet have disclosed certain anomalies and previously unsuspected phenomena which will be described in future communications. Because of current world conditions and the need for more adequate tung oil substitutes of domestic origin, it seems advisable t o state that the isomerization processes here described and other processes investigated have enabled us to develop such improved oils.
Conclusions 1. Sodium, potassium, and lithium hydroxides isomerize polyene fatty acids and oils in aqueous solutions a t temperatures within the range 160-280" C., and yield conjugated isomers. 2. Ultraviolet absorption spectra enable the quantitative estimation of each of the several forms of conjugation, and show that the isomerization of soybean or of linseed oils yields mixtures containing between 30 and 50 per cent of conjugated acids. 3. Since the conjugated octadecadienoic acids are more thermally stable than the more highly conjugated acids and do not cyclize or polymerize so readily as the latter, the isomerizations yield far larger percentages of the former than of the latter acids. The absence of any substantial proportion of linolenic acid in soybean oil further restricts the formation of triple-conjugated acids in that particular case. 4. Partial fractionation of the isomerized fatty acids has been found possible a t 1-2 mm. mercury pressure within the
Vol. 34, No. 2
range 170-210" C.; thus more highly conjugated fractions can be isolated, and appreciable concentration of the acids containing three or more conjugated linkages can be attained. 5 Fractionation of tung oil fatty acids and analysis by ultraviolet absorption spectra have shown the presence of significant, previously unreported amounts of an acid containing four conjugated double bonds. 6. When the isomerization process is applied to a mixture which contains a major proportion of a triple-conjugated component such as tung oil, the normal effect is reversed and a net loss of conjugation results. This loss is associated with or is due t o intramolecular and intermolecular additions which result in the creation of a double-unsaturated conjugated component and the formation of polymer. 7. When the isomerization process is applied t o a mixture of 9,11- and 9,12-octadecadienoic acids such as are found in the acids of dehydrated castor oil, the ratio of the conjugated to nonconjugated component is substantially increased. 8. The simplicity and nature of this aqueous isomerization process renders it admirably suited for commercial production. 9. Isomerizations of the fatty acid soaps have been effected as rapidly in aqueous as in nonaqueous solutions by suitable increase of the temperature. 10. The isomerized polyene acids are of value for the production of improved drying oils and resins.
L4clcno wledgment The authors are grateful for the valuable assistance rendered by many of their associates of the Physics, High Pressure, and Organic Research Laboratories and to the management of the American Cyanamid Company for its keen interest in and support of this work.
Literature Cited (1) Bradley, T. F., and Richardson, D., IND. ESG.Camt., 32, 983 (1940). (2) Burr, G. O., U. 5. Patent 2,242,230 (May 20, 1941). (3) D a m , W. J., and Moore, T., Biochem. J . , 27, 1166 (1933) ; 29, 138 (1935). (4) Dingwall, A., and Thomson, J . J., J . Am. Chem. Soc., 56, 899 (1934). (5) Edisbury, Morton, and Lovern, Biochem. J., 29, 899 (1935). (6) Hulst, L. J. N. van der, Rec. trav. chim., 54, 639 (1935). (7) Kass, J. P., Miller, E. S., and Burr, G. O., J . Am. Chem. floc., 61, 482 (1939); Kass, J. P., and Burr, G. O., Ibid., 61, 3292 (1939). (8) Kaufmann, H. P., Biltes, J.. and Funke, S., Fette u. Seifen, 45, 302 (1938). (9) Miller, E. S., and Kass, J. P., A. C. S . Meeting, St. Louis, April, 1941. (10) Moore, T., Biochem. J., 31, 138-54 (193i). (11) Richardson, David, U. S. Patent 2,221,170 (Nov. 12, 1940). PREBENTED before the Division of Paint, Varnish, and Plastics Chemistry SOCIETY,Atiantio City, a t t h e 102nd Meeting of the AMERICANCHEMICAL N J.
