INDUSTRIAL AND ENGINEERING CHEMISTRY
86
samples at our disposal. The cleaning and carding were done through the courtesy of R. W. Webb and J. ?VI. Cook of the United States Department of Agriculture.
(13) Houwink, R., "Elasticity, Plasticity and Structure of Matter", p. 262 (1937). (14) Knecht, E., and Hall, W., J . SOC.Dyers C o l o u ~ i s t s ,34, 220 (1918). (15) Mangin, L., Compt. rend., 107, 144 (1888); 109, 579 (1889).
Literature Cited (1) Anderson, D. B., and Kerr, T., IND. ENG.CHEM., 30,48 (1938). (2) Baker, G. L., and Goodwin, hI. W., Del. Am. - Exgt. . Sta., Bull. 216 (1939).
Brown, K. C., Mann, J. C., and Peirce, F. T., J . Textile I n s t . , 21, T186 (1930). Calvert, M. A,, and Summers, F., I b i d . , 16, T233 (1925). Car& M. H., et al., Biochem. J . , 1 6 , 6 0 , 7 0 4 (1922) : 19, 257 (1925). Clegg, G. G., and Harland, S. C., J . Textile I n s t . , 14, T489 (1923).
Clifford, P. H., and Fargher, R. G., Ibid., 14,T117 (1923). Compton, J., and Haver, F. E., Contrib. Boyce T h o m p s o n I n s t . , 11; 105 (1940).
Denharn, H . J., J. Teztile Inst., 13, T99 (1922). Diokson, A . D., Otterson, H., and Link, K. P., J . Am. C"hem. S'oc.. 52.775 (1930). Fair, W . K., Contrib.'Boyce T h o m p s o n Inst., 10,71 (1938). Harris, S. A., and Thompson, H. J., I b i d . , 9, 1 (1937).
Vol. 33, No. 1
(16) (17) (18) (19) (20) (21) (22)
Branfoot, Dept. Sei. Ind. Research (Brit.), Food Invest. Special Rept., 33 (1929). Olsen, A. G., Steuwer, R. F., Fehlberg, E. R., and Beach, N. M., I S D . E S G . CHEX.,31, 1015 (1939). Osborne, G. G., Teztile Research, 5, 275, 307 (1935). Peircc, F. T . , and Lord, E., J . Teztile I n s t . , 30,T173 (1939). Schunck, Mem. Manchester Lit.P h i l . Soc., 24, ( 3 ) ,95 (1871). Urquhart, A. R., J . Teztile Inst., 20,T125 (1929). Vincent, P. D., Ibid.,15,T281 (1924). Whistler, Martin, and Harris, M., A m . Dyestuff Reptr., 29,244
(1940). (23) Thistler, Martin, arid Harris, M.,Textile Research, 10, 109 (1940). (24) Willows, R. S., and Alexander, A. C., J . Textile Inst., 13,T237 (1922). P R E S E N T E D before the Divisiaii of Cellulose Chemistry a t the 99th Mceting of the American Chemical Society, Cincinnati, Ohio. Contribution from the Multiple Fellowship of t h e Cotton Research Foundation a t Mellon Institute.
DRYING OILS AND RESINS Purification of Polymerized Methyl Linoleate by Molecular Distillation THEODORE F. BRADLEY AND WILLIAM B. JOIINSTON American Cyanamid Company, Stamford, Cpnn.
Molecular distillation of polymerized methyl linoleate has been found possible within the range 160-290' C. at 2 microns. The polymerized esters are chieffy the dimer but contain a lesser proportion of trimer. The physical and chemical constants indicate these to be hydroaromatic and their mechanism of formation to be analogous to that already established for buladiene and numerous substituted butadienes (to which latter class 9,ll-linoleic acid belongs). INCE the presentation of the theory that the thermal polymerization of the drying oils involves n primary chemical reaction of the double bonds resulting in the formation of a cyclic dimer, considerable supporting evidence has been published by various workers. Previous cornmunications in this series' have attempted to interpret and expand this evidence, to show that the gelation of the drying oily could be considered the normal reaction of an unsaturated material having the requisite degree of functionality. Polymerization of the drying oils results in three-dimensional polymers which are rigid, insoluble gels ( 2 ) . The difficulty in handling such material-i. e., either to complete the polymerization or to analyze the product-has gradually led
S
1 This paper 18 the ninth in the series 1939, and in May, June, and July, 1940.
Others appeared in 1937, 1938,
to the study of the methyl or ethyl esters rather than the naturally occurring glycerol esters. Recent investigators (6) made an intensive study of the polymerization of mixed ethyl 9 , l l - and 9,12-Iinoleates which strongly supported previous indications that the end product is essentially a substituted cyclohexene formed by a modified Diels-Alder reaction, and that it involved as an intermediate reaction step the isomerization of nonconjugated to conjugated linoleztes. More recent work of the present authors and their associates (4, 5 ) yielded additional supporting evidence both for the isomerization step and the subsequent loss of the conjugated intermediates by diene polymerization. However, the nonuniformity of the polymeric residues (due apparently both to impurities and to the existence of several classes of polymers), the occurrence of side reactions involving decompositions, and the subsequent reaction of certain of the decomposition products and various other observations which we had made compelled continued investigation of these phenomena. It became imperative to seek some effective means of purifying the polymer residues which had been found nonvolatile up to 300' C. a t 1mm. or, according to others, even in a Hickman high-vacuum still (6). Molecular weight determination. had shown these to be predominantly dimeric and to range between 500 and 600 in molecular weight. It was therefore believed that these polymers should be distillable in high vacuum. Appropriate samples were then subjected to molecular distillation in a cyclic molecular still and analyzed. The methyl esters of the fatty acids of dehydrated castor oil were chosen to initiate the proposed work since they are comprised mainly of the 9,12- and 9,11-octadecadienates (linoleates) and had been indicated to form a monocyclic,
87
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
January, 1941
less complex dimer than in the case of the methyl or ethyl esters of more unsaturated fatty acids.
Experimental Procedure A commercial dehydroxylated castor oil (‘‘Isoline”) was converted to the methyl esters by metholysip as previously reported (4). Fifteen hundred grams of Isoline, 1500 grams of anhydrous methanol, and 2 grams of potassium hydroxide were refluxed until clear and then for an additional 1.5 hours. The crude ester was isolated by addition of water containing a little hydrochloric acid, washed thoroughly with water, and dried over calcium chloride. Distillation under vacuum gave 927 grams of methyl esters, boiling at 160-185’ C . under 1mm. pressure. This product then consisted primarily of mixed 9,11-and 9,la-methyl linoleates and inert esters, mostly methyl oleate. Nine hundred grams of the ester were polymerized by heating for 6 hours a t 300” C. under carbon dioxide in an electrically heated air bath as previously described (4). The product was then distilled in an ordinary Claisen flask at a pressure of 1mm., the temperature bein taken to about 300” C. to remove all volatile material. The ofymeric residue, which weighed 491 grams (54.6 per cent yie&) was a viscous, pale yellow liquid. The crude dimer was processed in a cyclic molecular still (7), and a series of fractions was obtained, distilling between 180’ and 290” C . at 2 microns, The data obtained are given in Table I.
DISTILLATION OF HEAT-BODIED METHYL TABLE I. MOLECULAR LINOLEATEO Fraction
Temp.,
Original
...
Weight, Refractive Grams % Cut Index (40” C.) 400 100 .... 17.2 4.3 1 17.6 70.5 2 87.5 21.9 3 19.6 78.5 4 7.9 31.5 6 18.2 4.6 6 14.5 3.6 7 1.4 8 5.6 5.8 23.3 9 48.2 Residue 12.1 Total 98.7 395.0 These data were obtained by R. S. Morse of Distillation Products, Inc.
c.
No.
c _
*
-
I n this type of distillation i t is considered that material u p to about 1000 in molecular weight normally can be volatilized, so that in this case any dimer or trimer would be contained in the distillate. It is noteworthy that only 12.1 per cent of the sample was nonvolatile, and that most or all of this residue was probably holdup from the still. The various fractions from the distillation were subjected to analysis as recorded in Table 11. As the boiling points of the distillates increase, the molecular weights also increase and the other physical constants vary as expected. Since both the dimer and the trimer are volatile and the still could not be expected to give sharp fractionation, any trimer present would appear in greater con-
WAVE NUMBER (MM-I)
FIGURE 1.
ULTRAVIOLET ABSORPTION SPECTRA O F ORIGINAL METHYLESTER AND SOME O F THE PRODUCTS
centrations in the higher fractions. The ultraviolet spectra and other constants showed that the lower fractions contained some monomeric esters not removed in the previous vacuum distillation. Since the residue and the last distilled fraction have similar physical constants, i t seems likely that the residue contains little or no high polymer. Fractions 3 ~
TABLE11. ANALYSESOF FRACTIONS REPORTED IN TABLE I
Fraction
No.
Original 1 2 3 4 5 6 7 8 9 Residue a
%
yield
100 4.3 17.6 21.9 19.6 7.9 4.5 3.6 1.4 5.8 i2.1
index, n’n” 1 4791 1.4937 1.4966 1.4771 1.4779 1.4792 1.4806 1.4818 1.4829 1.4836 1.4864
Molecular refraotion =
Viscosity Sp gr. (25’ C 1, 26/25’ C. poises 0.9403 1.65 0.9230 0.5 0.9352 1.0 0.9373 1.12 0.9398 0.9418 0.9442 0.9463 0.9488 0.9502 0.9554
ex n?
+
1.25 1.4 2.25 2.75 3.85 4.7 10.7
Observed I-Hr.. Rast saponlmol. fication weight No. 187 186 ... 540 192 576 193
...
591 634 764 825 860
858 899
189 189 188 183 183 183 172
2-Hr. Iodine Values Acid
No.
ICauf-
5.4 8.6 4.1 5.0
mann 86.2 96.2 87.3 85.8
5.8 7.0 4.0 6.6 5.9 8.5 4.8
86.0 86.3 86.5 85.7 84.5 83.2 79.8
X mol. wt., using observed molecular weights.
Wijs 99.8 104.9 100.0 97.2 97.7 98.2 101.1 101.0 100.2 99.8 100.3 Theoretical
Ultimate Analysis
%C
C:H
%H
ratio
%:‘it
c:$
: E: ;]
76.34 76.01
11.45 10.93
6.66’1 6.95;1]
...
... ...
... ...
.... .... ....
76:62
ii:ie
.... .... .... 6.75:i
7+:75 77.20
li:i6 11.64
6:66:1 6.64:l
...
... ...
Calculated Density MOL. 25/4O C. refraction5 0 9375 0.9203 0.9325 0.9346 174.2
...
... ...
0’9370 0.9391 0.9414 0.9435 0.9460 0.9474 0.9526
180.’
...
... ... 2b9:5 274.1
INDUSTRIAL AND ENGINEERING CHEMISTRY
88
Vol. 33, No. 1
C. P. cyclohexane and yielded absorption spectra which are illustrated in Figure 1. Table V indicates the inIodine tensity of absorption a t 3600 and a t value saponi- "$:i!* Ultimate Fraction Temp., % Refractive sp. Gr* 1cauf-' fieation RefracAnalyses 4350 mm.-l, which represent the No. C. Yield Index, ng ~2: dZ: mann No." tion %C %H m a x i m a of t w o b r o a d a b s o r p t i o n Original . . . . . .... . . . . . . . . .. ... .... . . . . . . bands characteristic of conjugate un180 16.1 1.4768 0.9372 0.9346 86.2 {i:!. 178.0 { 77.55 11.66 1 saturation. 187 3 77.81 11.76 Previous studies (6) of methyl octa2 190 38.9 1.4774 0.9392 0.9365 86.2 177.8 { 77.87 11.50 decadienate and its polymers showed 186.o 77.81 11.52 .... ........ .. ... .... .. .. .. ... .. .. 3 200 24.3 that the monomer absorbs ultraviolet Residue ........ .. ... .... . . . 14.5 .... light near 4350 mm.-1 more strongly Theoretical than the dimer because of the presence dimer (2 double of the conjugated 9,ll-octadecadienate bonds) .... 86.2 190.5 177.86 77.20 11.64 ester. The previous work also indicated I n .determining saponification numbers b y a standard method using 0.5 N alcoholic potassium hydroxide, it was found t h a t 1-hour refluxing was insu5cient t o obtain t h e maximum value, particularly that cyclization resulted in a wide or for the fractions of higher molecular weight. general increase of absorption; therefore a bicyclic trimer should be expected TABLEIV. COMPARISON OF CONSTANTS OF DISTILLEDFRACto show more of this type of absorption TIONS WITH THEORETICAL VALUES than a monocyclic dimer. It is significant therefore t o find Dimer Trimer that the absorption reaches a minimum in fraction 3 (the Fraction 1 Fraction 8 Residue purest dimer) and thereafter increases progressively until a Theoretifrom Theoreti- from 1st from 1st cal redistn. ea1 distn. distn. second maximum is reached in the trimeric residue. MaxiMol. weight 588.9 580" 883.4 860" 899 mum absorption a t 4350 mm.-l, which is attributed t o doubly 183b 1726 190.5 Sa onification No. 190.5 193-198 84.5C 79.80 86.2' 57.5 IoJine NO. 86.2 conjugated ester, was reached in fraction 1, apparently ben% .... 0.9346 1.4768 .... 1.4836 1.4864 cause of monomeric impurities. .... .... 0.9474 0.9526 a=: Using the extinction coefficient K4,ao = 120 reported by 76.62 77.75 77.68 77.20 % carbon 77.20 11.19 11.16 11.71 11.64 % hydrogen 11.64 van der Hulst (9) for pure 9,11-linoleic acid, the data of Table 268.8 274.1 178.0 265.05 Mol. refraction 177.86 V indicate that the original methyl esters contained 30.4 per Rast. b One-hour. 0 Kaufmann. cent of this conjugated component in esterified form. If all of the absorption a t 4350 mm.+ be due to this conjugated component, the amount of conjugated monomer in fraction 3 and 4, which together comprise 40 per cent of the original would be not more than 1.8 per cent. However, one should polymer, were indicated to contain the purest dimer, and were hesitate t o carry the analyses this far since the dimer and therefore combined and subjected t o a second molecular distrimer may exhibit some absorption in this region. Such tillation for further purification. The results of this second indications are present. molecular distillation and the physical constants of the products are given in Table 111. Redistilled fraction 1,which represents a highly pure dimer, TABLE V. ULTRAVIOLET ABSORPTION OF ESTERS and fraction 8 and the residue, which are considered to conSpecific Extinction tain mostly trimer, are compared with the theoretical mateSample At 3600 mm.-1 A t 4350 mm.-I rials in Table IV. Original ester 0.269 36.6 Crude polymer 0.355 3.3s Fraction 1 closely conforms t o the theoretical dimer, but Fraction 1 0.501 11.0 2 2.75 0.295 in the case of the trimer there are some discrepancies, mainly ? 2.20 0.246 in iodine values. I n polymerizing the methyl esters, the time 2.42 4 0.254 2.76 5 0.331 of heating was restricted in order to minimize the formation 6 3.31 0.398 4.00 7 0.479 of abnormal "polymers" resulting from thermal cracking; 3.93 0.547 8 yet small amounts may have become concentrated in the 4.19 0.582 9 Residue 0.898 4.57 higher fractions and residue. To confirm the presence of trimer in addition to dimer in the higher boiling distillates, fractions 2 and 5 from the first molecular distillation were saponified and hydrolyzed to obDiscussion tain the free acids. When a dibasic acid reacts with a glycol, Prior work (Q,6)indicated that the active or polymeriaable linear or fusible polymers are normally formed by esterificamonomer of the present composition is the methyl ester of tion, but a tribasic acid under the same conditions will form 9,ll-octadecadienoic (linoleic) acid and that during its polya three-dimensional polymer (an infusible, insoluble gel). merization additional amounts are formed by isomerization of Each of the acids was therefore re-esterified with triethylene the 9,12 isomer. glycol. The acids of fraction 5 reacted to form a soft in9,ll-Octadecadienoic acid and its methyl ester may be refusible gel a t 200" C. in 21 hours; those from fraction 2 formed garded as a substituted 1,3-butadiene and thus like the latter a viscous liquid which had an acid number of 13.1 and did is capable of undergoing a 1,2-1,4 addition polymerization a t not show any gelation even after 41 hours a t 200" C. This elevated temperatures. result is added proof that there are increasing amounts of The work of Hofmann and Tank (8) supported by that of trimer in the higher fractions. Lebedev and Segienko (10) and of Alder and Rickert (1) showed that butadiene readily polymerizes a t elevated temUltraviolet Absorption Spectra peratures t o yield the dimer A%inylcyclohexene, and that the latter can react with additional butadiene to yield the I n continuation of prior work (6), Richardson determined the trimer A3,3'-octahydrodiphenyl. Substituted butadienes, ultraviolet absorption spectra of the original methyl esters and including isoprene, piperylene, and the dimethyl butadienes, of various of the products obtained in the present work. are also known to undergo analogous polymerization to yield The samples were examined a t 2 per cent concentration in
TABLE 111. REDISTILLATION OF COMBINED DISTILLATES 3 AND 4 AND ANALYSIS OF PRODUCTS O
1 -);:! -1
.....
0
5
........
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1941
the terpenes and diterpenes or analogous cyclic polymers either a t elevated temperatures or under the influence of strong acids and related catalysts. While substituents, especially terminal substituents, may reduce or otherwise influence the velocity and extent of the polymerization, i t is obvious that 9,ll-linoleic acid and its esters should be found capable of undergoing this same type of polymerization, that the predominant polymer should be dimer, and that polymerization should cease a t the trimeric stage because of the terminal substituents and loss of conjugate unsaturation. This is illustrated and contrasted with the polymerization of butadiene as follows:
89
association colloids. Future work may be expected to throw more light upon their structure and to demonstrate whether the butadiene analogy will hold in accordance with the present strongly positive indications. The dimerization of the acid radicals of the esters of drying oil acids is sufficient to explain the formation of three-dimensional or gelled polymers in the case of the glycerol esters (2); yet the present detection of some trimerization of such acid radicals shows the polymerization to be even more complex. A more deep-seated addition such as this may contribute to the apparent extraneous or intramolecular additions which accompany the thickening of stand oils and which were previously detected from the iodine value-molecular weight relation (3).
Conclusions
Thermal Polymerization of Butadiene
R AH
AH bH
8H I
-
R
R
R'
Thermal Polymerization of Methyl 9,ll-Octadecadienate whereR = CHs-(CH)&-
R'
0
//
-(CHz)rC-OCHs
The present work shows conclusively that the thermal treatment of the methyl linoleates yields polymers which are distillable in a molecular still and possess physical and chemical constants which place these compounds in the class predicted by theory. While the cyclic molecular still is not a particularly efficient means of fractionation, i t has now proved the first, and as yet the only, tool to accomplish the isolation of fairly pure methyl linoleate dimer, and the separation therefrom of the less pure trimer, on the one hand, and of unreacted or isomerized monomer, on the other hand. The dimer now reported may prove sufficiently pure for future analyses and structure proof in view of the general agreement of the observed and theoretical physical and chemi,cal constants. It is obvious, however, that only a beginning has been made toward the successful separation and isolation of the pure trimer of methyl linoleate. Moreover, the polymers of methyl linolenate, eleostearate, licanate, and analogous esters remain for similar investigations. Our previous work has indicated that these also are essentially dimeric, yet more complex than the linoleate dimers and presumably bicyclic. Molecular distillations now promise to isolate these polymers in more suitable condition for adequate characterization and eventual structure proof. It may be well to emphasize that these simplest esters of the natural polyene fatty acids, although of comparatively low molecular weight for polymers, are nevertheless sufficiently complex t o render their isolation and purification difficult. How much more formidable remains the task of developing the means for adequate treatment of the polymeric glycol or glycerol esters? It is encouraging, however, to note the isolation of the present polymers and the extent of the agreement with polymerization theory. These dimers, then, are definitely isolated as chemical polymers and not obscure
Methyl linoleates were polymerized at 300' C.; after the polymer was freed of the excess of monomer by a normal vacuum distillation, i t was subjected to a successful distillation in a molecular still. The almost complete volatilization of this polymer and the investigation of the distilled product leads to the following conclusions: 1. The polymer consists of esters having a molecular weight of less than 1000, the preponderant constituent of which is the dimer. 2. The dimer possesses the hysical and chemical constants that would be expected of a sul%,ituted cyclohexene compound of the type predicted by theory-i. e., 5,6-dihexyl-3-cyclohexenel-(decenoic-A9-acid)-2-(octanoic acid) and/or 5-hexyl-B-( A7octenyl)-3-cyclohexene-l,2-dioctanoicacid methyl esters. 3. There are no indications that polymerization proceeds beyond the trimeric form. Although the trimer has not yet been isolated in so pure a condition as the dimer, the preparations exhibit properties which appear sufficiently characteristic to permit of such designation. 4. The experimental observations are not only in line with general polymerization theory but further su gest that the mechanism of reaction is probably analogous to &at which has been established for the 1,2-1,4addition polymerization of butadiene. 5. Polymerization of linoleate esters beyond the dimeric stage, in so far as the fatty acid radicals is concerned, is unnecessary to explain the gelation of the lycerol esters. However, the present detection of some addition3 trimerizntion of acid radicals may help to account for the extraneous additions in the thermal treatment of the glycerol esters such as had been detected from the iodine value-molecular weight relations (3). 6. Molecular distillation is a promising tool for the isolation of compounds within the molecular weight range of 400 to 1000, end particular1 for the study of the polymerization of the methyl esters of the poLene fat acids.
Acknowledgment The authors are deeply appreciative of the cooperation of N. D. Embree, R. S. Morse, and Distillation Products, Inc., without whose help this work would not have been accomplished. They are likewise grateful for the valuable assistance of D. Richardson and other associates of the American Cyanamid Company who have contributed so freely to the present investigation.
Literature Cited (1) Alder, K.,and Rickert, H. F., Ber., 71B,373-8 (1939). (2) Bradley, T. F., IND. ENG.C H ~ M29, . , 440-5, 579-84 (1937). (3) Ibid., 30,689-96 (1938). (4) Bradley, T.F., and Johnston, W.B., Ibid., 32,802-9(1940). (5) Bradley, T. F., and Richardson, D., Ibid., 32,963-9 (1940). (6) Brod, V. S., France, W. G., and Evans, W. L.,Ibid., 31, 114-18 (1939). (7) Hickman, K.C.D., Ibid., 29,968 (1937). (8) Hofmann, F.,and Tank, L., Z. angew. Chem., 25,1465 (1912). (9) Hulat, L. J. N. van der. Rec. trau. chim., 54,639 (1935). (10) Lebedev, S., and Segienko,S., Compt. rend. a d . mi.,U.5.S.R., 3,79-82 (1935), PEEBENTBD before the Division of Paint and Varnish Chemistry a t the 100th Meeting of the Amerioan Chemical Society. Detroit, Mi&.
