694
1NDUSTKIAL ZXD ENGINEERISG CHEXIISTRY
only of n ater has separated. The product is fractionated in until all the glycol or glycerol is removed. The hot residue is treated with decolorizing carbon and filtered to remove any color. The filtrate is a high-grade glycol or glycerol monolactate. The purity and yield of these esters will depend on how efficiently the excess alcohol has been separated from the ester. These esters distill with some decomposition a t 140-5' and 180-90" C. a t 10 mm., respectively, with the formation of some lactide and a small amount of other decomposition products with yellow color and caramel-like odor. The lactide may be removed in crystalline form by filtering the distillate which has been allowed to cool and stand overnight. The alpha acetoxy derivatives of these lactic esters were prepared by reacting them n-ith the acetic anhydride or with ketene in accordance with the methods described by Claborn and Smith (6). Table I gives several of the physical characteristics of these esters.
VOL. 32, NO. 5
Literature Cited
DUCUO
-Auger, V.,Compt. rend., 140, 938 (1905). Bogin, C. (to Commercial Solvents Corp.), U. 8. Patent 1,927,-
539 (Sept. 19, 1933). Burns, R., Jones, D. T., and Ritchie, P. D., J . Chem. Soc., 1935,400. Burton, L. V., Food Industries, 9, 634 (1937). Claborn, H. V., and Smith, L. T., J . Am. Chem. SOC.,61, 2727 (1939). Gabriel, C. L., and Bogin, C., U. S. Patent 1,668,806 ( M a y 8 , 1928). Kalle & Co., German Patent 216,917 (Sept., 1908); Lock, R H. (to Howards & Sons Ltd.), U. S. Patent 2,089,127 (Aug. 3, 1937). Lock, R. H., U. S. Patent 2,107,202 (Feb. 1, 1938); Howards & Sons Ltd. and Lock, R. H., British Patent 467,510 (June 17, 1937). Olive, T. R., Chem. & Met. Bng., 43, 480 (1936). Schreiner, L., Ann., 197, 12 (1879). Silva, R. D., Bull. aoc. chim., [2] 17, 97 (1872). Whittier, E. o., and Rogers, L. ii., IND. EKQ.C H E ~ I23, . , 532 (1931). Q'islicenus, J.. Ann., 125, 58 (1863).
DRYING OILS AND RESINS Constitution of a Drying Oil Gel' THEODORE F. BRADLEY AND HARRY F. P F A " American Cyanamid Company, Stamford, Conn.
I
K THE fourth article of this series (1) reference was made
to the work of Elod and Mach (6) and to the probability that, upon closer examination of the isolated fractions from solvent-extracted stand oils and their gels, one would find definite evidence relating the several phases not only to the degree of polymerization but to the extent and nature of the intramolecular reactions as well. An excellent opportunity to ascertain the facts appeared when Ralph H. Huff presented the authors with one of the most thoroughly heat-gelled drying oils which they had encountered, together with samples of the oils represented prior to their heat treatment. Huff stated that the sample (Figure 1) was "a gel taken from a 500-gallon batch of varnish oils (89 per cent oiticica and 11 per cent alkali-refined sardine oil by weight). The oils were heated slowly to 480" F. (248.9" G , ) , the temperature coasting to 500" F. (260" (2.). The kettle was left (by an unadvised varnish maker) to cool overnight. I n the morning there was found, as might be expected, a n entirely Polymerized mass in the kettle, which was still very hot. The kettle was not disturbed until about noon, at which time it began to look as though it might take fire by spontaneous combustion. The batch was taken out of doors and dumped out. The material was still warm after 36 hours. Some portions of the oil had become so hot before the kettle was dumped that charring had started. The sample supplied was cut from a piece not more than 6 inches from the partly charred portion, so is therefore believed to represent a completely polymerized oil." The gel, as submitted, was found to possess a refractive 3
Previous papers i n this series appeared in 1937, pages 440, 579. and 1270;
in 1938, page 689; and in 1939, page 1512.
index of 1.5140 a t 25" C. and a saponification number of 182 as compared to corresponding values of 1.5100 and 186 of the original, unreacted oils. Because of the substantial insolubility and infusibility of the product, the scheme of preparation for analysis was adopted as shown in Figure 2.
Solvent Extractions The total amount of soluble phase in the gel was first determined by the technique previously perfected by one of the writers in collaboration with Dean ( 5 ) . Twelve grams of gel were cooled with solid carbon dioxide, crushed to a powder with mortar and pestle, and spread on a strip of muslin; the muslin was rolled and inserted in a 160-cc. Soxhlet extraction thimble, extracted for 3 hours, and removed from the thimble. After evaporation of excess solvent, the muslin roll was squeezed between the plates of a hydraulic press to disperse the swollen particles between the threads of the cloth. Extraction was repeated for 3 hours and the soluble portions from both extractions were combined. The percentage of soluble material was determined by evaporation of an aliquot portion of the solution in a vacuum desiccator to constant weight : M x t . No. I I1
Solvent Used, Volumes 1 petroleum ether 2 acetone 1 ethanol 1 benzene
+
+
% by Weight of Sol. Phase in Gel 30.2 31.4
Three hundred and ten grams of original gel A (Figure 2 ) were cut into quarter-inch (6.35-mm.) sections, laced in a flask equipped with a mechanical stirrer and refluxecfwith an excess of solvent mixture I for 8 hours. The extracted gel was recovered by filtration and, while still swollen by solvent, was pulverized and again extracted for 8 hours. The gel was recovered on a filter, washed with fresh solvent, and dried t o constant weight in a vacuum desiccator to yield extracted gel M . The collected extracts were combined, concentrated by distillation of the solvent, and dried to constant weight in a vacuum desiccator to give viscous liquid B (yield, 30 per cent).
INDUSTRIAL AND ENGINEERING CHEMISTRY
MAY, 1940
695
A. Originai gel A gelled pmduet derived fmm the thermal treatment of a m t t u r e of 89 per cent oiticica oil and 11 per Oent sardine oil has been found to contain 70 per cent of polymerized glycerides whioh are amorphous solids insoluble in common organic solvents, together with 30 per cent of a soluble liquid phase of polymerized glycerides. The insoluble phase of the gel contains dihasio and monohasio acids in the molar ratio of 3 to 2 whioh, from statistical considerations, m a y represent an average molecule composed of 8 moles of triglyceride united intermolecularly with intramolecular linkages at two additional points and having a calculated moleeula= weight of 731i. The soluble phase of the gel is definitely less highly polymerized, sinoe the acids recovered therefrom exist in the ratio of hut 9 moles of dihasie acid to 22 moles of monohasic acid. The calculated equivalent comprises a mixture of 3 moles of tetramerizcd glyceride with 22 molea of trimerized glyceride having an average molecular weight of 2852. T h e ohserved niolecdar weight of 1157 to 1195 is accounted for b y the presence of 10 per cent of free acid in the soluble glyceride together with other products of thermal decomposition and intramolecular additions. During the heat-bwlying processes not only do inter- and intramolecular addition reactions of the unsaturated esters proceed, hut partial thermal decompoaitioni of the esters also occur. These decomposition products are found mainly in the acctonr-sohrble liquid phase of tho gelled oils.
I
Solvent extraction
I
1
extract_ -II. Soluble ~ _
1
Ssponlfioation and hydrolysis
I
-._.____._ 1. Extracted gel
I
Saponification and hydrol>.sis
I
N . Free acids
Free acids
I
I + Methanol
D.
i- Methanol
I
i
Methyl esters -
0. Methyl esters _.-____.
I
I
Distillation in U Y C U U
Dist.illation in MCUO
r
I
E. Distillate
!-_,
FIGURE 2. SCHEME OF PREPARATION FOR ANALYSIS One hundred and thirtyideven grams of the fatty acids, 137 CC. of concentrated sulfuric acid were refluxedfor 4 hours. Thc methyl esters formed were thrown from the alcohol solution by dilution with water. The ester layer wa6 washed with water and then dried in a vacuum desiccator over sulfuric acid to yield 120grams of ester 0 (Figure 2). The soluble extract was saponified and the free wid%were liberated and then re-esterified with methanol in manner similar to that described above. The methyl esten of the extract arc labeled D in Figure 2. The ratio of golFeriri.ed to unpolymerized acid in the eaters was determined y distillation of the esters under reduced premu~e. A known quantity of the methyl esters was placed in a Clnisen distilling flask, the flask was heated in an oil bath to 260' C., and the esters volatilizing a t 1 mm. m e r c y wefe collected in a tared receiver. The ratios obtained by Istfihug the meth I esters from the gelled and soluble portions are shown in Table%. gram of methanol, and 2
T.4BLE
I.
SEPARATION OF
DIMEXZED ESTERS
From Ertraated Gel
fatty scids werebht.ained.
&. Residue
P. Distillate
F. Residue
From Extract
I
Methods of Analysis
~
~
..~ ~~~~
~
__
cc. of %-butanoland'50 ce. of mcdanol, and the mixture was backtitrated with 0.5 N hydrochloric acid, using phenolphthalein as indicator. ACID NUMBER Three-gram samples were dissolved in acetone and titrated with 0.5 N sodium hydroxide, using phenolphthale,"
IODINF. NUMBXR was determined by the %hour Wijs method.
MOLECULAR WEIGHTSwere determined by the Rast camphor
.I."".."y. rnaihnd
REFRACTIVE LvnrcEs were determined at 25.0' C. with an Ahhe refractometer and an incandescent lamp with a blue glass filter. SPECIFICGRAVITY was determined at 25.0' C. with a 25-c~. pycnometer.
FIGURE1.
SAMI'LE O F A TRORODGRLY
DRYING OIL
HEAT-GELLED
The results are shown in Tables I1 and 111. The analyses were supplemented by ultraviolet absorption spectra in each case; the data will be given in another paper (8). The esters listed in Table IV were prepared purely for comparative purposes to show the difference before and after polymerization. As Table IV shows, even the lieating required to distill these esters at 1 mm. pressure is sufficient t o influence certain of the constabts, particularly the density.
INDUSTRIAL -4ND ENGINEERIISG CHEMISTRY
696
VOL. 32, NO. 5
proceeded a t additional points and therefore intramolecularly as well as intermolecularly. (Only the latter should be termed “polymerization” Rast Since these alone will increase the molecular Mol. Wt. weight.) Application of these statistics to the ratios 331 observed becomes interesting, since in the case 650 of the acetone-insoluble phase there have been recovered 75 per cent of dimer and 25 per cent 335 of monomer by weight equivalent to a molar ratio of 3 to 2. This ratio is identical with the 1157 equilibrium proportions found for ethyl eleostearate and ethyl linoleate by Brod, France, and Evans (4), in which case gelation does not occur t o restrict the reaction; then it seems likely that the gelled fraction now reported represents the highest degree of polymerization which such material may undergo. Since this ratio exceeds the theoretical possibilities for the purely
TABLE 11. PROPERTIES OF FRACTIONS DERIVED FROM THE GEL Sample No.
0
P
Q
D
E F
B
Iodine No., 2-Hr. Wijs
Description
n% dt! From the Extracted Gel Total methyl esters 1.4908 137.0 Methylester dist. 1.4511 0.’8839 64.8 Methyl ester residue 1.5052 1.0284 151.6 From the Soluble Extract Total methyl esters 1.4761 0 . 9 4 8 1 114.8 Methyl ester dist. 1,4550 0.8917 67.6 Methyl ester residue 1.5053 1 , 0 2 4 9 1 4 9 . 8 Total ext. (glyceride) 1.4913 0.9886
. ..
Saponification No.
Acid No.
186.5 194.5 183.0
4 4.8
186.6 191 174.5
6.6 5 8
”’.’
..
27.5
Discussion of Results The gel is composed of 70 per cent of insoluble solid phase and 30 per cent of soluble liquid phase, both in esterified glyceride form. Upon saponification, hydrolysis, and reesterification with methanol, only liquid esters are obtained. Upon distillation, these methyl esters are separated into volatile monomeric esters and nonvolatile dimeric esters. The most striking observation is the h d i n g that the ratio of the monomers to the dimers is markedly different for the two phases of the original gel. Obviously the gelled insoluble phase was more highly polymerized than F~~~~~3. M~~~~~~~ the liquid phase. Can one draw OF DRYING OIL (TRIany quantitative conc~usions? GLYCERIDE) Let us represent a molecule of the reactant by Figure 3 in which a glyceryl radical (black T) is attached through ester linkages to three linear fatty acid radicals. Now suppose that these react intermolecularly2 through the double bonds of the fatty acid radicals. The mechanism is probably a 1,4 addition of the conjugate systems or modified diene reaction (Y), but this need not concern us since any analogous intermolecular reaction will do as well for purposes of illustration. Figure 4 pictures both a dimer and a trimer of the original glyceride. Upon splitting these esters by saponification, we perceive that both monomeric and dimeric acids will result; their ratio will vary so that if 2 equals the number of triglyceride molecules united, then (z - 1) moles of dibasic
T
TABLE 111. ANALYSES OF OILS (PRIOR TO HEATTREATMENT) n’ns di: Description I. Sardine oil 1.4798 0 . 9 2 7 9 11. Oiticica 1.5140 0 . 9 7 1 3 111. 89% I 11% I1 1.5100 0.9663
+
Iodine No.. 2-Hr. Wijs 197.0 164.9 164.9
Saponification No. 189.3 185.0 186.0
Acid No.
3 5.7 5.4
TABLEIV. AKALYSESOF METHYLESTERSPREPARED FROM UNPOLYMERIZED OILS (OF THE GRADES USEDFOR THE GEL) Oil Oiticica Sardine
Condition Before distn. After distn. Before distn. After distn.
ny 1.4932 1.4911 1.4633 1.4623
Saponification No. 187.1 188.8 188.3 191.7
di! 0.9400 0.9227 0.8920 0.8895
Acid No. 6.2 5.6 16.4 15.0
Iodine No. 168.4 160.9 195.9 191.5
intermolecular addition of triglyceride esters a t infinite molecular weight, intramolecular additions must have occurred also. Their occurrence would necessarily involve some ring closures of the triglyceride polymers, presumably through the mechanism of the diene reactions of the unsaturated fatty acid radicals, and thus provide a most complex cyclized body. Perhaps the simplest conception of the nature of the gel structure which accounts for the observed ratio of monomer to dimer acids is that shown in Figure 5 ,
TABLE V. CALCULATED MONO-AND DIBASICACIDEQUIVALENTS OF HEAT-BODIED DRYING OILS, ASSUMING THE ADDITION REACTIONS TO HAVEBEEXEXCLUSIVELY IKTERMOLECULAR~ No. of Triglyceride Molecules United
DIMER
FIGURE4. DIMERA N D TRIMEROF
GLYCERIDE
THE
ORIGINAL
+
acid and (z 2) moles of monobasic acid may be recovered (Table V). Therefore, a t infinite molecular weight the moles of dibasic acid recovered could not equal the number of moles of monobasic acid recovered, and this limiting ratio per cent of dibasic acid and 3 3 l / ~per cent (equivalent to 662/~ of monobasic acid by weight) becomes of critical importance. For if equaled or exceeded, the addition reactions must have 2 The authors consider i t necessary and important t o recognize t h a t addition reaction0 may proceed “intermolecularly” and thus serve t o unite molecules, a n d that they may also take place “intramoleoularly” or within any given molecule. Only the intermolecular additions are considered t o result in polymerization; the intramolecular additions serve rather t o reatrict the growth funotions and t o modify the structure of the polymer.
Monobasic Acids -Moles4 5 6 7 8 9 10 11
Dibasic Acids
Monobasic Acids
--yo
Dibasic Acids
by weight-
1 33.33 66.66 2 2 44.44 55.55 3 50.00 3 50.00 4 53.33 4 4 6 . 6 6 5 55.55 5 44.44 6 57.13 4 2 . 8 6 6 7 58.33 41.66 7 8 59.25 40.74 8 9 60.00 40.00 9 12 10 66.00 34.00 99 102 100 66.60 33.30 999 1002 1000 a This table is derived from the statistical relations for intermoleoular rethe number of triglyceride actions according t o the formula that when z 2) moles of monobasio soids and ( z 1) moles of diesters united, (z basic acids may be derived therefrom; z times the molecular weight of the original gl oeride provides the calculated molecular weight of the polymer. Them mo%cular weights and proportions represent the highest statistical values and will be in eFror only t o the extent that intra,molecular addition and thermal decomposition reactionn ocour. Side reactions of these types may be expected t o reduce the molecular weight and t o increase the ratip of dibasic t o monobssic acids. I n every oase investigated. these side reactiom occur and have been oonfirmed by two additional independent methods (I,#).
+
-
-
INDUSTRIAL AND ENGINEERING CHErvIISTRY
MAY, 1940
where the connecting linkages, represented by straight lines, are in reality considered as six-membered unsaturated rings or bicyclic derivatives thereof. This represents only an average molecular structure of the gelled oil of the minimum molecular weight which would permit of the isolation of 3 moles of dibasic acid to 2 moles of monobasic acid upon saponification and hydrolysis. For the oils represented this would place the molecular weight a t about 7317 or double that of the highest polymeric but still soluble fractions of stand oils reported by Elod and Mach (6).
k
U U
FIGURE 5 . NATUREOF INSOLUBLE GEL STRUCTURE 8 moles triglyceride as octamer = 6 moles monobasic acid 9 moles dibasic acid (calculated molecular weight, 7317)
+
Similar treatment of the soluble phase of the gel shows that the recovery of 45 per cent of dimer and 55 per cent of monomer by weight (equivalent to a molar ratio of 9 to 22) is well below the critical limit. On the assumption of intermolecular reaction exclusively, this corresponds to a mixture of 22 moles of trimerized glyceride with 3 moles of tetramer, having an average molecular weight of 2852. The observed acid value, however, shows about 10 per cent of free fatty acid present, which would reduce the average molecular weight to about 2596. The observed molecular weight was 1157 to 1195 and again suggests other intramolecular reactions. This conclusion, moreover, is corroborated by the finding that products of thermal decomposition exist in this soluble phase. The analyses of the methyl esters isolated from both phases of the gel (including the ultraviolet absorption spectra) show that the monomeric and dimeric esters differ markedly in structure from the original esters. Conjugation has been lost and the unsaturation reduced, the latter especially in the case of the monomeric fractions. Although the monomeric and dimeric fractions from the soluble and insoluble phases are similar, there are important differences shown both by the ultraviolet spectra (3) and the saponification values. A succeeding paper (2) will show that these differences are due
697
to the fact that, aside from addition polymerization during the high-temperature processing of oils, a certain amount of thermal decompositions occur and result in the cracking of the esters. This creates low-molecular-weight esters and unsaturated hydrocarbons. The former may be recovered in the case of the methyl esters by distillation, whereas the latter are found in the polymeric esters. The saponification values show that the low-molecular-weight esters frorn these side reactions occur in both fractions of the gel, whereas the hydrocarbon fragments occur mainly in the dimerized portion of the soluble fraction of the gel. Linseed stand oils of less highly polymerized nature have been subjected to similar analysis by others. Kino (8) reported a linseed stand oil, the acetone-soluble phase of which yielded monomer and “dimer” acids in the ratio of 80 to 20 weight per cent; the corresponding values for the acids isolated from the acetone-insoluble phase were in the ratio of 40 to 60. The dimer acids, however, had a molecular weight of but 466 in the case of the acetone-soluble phase, whereas those from the acetone-insoluble phase had a molecular weight of 564 (theoretical, 560). These results indicate that linseed esters undergo more decomposition reactions than the present material which was derived mainly from the conjugated oiticica esters. Otherwise they are in substantial agreement and help to corroborate the point that the acetonesoluble phase of stand oils results not merely from a lower degree of polymerization than exists in the acetone-insoluble phase but mainly is the result of such thermal decompositions as occur during the kettle-bodying treatment.
Acknowledgment The authors desire to acknowledge the analytical assistance of R. L. Sperry and the help rendered by T. G. Moore and W. Letteris in connection with the preparation of figures and other illustrations. Thanks are also due the management of the American Cyanamid Company for its generous support of this work and permission to publish. Particular credit is due Ralph H. Huff without whose interest and cooperation this work would not have been accomplished.
Literature Cited (1) Bradley, T.F.,IND. ENG.CHEM., 30,689-96 (1938). (2) Bradley, T. F , and Johnston, W. B., Zbid., 32, to be published (1940). (3) Bradley, T. F., and Richardson, D., Zbid., 32, to be published (1940). (4) Brod, J. S.,France, W. G., and Evans, W. L., Ibid.. 31, 114-18 (1939). (5) Dean, R. T., and Pfann, H. F., unpublished research. (6) Elod, E., and Mach, U.,Kolloid-Z., 75, 338-48 (1936). (7) Kappelmeier, P.C.A., Farben-Ztg., 37, 1018, 1077 (1933). (8) Kino, K.,Sci. Papers Inst. Phys. Chem. Research (Tokyo), 15, 130-6 (1931). PRESENTED before the Division of Paint and Varnish Chemistry at the 98th Meeting of the American Chemical Society. Boston, Mass.
