Soap Ingredients as Retarders in Butadiene-Styrene Copolymerization J.
w. WIIASON1AND
E.
s. PFAU
The B. F. Goodrich Company, Akron, Ohio
Linoleic a n d linolenic acids a r e retarders of t h e r a t e of copolymerization of butadiene a n d Btyrene i n t h e GR-S recipe. T h e replacement of u p t o 10% of sodium p a l m i t a t e emulsifier h y sodium linoleate resulted i n a reduction of t h e conversion obtained i n 12 hours of 1.4% for each per cent of sodium palmitate replaced. Linolenic acid exerts approximately three times as great a retarding action as does linoleic acid. No evidence was found for t h e presence i n prime tallow, No. 1tallow, or yellow grease of substances inhibiting or retarding t h e emulsion copolymerization of butadiene a n d styrene GR-S recipe o t h e r t h a n linoleic or, if present, linolenic acid. 1,4-Pentadiene, which cont a i n s t h e s a m e double-bond s t r u c t u r e as is present i n linoleic acid, gave a retarding effect of t h e s a m e magnitude as did linoleic acid. Linoleic acid, isomerized t o t h e conjugated acid, did n o t retard. Highly purified oleic, elaidic, stearic, a n d palmitic acids, when employed as emulsifying agents for t h e copolymerization of butadiene and styrene, gave essentially identical hydrocarbon conversions i n 12 hours, Hydrogenated soybean oil soap (iodine value of 40 t o 50) employed as t h e emulsifier resulted i n a r a t e of polymerization equal to t h a t obtained with highly purified f a t t y acid soaps.
R
ESEARCH work on emulsifiers for the copolymerization of butadiene and styrene in the GR-S recipe mas carried on
during the war by several laboratories participating in the synthetic rubber program. Workers in this field soonobserved that the composition of the fats and oils used to prepare the soap employed for the emulsion polymerization had a significant effect on the rate of polymerization. Although it was generally recognized that large amounts of highly unsaturated fatty acids, such as linoleic and linolenic acids, were undesirable, the data from the various participating laboratories were not entirely in agreement. Also, some experimental work was initiated in the belief that inhibition or retardation was caused by certain materials other than fatty acids in the fats and oils employed in preparing the soaps. Three types of substances which might occur in fats and particularly in vegetable oils, and to which antioxidant properties have been ascribed, are the tocopherols, crude lecithin, and quinones (8, 9, 18, I f , 2 2 ) . These substances, which have been called inhibitols, might inhibit or retard the rate of polymerization. Various processes of refining, bleaching, air oxidation, etc., were tried by other workers with the hope that such inhibiting materials would be removed or destroyed. Our laboratory data indicated that linoleic and linolenic acids were the principal sources of the retardation encountered. A program was initiated to determine experimentally the magnitude of the retarding effects caused by (a) linoleic and linolenic acids, and ( b ) the so-called inhibitols. Copolymerization of butadiene and styrene was carried out in a GR-S recipe (Table I). The hydrocarbon conversion obtained in 12 hours at 50" C. was determined as described in the experimental part. The fatty acid soaps which xere evaluated were charged either as partial or complete replacements for the 5 parts 1
Present address, Union Oil Company, Oleum, Calif.
of sodium palmitate employed as the control emulsifying agent. Rlaterials other than soaps, which were tested as retarders, were charged as additives to the recipe.
TABLE I. POLYMERIZATION RECIPEIN PARTS BY WEIGHT Butadiene Styrene n-Dodecyl mercaptan, or: Commercial mixture of primary mercaptans (principally n-dodecyl mercaptan) Soap (sodium salt) Potassium permlfate Water Temperature, "C.
75 25
0.30 or 0 . 4 0 0.34 or 0. 60 6.0
0.30 180 60
RETARDING EFFECT IN THE GR-S RECIPE
Sodium linoleate (from carefully purified linoleic acid) was used to replace up to 10% of the sodium palmitate employed as the emulsifier for the GR-S recipe. Up to at least 10% sodium linoleate, the decrease in the hydrocarbon conversion obtained in 12 hours was 1,4y0 for each per cent of sodium linoleate present in the soap (Table I1 and Figure 1). Omission of 10% of the sodium palmitate with no addition of sodium linoleate docs not reduce the yield significantly. The factor 1.4 does not hold over the entire range of sodium linoleate concentrations; if it did, zero yield would be indicated for soap consisting of more than 72% sodium linoleate, whereas polymerization does occur even with 100% sodium linoleate (76% in 36 hours).
I - SODIUM LINOLEATE 2 20
O : '
- SOD/UN 2
"
LINOLENATE
4"
6"
8
"
'
10
% LINOLEATE 012 LlNOLEN4TE SOAP Figure 1. Effect of Linoleate a n d Linolenate Soaps Sodium linolenate was found to exert approximately three times the retarding action shown by sodium linoleate (Table I11 and Figure 1). Data were obtained by testing mixtures of sodium palmitate and the sodium soaps of the fatty arids from linseed oil. These fatty acids were recrystallized at low temperatures several times, and gave a mixture of 80% linolenic acid and 20% linoleic acid. Values were corrected to 100% linolenic acid for plotting in Figure 1.
March 1948
531
INDUSTRIAL AND ENGINEERING CHEMISTRY /OO\
I
,
1
I
t
I
TABLE 11. EVALUATION OF SODIUM LINOLEATE-SODIUM PALMITATE
Emulsifier, Sodium palmitate
a
MIXTURES IN GR-S RECIPE Sodium linoleate
Hydrocarbon Conversion in 12 Hr., $’ 5 Run 1 Run 2
10% of sodium palmitate omitted.
TABLE111. EVALUATION OF SODIUMLINOLENATE~-SODIUM P~LMITATTE M I X T U R IIN ~ GR-S RECIPE Emilsifier, % Sodium Sodium palmitate linolenatea
..
100
a
99 1 98 2 97 3 96 4 5 95 6 94 7 93 8 92 90 10 Linolenic acid was a mixture
Hydrocarbon Conversion in 12 Hr., % Run 3 Run 4 79 80 75 73 67 67 63 61 48 54 43 . 51 of 80% linolenic and 20% linoleic acid.
Figure 2 illustrates the type of retarding action encountered when a small amount of linoleic acid soap is present in the fatty acid soap. Mercaptan analysis of the latex by the method of Kolthoff and Harris (14) indicated that the rate of mercaptan disappearance with conversion was the same in recipes containing from 0 to 3.2% sodium linoleate (Figure 3). Evidently the retarding effect on rate of polymerization is not due to a side reaction of mercaptan with the linoleic acid. EFFECT O F HIGHLY PURIFIED FATTY ACID SOAPS
The use of the soaps of several highly purified fatty acids of widely different origins and characteristics [elaidic, oleic, palmitic, and stearic acids) in the polymerization recipe resulted in hydrocarbon conversions agreeing within experimental error (81* 2731. It can be assumed, then, that none of these contains inhibitory materials. Table IV shows the conversions obtained using the soaps of elaidic acid freshly prepared and four years old, pure oleic acid, Eastman Kodak palmitic acid, mixtures of Eastman Kodak palmitic and stearic acids, and myristic, palmitic, and stearic acids. Unsaturation such as that found in oleic and elaidic acids has no retarding influence on the rate of polymerization. When linoleic acid, which had been isomerized to give the conju-
t
I
8
4
0
POLYM€E/ZATiON Figure 2.
/6 20 TIME IN ffOffQ.3 AT 12
I
E4
50°C.
Retarding Effect of Sodium Linoleate
gated acid, was tested as a 25% replacement for palmitic acid, it was found to lower the 12-hour conversion by 3%, whereas a corresponding amount of sodium linoleate would have reduced the conversion by more than 25%. UNSAPONIFIABLE MATERIAL FROM ANIMAL FATS
Samples of prime tallow, tallow of lower grade (No. 1 tallow), and yellow grease were obtained from Armour and Company. Prime tallow represented approximately 7Oy0 of the available tallow a t the time this work was begun and was therefore of principal interest. The unsaponifiable fraction of the tallows and the grease was separated by the method of Olcott and Mattill (19). The soap solution obtained from the saponification was divided into two parts, one of which was extracted with ethyl ether. The unsaponifiable fractions were tested in the GR-S recipe; they were added in an amount ten times as large as that in which they occurred in the tallow. Sodium palmitate was employed as the emulsifying agent. As the results in Table V show, there was no effect upon the rate of polymerization. The fatty acids from the extracted and from the unextracted soap solutions were compared as the emulsifying agents in the GR-S recipe, and the rates of polymerization checked within experimental error (Table VI). Furtheimore, it can be shown that there are no unextractable inhibitols in these fatty acids, because the lower conversions obtained with the fatty acids as compared with pure fatty acids can be entirely accounted for on the basis of their linoleic acid content.
~~
TABLE IV.
COMPARISON OF FATTY ACIDSOAPS AS IN GR-S RECIPE
F a t t y Acids as Sodium Soap Eastman Kadak Dalmitir. Eastman Kodak palmitic Eastman Kodak palmitic Palmitic from recrystalhaed Armour’s Neofat 156 Eastman Kodak stearic Eastman Kodak palmitic (70%) f stearic (30%) Eastman Kodak palmitic (60%) atearic (20%) myristic (20%) Pure oleic Pure oleic Pure elaidic Pure elaidic Pure elaidic (4 years old) conjugated linoleic Eastman palmitic (75%) (25%). Pure oleic Pure linoleic Commercial soap from Procter & Gamble. Rubber Reserve quality Commercial soap from Procter & Gamble, Rubber Reserve quality
+
+
+
EMULSIFIERS
Time, Hr. 12 12 12 12 12 12
Hydrocarbon Conversion, % 80-81 (8 values) 79 83 80 83 81
12 12 12 12 12 12
81 81 82 80 81
81
12 13 36
77 84 76
12
77
13
81
.
O*
Figure 3.
20
40
60
% flYDROCAR80N
80
/ob
CONVERSION
Rate of Mercaptan Disappearance
532
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE V. EFFECTO F ADDITIOKO F UNS4POSIFIABLE hkTTER FROM - ~ R ' I X A L FATSON RATE O F POLYMERIZATION OF GR-S RECIPE *
Source Prime t a l l n m N O . 1 tallow Yellow grease ~
~~~~
Quantity Found in Fat, % 0 8
i,i
Quantity Tested Based on Sodium Palmitate, %
Hydrocarbon * Conversion in 12 Hr., %
8
ii
Vol. 40, No. 3
t o exert slight, if any, retarding effect; crude lecithin was without effect. 2-Methyl-l,4-naphthoquinone exerted an appre-
ciable retarding action when present in a concentration of 0.40% on the soap (Table VIII). E F F E C T , O F STRUCTURE
nn --
80 7 80 Sodium palmitate control 81
I t appeared probable that the portion of the linoleic acid molecule responsible for the retardation was the activated methylene group. Linolenic acid has two such TABLE VI. EVALUATION OF S o a h OF FATTY ACIDS FROM ASIMALFATSIS groups. The simplest hydrocarbon molecule having GR-S RECIPE a structure similar to linoleic acid is 1,Cpentadiene. This compound, employed as an additive to t8herec12-Hr, Estd. Actual Con12-H~. ipe, was found to exert a retarding etect of a comUnsaponiCalcd. version, CopSource of fiables Acid Titer, Iodine (SCN)% Linoleic % version, parable magnitude (Table Ix). Calculations show F a t t y Acidsa Extracted No. C. Value Value Acid, % (Fig. 1) % that 1 millimole of 1,4-pentadiene added to 50 Prime tallow No 201 42.8 48.0 44.4 4.0 75 grams of monomers reduces the yield obtained Prime tallow Yes 199 42.8 KO.1 tallow No 202 42.7 48.2 44.7 3.9 75 75 in 12 hours by precisely the same amount No. 1 tallow Yes 204 42.9 75 Yellowgrease No 198 3 6 . 9 68.4 57.9 11.5 65 68 (17%) as does 1 millimole of sodium linoleate. Yellow grease Yes 200 37.3 66 As with linoleic acid, greatly increased amounts Sodium palmitate control 81 a A11 tallows and greases obtained from Armour & Co. of 1,4-pentadiene did not cause a moportionate . * . reduction in yield. 0.7
7:
Linoleic acid contents of the fatty acids were determined by iodine ( 1 ) and thiocyanogen titrations ( 2 ) . The 12-hour conversions which would be obtained using soaps containing such amounts of linoleic acid \yere estimated from Figure 1. As shown in Table VI, the estimated and experimental values are in close agreement. EVALUATION O F VARIOUS MATERIALS
Considerable experience with a commercial soap of Rubber Reserve quality has indicated that approximately a 5 r 0 lon.er yield is obtained with it than with the best pure fatty acids. This can be accounted for by the linoleic acid content of this commercial soap. For example, one sample had iodine and thiocyanogen values indicating a linoleic acid content of 3.3%. Soybean oil, hydrogenated to iodine values of 40 to 50, yields soaps comparable with pure fatty acid soaps in influence upon the rate of polymerization (Table VII). This degree of hydrogenation is sufficient to convert practically all of the linoleic acid to oleic, iso-oleic, and stearic acids. The soaps were furnished by Lever Brothers Company with the information that they contained a fair amount of tocopherol. I t would appear that, in the case of vegetable oil fatty acids also, the principal retarders are linoleic and linolenic acids,
OF SOYBEAX OIL SOAP TABLE VII. EFFECTOF HYDROGEXATIOX ON RATEOF POLYMERIZATION
Hydrocarbon Conversion Emulsifier Iodine No. in 12 Hr., % Hydrogenated soybean oil soapQ 70 77 50 77 Same 50 79 Same 40 80 Same Commercial soap from Procter & Gam.. 77 ble, control Commercial soap from Procter & Gam.. 76 ble, control a Hydrogenated soybean oil soaps obtained from Lever Brothers Co.
Although no evidence was found for the presence of any inhibitols in animal fats, it was thought desirable to test certain representative materials of this type (8, 9, 18, 11,d d ) . Tocopherols have been found in a wide variety of vegetable fats but are much less commonly found in fats of animal origin. Ault (3)has pointed out that tocopherols rarely occur in fats and oils (except wheat germ oil) in percentages exceeding 0.2%, and that it seems probable that the amount to be found in tallow would not exceed at most a few hundredths of one per cent. a-Tocopherol was found
TABLEVIII. EFFECTOF ADDITIONOF WTOCOPHEROL, CRUDE LECITHIN, AND 2-b~ETHYL-1,4-NAPHTHOQCIA-OXC T O GR-S RECIPEOK RATEOF POLYMERIZATION Quantity Tested Based on Substance Added hIonomers, % Eastman a-tocopherol 0.8 Eastman a-tocopherol 8.0 Crude lecithin (Eastman) 0.8 Crude lecithin (Eastman) 8.0 2-iMethyl-1 4-naphthoquinone 0.8 2-Methyl-l:B-naphthoquinone 8.0 Commercial soap from Procter & Gamble, Rubber Reserve quality, control
Hydrocarbon Conversion in 12 Hr., % 75 74 76 77 74
68 77
TABLE Ix. EFFECTO F LkDDITIONO F 1,4-PEKTADIEi\.EO N RATE OF POLYMERIZATIOX Amt. Added Based on Millimoles/BO g. monomers, % of monomers 0 0 0.18 1.4 2.3 0.30 0.60 4.6
Hydrocarbon Conversion in 12 Hr., % 81 58 53 43
A few compounds which contain three conjugated double bonds were tested. A sample of 8-eleostearic acid (obtained from the Eastern Regional Laboratories) and a sample of a-eleostearic acid prepared from tung oil by a method essentially that of Thomas and Thomson (16)were evaluated for retarding action in the GR-S recipe. As the results in Table X indicate, when aand p-eleostearic acid soaps were tested as partial replacements for the sodium palmitate emulsifier, retardation of polymerization was of approximately the same degree as that found with linolenic acid. When allo-ocimene, which also contains three conjugated double bonds, was added to the recipe, it was found to retard polymerization even more seriously than did linolenic acid a t equimolar concentrations (Table XI). O F ELEOSTEARIC-PALMITIC ACID S0.4P TABLEx. EVALUATION MIXTURESIN GR-S RECIPE
Emulsifier 100% sodium palmitate .... 98% sodium palmitate 2 % sodium a-eleostearate 4% sodium a-eleostearate 913% sodium palmitate 6% sodium a-eleostearate 94% sodium palmitate 8% sodium a-eleostearate 92% sodium palmitate 2% sodium 8-eleostearate 98% sodium palmitate 4 7 sodium 8-eleostearate 96% sodium palmitate 94% sodium palmitate 6% sodium p-eleostearate 92% sodium palmitate 8% sodium p-elesotearate
++ + + ++ ++
Hydrocarbon Conversion in 12 Hr., % 79 69 60 50 47 70 60 53 42
March 1948
TABLEXI. EFFECTOF ADDITIONOF ALLO-OCIMENE TO GR-S RECIPEON RATEOF POLYMERIZATION Amt. Added Based on monomers, %
0 0.27 1.36 6.80
533
INDUSTRIAL AND ENGINEERING CHEMISTRY
Millimoles/50 g. of monomers 0
1
6 25
Hydroosrbon C o o v e r ~ o n in 12 Hr., % 79 32 Very low Very low
Thus these tests have shown that the soaps of pure saturated fatty acids (palmitic, stearic) and' pure acids having a single double bond (oleic, elaidic) give equivalent and rapid rates of polymerization in the GR-S recipe. When the two double bonds in linoleic acid are isomerized, this conjugated linoleic acid soap is also satisfactorv. Comoounds containing one or more activated " H H H H H methylene groups (-c=c-c-C=c-), such as linoleic and H linolenic acid and 1,4-pentadiene, are retarders. Compounds containing three conjugated double bonds, such as a- and p-eleostearic acid and allo-ocimene, were also found to be retarders. Further, these experiments indicate that, in the preparation of soaps from animal fats for emulsifiers in polymerization, inhibitols are not present. If any polymerization inhibitors or retarders were present in the fats tested, they must have been either destroyed by the alkali or extracted by the water. It is known that alkali-labile antioxygenic substances occur in certain vegetable fats and oils (9). However, it may be anticipated that any material destroyed by the alkali or extracted by water under the conditions of our techniques would similarly be eliminated in the soapmaking process. The retarders in such soaps are linoleic acid and, if present, linolenic acid. Processes designed,to improve fats by removal of small amounts of impurities, by bleaching, refining, or similar treatments, appear to be of no value as regards improving the soap for use in emulsion polymerization of the GR-S recipe. Clearly, methods which remove or modify linoleic acid, such as hydrogenation, isomerization, and dimerization, show more promise. EXPERIMENTAL PROCEDURES
EXTRACTION OF UNSAPONIFIABLE MATTER. The tallows and the grease were saponified according to the directions given by Olcott ahd Mattill @I). I n our experiments 250 g r a m of fat were saponified and the resulting soap solutions divided into two parts after dilution with water. One part was extracted with ether, and the ether solution evaporated to dryness. The unsaponifiable.materia1 so obtained was an orange-colored sticky solid of characteristic odor liquefying a t about 60" C. The fatty acids were liberated from both the extracted and unextracted soap solutions by acidification with 30% sulfuric acid, washed with water, filtered, and dried by heating at reduced pressure. OLEICACID. A highly purified sample was prepared by repeated crystallization of olive oil fatty acids from acetone at low temperatures as described by Brown and Shinowara ( 5 ) ; m.p. 12.5" C.; n p 1.4604; iodine value 87.9. LINOLEICACID. High purity acid was prepared by repeated crystallization of cottonseed oil fatty acids from acetone and from petroleum ether at low temperatures according to the directions of Frankel and Brown (6) and of Frankel, Stonebruner, and Brown ( 7 ) ; m.p. -5.2"C.; ng 1.4700; iodine value 180.5. CONJUGATED LINOLEICACID(10,1.%OCTADECANDIENOICACID). The fatty acids of dehydrated castor oil were isolated essentially by the methods of Kulikov (15)and of Killiffer (12). These fatty acids were distilled and a fraction was collected at 188-192" C. at 1-2 mm. Any saturated acids present were removed by low temperature crystallization from acetone (-50" C. and then a t -75' C.). The acetone was evaporated off, and the acids remaining were isomerized using a method espentially that of von
Mikusch (17) and of Bradley and Richardson (4). This product was dissolved in water, acidified, and washed three times with hot water. The filtered product was distilled and a fraction collected a t 200-208" C. a t 3 mm. The product was subjected to several low temperature crystallizations (acetone, 30 C. ; acetone, -40" C., four times; petroleum ether, -40" C.; methanol, -40" C.); m. p. 34' C.; ng 1.4780; n",7 1.4803; Woburn iodine value, 161; partial Wijs iodine value, 87.3; conjugated fatty acid by maleic anhydride in acetone, 70.70jo0.) ELEOSTEARIC ACID. The method employed was essentially that of Thomas and Thomson (86). Tung oil was saponified by the method of Olcott and Mattill (80). The fatty acids were liberated from the soap, extracted with hexane, washed with water, and allowed to stand overnight a t -20" C. The crystal crop was filtered, washed with hexane a t -20' C., redissolved in hexane, and recrystallized. The product from this crystallization, which had a melting point of 44.5-46.5' C., was recrystallized two more times and dried in a vacuum desiccator. Care was exercised to exclude air in handling. @-ELEOSTEARIC ACID. A sample was received from the Eastern Regional Laboratories described as p-eleostearic acid. ALLO-OCIMENE.A sample was received from the Hercules Powder Company; ng 1.5425, d:' 0.8127, b. p. 194-196' C. a t 760 mm. This sample was distilled at 95" C. at 30 mm. and an intermediate fraction collected. LINOLENICACID. A material of 80% purity, the remainder being linoleic acid was prepared by crystallization of linseed oil fatty acids from acetone and from petroleum ether at low temperatures according to the method of Shinowara and Brown (89) ; n:' 1.4771; iodine value 255. This hydrocarbon was synthesized by the ~,~-PENTADIENE. successive preparations of or-chloroethyl ethyl ether, a,p-dibromoethyl ethyl ether, or-allyl-P-bromoethyl ethyl ether, and 1,4pentadiene (13, $4,85). SODIUMPALMITATE. Armour's Neofat-156 (iodine number 2.0) was recrystallized from ethanol, and the product (iodine number 0.9) dissolved in ethanol and neutralized with the calculated quantity of sodium hydroxide in ethanol-water using volumes such that theregwas no precipitation of soap. The solution was then evaporated to dryness and finally dried in a vacuum oven. ELAIDIC ACID. Pure oleic acid prepared as described was isomerized with Poutet's reagent (a solution of mercury in nitric acid) and recrystallized from alcohol (IO); m.p. 45" C.; iodine value 88.4. A seconds ample was prepared from U.S.P. oleic acid crystallized once from acetone at low temperatures. The four-year-old sample was prepared by David Craig by isomerization of pure oleic acid with nitrous fumes (16). DETERMINATION OF LINOLEIC ACID. The fatty acids from the prime tallow, No. 1 tallow, and yellow grease were analyzed by the conventional iodine ( I ) and thiocyanogen number determinations (a). Linoleic acid in the fatty acids from the yellow grease was also estimated by determination of the iodine number of the fatty acids found in the filtrate after crystalliaation of a 5% solution in acetone at -50" C. Two determinations indicated 9.2 and 9.4% linoleic acid. These are minimum values because the filtrate does contain some saturated fatty acids. These were conducted in 8-ounce crown POLYMERIZATIONS. cap bottles, employing 50 grams of monomers and proportionate concentrations of all reagents used in the GR-S recipe (Table I). Aqueous soap solution and potassium persulfate were added, and the bottles placed in a cooling bath a t 1" C. The solution of styrene containing the dodecyl mercaptan was weighed out and added to the cooled bottle. Butadiene was weighed in a small Dewar flask, transferred to the bottle, and allowed to vent to correct weight; the bottle was capped immediately and placed in the 1 " C. bath until the desired starting time. The soap gel was
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
534
broken by warming a t 50’ C. and by vigorously shaking the bottle. The bottle was placed in a pater bath thermostated a t 50’ C. and rotated for the required period of time. At the completion of the run the bottle was removed from the 50” C. bath, cooled slightly with cold water, and then immersed in a bath a t 1” C. After cooling for approximately one half hour, the bottle was opened and the latex stabilized immediately with a 95y0 ethanol solution of phenyl-@-naphthylamine (2% on monomers). The latex was coagulated by the addition of salt and alcohol employing vigorous mechanical stirring. The small crumbs obtained were washed several times with warm distilled water to remove all but negligible amounts of soap and salt. The polymer in the form of crumbs was dried to constant weight in a 60” C. air oven. The weight of phenyl-@-naphthylamine added t o the latex was subtracted from this final yield and the per cent conversion calculated from the corrected yield. Samples of latex for mercaptan analysis and for the determination of hydrocarbon conversion (data in Fjgures 2 and 3) were obtained using a hypodermic syringe technique developed by Houston (11)of this laboratory. The butadiene which was of 98.5y0 purity or better was distilled with refluxing through a short column prior to its use. The styrene was steam-distilled before using. Either a commercial mixture of primary mercaptans (principally n-dodecyl mercaptan) or n-dodecyl mercaptan was used as the modifier. Distilled water was utilized in the preparation of all aqueous solutions. Either Procter and Gamble Company soap of Rubber Reserve quality, or Eastman Kodak palmitic acid converted to soap, was used as the emulsifying agent unless otherwise specified. ACKNOWLEDGMENT
This investigation was carried out under the sponsorship of the Office of Rubber Reserve, Reconstruction Finance Corporation, in connection with the Government Synthetic Rubber Program.
Vol. 40, No. 3
LITERATURE CITED
Bm. Soc. Testing Materials, A.S.T.M. Designation 460-41. Assoc. Official Agr. Chem., “Methods of Analysis,” 5th ed., P. 431 (1940). Auk, W. C., U. S. Dept. of Agr., private communication to H. L. Trumbull (Feb. 15, 1944). Bradley, T. F., and Richardson, D., IXD. ENG.CHEY.,34, 237 (1942). Brown, J. B., and Shinowara, G. Y., J . Am. Chem. Soc., 59, 6 (1937) Frankel, J. S.,and Brown, J. B., I b i d . , 63, 1483 (1941). Frankel, J. S., Stonebruner, W., and Brown, J. B., Ibid., 65, 259 (1943). Golumbic, C., I b i d . , 63, 1163 (1941). I b i d . , 64, 2337 (1912). Griffiths, H. N., and Hilditch, T. P., J . Chem. SOC.,1932, 2315. Houston, R. J., IND. ENG.CHEM.,ANAL.ED.,t o be published. Killeffer, D. H., IND. ENG.CHEM.,32, 1466 (1940). Kistiakowsky, G. B., Ruhoff, J. R., Smith, H. A., and Vaughan, W.E., J . Am. Chem. Soc., 58, 146 (1936). Kolthoff, I . M., and Harris, W. E., unpublished report [adaptation O f I X D . ENG.CHEM.,ANAL. ED., 18, 161 (1946) 1. Kulikov, A. M., ByuZZ. Obmen Oput. Lakokrasochnoi Prom., 1939,NO.9, 21-5. Meyer, Hans, “Nachweis und Bestimmung Organischer Verbindungen,” p. 127, Berlin, J. Springer, 1933. Mikusch, J. D. von, J . Am. Chem. SOC.,64, 1680 (1942). Olcott, H. S.,and Mattill, H. A., Chem. Reus., 29, 257 (1941). I b i d . , J . Am. Chem. Soc., 58, 1627 (1936). I b i d . , p. 1628. I b i d . , p. 2204. Olcott, H. S., and Mattill, H. A., OiZ &. Soap, 13, 98 (1936). Shinowara, G. Y., and Brown, ‘J. B., J . Am. Chem. Soc., 60, 2734 (1938). Shoemaker, B. H., and Boord, C. E., I b i d . , 53, 1508 (1931). Swallen, L. C., and Boord, C. E., I b i d . , 52, 654 (1930). Thomas, -4.W., and Thomson, J. C., Ibid., 56, 899 (1934). i
RECEIVED May 13, 1947. Presented before the Division of Rubber Chemistry a t the 111th Meeting of the AxiERIcAx CxExcAL SOCIETY,Atlantic City, l i.J.
Acetylation of ~ k v Lactates l and Similar Hvdroxv Esters with Acetic Acid J
J
M. L. FEIN AND C.H. FISHER Eastern Regional Research Laboratory, Philadelphia 18, Pa.
Alkyl lactates have been acylated conveniently and in high yields with acid anhydrides, acid chlorides, and ketene, but prior to the present investigation little was known about the suitability of organic acids for the acylation. Results obtained in a study of the interaction of acetic acid and methyl lactate under various conditions show that acylation and acidolysis occur simultaneously, the principal products being methyl a-acetoxypropionate, a-acetoxypropionic acid, methyl acetate, and water. The combined yields of methyl a-acetoxypropionate and aacetoxypropionic acid were high. Similar results were obtained when the study was extended to several alkyl lactates, glycolates, and a-hydroxyisobutyrates.
A
LKYL lactates can be made in large quantities at low cost @ I ) , and their acyl derivatives (alkyl a-acyloxypropionates, Equation 1) are of value as solvents, plasticizers (1, d ) , and intermediates for the pyrolytic preparation of methyl acrylate (3, 19) and certain other polymerisable esters (7, 11, do). Thus far, ketene (4, vinyl acetate (16, 16), acid anhydrides ( 6 ) , and acid chlorides (6) have been ‘used in the acylation of alkyl lactates.
Organic acids, although less expensive than their anhy’drides and chlorides, have been considered less suitable for the acylation of alkyl lactates. It has been reported, for example, that methyl and ethyl acetate are formed when methyl and ethyl lactate, respectively, are treated with acetic acid (13). The present authors have studied the reaction of alkyl lactates with acetic and propionic acids for the purpose of finding suitable conditions for making alkyl a-acyloxypropionates (reaction 1) and a-acyloxypropionic acids (reaction 2). HOCH(CH3)COOR
+ R’COOH R’COOCH(CH3)COOR 4- HzO +
+
HOCH(CH3)COOR 2R’COOH + R’COOCH(CH3)COOH
+ R’COOR 4- HzO
(1)
(2)
Most attention was directed to the interaction of methyl lactate, now commercially available, and acetic acid primarily because pyrolysis of the acetyl derivative of methyl lactate gives methyl acrylate, a resin and elastomer intermediate (17,18), in high yield. As examples of other hydroxy esters, alkyl glycolates and ahydroxyisobutyrates were included in the study. The present
