July 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
1409
CONCLUSIONS
TABLE V.
EQUILIBRIUM CONSTANTS FOR REACTION OF CRUDE 44% LACTICACIDWITH METHANOL
Temperature Series: M / L . Approximately 4; Catalyst, Approximately 0.1% HzSOr Equilibrium Temp., O C . Constant, K 25 3.40 40 3.40 60 3.28 80 3.38 100 3.26 Average 3.34 Catalyst Series: M / L , Approximately 4; Temperature, 100” C. Equilibrium H1SOr. % Constant, K 0.0 3.10 0.0968 3.26 0.145 3.24 0.260 3.31 0.476 3.27 1.038 3.23 Average 3.24 Production Series: Temperature, 100’ C.: Catalyst, Approximately 0.1% Ha904 Equilibrium M/L Constant, K 1.005 4.42 2.05 3.98 3.95 3.26 7.87 2.65
The data and results presented here show that an excess of sulfuric acid, over that needed to react with the impurities in the commercial lactic acid, must be present in the reaction mixture to ensure catalytic activity. High ratios of methanol to lactic acid and short contact times a t high temperatures favor high yields and low decomposition. NOMENCLATURE
-
A b = original titratable acidity, moles per liter a = constant, corresponds to the theoretical value of k for 0% catalyst C = weight % catalyst based on total weight of mixture K = equilibrium constant k = specific reaction rate constant, liters per (mole)(minute) L = moles lactic acid per 100 grams of solution M = moles methanzl per 100 grams of solution T = temperature, K. t = temperature, C. X = moles lactic acid, converted a t time 8, per 100 grams solution e = time, minutes or hours as specified
~
LITERATURE CITED
(1) Glasstone, S., “Textbook of Physical Chemistry,” New York,
Table V shows that temperature and catalyst concentration have no appreciable effect on the equilibrium constant in the ranges studied. However, a definite trend can be seen when the ratio of reactants is varied. This is similar to that found when the 85% lactic acid was used (3).
D. Van Nostrand Co.,1946. Troupe, R. A . , and Kobe, K. A., Anal. Chem., 22,545 (1950). (3) Troupe, R.A., and Kobe, K. A., IND. ENG.CHEM.,42,801 (1950). (4)Watson, P.,Ibid., 32,399-401 (1940). (2)
RECEIVEDMarch 13, 1950.
Diglycol Bis(Carbonates) of Lactic Esters LACTIC ACID DERIVATIVES AS PLASTICIZERS C. E. REHBERG, MARION B. DIXON, T. J. DIETZ, AND C. H. FISHER Eastern Regional Research Laboratory, Philadelphia, Pa. Plasticizers made by acylating twenty-three lactic esters with diethylene glycol bis(chloroformate)[O(CH&Hp OCOC1)2] are described. As a class, these plasticizers were high boiling and compatible with a vinyl chloridevinyl acetate copolymer, ethylcellulose, and cellulose ace-
tate. The esters prepared from the n-butyl, n-hexyl, 2ethylhexyl, 2-butoxyethyl, and 2-(2-butoxyethoxy)ethyl esters of lactic acid were relatively fluid and more efficient than many of the commercial plasticizers in plasticizing the vinyl chloride-vinyl acetate copolymer.
B
Considerable work has been done in this laboratory on the preparation and evaluation of high boiling lactic acid derivatives as plasticizers. The present paper describes diglycol bis(carbonates) [diethylene glycol bis( 1-carbalkoxyethyl carbonates) ] made (15, 16) by acylating certain lactic esters with diglycol bis(chloroformate),
ECAUSE the production of plasticizers in the United States has increased tremendously in the last decade-from 30,000,000 pounds in 1939 to about 190,000,000 pounds in 1949 ( 1 ) much effort has been expended to find improved plasticizers and new raw materials for their manufacture. Lactic acid, commercially available as such and as the methyl, ethyl, and butyl esters, is of interest as a starting material for plasticizers because it can be made easily and efficiently (6, 10) from inexpensive materials such as corn sugar, whey, molasses, and sulfite waste liquor (9); its manufacture is not necessarily associated with or limited by other commercial operations; and having two functional groups, it can be transformed into many high boiling derivatives (6,14-16) having ester and other compatibilizing groups. Although the preparation of plasticizers from lactic acid has been described (2-6, 16), appreciable quantities have not been used for this purpose.
+
O(CH2CH20COCI)z 2HOCH(CHa)COOR + Diglycol bis( chloroformate) 0 [CHzCHzOCOOCH(CHa)COOR 12 Diglycol bis( carbonate) Compatibilities of these bis(carbonates) with cellulose acetate and ethylcellulose and the properties of vinyl chloride copolymer plasticized with the bis(carbonates) are given also. The chemicals required to make most of the bis(carbonates) discussed here are available commercially.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1410
Vol. 42, No. 7
TABLE I. DIETHYLENE GLYCOL BIS(CARBOKATES) OF LACPATES ~ Lactate Methyl Ethyl n-Propyl Isopropyl n-Butyl Isobutyl sec-Butyl n-Hexyl 2-Ethylbu tyl 4-Methyl-2-pentyl n-Octyl 2-Ethylhexyl 2,6-Dimethyl-Pheptyl Cyclohexyl AIethylcyclohexyl nA,,.., llyl
~
Wt. 366 394 422 422 450 450 450 507 507 507 663 563 491 503 531 418 563 454 482 539 551 627 506 422
1 B.P., . ' C. (16,16) 1 mm. 4 mm. 195 200 210 20 1 221 215 211 242 237 223 260 251 242 251 257 215
222 228 238 230 251 243 239 271 265 252 29 1 279 271 279 285 243
Viscosity, Cp. 40" c.
,
20° C. 1,818 375.4 309.8 555.4 206.3 482.2 476.2 232.1 327.5 593.5 204.5 307.5 1,313 22,565 16,240 262.9 1,631 741.8 431.8 329.7 822.2 135.5 4,438 471.7
1-Carballyloxyethyl~ ... 2-Methoxyethyl 238 266 2-Ethoxyethyl 245 273 2-Butoxyethyl 256 285 2- (2-Ch1oroethoxy)ethyld 2- (2-Butoxyethoxy)ethyId ... Tetrahydrofurfuryl 266 295 Isobutyl glycolate 221 249 Diglycol bia(buty1 carbonate) 306 1656 175(3) 20.1 2-Ethylhexyl phthalatef 391 229 (5) 84 Triglycol dihexoateg 346 202 (5) 17 Viscosity ratio = cp. 40°/ep. 20'. b hI1. N NaOH per 100 grams of plasticizer. M1. N NaOH per 100 g r a m of plasticizer after boiling in water for 24 hours. d Undistilled material.
...
... ,..
... .. .
EXPERIMENTAL
Redistilled samples of the commercially available methyl, ethyl, and wbutyl esters of lactic acid and several other lactic esters prepared as previously described (4, 13, 14) were used. Allyl lactyl lactate (16) [HOCH(CHs)COOCH(CH8)COOCHzCH: CHZ],needed for the preparation of the diglycol bis(carbonate) of 1-carballyloxyethyl lactate, was obtained as a by-product in the preparation of allyl lactate (13 ) . Commercial diglycol bis(ch1oroformate) was used as received. The lactic esters were acplated with the bis(chloroformate) in the presence of pyridine and ether a t about 0" F. The products were washed successively with dilute acid and with water; most of the carbonates were then distilled at reduced pressure. The washed products, however, were almost colorless or light amber, and hence were suitable as plasticizers without distillation. The bis(carbonates) were thermally stable below about 225' to 250" F. The yields, higher than 90% of the theoretical in some instances, were usually good. Analytical data, including carbon and hydrogen contents, saponification equivalents, and molecular refractions were in agreement with the theoretical value (16,16). The diglycol bis(carbonate) of isobutyl glycolate was prepared, and its properties were compared directly with those of the /
\
__ RatioQ
Water Solubility, G./100 G.
187.0 70.76 68.61 88.93 52.80 87.77 88.22 59.83 75.01 96.28 58.6 73.18 169.0 1092 832.0 63.01 115.3 127.3 88.33 77.96 155.0 43.11 516.0 93.61 9.7 26 10.5
Free Acidityb 0.50 0.45 0.10 0.40 2.05 0.0 0.50 0.50 0.25 1.25 0.25 0.0 0.0 0.60 1.85 1.05 0.90 0.27 0.10 0.70
492 8.5
0.55 0.35 0.60
33.5 122.1 9.90
...
0,486 0.310 0.618
0.01 0.01 0.02
Boiling Water Stability c
... . I .
...
2.2 2.5 0.90 0.50 0.75 0.25 0.05 0.38 0.25 2.95 1.75 0.65
...
304 296 61.1 1.45
...
...
I
.
.
,..
Pressure, mm. I Flexol DOP. 8 Flexol3GH.
Tensile properties of molded compositions were obtainrd from A.S.T.M. Type D dumbbell test specimens cut from a 0.065inch thick slab molded a t 300' F. in a sandwich-type mold with polished ferrotype face plates. The tensile test was performed on a Scott IP-4 inclined plane machine in accordance with A.S.T.M. D 882-46T except for the width of the test specimen. The rate of loading was 80 pounds per minute. lWodulus was obtained a t 100% elongation by tapping the autographic chart lightly to form a "pip" on the curve at the instant the specimen had elongated 100% between bench marks, Brittle points of the copolymer compositions were determined with small samples cut from molded sheets or slabs (approximately 0.065 inch thick); equipment similar to that of Belker, Winspear, and Keinp (19) was used, An estimate of the stability to heat was obtained by heating small squares of the molded sheets (0.08 inch thick) in an oven at 150' C. and observing them at hourly intervals. Of those tested, the alkyl derivatives were most stable; they showed no appreciable discoloration after 7 hours. The alkoxyethyl esters showed little change, but the tetrahydrofurfury1 ester (undistilled material) darkened in 4 hours. Free acidity and stability to boiling water of the esters were determined by the method of Fordyce and M q e r ( 7 ) .
CH&HzOCOOCHzCOOCHzCH (CH3)2 PROPERTIES OF BIS(CAHBQNATES)
CHzCHzOCOOCIlzCOOCH,GH (CHs)*
diglycol bis(carbonate) of isobutyl lactate (Table I). Compatibilities (Table 11) with cellulose acetate and ethylcellulose were determined by examining plasticized films of these materials prepared by casting from solutions. Clear, transparent films indicated compatible plasticizers. Because large quantities of plasticizers are used with vinyl chloride polymers, most attention was given to compositions containing the bis(carbonates) and Vinylite VYDR, a 95% vinyl chloride-5% vinyl acetate copolymer. The formulation, as follows, and milling procedure have been described (17, 18): Vinyl chloride copolymer Basic lead carbonate Stearic acid Plasticizer
Parts 63 5 1.0
0 5 35.0
The bis(carbonates) were dense liquids (dzo always higher than 1 ) having molecular weights ranging from 366 t o 627. I n spite of their relatively high content of oxygen, they were insoluble in water (Table I). They differed greatly in their stability t,oward boiling water, the esters of high oxygen content being relatively unstable (Table I). As a class, the bis(carbonates) Rere more viscous (Table I) than several of the plasticizers reported t u be eEcient in softening vinyl chloride polymers (11, 12, 17, 18). The less viscous bk(carbonates) mere characterized by relatively long straight chains--that is, such as those made from m-butyl, n-hexyl, rboctyl, and 2-(2-butoxyethoxy)ethyl lactates. As is evident from the viscosities of the cyclohexyl, methylcyclohexyl, and tetrai hydrofurfuryl esters, rings were particularly effective in increasing viscosity. Branching usually increased the viscosity appreciably. Comparison of the viscosities of the isobutyl glycolate and isobutyl lactate esters indirates, however, that the side methyl
July 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
group of the lactic acid segment is relatively ineffective in raising the viscosity. The temperature coefficient of the viscosities (Table I) was usually greater than that of the commercial plasticizer, 2ethylhexyl phthalate. It has been suggested (1, 12) that relatively fluid plasticizers having viscosities little influenced by temperature are usually efficient. The results of the present work are in general agreement with this statement. Even the more volatile bis(carbonates) had high boiling points, comparable with that of octyl phthalate (8) and higher than those of many commercial plasticizers (Table I). Because of their high boiling points, the bis(carbonates) should be outstanding in permanence,
TABLE 11. PLASTICIZING ACTION OF DIETHYLENEGLYCOL BIS(CARBONATES) OF LACTATES
Laotat e
A W N 0 W LEDGMENT
The authors are grateful to Franklin Strain, Columbia Chemical Division, Pittsburgh Plate Glass Company, for samples of diethylene glycol bis(ch1oroformate) and some of the bis(carbonates); to R. L. Bateman, Carbide and Carbon Chemicals Corporation for Zethylbutanol, 2-ethylhexanol, and the alkoxyethanols; and to K. R. Edlund, Shell Chemical Corporation, for methylisobutyIcarbino1 and diisobutylcarbinol. The interest and contributions of E. M. Filachione and P. E. Meiss are gratefully acknowledged. LITERATURE CITED
(1) Bergen, H.S.,Oflcdal Digest Federation Paint & Varnish Production Clubs, No. 289, p. 72 (February 1949). (2) Carruthers, T. F.,and Blair, C. M., U. S. 2,158,107 (May 16, 1939).
Polyvinyl Chloride-Acetate” Modulus a t 100% Tensile elongastrength, Elongation, Brittle lb./sq. tion, l:ntz. point, inch % O C.
...
3560 3590 3540 3480 3640 3960 34604 3140 3260 3580 36904 3440 3330
PLASTICIZED COMPOSITIONS
Table I1 gives the compatibilities of the bis(carbonates) with a 95% vinyl chloride-5% vinyl acetate copolymer (Vinylite VYDR), cellulose acetate, and ethylcellulose. Those data show that the bis(carbonates) as a class are compatible with these resins, presumably because of the abundance of ester groups. The bis(carbonates) of the lower alkyl lactates were incompatible with the vinyl chloride resin but compatible with cellulose acetate. As the size of the alkyl group increased, compatibility with the vinyl chloride resin improved, and compatibility with cellulose acetate decreased. All the bis(carbonates) higher than the hexyl ester (Table 11) were incompatible with cellulose acetate. A similar trend in the alkoxyethyl series (Table 11) is suggested, but the data are not adequate ’for broad generalizations. I n general, the esters containing the least oxygen were most compatible with the vinyl resin and least compatible with cellulose acetate. Many of the bis(carbonates), however, were compatible with both the vinyl chloride resin and cellulose acetate. All the bis(carbonates) were compatible with ethylcellulose (Table 11). Branched chain and secondary alkyl esters (Table 11) appeared to be slightly more compatible than the n-alkyl esters but less efficient in plasticiaing the vinyl chloride resin. As judged by modulus values (Table 11),several of the plasticizers approached Sethylhexyl phthalate, the most widely used plasticizer for vinyl chloride resins, in efficiency. In general, the relatively fluid esters were more efficient and produced oompositions having lower brittle points than the viscous esters. A comparison of the compositions plasticized with the bis(carbonates) of butanol on one hand and n-butyl lactate on the other suggests that bis(csrbonates) of WalkanoIs are more efficient plasticizers than the corresponding derivatives of +alkyl lactates. This improved efficiency of the simpler n-alkanol ester might be due in part to lower molecular weight. The data obtained with the bis(carbonate) of isobutyl glycolate (Table 11) indicate that this ester is more efficient than the corresponding derivative of isobutyl lactate. The lactate, however, is aonsiderably more resistant to water (Table I).
1411
...
...
240 290 290 270 300 330 290d 300 320 300 270d 320 330
2310 1920 2210 1870 2020 2080 1890d 1510 1570 2560 2330d 1590 1570
...
... ... ...
... - 13
--110 -8
-7
--88 d
- 16 14
-1 - 20d -17 14
-
Compatibilityb, Cellulose Acetate0 C
C
C C C C C C CI C C I I I
2-Ethylhexyl 2,6-Dimethyl-4heptyl 3360 310 1890 -9 I Cyclohexyld 3440
