April, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
nated rubber, the solvent strength as measurd by the dilution ratio is of considerable importance. 2. The compatibility of blown castor oil with chlorinated rubber, some other blown oils, and some alkyds, is dependent upon the strength of the solvent used. Strong solvents as measured by their dilution ratio enhance compatibility. 3. No particular plasticizer is best for use with chlorinated rubber. Different plasticizers impart totally different results at different loading percentages. The choice of plasticizers will be dictated by the ultimate properties desired. More frequently than not, the use of two or more plasticizers will be necessary to obtain the optimum properties for any given application. 4. Consideration of the fundamental principles and trends presented in this paper will be helpful in the formulation of chlorinated rubber finishes for a wider variety of uses, and products of an improved nature will be the result.
473
Acknowledgment The authors are indebted to Binney & Smith Company and The Raolin Corporation for permission to present this paper and to publish the results.
Literature Cited (1) Baxter, J. P., Chemistry & I n d u s t r y , 1936, 407-15; Baxter. J. P . , and Moore, J. G., J. Soo. Chem. I n d . , 57, 327-39 (1938). (2) Bradley and Gibbons, U. S. Patent 1,627,725 (May 10, 1927); Moffett, Ibid., 2,089,398 (Aug. 10, 1937). (3) Bradley and McGavack, Ibid., 1,519,659 (Jan. 16, 1924) ; Winklemann, Ibid., 2,047,987 (July 21, 1936). (4) Englehart and Haveman, Ibid., 26,175 (Nov. 22, 1859). (5) News E d . (Am. Chem. Soc.), 19, 399-400 (1941); North, U. S. Patent 2,148,830 (Feb. 28, 1939) : Raynolds, Ibid., 2,247,407 (July 1, 1941). (6) Peaohy, 5. J., U. 5. Patent 1,234,381 (July 24, 1917). (7) Raynolds, Ibid., 2,148,833 (Feb. 28, 1939).
Pyrolysis of Lactic A c i d Derivatives Conversion
OF
Methyl a-Acetoxypropionate to Methyl Acrylate
LEE T. SMITH, C. H. FISHER,
W. P. RATCHFORD, AND M. L. FEIN HE pyrolysis of certain lactic acid derivatives, such as T methyl acetoxypropionate, is of practical importance since the principal products are acrylic acid derivatives, which are used as intermediates in making acrylate resins. Inasmuch as lactic acid is manufactured by fermenting various sugars, the pyrolysis of suitable lactic acid derivatives affords a method for converting carbohydrates into an important class of resins according to the following scheme: Sugars + lactic acid
methyl acetoxypropionate + methyl acrylate + acrylate resins
4
The step in this series of operations that has received least attention is the conversion of lactic acid derivatives into esters and other derivatives of acrylic acid. Since improvements in this step should make possible the economical production (through intermediates such as methyl acrylate and acrylo-
Some of the economic and technological aspects of converting carbohydrates, particularly lactose in whey, into acrylate resins through lactic acid and acrylic esters as intermediates are discussed briefly. The pyrolysis of an inexpensive and readily available lactic acid derivative, methyl a-acetoxypropionate, was studied, and the effect of temperature, contact time, and various contact materials was determined. Conditions were found under which the pyrolysis products, methyl acrylate and
U. S.
Eastern Regional Research Laboratory, Department of Agriculture, Philadelphia, Penna.
nitrile) of acrylate resins, surface coatings, and rubberlike materials from abundant and domestic raw materials of agricultural origin, an extensive investigation of the conversion of lactic acid into acrylic acid derivatives is being conducted in this laboratory. Some of the results obtained in a study of the pyrolysis of methyl a-acetoxypropionate and a brief review of certain pertinent technological factors are given in the present paper.
Manufacture of Lactic Acid Lactic acid, a versatile low-cost chemical and a potential precursor of acrylate resins, alkyd resins, plasticizers, and solvents (22, 93), is manufactured by fermentation (19) of several inexpensive sugars, the cost of the raw material usually determining which sugar is to be used. Lactose in whey (22, 9 4 , starch from corn, potatoes, and other sources, cane or
acetic acid, can be produced with low contact times-i. e., with high throughput. A t temperatures above approximately 550" C. it is possible to convert virtually all of the methyl acetoxypropionate into methyl acrylate and acetic acid in one pass, and thus obviate the necessity of separating the unchanged starting material and recycling. A study of the effect of packing disclosed several satisfactory contact materials and demonstrated the desirability of high surface and free space.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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beet molasses, invert sugar, hydrolyzed sawdust, xylose from corncobs or oat hulls, and vegetable ivory are examples of starting materials (7) for making lactic acid. Some of these carbohydrates, such as lactose in whey (27), are available as waste products, and many of them are obtainable in almost unlimited quantities. One of the most interesting raw materials for making lactic acid is milk sugar or lactose, which, as the principal organic constituent of cow's milk, is present to the extent of approximately 5 per cent. Of the approximately 5.5 billion pounds of lactose in all the cow's milk produced annually in the United States, more than 2.7 billion pounds are potentially available for industrial purposes (d7). When lactose in whey is used as the starting material, the lactic acid fermentation is accomplished with B. bulgun'cus at 110' F. in about 20 hours. Lime is added intermittently to maintain the acid concentration below 1.3per cent so that maximum efficiency of the organism is obtained. The yield is above 95 per cent of the theoretical. According to reliable reports from the industry, about 5 million pounds of lactic acid (100 per cent basis), with a market value of nearly a million dollars, is produced annually from all sources in the United States. An additional 250 thousand pounds of plastic grade, essentially free from chlorides, sulfates, and heavy metals, and most of the U. S. P. and c. P. grades are manufactured or imported. The principal raw materials used in the manufacture of lactic acid are whey, blackstrap molasses, and starch.
Acrylate Resins Esters and other derivatives of acrylic acid play important roles in the synthetic resin and rubber industries, which have grown rapidly in recent years and may be expected to expand even more in the near future. The resins made from acrylic acid derivatives have many desirable properties and undoubtedly will be used in much larger quantities when production costs are lowered. The polymers of acrylic acid derivatives are characterized by colorless transparency, adhesive qualities, elasticity, and stability to light, moderate heat, and weathering. Resins made from acrylic acid derivatives, especially methyl acrylate, are particularly suitable as protective coatings, finishes for leathers, impregnating agents for textiles, and adhesives (14,17). The characteristics of the various acrylate resins depend t o a large extent upon the chemical constitution of the monomeric forms, although the conditions under which the polymerization is effected also have a considerable influence (16). Polymethyl acrylate is a colorless, transparent substance. At ordinary temperatures a film of it is tough, pliable, and so elastic as to be capable of being stretched 1000 per cent before
Vol. 34, No. 4
a break occurs. Polyethyl acrylate is softer and even more elastic than the methyl ester, but not quite so tough. The polymer of n-butyl acrylate is so soft that a t ordinary temperatures it remains rather tacky to the touch. In general, the softness of the polymers increases as the length of the alcohol chain increases (16). The same relationship as to the length of alcohol chain and comparative softness holds for the methacrylate polymers. However, as a class, the polymethacrylates are considerably harder than the polyacrylates. Polymethyl methacrylate, for example, is a hard, tough mass that may be sawed, carved, or worked on a lathe (16).
Pyrolysis of Esters I n attempting to convert lactic acid into acrylic acid derivatives, attention was directed in the present study to pyrolysis methods in view of the success enjoyed by Burns, Jones, and Ritchie (6, 6,dO, 21), and by Smith and Claborn (22) in making methyl acrylate from methyl acetoxypropionate by thermal decomposition as shown below: OCOCHI CHa&HCOOCHs
475" c.
CH*=CHCOOCH3
+ CH3COOH
(1)
I n preparing methyl acrylate, we preferred the pyrolysis of the acetyl derivative in reaction 1 to the direct dehydration of methyl lactate because of the well-known difficulty of removing water from alcohols containing a carbalkoxy group (X in the formula below) on the carbon bearing the hydroxyl group (11): where R
=
RCHaCRXOH H or alkyl group
From the foregoing and the data in Table I it is apparent that the presence of other functional groups (X in formula 2) in alcohols frequently alters the course of the thermal decomposition, with the result that simple dehydration does not occur. I n many instances, however, it is possible to achieve the equivalent of dehydration by converting the alcohol into a suitable ester, usually the acetate ( I S ) , followed by pyrolysis of the ester. As illustrated by the case of methyl ac-acetoxypropionate (reaction l ) , by Table I compiled from the literature, and by the following equations, the pyrolysis ( 1 1 ) of esters frequently, but not always, leads to the formation of an olefin linkage by production of the appropriate acid: CHsCH
OCOCHa
