Vapor-Phase Synthesis of Vinyl Acetate S. N. USHAKOV AND J. M.
V
ARIOUS m e t h o d s a r e known for synthesizing vinyl acetate, the main material (either alone or mixed with vinyl chlorides) used for o b t a i n i n g i t s polymersM o w i l i t h ( G e l v a ) , Vinylite, and Vinnapase-which play a n important part in the plastics industry. The chief technical method f o r synthesizing t h i s t y p e of vinyl ester consists in the action of acetylene on certain acids. With acetic acid the reaction is as follows : CHsCOOH
+ CHICH + CHICOOCH:CH2
FEINSTEIN, Institute of Plastic
+ CH j CH +(CH3COO)zCHCHs
This leads to the formation of ethylidene esters. For the most part the latter are liquids, and are good solvents for natural and artificial resins and for ethers of cellulose. Ethylidene esters can also be obtained from vinyl esters according to the following reaction: CH&OO\ CHCHI CH&OOCH :CHz CHICOOH + CHICOO/
+
Methods of obtaining a vinyl ester by the action of acetylene on acids can be carried out either in the liquid phase or in the vapor phase.
PREVIOUS WORKIN THE LIQUIDPHASE According to German patents (2), organic acids or alcohols are treated with acetylene in a moderately heated tube in the presence of salts of mercury, chiefly mercurous sulfates or phosphates. I n this way there may be obtained the ethylidene and vinyl esters of organic acids, such as acetic, mono-, di-, or trichloroacetic, benzoic, or lactic. Similarly the ethylidene ethers or acetals of various alcohols (isoamyl, isobutyl), glycols, or glycerol or its derivatives may be obtained. The vinyl esters can be obtained in good yield only when using chloroacetic acids. I n all other cases vinyl esters are produced in small quantities. I n order to increase the yield of vinyl esters, this method has been investigated by varying the temperature of the reaction, the type of catalyst, and its method of preparation, etc. The most important point is the possibility of preventing the vinyl ester, produced in the initial stage of the reaction, from being transformed later into ethylidene compounds by its further reaction with the excess acid. This can be brought about by various means: by diluting the reacting liquid with inert materials, b y having the excess acid enter into combination, by rapid polymerization of the vinyl esters produced or by their rapid removal from the reaction zone (treatment under diminished pressure, or by the introduction of excess gas or acetylene).
U. S. S. R.
A French patent (3) describes a procedure which secures high yields of vinyl esters from organic acids. The r e a c t i o n is conducted a t 70" C., excess acetylene is used, and decreased pressure is mentioned. M e r c u r i c acetate (4.3 p a r t s m e r c u r i c acetate to 100 parts acetic acid) or a mixture of mercuric acetate, mercuric oxide, and sulfuric acid is used as catalyst. The method is more fully described in another French patent (1). Vinyl acetate is produced a t 20" to 60" C. (according to the p a t e n t , a c o n s i d e r a b l e quantity of ethylidene diacetate is produced a t 70" to 100" C.). Acetylene is used in considerable excess in order to carry away the vinyl acetate as soon as it is formed. The vinyl acetate and the acetic acid carried away by the acetylene are then condensed by a double cooling. The condensed liquid is distilled through a column, and the remaining acetic acid, free of vinyl acetate, is returned to the reaction. The catalyst is prepared by introducing mercuric oxide into the acetic acid and precipitating by sulfuric anhydride or oleum. About 150 kg. of vinyl acetate are obtained per 1 kg. of mercuric oxide used. An American patent (8) describes a similar method. The reaction is also carried out in excess acetylene and in the presence of a catalyst obtained by precipitating mercuric acetate by sulfuric anhydride (10 parts of mercuric oxide are introduced to 100 parts of acetic acid; 4 parts of oleum are added at 70" to 80" C.). The reaction is carried out at a higher temperature than that described in the preceding patent-namely, 80" to 90" C. The ethylidene diacetate remaining in the reaction vessel is purified from sulfuric acid and other admixtures; the compound is then heated to 100-170" C.; the ethylidene diacetate is transformed into acetaldehyde, acetic anhydride, and vinyl acetate. According to American patents (b) the treatment of dehydrated acetic acid, heated to 80" C., is carried out by excess acetylene. The catalyst, mercuric orthophosphate, is obtained by precipitating mercuric oxide dissolved a t 80" to 90" C. in glacial acetic acid by orthophosphoric acid (98 to 100 per cent pure). There are also descriptions of processes in which the reaction of acetylene with an organic acid is carried out in the liquid phase under the application of increased pressure. According to a German patent ( 7 ) the reaction is carried out in an autoclave at 40" to 60" C. A pressure of 5 atmospheres is maintained by a n inert gas. Compounds of magnesium, iron, zinc, aluminum, boron, and iodine, as well as organic peroxides and anhydrides of acids, are used as catalysts. Thus 1 part of acetic anhydride to 60 parts of acetic acid is used, and 26 to 28 parts of dry acetylene are forced in. After a treatment which lasts several hours, varying amounts (up to 75 parts) of vinyl acetate are obtained. It is important to note that all the methods based on t h e action of acetylene on acetic acid in the liquid state are
A study of the methods for obtaining vinyl acetate by the interaction of acetylene and acetic acid has conJirmed the theory that the reaction may be eficiently carried out in the vapor phase. I n the vapor phase it is possible to obtain in the reaction zone a n y desired excess of acetylene, which excess favors a reaction in the monomolecular ratio of components. I n order to find the best conditions f o r the reaction between acetylene and acetic acid in the vapor phase in the presence of zinc or cadmium acetates as catalysts, the effect of the following variables were tested: temperature, proportion of reagents, amount of catalyst, speed of passage of the mixture through the converter, and principal dimensions of the contact apparatus.
W h e n t h e r e is insufficient acetylene present, two molecules of acid and one of acetylene may react thus: 2CHaCOOH
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