GB603471A - Improvements in or relating to the production of vinyl ethers and their homologues - Google Patents

Abstract

Vinyl ethers are produced by subjecting an acetal to thermal dissociation in the vapour phase in the presence of a volatilizable strong mineral acid or an adhydride thereof, stable under the reaction conditions, in the gaseous state as a catalyst. Suitable catalysts are sulphuric acid, sulphur trioxide or the hydrogen halides and they may be generated in situ, e.g. from alkyl sulphuric esters such as ethyl sulphuric acid and diethyl sulphate and preferably from di-isopropyl sulphate. Other compounds, including the reaction products between the strong mineral acids and acetals, which yield the gaseous acid on decomposition may also be used. Nitrogen-containing bases such as ammonia, alkyl amines and pyridines may be added to the reactants or to the reaction products prior to cooling, to inhibit recombination of the products. The inhibitors may be used in the form of salts of the nitrogen-containing bases, e.g. in the form of ammonium or pyridine salts of the acid catalyst, which in the reaction zone decompose to yield the catalyst and inhibitor. Reduced pressure or dilution by inert gases or vapours may be used and the gaseous catalysts may be employed in conjunction with known catalysts of a solid nature, such as fire clay. In examples, diethyl acetal is converted to ethylvinyl ether and dimethyl acetal to methylvinyl ether. The acid catalysts employed are sulphuric acid, ethyl sulphuric acid, diethyl sulphate, SO3 vapour, hydrogen chloride and di-isopropyl sulphate; and pyridine and gaseous ammonia are employed as inhibitors. Several experiments are carried out to show the effects of heating the acetals, at different temperatures with or without the acid catalysts and with or without the inhibotors. The catalyst is either added to the acetal feed or introduced separately into the reaction zone and tabulated results are given which show that in the conversion of diethyl acetal the di-isopropyl sulphate is the most active catalyst. Other acetals, such as acetone acetal which is convertible to methyl-a -methyl-vinyl ether, may be used.