GB654032A - Improvements in or relating to the purification of vinyl ethers - Google Patents

Abstract

Vinyl ethers which have been obtained by vinylating an alcohol of the C4-C8 range with acetylene are purified by a process which comprises the step of reducing the residual alcohol content of the substantially azeotropic mixture of vinyl ether and the corresponding alcohol obtained on distillation of the crude vinylation product by boiling the said mixture with an alkali metal hydroxide so as to convert the alcohol to its metal alkoxide while continuously removing the water simultaneously formed from the reaction zone by entrainment with the vinyl ether itself, condensing the mixed vinyl ether/water vapours so as to separate the condensate into two layers, continuously returning the upper layer to the reaction zone and subsequently separating the vinyl ether from the alkoxide formed. The alcohol content of the initial azeotrope together with any vinyl ether remaining in the reaction vessel may be recovered by adding water to the alkoxide and distilling the mixture when the distillate consists of a lower aqueous layer and an upper layer comprising a mixture of alcohol and the residual vinyl ether. Distillation of this upper layer yields pure alcohol and the vinyl ether as its azeotrope with the alcohol. An alternative method of recovering the alcohol content is to add water to the alkoxide, removing the solution, separating into two layers and isolating the upper layer comprising a mixture of vinyl ether and alcohol. The amount of the alkali metal hydroxide used in the process may be from 25 to 200 per cent and preferably 33 to 50 per cent of that which is chemically equivalent to the amount of alcohol present in the azeotrope. In examples: (1), (2) and (3) an azeotropic mixture of isoamyl vinyl ether and isoamyl alcohol which has been prepared by reacting acetylene with isoamyl alcohol in the presence of caustic potash at 150-165 DEG C. and then distilling to separate the azeotrope from excess alcohol is treated with sodium hydroxide and then boiled under reflux in a still with a fractionating column. The distillate is run into a separator and the top liquid layer returned to the still, the distillation being continued until the water has separated out. The vinyl ether is collected by further distillation. Water is added to the residue in the still base and further distillation yields two layers, a portion of the aqueous layer being returned to the still until no more organic material distils over; (4) an azeotropic mixture of 2-ethylbutyl vinyl ether prepared by reacting the alcohol with acetylene as in (1) is treated with caustic soda as in (1); (5) a mixture of n-hexyl vinyl ether and n-hexyl alcohol prepared as in (1) from the alcohol and acetylene are treated with potassium hydroxide as in (1) to recover the vinyl ether.