GB577364A - Process for the dehydration of 3-methyl-butenol - Google Patents

Abstract

Isoprene is produced by heating 3-methyl-1-butene-3-ol with a salt of a weak nitrogeneous aromatic base with a strong acid, for example aniline hydrobromide, aniline benzene-sulphonate, o-toluidine o-toluene sulphonate, and a -naphthylamine p-toluene sulphonate. These salts selectively dehydrate the 3-methyl-butenol in the presence of the corresponding saturated alcohol. The quantity required is 2-10 per cent by weight of the alcohol. Solvents or diluents of higher boiling point than the alcohols may be used, for example aromatic hydrocarbons such as toluene, xylene and ethylbenzene, solvent naphtha, ethers such as dibutyl ether, esters such as butyl acetate, acetals, and ketones such as methyl-isobutyl-ketone. The salts are soluble in the unsaturated alcohol and may be precipitated when this has been converted. Instead of the pure salts, mixtures of the base and acid with either in slight excess may be used. Fresh alcohol or mixtures containing it may be added to the boiling reaction mixture at the same rate as that present is dehydrated and isoprene distils off. In examples: (1) a mixture of the methyl-butenol and methyl-butanol is heated with aniline hydrobromide in a still with reflux, pure isoprene distilling over; (2) the methyl-butenol is heated with aniline hydrobromide and ethyl-benzene; (3) and (4) aniline benzene sulphonate is used with xylene or dibutyl ether; (5) and (6) mixtures of the unsaturated and saturated alcohols are treated with the same salt with or without butyl acetate.