GB776056A - Process for the production of unsaturated ethers - Google Patents

Abstract

Unsaturated ethers are obtained by subjecting a saturated acetal containing less than 15 carbon atoms in the molecule and the aldehyde component of which contains from 3 to 9 carbon atoms to thermal decomposition in the presence of an aromatic sulphonic acid in an amount of from 0.01 to 0.3 per cent and preferably from 0.03 to 0.15 per cent by weight of the acetal. The thermal decomposition is preferably effected at a temperature between 80 DEG and 150 DEG C. and the aldehyde component of the acetal should preferably contain no more than six carbon atoms. Specified aromatic sulphonic acids are benzene sulphonic acid, toluene sulphonic acid, a naphthalene sulphonic acid, and a naphthol sulphonic acid, e.g. 1-naphthol-4-sulphonic acid. The acetal subjected to the thermal decomposition may be obtained by subjecting a saturated C3-C9 aldehyde and a saturated alcohol to condensation in the presence of less than 0.1 per cent of an acid, particularly an aromatic sulphonic acid, the condensation being preferably carried out in the presence of an azeotropic entraining agent, e.g. benzene, carbon tetrachloride or a C5-C7 aliphatic hydrocarbon, for the removal of the water formed in the reaction. The resulting acetal is then subjected to thermal decomposition in the presence of 0.01 per cent to 0.3 per cent by weight of the acid based on the acetal to form the unsaturated ether. The quantity of the sulphonic acid is brought to the optimum concentration required for the decomposition of the acetal either by the addition of further acid or by neutralization of part of it if it is present in excess of the amount required. If desired, the acetal formed may be purified, before subjecting it to the thermal decomposition. When the acetal contains from 6 to 14 carbon atoms in the molecule it is preferably purified by steam distillation. When the alcohol or aldehyde component of the acetal has more than six carbon atoms the thermal decomposition may be effected at sub-atmospheric pressure. In an example a mixture of technical grade propionaldehyde, n-butanol and hexane containing a small amount (0.027 per cent) of p-toluene-sulphonic acid is boiled in a distillation column with removal of water together with the hexane, and the acetal-containing mixture is then thermally decomposed at 120-130 DEG C. without further addition of p-toluene sulphonic acid to form propenyl butyl ether. In other runs additional amounts of p-toluene sulphonic acid are added to the acetal formed before the thermal decomposition step. A comparative example is also given in which the amount of p-toluene sulphonic acid present in the acetal decomposition is 0.34 per cent of the acetal, the yield of unsaturated ether being lower in this case. Both the acetal formation and the acetal decomposition processes may be carried out batchwise or continuously.