GB869959A - Production of dicyclohexyl phthalate - Google Patents

Abstract

Dicyclohexyl phthalate is produced by heating a mixture of phthalic acid and/or phthalic anhydride and a stoichiometric excess of cyclohexanol in the presence of an acid dehydrating-catalyst, at a pressure not exceeding atmospheric pressure, the temperature of the reaction-mixture being at least sufficient to vaporize the cyclohexanol/water azeotrope, passing the vapours, which contain cyclohexene (formed by decomposition of cyclohexanol), to a cooling-zone where in the cyclohexanol is condensed but cyclohexene (and its water-azeotrope) remains in the vapour phase, and removing cyclohexene from the system. The following catalysts may be used:- sulphuric acid, p-toluene p sulphonic acid, the alkane sulphonic acids, and the sulphamic acids. In an example, a mixture of phthalic anhydride, cyclohexanol and sulphuric acid is heated at a temperature of 117 DEG -125 DEG C. and an absolute pressure of 170-220 mm.; and the vapours are passed to a fractionating column, the head of which is maintained at a temperature between 55 DEG and 75 DEG C. The uncondensed vapours, consisting chiefly of cyclohexene and water, are withdrawn overhead, while the condensate, consisting chiefly of cyclohexanol, is returned to the reaction-mixture. The cooled product is washed with aqueous sodium hydroxide followed by water, and then subjected to steam-distillation to remove volatile material. The dicyclohexyl phthalate so obtained is dried; and a crystalline almost-colourless product is obtained.