GB476898A - Manufacture of esters of salicylic acid - Google Patents

Abstract

Esters of salicylic acid with phenol and homologues thereof are manufactured by heating a salicylic ester of an alcohol of low boiling point with phenol or a homologue thereof in the presence of a catalyst consisting of an alkali or alkaline-earth metal salt of phenol or a homologue or substitution product thereof or a mixture of such salts. The catalyst may be prepared by dissolving an alkali or alkaline-earth metal in the mixture of the phenol and salicylic ester used as starting material, or it may be prepared separately by the action of an alkali or alkaline-earth metal on a phenolic compound, especially the phenol or salicylic ester used as starting material or the salicylic ester forming the product of the reaction, or by using a caustic alkali or an alkaline-earth oxide or hydroxide instead of the metal and removing the water formed from the catalyst before use, taking care to avoid saponification when the catalyst contains an ester group. The reaction temperature should be such that the alcohol liberated is continuously distilled off. In order to avoid reactions of condensation of the salicylic esters, the phenol is preferably used in excess and it is advisable to interrupt the reaction when 60 per cent of the parent salicylic ester has undergone conversion, the catalyst then being removed by washing or decomposed with acid and the unchanged reactants distilled off under reduced pressure and, if desired, used in a subsequent batch, the operation being repeated several times if necessary. In examples: (1) sodium is dissolved in a dry mixture of phenol and methyl or ethyl salicylate which is then heated to boiling; (2) phenol and methyl salicylate are heated with the sodium salt of methyl salicylate, prepared by reacting caustic soda with methyl salicylate in alcohol, filtering and drying the precipitate; (3) thymol, or "Iso-thymol oil," is heated with methyl salicylate and the sodium salt thereof.