Spectrophotometric determination of alkyl salicylate from the mixture of phenyl and alkyl salicylates by the use of the selective reactivity of phenyl salicylate toward secondary amines

Abstract

Salicylate esters have been used as topical analgesics where an alcoholic component acts as the solvent. Phenyl salicylate, for example, is used in salol aqueous cream which contains a cream base with 5% propylene glycol. Recently, Irwin et al. [1-3] have shown the occurrence of transesterification of salicylate esters in alkaline alcoholic medium which could lead to serious problems in such pharmaceutical formulations. The kinetic studies on these transesterification reactions carried out by Irwin et al. [1-3] involve the high-performance liquid chromatographic (HPLC) technique. Recently, the author observed that piperidine is highly reactive toward phenyl salicylate and completely nonreactive toward methyl and ethyl salicylates [4, 5]. This selective reactivity of piperidine toward phenyl salicylate could be used to quantitatively estimate the alkyi salicylate (formed when phenyi salicylate is mixed with alkanol) by using an alternative spectrophotometric technique. The details of the method, and its use in the estimation of the 2-hydroxyethyl salicylate formed in the reaction of phenyl salicylate with 1,2ethanediol, are described in this paper.