Studies on oxidation of benzylidene derivatives

Abstract

Perfumery compoiinds isoeugenol and isosaftole can be oxidized to their aldehydes, vanillin and heliotropin respectively. The aldehydes obtained axe very useful and commercially valuable products. Apart from their importance as perfumery compounds, they form hnportant intermediates in the pharmaceuticals arid pesticide industries. Liquid phase oxidation of isosafrole using different oxidizing agents were tried. Sodium dichromate as oxidizing agent in aqueous acetic id was found to be most suitable because of its higher 3delds and mild reaction conditions. This reaction was taken up for detailed study. Since the kinetic study of dichromate oxidation in aqueous acetic acid medium of isosafrole has not been mentioned in the literature, various parameters like isosafrole, dichromate and acetic acid concentrations were studied. The experiments were conducted at different temperatures to estimate the activation energy of the reaction. The effect of added salts like manganese sulfate, manganese acetate and cobaltous acetate has also been studied. For all the experiments the change in isosafrole concentration was observed. The rate of reaction increases with increase in isosafrole concentration. The order of the reaction with respect to isosafrole concentration is foimd to be one. The rate of reaction increases with increase in initial sodium dichromate concentration. The reaction is foimd to be half order in dichromate ion concentration. The rate of reaction increases with increase in acetic acid concentration with an order two. The atmospheric oxygen does not affect the reaction rate suggests that the reaction may not be free radical reaction. The rate of reaction increases with increase in temperature. The activation energy was found to be equal to 14.59 kcal/mol. The reaction is expressed in terms of power-law kinetics and the corresponding rate expression is given as The scale up batches using the above results were carried out and the yield of heUotropin was found to be equal to 85 to 90% based on the starting material, isosafrole. The studies on the effect of added salts on the rate of reaction showed enhancement m the rate of reaction with Mn(Il) salts; and retardation with Co(II) salts.