An ecofriendly catalytic route for the preparation of perfumery grade methyl anthranilate from anthranilic acid and methanol

Abstract

Methyl anthranilate is a very important perfumery ester and also a precursor to a number of Schiff bases which are used in several fragrance formulations. The current practice is to use homogeneous acids as catalysts in the manufacture of methyl anthranilate either starting with isatoic anhydride and methanol or by the esterification of anthranilic acid with methanol. These routes pose problems of disposal of liquid acids after the reaction, and substantial quantities of acids are required in order that the amine group be initially blocked as an amine hydrochloride. This paper deals with the application of ecofriendly heterogeneous catalysts including ZSM-5; acid-treated clays such as Filtrol-24 and K10; ion-exchange resins such as Nafion-H, Indion-130, Amberlyst-15, Amberlyst-18, Dowex M-32 and Bayer K-24; and dodecatungstophosphoric acid, a heteropolyacid. Among these catalysts, Amberlyst-15 and Indion-130 resins were found to be the most effective. Other heterogeneous catalysts such as ZSM-5, Filtrol-24, and dodecatungstophosphoric acid were found to be totally ineffective. A theoretical model was employed for the analysis of this solid-catalysed slurry reaction, and effects of various parameters on the rate of reaction were evaluated. There was no effect of external as well as internal mass-transfer resistance on the rate of reaction. The reaction was found to be intrinsically kinetically controlled, and the kinetic parameters were established. The product was isolated and confirmed by spectroscopic methods. The odour value matched with that of the commercially available perfumery grade sample.