Selective oxidation of methyl diphenyl methyl mercapto acetate to methyl diphenyl methyl sulfinyl acetate using a novel catalyst UDCaT-3

Abstract

The synthesis of modafinil involves oxidation of methyl diphenyl methyl mercapto acetate (MDMMA) selectively to methyl diphenyl methyl sulfinyl acetate (MDMSA). The existing industrial process involves oxidation of the sulfide derivative with hydrogen peroxide in the presence of acetic acid as the solvent. If the temperature is not controlled, this reaction, being exothermic, involves the formation of the sulfone derivative also to some extent. The reaction also generates an effluent, which is corrosive and hazardous. This paper deals with the application of a new heterogeneous catalyst prepared in our laboratory, UDCaT-3, a ternary oxide of manganese and vanadium, for the oxidation of MDMMA with hydrogen peroxide in methanol as the solvent. The reaction was found to give the product sulfoxide selectively. A theoretical model was employed for the analysis of this solid−liquid slurry reaction, and effects of various parameters on the rate of reaction were evaluated. There was no effect of the external or of the internal mass transfer resistance on the rate of reaction, and the reaction was found to be intrinsically kinetically controlled, and the kinetic parameters were established.