Patent ID: 8957238
Filing Date: 2015-02-17
Classification: A01N,A61P,C07F

Abstract:
1. A process for preparing malathion, comprising the steps of (a) preparing a solution of O,O-dimethyldithiophosphoric acid by reacting phosphorous sulfide with methanol in an organic solvent selected from the group consisting of toluene, xylene and benzene; (b) extracting the O,O-dimethyldithiophosphoric acid into water to generate an aqueous solution of O,O-dimethyldithiophosphoric acid; (c) reacting the aqueous solution of O,O-dimethyldithiophosphoric acid with diethyl maleate to form malathion; and, (d) treating the malathion from step (c) with a sulfur reagent selected from the group consisting of alkali metal bisulfites and alkaline earth metal bisulfites, wherein the sulfur reagent has a pH less than 7.0.