Patent ID: 8138366

Claim:
A process for the preparation of Malathion of formula (I), which comprises the steps of: i) adding methanol to phosphorous sulfide in organic solvent at 25-50° C. for a period of 1.5-2 hours; ii) stirring the above suspension for a period of 5-6 hours at 50-55° C.; iii) expelling the H 2 S gas with nitrogen, after cooling the above suspension to 25-28° C.; iv) filtering the above suspension to remove insoluble impurities to obtain crude O,O-DMDTPA; v) the crude O,O-DMDTPA is subjected to dissolution in suitable solvent and ammonia gas is purged to precipitate pure O,O-DMDTPA.NH 3 salt; vi) the above obtain O,O-DMDTPA.NH 3 salt is subjected to neutralization with concentrated sulphuric acid to get O,O-DMDTPA; vii) the O,O-DMDTPA obtained in the above step is once again purified through ammonia salt formation and neutralization method as mentioned in above steps v) and vi) to get chromatographically pure O,O-DMDTPA of the formula II viii) adding the above obtain pure O,O-DMDTPA to diethyl maleate at low temperature of −30 to −25° C. in four lots, each at regular interval of 20 minutes; ix) maintaining the above reaction mass at temperature of −30 to −25° C. for a period of 4 hours; x) water washing the above mass to remove O,O-DMDTPA; xi) treating the above obtain crude Malathion with a sulfur reagent at 5 to 10° C. for a period of 13 hours; xii) crystallizing the above obtained Malathion from methanol at low temperature and xiii) drying the above obtain mass with anhydrous sodium sulphate in isopropanol to obtain Malathion of formula (I).