Process for preparing malathion for pharmaceutical use

  • US 7,560,445 B2
  • Filed: 06/30/2006
  • Issued: 07/14/2009
  • Est. Priority Date: 07/06/2005
  • Status: Active Grant
First Claim
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1. A process for preparing malathion for a topical pharmaceutical composition comprising the steps of:

  • (a) preparing a solution of O,O-dimethyldithiophosphoric acid 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, wherein the sulfur reagent has a pH less than about 7.0;

    wherein the malathion comprises greater than about 98.5% (w/w) malathion, less than about 0.1% (w/w) MeOOSPO, less than about 0.1% (w/w) MeOSSPO, less than about 0.2% (w/w) MeOOSPS, less than about 0.3% (w/w) malathion carboxylic acid, less than 0.1% (w/w) methyl malathion, less than about 0.1% (w/w) malaoxon, and less than about 0.1% (w/w) isomalathion.

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