PROCESSO PARA PREPARACAO DO ESTER DO ACIDO O,O-DIETIL-O-(1-FENIL-2-CIANO-PROP-1-ENIL)-TIONO-FOSFORICO

In the preparation of O,O-diethyl-O-(1-phenyl-2-cyano-prop-1-enyl)-thionophosphoric acid ester by reacting a benzoic acid ester with propionitrile in the presence of an alkali metal alcoholate and then reacting the reaction mixture with O,O-diethyl-thionophosphoric acid diester chloride, the improvement which comprises employing about 5 to 50 moles of the propionitrile per mole of benzoic acid ester, distilling off the alcohol obtained during the reaction of propionitrile, benzoic acid ester and alcoholate before the addition of the O,O-diethyl-thionophosphoric acid diester chloride, and maintaining the volume of the reaction mixture approximately constant by adding propionitrile during the distillation. Advantageously the alcoholate is sodium methylate, ethylate or tert.-butylate or potassium methylate, ethylate or tert.-butylate, the reaction is effected at about 80 DEG to 120 DEG C., about 5 to 25 moles of propionitrile are employed per mole of benzoic acid ester, about 1 to 1.3 moles of benzoic acid ester and about 1 to 1.15 moles of alkali metal alcoholate are employed per mole of O,O-diethyl-thionophosphoric acid diester chloride, and the benzoic acid ester is the methyl ester or ethyl ester.