METHOD OF MAKING 5,6-DIHYDRO-2-METHYL-N-PHENYL-1,4- OXATHIIN-3-CARBOXAMIDE

This method of making 5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxamide is based on the use of an oxathiolane, namely, 2-methyl-N-phenyl-1,3-oxathiolane-2-acetamide, which may be formed by condensing 2-mercap-toethanol with acetoacetanilide under acidic conditions in a solvent medium (aromatic hydrocarbon, chlorinated hydrocarbon or alkyl ester of an aliphatic acid). The said oxathiolane, with or without purification, is reacted with hydrogen peroxide in water or in a water-organic solvent mixture under basic conditions in the presence of a catalytic amount of a metal compound such as sodium tungstate to form 2-methyl-N-phenyl-1,3-oxathiolane-2-acetamide 3-oxide. The said oxathiolane oxide, while dissolved in a chlorinated hydrocarbon or an alkyl ester of an aliphatic carboxylic acid, or while suspended in an aromatic hydrocarbon, is subjected to a ring expansion reaction by heating under acidic conditions in the presence of a catalytic quantity of a quaternary ammonium salt to form 5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxa-mide with evolution of water. The product is a known bactericide and fungicide.