FREMGANGSMAADE TIL FREMSTILLING AF 0,0-DIALKYLTHIONOPHOSPHORSYRECHLORIDER

O,O-dialkylthionophosphoric acid chlorides are produced by chlorinating a dialkyldithiophosphoric acid in two stages. In the first stage, the acid is reacted with chlorine in a molar ratio of 1:1.15 to 1:1.50, resulting sulfur is separated, the liquid phase is admixed with a distilled product of a previous batch chlorinated in the second stage and with a further 0.25 to 0.7 mol of O,O-dialkyldithiophosphoric acid per mol of acid initially used, and desirable final product is distillatively separated from said mixture. In the second stage, the distillation residue of the first stage is reacted with a total proportion of 0.9 to 1.0 mol of chlorine per mole of acid initially used, precipitated sulfur is separated from the second stage chlorination product, the liquid phase is distilled off, and resulting distillate is recycled to the first chlorination stage.