Studies on Organophosphorus Compounds XVI On O,O-Dialkyl Dithiophosphoric Acids and N, N, N′, N′-Tetramethylthiophosphoric Diamide as Thiation Agents: Conversion of Carboxamides into Thiocarboxamides, Alkyl Dithiocarboxylates, or Nitriles†

By heating carboxamides with O,O-diethyl dithiophosphoric acid, 1, at 110-125 °C the corresponding thiocarboxamides and/or ethyl dithiocarboxylates were formed. ortho-Substituted N, N-dimethylbenzamides only gave the corresponding thiocarboxamides. By using O,O-dipropyl dithiophosphoric acid and O,O-diisopropyl dithiophosphoric acid, thiocarboxamides were also prepared, and the corresponding propyl and isopropyl dithiocarboxylates were isolated after prolonged reaction time. Reactions of sec- and tert-carboxamides with N, N, N,' N′-tetramethylthiophosphoric diamide, 2, In HMPA at elevated temperatures produced the corresponding thiocarboxamides in high yields. Primary carboxamides were converted into the corresponding nitriles after heating with 2 in HMPA. Small amounts of primary thiocarboxamides were isolated in most of these reactions. Formanilide reacted with 2 in HMPA to give N, N-dimethyl-N′-phenylformamidine in 95% yield.