Perfluoro and polyfluorosulfonic acids: XVI. Difluoromethanesulfonic acids as a precursor of CF2: In the synthesis of difluoromethyl poly- and perfluoroalkanesulfonates

Difluoromethanesulfonic acid (1) readily reacts with P₂O₅ at room temperature to give difluoromethyl difluoromethanesulfonate (2) and SO₂ in stead of the expected acid anhydride. If perfluorosulfonic acid (3) perfluorocarboxylic acid (5) or KI was added to this reaction mixture, difluoromethyl perfluorosulfonate (4), difluoromethyl perfluorocarboxylate (6) and HCF₂I (7) was formed respectively in addition to 2. A similar result was obtained using POCl₃ or SOCl₂ instead of P₂O₅ as dehydrating agent. The mechanisms of the formation of difluorocarbene were discussed.