Difluoromethanesulfonic acid Part II. A two-step route to the free acid from monohydrated sodium difluoromethanesulfonate

Anhydrous difluoromethanesulfonic acid (“diflic acid”) can be obtained, in a two-step procedure, from monohydrated sodium difluoromethanesulfonate, a very stable salt not easily dehydrated. In the first step, stable hydronium difluoromethanesulfonate is distilled from a mixture of CHF 2 SO 3 Na,H 2 O and pure sulfuric acid in a 86 % yield. In the second step, diluted oleum (10 % S0 3 ), containing a slight excess of sulfur trioxide, is slowly dropped into hydronium difluoromethanesulfonate and anhydrous difluoromethanesulfonic acid is distilled from the resulting mixture in a 51 % yield. The use of more concentrated oleum and excess of sulfur trioxide causes a rather violent decomposition to gaseous products for which a chain mechanism is proposed. The same process is invoked to explain the more violent degradation of hydronium difluoromethanesulfonate observed with thionyl chloride. This chain reaction seems to be governed by the great ability of the α-acidic hydrogen to form hydrogen bonds