DIFLUOROMETHANESULFONIC ACID. PART II. A TWO-STEP ROUTE TO THE FREE ACID FROM MONOHYDRATED SODIUM DIFLUOROMETHANESULFONATE

Article abstract of DOI:10.1016/S0022-1139(00)80440-6

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 difluoromethanesulfoate is distilled from a mixture of CHF2SO3Na, H2O and pure sulfuric acid in a 86percent yield.In the second step, diluted oleum (10percent SO3), containing a slight excess of sulfur trioxide, is slowly dropped intohydroniumdifluoromethanesulfonate and anhydrous difluoromethanesulfonic acid is distilled from the resulting mixture in a 51percent 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.