The enormous acidifying effect of the supersubstituent =NSO2CF3 on the acidity of derivatives of benzenesulfonamide and toluene-p-sulfonamide in the gas phase and in dimethyl sulfoxide

The effect of stepwise replacement of =O oxygen atoms by =NSO2CF3 fragments in the sulfonyl group of toluene-p-sulfonamide and benzenesulfonamide on their acidity has been studied in the gas phase and dimethyl sulfoxide (DMSO). Incorporation of the first =NSO2CF3 group into 4-MeC6H4SO2NH2 increases its gas-phase acidity by 23.6 kcal mol(-1). Substituting the second =O by the =NSO2CF3 group leads to an additional acidity increase of 10.7 kcal mol(-1); the total acidity increase is thus 34.3 kcal mol(-1) (25 powers of ten!). In DMSO solution the total acidity increase is 13 pK(a) units (17.7 kcal mol(-1)). These findings are also supported by computational studies using DFT B3LYP at the 6-31+G* level and the semiempirical PM3 method. The results of this work have potentially important implications for the design of new strongly acidic catalytic materials.