GAS-PHASE REACTIONS OF WEAK BRONSTED BASES I-, PO3-, HSO4-, FSO3-, AND CF3SO3- WITH STRONG BRONSTED ACIDS H2SO4, FSO3H, AND CF3SO3H - A QUANTITATIVE INTRINSIC SUPERACIDITY SCALE FOR THE SULFONIC-ACIDS XSO3H (X = HO, F, AND CF3)

Using a selected ion flow tube at 368 K, we have measured rate constants for ion-molecule reactions between I-, PO3-, HSO4-, FSO3-, CF3SO3-, NO3-.HNO3, FSO3-.FSO3H, and H2SO4, FSO3H, CF3SO3H. Channels observed include proton transfer and clustering. These results allow free energies (enthalpies) of deprotonation (kJ/mol) to be estimated (within +/- 10 kJ/mol) as follows: HPO3, 1270 (1300); H2SO4,1265 (1295); FS03H, 1255 (1285); CF3SO3H, 1250 (1280). In two cases, electron affinities are estimated as follows: HSO4, 4.7 +/- 0.2 eV; FSO3, 4.8 +/- 0.2 eV. For the title acids, the gas-phase acidity order is discussed and is used to explain the differing acidity orders found for these acids in different solvents. The same data measure basicities for the conjugate bases, and these are related to nucleophilicity and leaving group ability. This study explores a region of the acidity scale where no acidities are established that would calibrate the scale. The scale is calibrated here using cluster ions whose free energy of protonation can be reliably estimated.