Gas-phase acidities of thiocarboxylic acids

The gas-phase acidity of thioacetic acid, determined using ion–molecule equilibrium reactions, was found to be ΔGacid = 329.0 ± 1.5 kcal mol−1. The gas-phase acidity of thiobenzoic acid was determined by ion–molecule bracketting reactions to be ΔGacid = 323 ± 5 kcal mol−1. Gas-phase acidities of these compounds, as well as of thioformic acid, were calculated; our calculations and experiments are in good agreement. The calculated value of the enthalpy of deprotonation of thioformic acid is consistent with previously published computational results.