Protonation Equilibrium of 4-Substituted Benzohydroxamic Acids in Mineral Acids

The protonation equilibria of some 4-substituted benzohydroxamic acids 4-X(C(6)H(4)CONHOH) (X = H, OMe, Cl) have been investigated in aqueous sulfuric, perchloric, and hydrochloric acids at 25 degrees C UV spectrophotometrically. The Hammett acidity function method, the Bunnett-Olsen method, Cox-Yates excess acidity function method, and Marziano-Cimino-Passerini method have been compared in order to rationalize the differences observed between pK(BH)()+ values determined by each method. An attempt has been made to apply multivariate analysis to separate the effect of protonation from the medium effect for benzohydroxamic acid.