Spectrophotometric determination of protonation constant of N-phenylbenzohydroxamic acid in mineral acids

The UV spectra of N-phenylbenzohydroxamic acid (C6H5CON(OH)C6H5) in sulphuric, perchloric and hydrochloric acid solutions have been analyzed by the characteristic vector method in order to separate protonation from the medium effect. Using the first vector coefficient values, protonation constant (pK(BH+)) and solvation parameters have been estimated. In the high acidity range, results obtained according to the Cox-Yates excess acidity function, Marziano Mc function, Bunnett-Olsen and Hammett-acidity function methods are in good agreement.