The acidolysis of p-nitrophenyl sulfate. A kinetic spectrophotometric method for evaluation of pKa

Abstract

A kinetic spectrophotometric method for evaluation of pKa has been developed. In the present study this has been utilized towards the pKa determination, in methanol, of the conjugate acids of 4-picoline, aniline, hydroxylamine, methoxyamine, and hydrazinium ion. For the first two cases the pKa values determined by the present method could be compared with the potentiometrically measured values, in a methanol solvent, with satisfactory agreement. Our proposed method involves essentially the spectrophotometric determination of the rate of the acid catalyzed conversion of p-nitrophenyl sulfate to p-nitrophenol in methanol in the presence of the acidic species whose pKa in this medium is required.