Use of p-Nitroaniline to Determine Protonation Equilibrium Constants of Oxygen-containing Molecules in Aqueous Solution

Abstract

Thccriticismscontaincd in a recent paper 1 of the interpretation in termsof protonation equilibria 2,3 involving (H20)4 Haq+ of the changes in optical density of acidic solutions of p-nitroanilinc on addition of organic oxygen containing substrates arc discussed. It is concluded that the effects of activity coefficients arc too small to influence the interpretation, and it is indicated how attacking molecules distinguish between protonated and unprotonated molecules of substrate in oxidation reactions and complexing equilibria. Good agreement is obtained for protonation equilibrium constants between values from this spectrophotometric method and values obtained using a range of other independent techniques.