Effect of partially aqueous solutions of different pH's on the hydrolysis rate of some Schiff bases

The mechanism of the hydrolysis of a series of Schiff bases derived from p- phenylenediamine and various aromatic aldehydes has been examined in aqueou s media containing 40 wt% methanol, in the presence of NaOH. The base hydro lysis reaction of these compounds is strictly second-order kinetics, first- order with respect to the Schiff base and also to hydroxide ion, and the hy droxide ion attack on the free base becomes the rate-determining step under these basic conditions. The work is extended to include a systematic kinet ic study on the hydrolysis reaction of the Schiff bases under investigation , in partially aqueous solutions of different pH's, in media containing 40 wt% methanol. A rate profile diagram of pH versus hydrolysis rate constant for all of the Schiff bases shows that the rate is minimal at alkaline regi on (pH > 8.96), and too rapid at strongly acidic media (pH < 3.53).