Kinetics and mechanism of acid hydrolysis of some mono-, bi-functional and double Schiff bases

ABSTRACT

Kinetics of acid hydrolysis of some mono-, bi-functional or double Schiff bases derived from p-phenylenediamine and certain aromatic aldehydes have been investigated in aqueous media containing 40 wt% methanol, in the presence of acetic acid. The acid hydrolysis reaction of these imines was found to follow second-order kinetics, strictly first-order with respect to each of the Schiff base and the acetic acid. Thus, the attack of water molecules on the protonated substrate is considered as the rate-determining step under these acidic conditions. The mono-functional imines showed relatively fast acid hydrolysis compared to that observed for bi-functional or double Schiff bases. This was discussed on the basis of the geometric flexibility of the molecular structure of such compounds. The effect of nature of the organic co-solvent on the hydrolysis rate was investigated and related to the polarizability of the hydrolysis medium. Furthermore, the various thermodynamic parameters have been calculated and discussed