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

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

Effect of H-bond formation on the electronic spectra of some azo compounds derived from 3-amino-1, 2, 4-Triazole

Despite the absorption spectra of azo compounds having been studied by several workers [1-12], little information has been reported about the spectral behaviour of the azo compounds derived from heterocyclic amines containing more than one heteronitrogen atom. The present investigation concerns a study on the electronic spectra of some azo compounds derived from 3-amino-1,2,4-triazole and various active methylene or active hydrogen compounds, in solvents of different polarities and basicities as well as in ones having hydrogen-bonding ability. This study was made with the intention of assigning each of the different observed absorption bands to their possible electronic transition and to investigate the effect of substituents on the tautomeric equilibrium of the azo compounds in solution. Moreover, the effect of aqueous buffer solutions of varying pH's on the spectral behaviour of the studied compounds was examined and used to determine the acidity constants of these compounds

Retarding effect of Ce [IV] Co [III], Cu [II], and Zn [II] as acceptor centres on the hydrolysis rate of H2 salen

The rate of hydrolysis of N-N/-salicylidene-ethylenediamine [H2 salen] has been investigated in the pH range. 1.50-11.30, at 25 degree, in aqueous media containing 7% V methanol. It was observed that the rate was pH-dependent at values more basic than 9.20. The rate- limiting step, in basic media, was suggested to be the attack of hydroxide ions on the H2 salen as a keto-form. The pH-independent, reaction occurred at pH region 9.20-6.35. At pH values more acidic than 6.35, the hydrolysis rate became again pH-dependent, being correlated with the conversion of the substrate to its conjugate acid. Under these acidic conditions the predominant reaction was the attack of water molecules on the protonated substrate. Furthermore, the effects of transition metal ions viz. Ce [IV], Ce [III], Cu [II] and Zn [II] on the hydrolysis reaction rate have been examined and interpreted on the basis of formation of tricyclic chelate rings. Thermodynamic parameters were also determined and discussed