Kinetic and thermodynamic study on tautomerism of dyes formed by reactions of aromatic imines with diazotized sulphanilic acid

Author(s): A.S.P.Azzouz*, T.S.Al-Ghabsha, A.N.Obed Agha

The diazotization coupling reactions were carried out by reactions of salicylidene aniline (SA) and salicylidene-4-aminoaniline (S-P-AA) with diazotized sulphanilic acid at optimal conditions.At pH 9, a reverse calibration curves fromtheortical and practical point of viewfor these imines were observed at 30 and 15 minutes respectively from the beginning of reactions. These were due to the side reactions or tautomerism of dye under basic medium. The tautomerism reaction order was found to be of pseudo first order with respect to imines, the last were supported by thermodynamic method, which showed that the tautomerism reactions were spontaneous (G = -) or nonspontaneous (G = +), endothermic (H = +) and were accompanied by an increase of entropy (S= +). The average recoveries for the determination of trace amountswere 99.3%and 100.38% for S-P-AA and SA respectively and precision (RSD) was less than 6.3%. The kinetic method was found simple and fast during determination of imines under study.

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