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Hydrolysis and extraction properties of aroylhydrazones derived from nicotinic acid hydrazide

The kinetics of hydrolysis of N'-salicylidene-3-pyridinecarbohydrazide (1) and N'-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide (2) was investigated in dioxane/water 1/1 solvent system in acidic and basic media, and the corresponding reaction mechanisms were proposed. The kinetic results suggested that in the acidic solution rate-determining step of hydrolysis reaction was the attack of water molecule on the protonated azomethine group, whereas in the basic medium that was the attack of water on the completely deprotonated hydrazone. By analyzing the temperature dependence of the reaction rate, the thermodynamic activation parameters, i.e. activation enthalpy and entropy, were also evaluated and discussed. The complexation reactions of vanadium(V) with aroylhydrazones 1 and 2 as well as the extraction of V(V) from aqueous to organic phase were studied spectrophotometrically. The optimum conditions for complex formation and extraction of vanadium(V) to chloroform solution of 1 or 2 have been evaluated. Based on the results obtained by Job’s and equilibrium shift methods the stoichiometries of the complexes were determined to be 1:1. The effect of foreign ions on V(V) extraction by 2 has been determined as well.

aroylhydrazones ; hydrolysis ; vanadium(V) ; extraction ; complexes ; spectrophotometry

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