Kinetics and mechanism of formation of [Fe(CN)5INH]3- by ligand substitution in acidic media (INH = isoniazid)

The kinetics and mechanism of formation of [Fe(CN)(5)INH](3-) by a ligand substitution reaction between aquapentacyanoferrate(II) ion and isoniazid, (pyridine-4-carboxylic acid hydrazide) (INH) have been investigated spectrophotometrically in acidic media at 435 nm (lambda(max) of product), under pseudo-first order conditions, using excess of INH over [Fe(CN)(5)H2O](3-). The reaction was studied as a function of [Fe(CN)(5)H2O3-], [INH], pH, ionic strength and temperature, by varying only one of these variables while other variables were held constant. The reaction exhibited first-order kinetics in [INH] while it was independent of [Fe(CN)(5)H2O3-] in the chosen concentration range. The effect of temperature on the reaction rate yielded the activation parameters. The most plausible mechanism consistent with the experimental results has been proposed.