Kinetics and Mechanism of Formation of [Fe(Cn)₅Inh]^3- by Ligand Substitution in Acidic Media (Inh = Isoniazid)

Abstract

The kinetics and mechanism of formation of [Fe(CN) 5 INH] 3 À 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 (l max of product), under pseudo-first order conditions, using excess of INH over [Fe(CN) 5 H 2 O] 3 À . The reaction was studied as a function of [Fe(CN) 5 H 2 O 3 À ], [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 H 2 O 3 À ] 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.