Investigation of electron-transfer reaction between alkaline hexacyanoferrate(III) and ranitidine hydrochloride - a histamine H2 receptor antagonist, in the presence of homogenous ruthenium(III) catalyst

The ruthenium(III)-catalyzed electron-transfer reaction between hexacyanoferrate(III) and ranitidine hydrochloride is studied in alkaline medium at 25 degrees C and at an ionic strength of 1.10mol/dm(3). The reaction stoichiometry is established and is found to be 1:4, that is, for the oxidation of one mole of ranitidine, four moles of hexacyanoferrate(III) are consumed. The reaction products were characterized by spectral studies such as IR, GC-MS, H-1-NMR and C-13-NMR. The reaction rate shows a less than unit order in substrate and alkali and a first-order dependence in oxidant, [Fe(CN)(6)](3-) and the catalyst, ruthenium(III) concentrations. The active species of ruthenium(III), [Ru(H2O)(5)OH](2+), forms an intermediate complex with the substrate. The attack of complex by hexacyanoferrate(III) in the rate determining step produces a radical cation, which is further oxidized in the subsequent step to form the oxidation product. The effect of the reaction environment on the rate constant upon adding varying concentrations of KNO3 and t-butanol was studied. The initially added products did not have any significant effect on the reaction rate. A plausible mechanism is proposed based on the experimental results. The effect of varying temperature on the reaction rate was also studied. The activation parameters for the slow step and the thermodynamic quantities for the equilibrium steps were evaluated.The mechanism of title reaction has been studied and one mole of ranitidine consumes four moles of [Fe(CN)(6)](3-), as shown in the following equation; [GRAPHICS] .