Electron Transfer Reaction of Pyridoxine (Vitamin B6) with Keggin Type 12 Tungstocobaltate (III) in Aqueous Perchlorate Medium

Abstract

Transition metal substituted heteropolymetalates exhibit different chemical and electrochemical properties.  The complexes of transition metal ions with polyoxanions such as polytungstates are well known as outer-sphere electron transfer reagents. 12-tungstocobaltate (III) has the well-known twelve tungsten atoms Keggin structure. Such  clusters  are  known  for  photochemical, hydrogen  generation  and are involved in multi-step  electron  transfer  processes. Keeping this view in mind the interaction of vitamin B6 with 12-tungstocobaltate (III) has been carried out. The kinetics of the electron transfer reaction of vitamin B6 with 12-tungstocobaltate (III) complex has been studied spectrophotometrically over the range 0.01 ≤ (pyridoxine)          ≤ 0.07mol dm-3, 3.3 ≤ pH ≤ 5 and at 298 K ≤ T ≤ 318K in aqueous perchloric acid medium. Kinetics measurements were run under pseudo-first order conditions. The rate of electron transfer reaction was found to be first order with respect to pyridoxine. The results showed that the rate depends on size and strength of the ligand. The activation parameters favored the electron transfer reaction. Interaction of pyridoxine (Vitamin B6) with 12-tungstocobaltate (III) in aqueous perchloric medium involves formation of a precursor complex between reactants. The precursor complex undergoes a reorganisation towards a transition state in which electron transfer takes place to form pyridoxal as an intermediate. The pyridoxal is further oxidized to a final product 4-pyridoxic acid by another oxidant molecule in the fast step. The product is confirmed by FTIR and 1H NMR spectra.