The vanadium(III) chloride-dioxygen reaction in anhydrous pyridine: Evidence for a vanadium(III)-dioxygen adduct

Abstract

The kinetics of the reaction between vanadium(III) chloride and dioxygen in pyridine has been examined. In both excess O 2 and V(III) the forms of the rate law are constent with the mechanism V(III)+O 2 ⇌ K V(III)O 2 , V(III) → k products Due to equilibria involving VCl 3 in pyridine, the values of K and k depend on the concentration of VCl 3 used. At large concentrations of V(III) when (py) 3VCl 3 is the dominant species: [V(III)] in excess, k = (9.2 ± 6.3) × 10 −2 sec −1 and K = 40 ±24 M −1 at 25°C. At small concentrations of V(III) when an appreciable amount of (py) 4VCl 2 + is present: [O 2] in excess, k = (7.1 ± 0.5) × 10 −2 sec −1 and K = 265 ± 18 M −1 at 25°C. Once the V(III)−O 2 reaction is initiated, “reacted” V(III) can be regenerated, supporting the view that a V(III)-O 2 adduct is formed.