Reaction mechanism of N-benzoyl-N-phenylhydroxylamine with vanadium(IV) in the weakly acidic medium

The N-benzoyl-N-phenylhydroxylamine(BPHA)–V(IV) system, if kept de-aerated, gives no color reaction. In an open vessel a color reaction does take place. This reaction was studied in solution by spectrophotometry, and the product prepared as solid by scanning thermal analysis, X-ray photoelectron spectrometry(XPS), elemental analysis and magnetic susceptibility measurement. The reaction and product of the corresponding V(V) system were also studied for comparison. All of these experimental data revealed that BPHA reacts with V(IV) to form a V(V)-chelate. The proposed mechanism involves aerial oxidation of V(IV), the equilibrium of which is shifted favorably in the presence of excess BPHA. As V(IV) has the natural tendency to aerial oxidation in the weakly acidic medium, other V(IV) chelate systems may obey also this mechanism if the chelating ligands react preferentially with V(V) as BPHA. Examples are given to demonstrate the significance of the proposed mechanism in a broad sense.