Peroxy Acid Oxidations. I. A Kinetic and Mechanistic Study of Oxidation of Acetylacetone by Peroxomonophosphoric Acid and Hydrogen Peroxide in Alkaline Medium

Abstract

Abstract The kinetics of oxidation of acetylacetone by peroxomonophosphoric acid and hydrogen peroxide have been investigated in the pH range 8–13.7. The oxidations by peroxomonophosphoric acid at 308 K and I=0.6 mol dm−3 follow the rate expressions, (i) −\fracd[PMPA]Tdt={k1[A]+k2[A−]}[HPO52−] in the pH range 8–10.63, where k1=1.96 dm3 mol−1 s−1 and k2=0.177 dm3 mol−1 s−1, and (ii) −\fracd[PMPA]Tdt={k3[A]+k4[A−]}[HPO52−]+{k5[A]+k6[A−]}[PO53−] in the pH range 11.5–13.7, where k3=30.4 dm3 mol−1 s−1 and k6≈0. The rate law for hydrogen peroxide oxidations in the pH range 9.2–13 at 308 K and I=0.1 mol dm−3 is given by, −\fracd[Hydrogen peroxide]Tdt={k7[A]+k8[A−]}[H2O2]+{k9[A]+k10[A−]}[HO2−] the k7 and k10 values being 0.393 dm3 mol−1 s−1 and 0.143×10−2 dm3 mol−1 s−1 respectively. A and A− represent the diketo and enol form of acetylacetone respectively. The kinetic data and activation parameters are consistent with nucleophilic attack by peroxo species on both diketo and enol form of acetylacetone followed by oxygen–oxygen bond fission.