New aspects of ionic catalysis in oxidation of organic compounds by oxygen

Abstract

The kinetics of methylethylketone oxidation in aqueous solutions has been studied. The catalysts used were Fe³⁺ ions and complexes: Cu²⁺-pyridine, Fe³⁺-phenanthroline, Mn²⁺-phenanthroline. A mechanism has been proposed involving the following enolization, [graphic omitted] and oxidation steps, EnH + Me⁽ⁿ⁺¹⁺⁾→ R·+ Meⁿ⁺+ H⁺, R·+ O₂→ RO₂·, RO₂·+ Meⁿ⁺→^H+ ROOH + Me⁽ⁿ⁺¹⁺⁾, ROOH + Meⁿ⁺→ RO^–+ Me⁽ⁿ⁺¹⁺⁾+ HO·, HO·+ RH → H₂O + R·, ROOH^H+→ CH₃COOH+ CH₃CHO.

A general scheme of catalytic oxidation has been proposed on the basis of the scheme for the catalytic oxidation of ascorbic acid (non-chain oxidation with a cycle Me⁽ⁿ⁺¹⁾⁺[graphic omitted]Meⁿ⁺[graphic omitted]Me^(n+1)+), the scheme for catalytic chain oxidation of hydrocarbons and aldehydes, and the scheme for oxidation of methylethylketone. The Br^– and H⁺ catalysts may be those converting ROOH into free radicals.

A different mechanism of catalysis has been found for the oxidation of benzene in aqueous solution in the presence of Fe²⁺ and Cu²⁺. This reaction is autocatalytic. Autocatalysis is due to formation of free radicals in phenol oxidation. Benzene is supposed to be oxidized to phenol by a reaction C₆H₆+ HO·→Ċ₆H₆OH[graphics ommited]C₆H₅OH + HO₂·.