Biomimetic oxidation of indole-3-acetic acid and related substrates with hydrogen peroxide catalysed by 5,10,15,20-tetrakis 2′,6′-dichloro-3′-sulfonatophenyl)porphyrinatoiron(III) hydrate in aqueous solution and AOT reverse micelles

Abstract

The reaction of indole-3-acetic acid (IAA) with hydrogen peroxide catalysed by 5,10,15,20-tetrakis(2′,6′-dichloro-3′-sulfonatophenyl)porphyrinatoiron(III)hydrate [Cl 8TPPS 4Fe(III)(OH 2) 2] gives indole-3-carbinol (IC) and indole-3-carboxaldehyde (IA) in aqueous buffer solution. The oxidation of IAA with H 2O 2 in the presence of Cl 8TPPS 4Fe(III)(OH 2) 2 in AOT reverse micelles gives higher yields of IA than in aqueous solution at the same pH. The yields of different oxidation products in AOT reverse micelles depend on the pH, the water to surfactant ratio (Wo) and concentration of Cl 8TPPS 4Fe(III)(OH 2) 2 in AOT reverse micelles. The oxidation of IC with H 2O 2 in the presence of Cl 8TPPS 4Fe(III)(OH 2) 2 gives IA, indole-3-carboxylic acid (ICA), 2-oxo-indole-3-carbinol and 3-methylene oxindole. The oxidation of indole-3-propionic acid and indole-3-butyric acid with H 2O 2 in the presence of Cl 8TPPS 4Fe(III)(OH 2) 2 in aqueous buffer solution as well as AOT reverse micelles do not give the oxidative decarboxylation products. The formation of IC may be explained by the hydrogen abstraction from IAA by high valent oxo-iron(IV) radical cations followed by decarboxylation and subsequent recombination of either free hydroxy radical or hydroxyiron(III)porphyrin. The same abstraction and recombination mechanism has been proposed for oxidation of IC to IA and IA to ICA.