Photocatalytic reactions in the 2,3,7,8,12,13,17,18-octaethylporphyrinatoiron(III)–ethanol–carbon tetrachloride system

Abstract

The photochemistry of ethanol solutions of 2,3,7,8,12,13,17,18-octaethylporphyrinatoiron(III), [Fe(oep)]⁺, has been investigated in the presence of CCl₄ and of different amounts of oxygen. Continuous irradiation with 330–440 nm light induces an ethanol-to-oxygen electron transfer occurring with the assistance of an iron(III) porphyrin ethanolate complex. At a partial pressure of oxygen ranging from 0.1 to 1 Torr, the photoproducts, hydroxyethyl radical and hyperoxide ion O₂^– give rise to a catalytic process, with > 100 turnovers of [Fe(oep)]⁺, leading to the reduction of carbon tetrachloride to chloroform and chloride ions and with oxidation of ethanol to acetaldehyde. The rate of the photocatalytic process was observed to depend on the oxygen concentration, excitation wavelength, and the presence of a radical scavenger. A chain mechanism has been formulated involving radical species that can be quenched by oxygen to yield peroxyl radicals.