Photochemical Oxidation-Reduction and Photocatalysis. The Photochemical Activity of FeCl4− in Alcohol as Oxidizing Agent and as Catalyst

A true photocatalytic reaction in which the concentration of the sensitizer remains constant is described in this paper. It is shown that FeCl4− acts as a photocatalyst for the oxidation of alcohol by thionine. In the absence of thionine FeCl4− is the oxidizing agent. A mechanism is put forward which includes (1) photoexcitation, primary dark back reaction and separation of the primary product, (2) oxidation of the CH3CHOH radical by FeCl4−, (3) reaction between two CH3CHOH radicals, (4) oxidation of FeCl4= by thionine. The latter occurs because of a considerable shift in the oxidation-reduction potential by the complexing of both ferric and ferrous iron. Various constants and constant ratios are evaluated from the experimental results.