The photochemical reduction of 2,1,3-benzothiadiazole-4, 7-dicarbonitrile in the presence of cationic micelles, and onward electron-transfer reactions

Abstract

Photolysis of solutions containing 2,1,3-benzothiadiazole-4,7-dicarbonitrile (BTDN) ethylenediaminetetra-acetic acid disodium salt (EDTA) and cetyltrimethylammonium bromide (CTAB) micelles at pH 5.5 produces the radical anion, BTDN˙^–, with BTDN acting both as an electron acceptor and as a chromophore. Variations in the efficiency of this reaction with pH, [CTAB] and [EDTA] are interpreted in terms of the formation of a complex between EDTA and BTDN which is broken down by the micelles. Net electron transfer does not occur within the complex. Alternative electron donors such as triethanolamine (TEOA) or 4-morpholine-ethanesulphonic acid (MES) can be employed, but not ascorbic acid or sulphite ion. The use of BTDN˙^– to reduce anthraquinones in stoichiometric or catalytic (with continuous photolysis) reactions is described. This allows an estimate of the redox potential of BTDN/BTDN˙^– when incorporated into micelles.