Effect of metal phthalocyanine complex aggregation on the catalytic and photocatalytic oxidation of sulfur containing compounds

Water soluble zinc (II) 2,9,16,23-phthalocyanine tetrasulfonic acid [ZnPc(S O3H)(4)], zinc (II) 2,9,16,23-phthalocyanine tetracarboxylic acid [ZnPc(COO H)(4)] and sterically hindered bulky zinc(II) 2,9,16,23-tetrakis(8-quinolin eoxy-5-sulfonicacid)-phthalocyanine [ZnPc(QnSO(3)H)(4)] complexes have been studied as photocatalysts for oxidation of 2-mercaptoethanol and sodium th iosulfate. The ZnPc(QnSO(3)H)(4) complex exhibited the highest photocatalyt ic activity due to its low aggregation degree in aqueous medium. In the pre sence of tetrabutylammonium chloride, quinoline and ethanol additives the m onomerization degree of the ZnPc(SO3H)(4) and ZnPc(COOH)(4) complexes is in creased, their photocatalytic activity being close to that of ZnPc(QnSO(3)H )(4). Because of high aggregation degree of ZnPc(SO3H)(4) and ZnPc(COOH)(4) in viscous medium, the quantum yields of singlet dioxygen generation and t he photocatalytic oxidation rates of the sulfur-containing compounds are de creased. The photocatalytic activity of ZnPc(QnSO(3)H)(4) is slightly chang ed in viscous medium and in the presence of additives. The low aggregation degree of this complex allowed to establish enhanced and lowered rates of p hotocatalytic oxidation of 2-mercaptoethanol and sodium thiosulfate, respec tively, on increasing medium viscosity. The effect of medium viscosity on Z nPc(QnSO(3)H)(4) photocatalyzed oxidation of the two substrates is discusse d. (C) 1999 Elsevier Science B.V. All rights reserved.