PHOTOOXIDATION OF 2-MERCAPTOETHANOL BY VARIOUS WATER-SOLUBLE PHTHALOCYANINES IN AQUEOUS ALKALINE-SOLUTION UNDER IRRADIATION WITH VISIBLE-LIGHT

A selection of charged water-soluble phthalocyanines was employed for the photocatalytic oxidation of 2-mercaptoethanol in aqueous alkaline solution in the presence of oppositely charged detergents. Most effici ent are Zn(II) and Al(III) phthalocyaninetetrasulfonic acids, which ox idize the thiolate to the sulfonic acid and sulfate, whereas Co(II)pht halocyaninetetrasulfonic acid does not exhibit a photoeffect. During t he photooxidation reactions, decomposition (photobleaching) of the zin c phthalocyanine derivatives occurs, whereas the analogous alumina che lates are more stable. Covalent binding of Zn(II)phthalocyanine deriva tives to silica carriers results in photocatalytic activities even in the absence of detergents, since the immobilization of the complexes p reserves the required monomeric state. Moreover, the photodecompositio n (bleaching) of the heterogenized complexes is strongly retarded. For the photooxidations mainly the pathway via the sensitized formation o f singlet oxygen with subsequent oxidation reactions is valid. Hydroge n peroxide as one reduction product of oxygen was found.