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

Abstract 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 efficient are Zn(II) and Al(III) phthalocyaninetetrasulfonic acids, which oxidize the thiolate to the sulfonic acid and sulfate, whereas Co(II)phthalocyaninetetrasulfonic acid does not exhibit a photoeffect. During the photooxidation reactions, decomposition (photobleaching) of the zinc phthalocyanine derivatives occurs, whereas the analogous alumina chelates are more stable. Covalent binding of Zn(II)phthalocyanine derivatives to silica carriers results in photocatalytic activities even in the absence of detergents, since the immobilization of the complexes preserves the required monomeric state. Moreover, the photodecomposition (bleaching) of the heterogenized complexes is strongly retarded. For the photo‐oxidations mainly the pathway via the sensitized formation of singlet oxygen with subsequent oxidation reactions is valid. Hydrogen peroxide as one reduction product of oxygen was found.

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