Low molecular weight, polymeric, and covalently bound cobalt(II)-phthalocyanines for the oxidation of mercaptans

Cobalt(II)-phthalocyanines in different environments are investigated as catalysts for the oxidation of thiols. Water-soluble low molecular weight 2,9,10,23-tetracarboxyphthalocyanine (1b) and polymeric phthalocyanine (2b) with carboxylic end groups are prepared. Compound1b is covalently bound at linear and cross-linked poly(chloromethylstyrene) in the presence of pyridine to obtain the water-soluble polymers (3a, b) and gel-type polymers (4a, b). Covalent binding of1b to surface modified silica was also realized. Low molecular weight and polymeric phthalocyanines (1a, 2a) are synthesized on silica, alumina, and charcoal. In addition,1a is encapsulated in the interior of NaX zeolite. All materials are efficient catalysts for the oxidation of 2-mercaptoethanol. The mechanism employing water-soluble catalysts is discussed in the direction of a mononuclear complex coordinating dioxygen and thiol. Heterogeneous catalysts containing1a and2a on the carriers show enhanced activity with increasing dispersion. The proposed mechanism considers different reaction sites for the coordination of O₂ and thiol.