Catalytic Action of Cobalt (II) Peroxomonosulfate Complexes in Fenton-like Reactions – Computational Research Using Density Functional Theory

Fenton reaction was observed more than 120 years ago, nevertheless it still remains in the center of an extensive scientific research. The question regarding the mechanism of the Fenton and Fenton-like reactions and the nature of the oxidizing species obtained has been just partially revealed as each catalytic system has its own specifications.

A large number of Fenton-like catalytic systems has been learned, while the last publications^[1,2] of Dan Meyerstein research group concerning Co^II_(aq)/H₂O₂ system (pure and combined with bicarbonate ion as co-enzyme) present a new interesting root of the mechanism. The system reacts by coordination of number of ligands to the central cation before releasing oxidizing species, which may appear as hydroxyl radical or as bicarbonate radical.

Our research is focused on Co^II_(aq)/HSO₅^-_(aq) system, which has many well-known applications in wastewater treatment. The system`s components suggest an integration of the forms of hydrogen peroxide and bicarbonate-like co-catalyst in peroxomonosulfate ion.

The search for plausible reaction mechanism has been performed on the basis of quantum-mechanical calculations on density functional level of theory using B3LYP/6-311+G(d,p)/SMD model.

At this stage, the following reaction mechanism key features can be pointed out:

Cyclic coordination of peroxomonosulfate ion (simultaneously through peroxy oxygen and sulfite oxygen atoms) to cobalt (II) complex.
Coordination (cyclic or through the peroxy oxygen atom) of the second peroxomonosulfate ion.
Formation of sulfate radical through homolytic cleavage of peroxy bond in one of the peroxomonosulfate ligands attached to cobalt (II) complex.

References:

Burg A., Shusterman I., Kornweitz H. and Meyerstein D., Dalton Trans., 2014, 43, 9111-9115
Burg A., Shamir D., Shusterman I., Kornweitz H. and Meyerstein D., Commun., 2014, 50, 13096-13099