INVESTIGATION OF SELECTIVITY OF HYDROPEROXIDE OXIDATION OF IRON (III) -PYRIDOXINE COMPLEX IN AQUEOUS SOLUTION

Abstract

Fenton reaction systems are applied in organic synthesis for the selective oxidative functionalisation of hydrocarbons, organonitrogen and organosulfur compounds. For the Fe³⁺/ H₂O₂ complex, a mechanism is proposed for the oxidative activation of hydrogen peroxide, which involves the transfer of a proton resulting in the formation of oxywater Fe^{3 + -}O-⁺OH₂, which dissociates heterolytically, liberating water and generating a complex of iron (III) -¹D-oxene [Fe³⁺O⁰(¹D)]³⁺, where the oxygen atom is in the singlet quantum state (2p [↑ ↓ ] [↑ ↓] [_]). This intermediate is intended to be a selective oxidant of organic compounds. The aim of the work is to study the selectivity of oxidation of pyridoxine with hydrogen peroxide in an aqueous solution in the presence of iron (III) ions, bound to complexes by organic molecules. The structure of the oxidation product was studied using proton and carbon nuclear magnetic resonance (NMR) methods. Based on the results of NMR spectroscopy, the primary conversion pathway in the system is based on oxidation of the primary alcohol group at the 4-carbon atom of the pyridine nucleus to the carboxyl group, which acylates the hydroxyl group at the 3-carbon atom of the neighbouring molecule to form an intermolecular ester bond. As a result, a cyclic oligomer is formed, comprising two or three monomeric units. Additional oxidative modifications of the basic oligomeric oxidation product are the oxidation of another primary alcohol group at the 5-carbon atom to the carboxyl group and N-oxidation of the pyridine nitrogen atom. In this case, individual monomer units either may not have additional modifications at all, or have one modification, or both of them at the same time.