Oxywater-oxenoid conception of mechanisms of benzylpenicillin oxidation and oxidant decomposition in aqueous hydrogen peroxide solution

Abstract

There are actuality and importance of confirmation or at least reasoned argumentation of molecular kinetics of hydrogen peroxide oxidation reactions because of currently unidentified true nature of oxygen intermediates, at one side, and widespread of these processes in natural biological and artificial anthropogenic systems, from other side. The building of common theory of hydrogen peroxide oxidative activity and dismutation decomposition can be based on determination of structure of individual model reactions products. The benzylpenicillin molecule has a heterofunctional structure. Its sodium salt was dissolved in aqueous hydrogen peroxide solution without Fenton catalysts addition. The system was protected from thermal and photochemical activation. As result, we observed a colloid solution formation, a water-insoluble sediment accumulation, and a hydrogen peroxide disproportionation with gas-phase molecular oxygen liberation. The NMR-spectroscopy data evidenced in favor of S-oxidation of sulfide fragment, N-oxidation of nitrogen atoms with amide groups dissociation, and aromatic ring hydroxylation and electrophilic carbonylation. The precipitate is a mixture of several substances, some of which have presumably an oligomeric structure due to neighboring molecules coupling in carbonylation and hydroxylamine fragments O-acylation reactions. The molecular kinetics of model organic molecule oxidative modifications and hydrogen peroxide dismutation is interpreted by oxywater-oxenoid conception. In accordance with one, there are different associates between water HOH and hydrogen peroxide HOOH molecules in solution system due to hydrogen bonds. These molecules are simultaneously Brønsted acids and bases. The rate of proton accepting and donation depends on temperature and concentration parameters. The hydronium H3O+ and hydroperoxonium H3O2+ cations, and the hydroxide HO− and hydroperoxide HO2− anions are generated. For hydrogen peroxide molecule H2O2, there is possibility for isomeric bipolar ion oxywater H2O+O− formation. The zwitter-ion heterolytically dissociates with water molecule liberation and singlet oxygen atom generation. The 1D-oxene (2p[↑↓][↑↓][_]) oxidizes sulfur and nitrogen heteroatoms through accepting their unshared electron pairs by own vacant atomic orbital. In addition, singlet oxygen atom hydroxylates an aromatic ring by hydride transfer and mediates decomposition of hydrogen peroxide. The dioxygen liberated during hydrogen peroxide dismutation is generated at first in singlet 1∆g-quantum state, the quenching of which, presumably, includes a dimerization of 1O2 antipodes by orbital moment. Inside the associate (1O2)2, the electron exchange interaction occurs. As result, two molecules of triplet dioxygen are generated, and they are antipodes by spin moment: first molecule has spin +1 and second molecule has spin −1.