Electrochemical and ESR studies of the oxidation mechanism of pyrazine-di-N-oxides in the presence of methanol and its deuterated derivatives

Comparative Electrochemical and Electron Paramagnetic Resonance Study of the Mechanism of Oxidation of 2,3,5,6-Tetra-Me-Pyrazine-Di-N-Oxide as a Mediator of Electrocatalytic Oxidation of Methanol at Glassy Carbon and Multi-Walled Carbon Nanotube Paper Electrodes

“…Similar effect of addition of CH3COOH and of H2O on catalytic oxidation of PhenDNO and Pyr2 in the presence of i-PrOH at GC and SWCNT paper electrodes observed earlier studies [48,49]. Based on the obtained experimental data, the oxidation of Pyr2 in the presence of MeOH at the GC electrode can be explained by the E1C1E2C2 mechanism proposed earlier [1][2][3][4][5][6][7][8][9] for the two- The next chemical stage (C2) corresponds to the interaction of the cation with a nucleophile or base (a water admixture in the solution). Since there are catalytic currents in the presence of organic substance, we assumed that the cation decomposes at the C2 stage to form the starting aromatic di-N-oxide and the product of the two-electron oxidation of organic substance.…”

“…Note that in the presence of MeOH in acetonitrile solutions, no EPR spectrum of radical cation of Pyr2 could be detected. The EPR spectrum of radical cation of Pyr2 was detected in [7] at electrolysis at Au electrode only at temperature close to the solvent freezing point at -90° C when deuterated derivatives of methanol (CH3OD and CD3OD) were used as a solvent and substrate simultaneously ( Fig. 6b and c).…”

“…The electrochemically generated aromatic di-N-oxide radical cations are carriers of active oxygen that is capable of activating the C-H bond of substrates: alcohols, ethers and cyclohexane [1][2][3][4][5][6][7][8][9]. The mechanism of the oxidation of phenazine-di-N-oxide (PhenDNO), pyrazine-di-N-oxide (PyrDNO), and its substituted derivatives as mediators of electrocatalytic oxidation alcohols, ethers, and cyclohexane was studied by cyclic voltammetry at glass carbon electrode in acetonitrile [1][2][3][4][5][6][7][8][9]. In the study of the oxidation of PhenDNO in methanol and its deuterated derivatives CH3OD and CD3OD by EPR electrolysis [3], EPR spectra of radical intermediates were recorded with g-factor of 2.0023 in CH3OH and CH3OD and 2.0023 and 2.0036 in CD3OD.…”

“…The detection of the same intermediate in CH3OH and CH3OD indicated that CH3 group of alcohol was involved in formation of the intermediate. To explain the results obtained in [1][2][3][4][5][6][7][8][9], the E1C1E2C2 mechanism of two-stage electrode process characterized by catalytic current at the second electrode stage was suggested. The overall two-electron catalytic oxidation of the organic substance in complex with aromatic di-N-oxide radical cation was assumed to occur.…”

Electrochemical and quantum chemical studies of peculiarities of 2,5-di-Me-pyrazine-di-N-oxide oxidation in the presence of methanol at single-walled and multi-walled carbon nanotube paper electrodes

“…It was shown [9][10][11][12][13][14][15] that the aromatic di-N-oxide radical cations of phenazine-di-N-oxide, pyrazine-di-N-oxide (Pyr 0 ) and its substituted derivatives, electrochemically generated at GC and Pt electrodes, are carriers of active oxygen that is capable of activating the C-H bond of substrates: alcohols, ethers and cyclohexane. It was assumed that the activation process is accompanied by the formation of a complex of radical cations with a substrate that was confirmed by the registration of radical intermediates by EPR electrolysis at oxidation of phenazine-di-Noxide in MeOH and its deuterated derivatives.…”