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Experimental and Theoretical Examination of the Radical Cations Obtained from the Chemical and Electrochemical Oxidation of 5-Aminothiazoles.

ABSTRACT: Chemical or electrochemical one-electron oxidation of 5-N-arylaminothiazoles was found to afford stable radical cations. For chemical oxidation, 1 equivalent of [(4-BrC₆H₄)₃N][SbCl₆] (Magic Blue, MB) was added to CH₂Cl₂ solutions of the thiazoles, and the thus-obtained radicals showed light absorption in the near-infrared region. Electrochemical oxidation also led to bathochromic shifts in the absorption bands, and the obtained spectra were similar to those derived from the chemically oxidized species. These radicals afforded electron paramagnetic resonance (EPR) spectra that are consistent with the notion of stable nitrogen radicals (half-life≤385 h). The EPR spectrum of a thiazole containing 4-dimethylaminophenyl groups on the nitrogen atom at the 5-position changed significantly upon adding >3 equivalents of MB. Details of the electronic structures of the experimentally obtained radical cations were generated from theoretical calculations.

SUBMITTER: Yamaguchi K

PROVIDER: S-EPMC5390811 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Experimental and Theoretical Examination of the Radical Cations Obtained from the Chemical and Electrochemical Oxidation of 5-Aminothiazoles.

Yamaguchi Kirara K Murai Toshiaki T Kutsumizu Shoichi S Miwa Yohei Y Ebihara Masahiro M Guo Jing-Dong JD Tokitoh Norihiro N

ChemistryOpen 20170315 2

Chemical or electrochemical one-electron oxidation of 5-N-arylaminothiazoles was found to afford stable radical cations. For chemical oxidation, 1 equivalent of [(4-BrC6H4)3N][SbCl6] (Magic Blue, MB) was added to CH2Cl2 solutions of the thiazoles, and the thus-obtained radicals showed light absorption in the near-infrared region. Electrochemical oxidation also led to bathochromic shifts in the absorption bands, and the obta ...[more]

PMID: 28413765

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Project description:The reaction mechanisms and kinetics of thiophene oxidation reactions initiated by hydroperoxyl radical, and decomposition of the related intermediates and complexes, have been considered herein by using high-level DFT and ab initio calculations. The main energetic parameters of all stationary points of the suggested potential energy surfaces have been computed at the BD(T) and CCSD(T) methods, based on the geometries optimized at the B3LYP/6-311 + g(d,p) level of theory. Rate constants of bimolecular reactions (high-pressure limit rate constants) at temperatures from 300 to 3000 K for the first steps of the title reaction have been obtained through the conventional transition state theory (TST), while the pressure dependent rate constants and the rate constants of the second and other steps have been calculated employing the Rice-Ramsperger-Kassel-Marcus/Master equation (RRKM/ME). The results show that the rate constants of addition to α and β carbons have positive temperature dependence and negative pressure dependence. It is found that the additions of HO2 to the α and β carbons of thiophene in the initial steps of the title reaction are the most favored pathways. Also, the addition to the sulfur atom has a minor contribution. But, all efforts for simulating hydrogen abstraction reactions have been unsuccessful. In this complex oxidation reaction, about 12 different products are obtained, including important isomers such as thiophene-epoxide, thiophene-ol, thiophene-oxide, oxathiane, and thiophenone. The calculated total rate constants for generation of all minimum stationary points show that the addition reactions to the α and β carbons are the fastest among all at temperatures below 1000 K, while the proposed multi-step parallel reactions are more competitive at temperatures above 1200 K. Furthermore, important inter-and intra-molecular interactions for some species have been investigated by two well-known quantum chemistry method, the NBO and AIM analyses. Thermochemical properties such as free energy, enthalpy, internal energy, and entropy for thiophene and hydroperoxyl radical and related species in the simulated reactions have been predicted using a combination of the B3LYP and BD(T) methods.

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Experimental and Theoretical Examination of the Radical Cations Obtained from the Chemical and Electrochemical Oxidation of 5-Aminothiazoles.

Publications

Experimental and Theoretical Examination of the Radical Cations Obtained from the Chemical and Electrochemical Oxidation of 5-Aminothiazoles.

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