Shigenobu Matsumoto

Degradation and dehalogenation of polychlorobiphenyls and halogenated aromatic molecules by superoxide ion and by electrolytic reduction

Polyhalogenated aromatic hydrocarbons are rapidly degraded by superoxide ion in dimethylformamide to carbonate and halide ions. The efficient destruction of such materials is accomplished via the in situ electrolytic reduction of dissolved oxygen to generate superoxide ion, which reacts with polyhalo aromatics by nucleophilic substitution. The reaction stoichiometries have been determined by cyclic voltammetric measurements, and the reactant/product profiles have been assayed by capillary gas chromatography and potentiometric titrations. Analogous complete destruction by superoxide ion occurs for PCBs that contain three or more chlorine atoms per aromatic ring. Another means to the dehalogenation of halo aromatic hydrocarbons is their electrolytic reduction to the parent hydrocarbon in oxygen-free dimethylformamide solutions. Electrochemical studies confirm that all PCBs can be dehalogenated via anaerobic electrolysis.

Electron spin resonance spectra of the chromanoxyl radicals derived from tocopherols (vitamin E) and their related compounds

The well resolved electron spin resonance (ESR) of the tocopheroxyl and chromanoxyl radicals derived from α-, β-, γ- and δ-tocopherols (vitamin E), 5,7-dimethyltocol, tocol and their model compounds in degassed toluene by treatment with 2,2-diphenyl-1-picrylhydrazyl were recorded. Their hyperfine coupling constants were determined and assigned using spectrum simulation. Their g-factors were also measured. On the basis of these parameters, the α-tocopheroxyl radical is similar to the 2,2,5,7,8-pentamethylchroman-6-oxyl, 5,7-dimethyltocoxyl and 2,2,5,7-tetramethylchroman-6-oxyl radicals. This suggests that the presence of methyl groups at C-5 and C-7 in tocopherols and chroman-6-ols is of great importance to their antioxidant action. The ESR parameters obtained here are very useful for the identification and quantification of a variety of tocopheroxyl radicals.

Reaction of 2,2,5,7,8-pentamethyl-6-chromanol, an α-tocopherol analogue, with NO in the presence of oxygen

An alpha-tocopherol model compound, 2,2,5,7,8-pentamethyl-6-chromanol, reacted with nitric oxide (NO) in the presence of various amounts of oxygen to afford four major products. Distribution of the products was varied depending on the ratio of NO and O2, and the preincubation time of NO and O2.

The revised structure of an oxidation product from the reaction of an α-tocopherol model compound, 2,2,5,7,8-pentamethylchroman-6-ol, with potassium superoxide; 6 -hydroxy -2,2,6,7,8- pentamethylchroman- 5 (6H) -one1

Abstract The previously reported structure of an oxidation product obtained from the reaction of an (α-tocopherol model compound(1) with KO2 is revised to 6-hydroxy-2,2,6,7,8-pentamethylchroman-5(6H)-one(3) on the basis of the X-ray crystallographic and 18O-labeling studies.

Potassium t-butoxide-catalysed oxygenation of an α-tocopherol model compund 2,2,5,7,8-pentamethylchroman-6-ol

The potassium t-butoxide-catalysed oxygenation of an α-tocopherol model compound, 2,2,5,7,8-penta-methylchroman-6-ol, gave 5-hydroxy-2,2,5,7,8-penta-methylchroman-6(5H)-one (2) and 7,8-dihydro-5,7-dihydroxy-8-methylene-2,2,5,7-tetramethychroman-6(5H)-one, and 6-hydroxy-2,2,6,7,8-pentamethylchroman-5(6H)- one which was found to be formed as the result of the acyloin rearrangement of (2).

Epoxidation of an α-tocopherol model compound, 2,2,5,7,8-pentamethylchroman-6-ol, with potassium superoxide; X-ray crystal structure of 4a,5;7,8-diepoxy-4a,7,8,8a-tetrahydro-8a-hydroxy-2,2,5,7,8-pentamethylchroman-6(5H)-one

An α-tocopherol model compound, 2,2,5,7,8-pentamethylchroman-6-ol, was oxidized in the presence of dicyclohexyl-18-crown-6 with KO2 to give a diepoxide, whose structure was determined by spectroscopy and X-ray crystallography.

Oxidation of a vitamin E model compound, 2,2,5,7,8-pentamethylchroman-6-ol, with the t-butylperoxyl radical

In a t-butylperoxyl radical-generating system, a vitamin E model compound, 2,2,5,7,8-pentamethylchroman-6-ol, was converted into 4a,5-epoxy-4a,5-dihydro-8a-hydroperoxy-2,2,5,7,8-pentamethylchroman-6(8aH)-one (3), the structure of which has been determined by X-ray crystallography, and 8a-t-butyldioxy-4a,5-epoxy-4a,5-dihydro-2,2,5,7,8-pentamethylchroman-6(8aH)-one (4).

Potassium tert-butoxide-catalysed oxygenations of vitamin E and its model compound 2,2,5,7,8-pentamethylchroman-6-ol

Oxygenation of vitamin E [1a, (RRR)-α-tocopherol] in tetrahydrofuran in the presence of potassium tert-butoxide under oxygen gave products 2a, 3a, 4a, 5a and 6a arising from oxidation of the aromatic moiety. Under similar conditions, a vitamin E model compound, 2,2,5,7,8-pentamethylchroman-6-ol 1b, gave the analogous products 2b, 3b, 4b, 5b and 6b. Initial attack at the 5 position leads to the acyloin 6b, which is converted into the isomer 5b. The hydroperoxide 7b is derived from the acyloin 5b and transformed into the 7-methylene compound 3b. The 8-methylene compound 2b is converted into the carbolactone 4b. The molecular structures of compounds 2b, 3b, 4b and 7b were confirmed by X-ray crystallographic analysis. Possible reaction pathways for the product formation and relationships between the product distribution and the basicity of reaction media are discussed.

Electron spin resonance spectra and hyperfine coupling constants of the [133C]α-tocopheroxyl (the [13C]vitamin E radical) and [13C]2,2,5,7,8-pentamethylchroman-6-oxyl radicals (Its model radical)☆

Abstract The electron spin resonance spectra of the [5a-, 7a-, or 8b-13C]2-ambo-α-tocopheroxyl and [5a-, 7a-, or 8b-13C]2,2,5,7,8-pentamethylchroman-6-oxyl radicals were obtained from the oxidation of [13C]2-ambo-α-tocopherol (13C]vitamin E) and [13C]2,2,5,7,8-penta-methylchroman-6-ol (a [13C]vitamin E model compound), respectively, with 2,2-diphenyl-1-picrylhydrazyl. The 13C hyperfine coupling constants of the 5a-, 7a-, and 8b-methyl groups in these radicals were determined using spectrum simulation. Their magnitude was compared with that of the 1H hyperfine coupling constants of the methyl groups. It was found to be simply proportional to the π-spin density on aromatic carbon atoms bonded to the methyl groups: i.e., ajc = Qjc· ϱiπ. The Qjc value was empirically determined to be −1.62 ± 0.05 mT.