The uranyl UO22+ (VI) cation has been shown to oxidize alcohols (methanol, ethanol, 2-propanol, and cyclohexanol) to the corresponding α-hydroxyalkyl radicals (●CH2OH, CH3CH●OH, Me2C●OH, and Cyclohexyl●–OH, respectively). In general, the reactions were shown by UV-Vis and EPR spectroscopies to take place thermally in the dark via a single-electron transfer (charge-transfer) from the alcohol α-CH bond to valence shell of the uranium center in UO22+. R1R2CHOH + UO22+ → R1R2C●OH + UO2+ + H+ (R1, R2 = alkyl and/or H) While the thermal oxidation of anhydrous CH3OH by UO22+ gave only the α-hydroxymethyl ●CH2OH radical, in the presence of water the oxidation gave both ●CH2OH and the methoxy CH3O● radical. The result indicated that a thermal isomerization of ●CH2OH to CH3O● had taken place, which was catalyzed possibly by the UO22+–H2O complex. Sulfuric acid was also found to catalyze the isomerizations of ●CH2OH and CH3CH●OH (initially produced from oxidation of the corresponding alcohols by UO22+) to CH3O● and CH3CH2O●, respectively. Photochemical oxidations of CH3OH and Me2CHOH by UO22+ was shown to be accompanied by a subsequent isomerizations of the initially formed ●CH2OH and Me2C●OH to CH3O● and Me2CH–O●, respectively. The photochemical isomerizations were possibly catalyzed by the preexisting, unreacted alcohol molecules. 2-Methyl-2-propanol Me3COH (a tertiary alcohol without α-H) was, on the other hand, oxidized very slowly by UO22+ to the tert-butoxy Me3CO● radical in the dark via a similar thermal charge-transfer from the OH group in Me3COH to uranium in UO22+. All the reactions were characterized by UV-Vis and EPR spectroscopies, and the mechanisms will be discussed.

Thermal charge-transfer oxidation of alcohols by uranyl (VI) to α-hydroxyalkyl radicals and their isomerization to alkoxy radicals catalyzed by the uranyl–water complex

2019 Spring National Meeting

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