English (United States)
The cathodic conversion of 1,1-diphenylacetone (1) to benzophenone (2) was investigated. Through divided-cell electrolyses, cyclic voltammetry, and reactions with authentic superoxide, it was demonstrated that molecular oxygen is likely reduced to the superoxide anion at the cathode, where it proceeds to react with 1 to form an α-hydroperoxy ketone intermediate. Nucleophilic attack at the carbonyl by a second molecule of superoxide facilitates cleavage of the carbon-carbonyl bond to afford 2. Analogously, it was determined through mechanistic studies that α-substituted 1,1-diphenyl ketones undergo α-cleavage of the acyl group in a remarkably mild cathodic reaction. This transformation is postulated to occur via reduction of oxygen to superoxide, which forms a hydroperoxy anion that then attacks the carbonyl to give a tetrahedral intermediate. As the intermediate collapses to reform the carbonyl, the carbon-carbonyl bond is cleaved to yield the hydrocarbon product. Observed superoxide-facilitated α-cleavage offers an explanation for the previously-described cathodic cleavage of α-alkoxyaldehydes to benzhydryl alkyl ethers. The significant structural changes that are afforded by the mild cathodic reactions discussed here demonstrate the synthetic capabilities of organic electrochemistry.
Tsui, Elaine, "Superoxide-Facilitated Cathodic Cleavage of 1,1-Diphenyl Ketones" (2015). Honors Theses - All. 1514.
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