ELECTROLYSIS OF ORGANOPHOSPHORUS COMPOUNDS - STUDY OF MECHANISM OF REDUCTION OF VARIOUS DIETHYL AROYLPHOSPHONATES AT A DROPPING MERCURY ELECTRODE

Dialkyl aroylphosphonates in acetonitrile were electrolyzed at the dropping mercury electrode (DME) in the presence of benzoic acid to give dialkyl α-hydroxyarylmethylphosphonates as the exclusive product. Coulometric studies revealed an n-value of 2 electrons. In the absence of benzoic acid, benzoins and dialkyl hydrogenphosphonates were the only detectable products by GLC analysis. This situation requires C—P bond cleavage probably after an initial formation of a radical anion. The aroyl radical must couple rapidly at the electrode surface to give a benzil which is further reduced to a benzoin. A wide variation in n-values was obtained in the electrolysis of dialkyl aroylphosphonates unless benzoic acid was added. A plot of E1/2 vs. Hammett σ-values indicates the reduction is facilitated by electron-withdrawing groups as expected. Half-wave potentials for the dialkyl aroylphosphonates are more negative than for similarly substituted benzils. It is tentatively suggested that a conjugative effect on the carbonyl function by the phosphoryl group may be responsible in part for the decreased ease of reduction in the aroylphosphonates. © 1969, American Chemical Society. All rights reserved.