Estimated distribution between one- and two-equivalent reaction paths in vanadium(V)-induced electron transfer
Abstract
The reactions of VV with [Co(NH3)5L]2+ complexes of α-hydroxy-acids, mandelic (α-hydroxybenzene-acetic), lactic, and glycolic acids yield CoII and a carbonyl compound to the extent of 50% of [CoIII]initial; [VV]consumed is 1.5–1.7 times [CoIII]initial. The other product of the reaction, phenylglyoxylatocobalt(III) complex, obtained in 50% yield by a two-electron oxidation, is responsible for the 50% change in absorbance at 502 nm. The rate of the reaction is proportional to the concentration of a VV–CoIIIcomplex, observed spectrophotometrically. This is consistent with the one-electron route preferred by VV, producing a radical which, by nearly synchronous C–C fission and one-electron transfer to CoIII, produces CoII. Stoicheiometric studies made with VV and mandelic acid (CoIII-free system) reveal that the yields of PhCHO and phenylglyoxylic acid are nearly equal. When coupled with the results of the induced electron transfer using VV, this suggests that the one- and two-equivalent paths prevalent in the oxidation of α-hydroxy-acids by VV are very nearly of equal importance.