Mechanism of oxidation of the 2-hydroxycyclohexyl radical to cyclopentanecarbaldehyde by copper ions in aqueous solutions

Copper ions are known to catalyze the oxidation of cyclohexene by persulfate to yield cyclopentanecarbaldehyde. The mechanism suggested in the literature for this process involves the reaction of 2-hydroxycyclohexyl free radicals with Cu 2+ (aq). In the present study the kinetics of reaction of these free radicals with copper ions were studied by the pulse-radiolysis technique. The results indicate that the mechanism of the catalytic process involves the following reactions. The reaction of the free radical with Cu + (aq), and not with Cu 2+ (aq), yields the transient complex 1-cuprio-2-hydroxycyclohexane(1+). This transient complex rearranges in a reaction that involves the ring contraction step to form 6-hydroxy-7λ 2 -cuprabicyclo [3.2.0] heptane