Electro-organic reactions. Part 11. Mechanism of the kolbe reaction; the stereochemistry of reaction of anodically generated cyclohex-2-enyl radicals and cations
Cyclohex-2-enecarboxylate and cis-4-phenylcyclohex-2-enecarboxylate ions have been oxidised in methanol at a platinum anode. The products are markedly dependent on carboxylate concentration; at 0.4–1.0M two-electron oxidation and substitution to cyclohexenyl methyl ethers prevails whereas at higher concentrations substantial amounts of Kolbe dimers are formed (one-electron oxidation). For the cis-4-phenyl compound regio-and stereoisomeric products are formed by one- and two-electron oxidation. For one-electron oxidation (Kolbe) a comparison of the measured with the statistically predicted proportions of isomers leads to the conclusion that the intermediate cyclohex-2-enyl radical is stabilised by adsorption at the anode.