Electrohydrodimerization of 2-cyclopenten-1-one in basic aqueous media on a mercury electrode

Abstract

The electrohydrodimerization of 2-cyclopenten-1-one in buffered aqueous solutions over the pH range 8.0−13.5 has been studied by polarography, cyclic voltammetry and controlled-potential electrolysis. A one-electron reduction process is always found which leads to the formation of the hydrodimer (1,1′-bicyclopentyl)-3,3′-dione. The voltammetric data show that the process follows two different radical-radical coupling pathways, depending on the pH of the solution. Both pathways are initiated by a one-electron reduction of 2-cyclopenten-1-one to give its radical anion. In the pH range 8.0−10.5, the final hydrodimer is formed via protonation of the radical anion to generate the neutral radical, followed by coupling of the radical anion with the neutral radical and further protonation of the resulting dimer anion. At pH>10.5, the same final hydrodimer is obtained via dimerization of the radical anion and subsequent protonation of the dimer dianion formed. The rate-determining step of each pathway depends on the experimental conditions employed.