Effect of surface protonation on the voltammetric behaviour of para chlorobenzophenone on glassy carbon

Abstract

The electrochemical responses on carbon surfaces depend greatly on the surface structure, surface chemistry and pretreatment procedures [1, 2]. Recently the effect of acidic functional groups present on the glassy carbon electrode (GCE) surface on the voltammetric behaviour of aromatic carbonyl compounds was investigated [3]. In addition to the voltammetric peaks noted on mercury electrodes under identical experimental conditions, benzaldehyde [4], vanillin [5], benzophenone [6] and benzil [7] gave rise to an additional prepeak on GCE due to the reduction of the adsorbed surface protonated carbonyl group. The adsorption process was also found to correlate well with the basicity of the carbonyl compounds involved [3-7]. In this work one further question on the surface protonation effect is addressed. What happens if the aromatic carbonyl compounds contain another reducible function, which itself will not exhibit a protonation effect, such as an aromatic C -X function? Will this compound still exhibit the surface protonation effect? p-Chlorobenzophenone is a good candidate for addressing these questions. The voltammetric behaviour of this compound in aprotic solvents such as DMF on mercury is well documented [8]. Saveant et al., for example, have observed three distinct cathodic peaks at slow sweep rates [8]. Constant potential electrolysis beyond the first reduction potential region established the dehalogenation reaction. The second and the third one-electron stages correspond to the formation of anion radicals and dianions of benzophenone formed during the first reduction stage [8]. At high sweep rates, p-chlorobenzophenone itself formed anion radicals and dianions in two le steps without C-C1 bond cleavage [81.