Competitive electrochemical deposition of barium salts of chloranil analogous anion radicals. Correlation with reactivity in homogeneous solution

Abstract

The reactions of the anion radicals of p-fluoranil ( p-FA), p-chloranil ( p-CA) and p-bromanil ( p-BA) with Mg 2+ or Ba 2+ (M 2+) were analyzed in homogeneous acetonitrile (AN) solution as well as on a platinum electrode surface. Using a stopped-flow method, the anion radicals of p-FA, p-CA and p-BA ( p-XA −) could be generated through the electron transfer between p-XA and decamethylferrocene (DMFc), so that the reactions with M 2+ could be followed easily in homogeneous solution. While the reactivity of p-XA − toward Mg 2+ was almost identical, the order of the reactivity was clearly determined to be p-CA −> p-BA −> p-FA − in the reactions with Ba 2+. Correlated with this reactivity, the prior formation of Ba 2+( p-CA −) 2 on the electrode surface was confirmed in the observation of the competitive electrochemical reactions. In particular, the transformation from Ba 2+( p-BA −) 2 into Ba 2+( p-CA −) 2 could be observed at the slower scan rate when the concentration of Ba 2+ was the same as the total amount of p-FA, p-CA and p-BA in AN solution.