Electrochemical analysis on the effect of ionic environment change on interfacial reaction kinetics

•We describe electrochemical analysis of interfacial organic reactions.•We demonstrated that the interfacial reactions were strongly affected by the ionization status of background molecules.•The direct interaction between the reactant and the background molecules is suggested as a governing mechanistic factor.

Electrochemical approaches provide useful tools for studying interfacial reactions. Interfacial reactions are often controlled by various factors in a different manner from that of bulk reactions. Understanding these differences is important for many applications. Particularly, the acid–base properties play a significant role in determining the characteristics of the surface and the reactions that take place on the surface. We investigated how the protonation and deprotonation of the surface-confined acid affected the interfacial Diels–Alder reaction occurring on gold electrode using cyclic voltammetry. The rate of Diels–Alder reaction showed a negative correlation to the extent of surface ionization, showing a response similar to a titration curve. The half maximum rate was observed at pH 7, which agreed with the pKa of surface-confined carboxylic acid. Subsequent investigation suggested that this dependence is likely due to the direct interaction of H-bonding between quinone and the surface-confined acid rather than the field effect.