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.