Toward the\nElectrostatic Catalysis of Nucleophilic\nSubstitutions: A Surface Chemistry Study of the Menshutkin Reaction

The catalysis of nonredox reactions by external electric\nfields\nis one of the most rapidly expanding areas of chemistry. The Menshutkin\nreaction, a classic example of bimolecular nucleophilic substitution\n(S<sub>N</sub>2), involves the conversion of a tertiary amine to a\nquaternary ammonium salt by coupling it with an alkyl halide. The\nreaction barrier of the Menshutkin reaction is theoretically predicted\nto be highly sensitive to the magnitude and direction of an external\nelectric field experienced by the transition state. In this study,\nwe investigate how near-surface electric fields can drive this prototypical\nnucleophilic substitution by examining the coupling of a diffusive\nredox-tagged tertiary amine with an electrode-tethered alkyl bromide\nunder a variable external bias. Our findings reveal a competition\nbetween electrostatically assisted reactions, solvent effects, and\nelectrochemically triggered side reactions involving radical intermediates.\nWe estimate that only about 5% of the coupling events are attributable\nto the external field, while the majority of the reaction products\noriginate from electrochemically generated radical intermediates.