Electrochemical ammoxidation of aldehyde in an aqueous electrolyte offers a sustainable and promising way toward nitrile synthesis. Unfortunately, the reaction efficiency, especially for nitrile selectivity, is fundamentally restricted by the competitive reaction of direct aldehyde oxidation, which is initialized from the inevitable but uncontrollable hydration of aldehyde itself. Here, we present a salting-out effect, induced by the concentrated potassium cation (K+) in a bulk electrolyte, which can achieve highly efficient nitrile synthesis. Molecular dynamics simulations and spectroscopic investigations unveil that the high K+ concentration renders the reorientation of the H2O structure to govern the stronger K+-H2O ion-dipole interaction. Such solvent microenvironment regulation, in turn, weakens the H2O affinity to aldehyde, thereby suppressing the aldehyde hydration. As a result, the condensation of aldehyde and ammonia is favored to facilitate the nitrile production. Using benzaldehyde as the proof-of-concept substrate, the production of benzonitrile is significantly boosted in a concentrated 3.0 M K2CO3 electrolyte, affording a high selectivity up to 97.3% and a considerable yield rate of 177.4 μmol cm-2 h-1 when feeding 10 and 100 mM benzaldehyde, respectively. Such salting-out-induced selectivity improvement also exhibits good reaction durability and aldehyde universality, underscoring the great merit for sustainable chemical manufacturing.
Liu et al. (Wed,) studied this question.