Sustainable oxime production via the electrosynthesis of hydroxylamine in a free state

Abstract

Hydroxylamine (NH₂OH) is an important feedstock for oxime production. Coreduction of NO_x and aldehydes or ketones enables sustainable one-step oximation by utilizing in situ *NH₂OH intermediates but suffers from side reactions and reduced current density due to the presence of multiple reactants in one reactor. Here we decouple oximation into two steps, the electrochemical synthesis of free NH₂OH via nitrite (NO₂⁻) electroreduction and the aldehyde or ketone oximation chemical step, circumventing the negative effects (such as site blocking, aldehyde or ketone electroreduction, or crossover) encountered in one-step oximation. By using a Ketjen-black-supported iron phthalocyanine as the catalyst, we achieve an exceptionally high partial current density of free NH₂OH (j_NH2OH) of 262.9 mA cm⁻² (corresponding to productivity of 2.452 mmol cm⁻² h⁻¹) in neutral conditions at an industrially relevant current density of 500 mA cm⁻². By coupling NH₂OH electrosynthesis with subsequent oximation in two steps, nearly stoichiometric oximes are produced with high efficiency and broad applicability. This work paves the way toward a sustainable oxime industry.