Catalyst Selection over an Electrochemical Reductive Coupling Reaction toward Direct Electrosynthesis of Oxime from NO_x and Aldehyde

Abstract

Aqueous electrochemical coupling reactions, which enable the green synthesis of complex organic compounds, will be a crucial tool in synthetic chemistry. However, a lack of informed approaches for screening suitable catalysts is a major obstacle to its development. Here, we propose a pioneering electrochemical reductive coupling reaction toward direct electrosynthesis of oxime from NO x and aldehyde. Through integrating experimental and theoretical methods, we screen out the optimal catalyst, i.e., metal Fe catalyst, that facilitates the enrichment and C−N coupling of key reaction intermediates, all leading to high yields (e.g., ∼99% yield of benzaldoxime) for the direct electrosynthesis of oxime over Fe. With a divided flow reactor, we achieve a high benzaldoxime production of 22.8 g h −1 g cat −1 in ∼94% isolated yield. This work not only paves the way to the industrial mass production of oxime via electrosynthesis but also offers references for the catalyst selection of other electrochemical coupling reactions.

Efficient electrochemical coupling of nitrate and biomass-derived acetone to acetoxime at a high current density over a Zn/Cu hexagonal nanosheet catalyst

“…56 Moreover, the oxime cannot remain stable under acidic conditions and will decompose into ketone and NH 2 OH spontaneously. 51 Additionally, a higher adsorption of protons *H on the catalyst surface under acidic conditions facilitates the hydrogenation reduction of *CH 3 COCH 3 , resulting in the detection of only isopropanol (Fig. 4a).…”

“…It is worth noting that NH 2 OH was almost undetectable in the post-reaction solution (Fig. S35†) and NH 2 OH was unstable under alkaline conditions which decomposed into N 2 and NH 3 spontaneously, 51 suggesting that CN coupling occurred between the adsorbed *NH 2 OH and *CH 3 COCH 3 on the electrode surface, rather than *NH 2 OH desorbing into the solution to couple with acetone. To elucidate the cumulative effect of Zn introduction on *CH 3 COCH 3 , electrochemical studies were conducted using Zn/Cu/CF-6, CuNWs/CF, and Zn as working electrodes to evaluate the individual activity of e-ARR (Fig.…”

“…43 Since Jiao successfully constructed acetamide from CO and NH 3 using an electrocatalytic method over Cu-based catalysts, 44 the green synthesis of organonitrogen compounds using readily available carbon/nitrogen-containing small molecules under mild conditions has become an emerging field. 8,45–48 In the field of electrosynthesis of oximes, researchers have successfully synthesized cyclohexanone oxime, 49,50 benzaldoxime, 51 formaldoxime, 52 cyclopentanoxime, 53 and pralidoxime 42 from C-containing (cyclohexanone, benzaldehyde, formaldehyde, acetone, pyridine aldehyde) and N-containing (NO 3 − , NO 2 − , NO) small molecules as reactants. Although there has been some progress in the electrocatalytic C–N/CN field, this reaction typically entails multi-step elementary reactions, rendering it a complex catalytic system.…”

Synthesis of Hydroxylamine via Ketone-Mediated Nitrate Electroreduction

“…Inspired by protective groups in organic synthesis and previous works in the electrosynthesis of NH 3 tuned by mediating the solvent of organic molecules, a viable route to mitigate HA overreduction is using molecular mediators to capture HA in situ and release it after electrolysis. , Electrosynthesis of cyclohexanone oxime (CH-O) through constructing CN bonds that are prone to hydrolysis between cyclohexanone (CH) and HA intermediates in situ generated by NO 3 – has been reported in the recent literature. − We hypothesize that ketone can act as a potential mediator for nitrate-to-HA electrosynthesis since it can transform active *NH 2 OH into nonactive oxime and produce HA as the final product over facile hydrolysis. In the search for the ketone candidates, water solubility and C–N condensation selectivity are critical factors.…”