Electrochemical reduction of acetonitrile to ethylamine

Abstract

Electrifying chemical manufacturing using renewable energy is an attractive approach to reduce the dependence on fossil energy sources in chemical industries. Primary amines are important organic building blocks; however, the synthesis is often hindered by the poor selectivity because of the formation of secondary and tertiary amine byproducts. Herein, we report an electrocatalytic route to produce ethylamine selectively through an electroreduction of acetonitrile at ambient temperature and pressure. Among all the electrocatalysts, Cu nanoparticles exhibit the highest ethylamine Faradaic efficiency (~96%) at −0.29 V versus reversible hydrogen electrode. Under optimal conditions, we achieve an ethylamine partial current density of 846 mA cm−2. A 20-hour stable performance is demonstrated on Cu at 100 mA cm−2 with an 86% ethylamine Faradaic efficiency. Moreover, the reaction mechanism is investigated by computational study, which suggests the high ethylamine selectivity on Cu is due to the moderate binding affinity for the reaction intermediates.

C-N triple bond cleavage via trans-membrane hydrogenation

“…Further, as the reaction onset is limited by the Pd hydrogenation potential, it is possible to carry out the reaction before the thermodynamic potential for the hydrogen evolution reaction is reached. This offers a substantial advantage over a conventional electrosynthetic scheme where, for example, onset potentials for a variety of metallic catalysts were on the order of -0.3VRHE 17,18 , with our work offering an improvement of 0.7V over this value.…”

“…S3). This is a remarkable improvement as recent screening of various metallic catalysts indicated that their onset of catalytic activity for acetonitrile hydrogenation is ~0.7V more negative than this 17,18 . We noted that if instead of using 'wet' acetonitrile with 60mM H2O present we added in 0.2% (V:V) 0.5M H2SO4, our partial current density more than doubled.…”

“…There is a substantial body of literature that deals with conversion of acetonitrile to amines through thermal catalysis with H2 [12][13][14][15][16] , while electrochemical routes which derive hydrogen directly from water and are thus more sustainable are not yet as prominent. Recently, Cu has been shown to be effective in generating ethylamine as a product in alkaline 17 or neutral 18 electrolytes. Earlier works detected ammonia and ethane from acetonitrile reduction on Pt in acidic electrolytes 19,20 A significant challenge in this direction is minimizing the competing hydrogen evolution reaction (HER) and completely hydrogenating acetonitrile and cleaving the C≡N bond.…”

“…Further, as the onset potential was determined by that of the Pd hydrogenation, we have demonstrated an improvement of ~0.7V over the previous state-of-the-art systems utilizing a conventional electrochemical approach. 17,18 An innovative infrared spectroelectrochemical setup was further utilized to probe the catalytic system as it functioned and extract out key mechanistic insights dictating the reaction process. It was determined that the reaction proceeds rapidly through a imine hydrolysis like pathway and the hydrogenation of the latent NHx species on the Pd surface is the slowest step in the reaction cycle.…”

An Electrochemical Ethylamine/Acetonitrile Redox Method for Ambient Hydrogen Storage

“…1 H NMR spectrum of the reaction product showed CH3CH2NH2 as a major product and minor fractions of (CH3CH2)2NH and (CH3CH2)3N side products (Fig. 1e) (18,19). This confirmed CH3CN can be effectively converted to CH3CH2NH2 via electrochemical hydrogenation.…”