Electrosynthesis of the Nylon-6 Precursor from Nitrate and Cyclohexanone over a Rutile TiO2 Catalyst

Electrocatalytic reduction of nitrate (NO3-) to valuable organonitrogen compounds beyond ammonia is a promising strategy for mitigating the human-caused unbalance of the global nitrogen cycle. Herein, we present an electrochemical strategy for synthesizing cyclohexanone oxime (CHO), an important feedstock in nylon-6 production through hydrogenative coupling of NO3- and cyclohexanone (CYC) using a rutile titanium dioxide (R-TiO2) catalyst under ambient conditions. The CHO productivity achieved 127.3 mu mol cm(-2) h(-1) with a high Faradaic efficiency (FE) of 68.2% at a current density of 30 mA cm(-2). Moreover, the yield of CHO reached 98.2%. We demonstrated that the electrosynthesis of CHO operated through a tandem reaction mechanism involving the in situ generation of hydroxylamine (NH2OH) from NO3- reduction, followed by a spontaneous nucleophilic addition-elimination reaction between NH2OH and CYC. Additionally, we revealed that R-TiO2 exhibited a superior scaling relation with a high NH2OH generation rate and excellent CYC adsorption ability, which promoted CHO production. This electrochemical strategy was also effective for the synthesis of different oximes. Finally, we designed a coupling reaction system to realize the simultaneous production of CHO and CYC by combining cathodic NO3- reduction and anodic cyclohexane oxidation, demonstrating a greener and more economical approach. [GRAPHICS] .