Electrocatalytic synthesis of nylon-6 precursor at almost 100% yield.

Abstract

The application of the cyclohexanone-hydroxylamine process using preformed hydroxylamine is widespread in the caprolactam industry, a crucial step to produce nylon-6. However, with strict demands on sustainability and safety, two shortcomings in this process-harsh reaction conditions and the potential danger posed by explosive hydroxylamine-need to be urgently overcome. In this study, we presented a direct electrosynthesis method for cyclohexanone oxime using nitrogen oxides and cyclohexanone with almost 100% yield, which eliminated preformed hydroxylamine and demonstrated a simple strategy for green production of caprolactam. Combining theoretical calculations and in situ characterizations, the high efficiency of electrocatalysts is attributed to their ability to accumulate adsorbed hydroxylamine and cyclohexanone. Fe electrocatalysts can meet the above requirements and achieve a production rate of 55.9 g h-1 gcat-1 in a flow cell with almost 100% yield of cyclohexanone oxime. Beckmann rearrangement of the resulting cyclohexanone oxime produced 8.6 g/cycle of caprolactam. This study not only provides a theoretical basis for electrocatalyst design for C-N coupling reactions but also illuminates the tantalizing possibility to upgrade the caprolactam industry toward safety and sustainability through direct electrosynthesis of cyclohexanone oximes.