CuO Immobilized Cellulose Paper as a Green Catalyst for the Acid/Base-Free Synthesis of Imines via a Nonconventional Approach

Abstract

Immobilization of 12 wt % of cupric oxide (CuO) nanoflakes (width 55−150 nm and length up to 235 nm) on fibers of cellulose in paper was conducted by an ultrafast (30 min only) microwave-assisted method at 80 °C without using any binder, linker, or retention aid. The synthesized material proves to be a highly efficient heterogeneous catalyst for the acid/base-free synthesis of imines by the nonconventional solvothermal method. The catalytic conversion of aromatic aldehydes (1 mmol) and aniline (1.5 mmol) was carried out within 60 min at 100 °C with only 2 mL of THF, resulting in 96% yield of N-benzylideneaniline with a moderate TON of 64. The product yield was estimated to be 23 and 72% when blank cellulose paper (without CuO) and CuO nanoflakes, respectively, were used, supporting the role of hydroxyl groups of cellulose in imine formation. The catalyst exhibited remarkable recyclability with 97% of its catalytic activity retained even after five consecutive cycles. Importantly, the catalyst was separated from the reaction mixture simply by using forceps without any filtration or centrifugation processes.