Facile Catalysis Using Glycol-Reduced Bentonite/Metal Nanoparticles as a Novel Heterogeneous Catalyst for the Hofmann Degradation of Amides to Amines

Abstract

The Hofmann degradation reaction converts amides into primary amines, which are essential intermediates in various industrial processes. In this study, we investigate the use of bentonite-supported metal nanoparticles (NPs)—specifically ruthenium and copper–as catalysts for the Hofmann degradation of benzamide to phenylamine. The metal nanoparticles were synthesized via a glycol reduction method, allowing precise control over their size and distribution. Bentonite was chosen as the support material due to its high surface area and cation exchange capacity, which enhance the dispersion and stability of the metal nanoparticles. The successful synthesis of Ru and Cu nanoparticles was confirmed through X-ray photoelectron spectroscopy (XPS), with binding energy values of 283 eV for Ru3d_5/2 and 933 eV for Cu2p_3/2, indicating the presence of metallic Ru and Cu. This confirms the effective reduction of metal ions to their elemental forms. We then conducted the Hofmann degradation of benzamide using bentonite alone, bentonite supported with copper nanoparticles (Bent/Cu-NPs), and bentonite supported with ruthenium nanoparticles (Bent/Ru-NPs) prepared via the glycol reduction method. Notably, Bent/Ru-NPs achieved a reaction efficiency of 62% within approximately 1.5 h at a catalyst dosage of 0.005 g. Additionally, Bent/Ru-NPs demonstrated catalytic stability over four consecutive cycles, maintaining significant activity.