Nickel Peroxide Nanoparticles as an Efficient Catalyst for Nitrile Hydration: Synthesis, Characterization, and Mechanistic Insights

Abstract

The catalytic systems NiCl2·6H2O, CuCl2·6H2O, and Fe(NO3)3·9H2O/NaOH/NaOCl (pH, 13) were investigated for the catalytic hydration of ten nitriles to their corresponding amides at room temperature. Benzonitrile was used as a model substrate to optimize reaction conditions, and nine additional substrates were selected to explore the reaction's scope. The resulting amides were obtained in moderate to high yields. Various parameters, such as yield (Y%), turnover (TO), and turnover frequency (TOF), were calculated to identify the most effective metal salt for maximizing amide yields. It was found that the NiCl2·6H2O/NaOH/NaOCl catalytic system exhibited the best catalytic performance, with a TOF of 15.8 h⁻¹. Consequently, the active species responsible for nitrile hydration was isolated and characterized as nickel peroxide nanoparticles, which were generated in situ. Characterization techniques included X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and zeta potential measurements. SEM and TEM images of the nickel peroxide samples revealed fine spherical-like
aggregates of NiO2 molecules with a nearly uniform particle size, ranging from 2 to 3 nm. The proposed mechanism involves the reaction of NiCl2·6H2O with NaOCl to produce NiO2 nanoparticles, which then react with the nitrile substrate to form the corresponding amides and NiO. The reaction continues until the substrate is fully consumed. The resulting NiO is recycled with excess NaOCl for further catalytic hydration reactions.