Microwave-Assisted Reductive Amination of Aldehydes and Ketones Over Rhodium-Based Heterogeneous Catalysts

Abstract

Microwave (MW)-assisted reductive aminations of aldehydes and ketones were carried out in the presence of commercial and homemade heterogeneous Rh-based catalysts. Ultrasound (US) was used to improve dispersion and stability of metal nanoparticles, while commercial activated carbon and carbon nanofibers were used as supports. Moreover, various bio-derived molecules were selected as substrates, and aqueous ammonia was used as a cheap and non-toxic reagent. MW combined with heterogeneous Rh catalysts gave a 98.2 % yield in benzylamine at 80 °C with 10 bar H₂ for 1 h; and a 43.3 % yield in phenylethylamine at 80 °C and 5 bar H₂ for 2 h. Carbon nanofibers proved to be a better support for the metal active phase than simple activated carbon, since a limited yield in benzylamine (10.6 %) but a high selectivity for the reductive amination of ketones was obtained. Thus, raspberry ketone was converted to raspberry amine in a 63.0 % yield.

Keywords: Rh nanoparticles; enabling technologies; heterogeneous catalysis; microwave chemistry; reductive amination; sonochemical synthesis.