Glycerol: An Optimal Hydrogen Source for Microwave-Promoted Cu-Catalyzed Transfer Hydrogenation of Nitrobenzene to Aniline

Abstract

The search for sustainable alternatives for use in chemical synthesis and catalysis has found an ally in non-conventional energy sources and widely available green solvents. The use of glycerol, an abundant natural solvent, as an excellent "sacrificial" hydrogen source for the copper-catalyzed microwave (MW)-promoted transfer hydrogenation of nitrobenzene to aniline has been investigated in this work. Copper nanoparticles (CuNPs) were prepared in glycerol and the efficacy of the glycerol layer in mediating the interaction between the metal active sites has been examined using HRTEM analyses. Its high polarity, low vapor pressure, long relaxation time, and high acoustic impedance mean that excellent results were also obtained when the reaction media was subjected to ultrasound (US) and MW irradiation. US has been shown to play an important role in the process via its ability to enhance CuNPs dispersion, favor mechanical depassivation and increase catalytic active surface area, while MW irradiation shortened the reaction time from some hours to a few minutes. These synergistic combinations promoted the exhaustive reduction of nitrobenzene to aniline and facilitated the scale-up of the protocol for its optimized use in industrial MW reactors.

Copper(0) nanoparticle catalyzed Z‐Selective Transfer Semihydrogenation of Internal Alkynes

“…The use of MW irradiation (Milestone MicroSynth, constant power: 120 W) greatly improved reaction performance, and 90 min were sufficient for reaction completion. As already observed in our previous studies, simultaneous irradiation with MW (2.45 GHz, 90 W) and US (20.3 kHz, 40 W) is able to enhance heat and the mass transfer, as well as catalyst deagglomeration, leading to improved reaction rate and selectivity [22a] . US significantly influenced Cu(0) nanoparticles with smaller size and narrower particle size distribution.…”

Impact of Microwaves on Organic Synthesis and Strategies toward Flow Processes and Scaling Up

“…Reduction by transfer hydrogenation has addressed this limitation, and recently, an example of the copper-catalyzed (Cu(0) nanoparticles) reduction of nitrobenzene in glycerol was described in MW large batch mode ( Scheme 10 ). 70 Because glycerol is a biobased and eco-friendly solvent with a high MW adsorption capacity and a low vapor pressure, and because the reaction demanded a high temperature, a large-scale synthesis of the MW batch mode was studied. The reaction was performed on an almost 1 L scale in a pilot MW reactor in 95% yield, and the study demonstrated that the sample temperature in the reaction mixture was between 130 and 115 °C, with a high absorbance of delivered MW power when the power was maintained constant ( Figure 5 ).…”

Microwave-assisted catalysis of water-glycerol solutions for hydrogen production over NiO/zeolite catalyst

“…It appears that the glycerol conversion increases significantly with the increase in NiO loading level and MAC power. In this reaction, glycerol also acts as an excellent “sacrificial” hydrogen source [ 47 ]. Additional nickel content on the zeolite support surface can improve the catalytic activity at the lower reaction temperature.…”