Cu–Pd/γ-Al₂O₃catalyzed the coupling of multi-step reactions: direct synthesis of benzimidazole derivatives

Abstract

Transfer hydrogenation and subsequent cyclization of o‐nitroaniline with alcohols, catalyzed by the title multifunctional catalyst, affords benzimidazole derivatives in high yields.

Heterogeneous Catalytic Synthesis of 2-Methylbenzimidazole from 2-Nitroaniline and Ethanol Over Mg Modified Cu-Pd/γ-Al2O3

“…From these results, it might be deduced that Cu-Pd bimetallic catalysts could effectively catalyze the formation of benzimidazoles from o-nitroaniline with ethanol. The higher activity of the Cu-Pd catalyst was attributed to the accompanying synergistic interaction between Pd and Cu by forming CuPd alloy compound [26]. Surprisingly the addition of alkali metal and alkaline earth metal could effectively promote the reaction and enhance the selectivity.…”

“…According to reported literature, Pd-Cu bimetallic catalysts were used in various reactions to improve the selectivity of target products such as the degradation of nitrates [30] and the steam reforming of methanol [31]. In our previous work [26], the superior catalytic performance of Cu-Pd/γ-Al 2 O 3 catalysts was attributed to the formation of the CuPd compound: The active component Cu promoted the dehydrogenation of alcohol to aldehyde, and at the same time, Pd promoted transfer hydrogenation of o-nitroaniline to o-phenylendiamine, the synergistic interaction between Pd and Cu makes the reaction proceed smoothly. Therefore, the enhancement of catalytic performance of the Mg-doped catalysts in this work might be related to the stimulative formation of the CuPd alloy.…”

“…In order to find an environmentally friendly, high efficiency, low cost, high atomic and economic method for the synthesis of benzimidazoles, various heterogeneous catalytic systems such as heteropolyacid catalysts [17], modified zeolite catalysts [18], complex metal oxide catalysts [19,20], supported noble metal catalysts [21][22][23], Cu-PMO catalysts [24] and photocatalytic systems over Pt-TiO 2 [25] were recently reported. In our recent work, the direct synthesis of benzimidazoles from 2-nitroaniline and alcohol in aqueous media catalyzed by Cu-Pd/γ-Al 2 O 3 solid catalyst was studied [26]. We reported a successfully coupled multi-step reaction including dehydrogenation (Scheme 1.…”

“…III) over a multifunctional heterogeneous catalyst (Scheme 1). The method used a cheaper and more readily available nitroaniline compound as a raw material for the reaction to achieve a simpler process and a substantial enhancement in the yields of desired products [26]. However, the activity of the catalyst was still low and the reaction took at least 12 h to ensure 100% conversion of 2-nitroaniline.…”

Bimetallic Nanoparticles in Alternative Solvents for Catalytic Purposes

“…Inorganic oxides and carbon-based supports generally facilitate the immobilization of metallic nanoparticles by impregnation, as well as their separation after the reaction and then their recycling. Li and co-workers synthesized CuPd BMNPs supported on γ-Al2O3 by the impregnation of Cu(NO3)2 and H2[PdCl4] [43]. Aqueous solutions of H2[PdCl4] and Cu(NO3)2 were successively added dropwise into the solution containing γ-Al2O3 in distilled water under vigorous stirring at 80 °C for 5 h. Then, the pH value was adjusted to 8-9 by the addition of an aqueous NaHCO3 solution.…”