Catalytic oxidative synthesis of quinones and binaphthones over crystalline silica-supported Au- and Ru-based bimetallic catalysts Tumisang Lekgetho, Mabuatsela Maphoru 1 , Letlhogonolo Mabena 1 , Matshawandile Tukulula 2 1 Tshwane University of Technology, South Africa, 2 University of KwaZulu Natal, South Africa The catalytic oxidation of phenols and naphthols is an important goal in fine chemical synthesis [1]. The products obtained serve as central building blocks for many synthetic and natural products in the formation biologically active compounds [2]. Quinones and binaphthones play a very important role in pharmaceutical and cosmetic sciences [2]. In this study, the oxidation of phenols and 4-methoxy-1-naphthol were conducted by using crystalline silica supported bimetallic Ru-Bi, Au-Ru and Au-Bi nanocatalysts in different reaction conditions (Scheme 1, attached). The catalysts were synthesized by microwave-assisted loading (MW) and deposition (DP) methods and characterized for their physical and chemical properties using N 2 physisorption, XRD, SEM-EDX and TEM (Figure 1 attached)analysis . Trimethylhydroquinone and 4-methoxy-1-naphthol were tested over the prepared catalysts for oxidation reactions in methanol and/or nitromethane at room temperature and under reflux with hydrogen peroxide as an oxidant. In the oxidation of trimethylhydroquinone (1) [Scheme 1, attached] in MeOH at r.t and 60ºC over MW-Au-Ru catalyst, yields of 96.6% and 100% for trimethyl-1,4-benzoquinone were obtained, respectively. However, there was no reaction when MW-Au-Bi and MW-Ru-Bi catalysts were used under the same reaction conditions. When 4-methoxy-1-naphthol (3) was used as a substrate over MW-Au-Ru catalyst at r.t., yielded 33.8% (Conversion: 34%) and 50.8% (Conversion: 99 %) for binaphthone in MeOH and MeNO 2 , respectively. The selectivity of this reaction depends on the solvent, temperature and catalyst used.
Figure 1: TEM image of MW-Au-Ru/SiO2
Scheme 1: Catalytic oxidation of trimethylhydroquinone and 4-methoxy-1-naphthol. References 1. Adeyini, A.A. & Ajibebade, P.A. Bioinorg. Chem. Apl., 2018. 2. Soto-Hernandez, M., Palma-Tenanango, M. & Garcia-Mateos, M. London Tech, 2017.
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