Oxidative Coupling of 2‐Methyl‐1‐naphthol: A Comparison between Bismuth‐Promoted Pt, Pd and Ag Catalysts

Abstract

Catalyst development for the oxidative coupling of naphthols is important for the synthesis of biomimetic compounds and pharmaceuticals. Carbon supported 5%M‐5%Bi catalysts (M=Pt, Pd, Ag) were prepared by electroless deposition. The resulting nanocomposites were characterized by N2 physisorption, XRD, SEM, HRTEM, EDX and TGA. Narrow particle size distributions of the noble metals were obtained, corresponding to an average particle size of 3.1–3.2 nm. Oxidative coupling of 2‐methyl‐1‐naphthol with H2O2 as the oxidant was the test reaction. The catalyst activities increase in the order Ag < Pd ≪ Pt. The outcome of the reaction depends on M, the solvent and the reaction temperature. Over Pt and Pd the binaphthol (3,3’‐dimethyl‐1,1’‐binaphthalenyl‐4,4’‐diol) can be obtained with yields of 89–94% in refluxing nitromethane. Under otherwise identical conditions, Ag gives the binaphthone (3,3’‐dimethyl‐1,1’‐binaphthalenylidene‐4,4’‐dione) with an isolated yield of 80%. The results show that apart from the solvent and the reaction temperature, also the choice of the catalytic metal can have an important influence on the outcome of the reaction.