Development of the enantioselective solid catalyst with high enantioselectivity

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Enantioselective solid catalyst is important for the syntheses of optically active compounds, which are important for the intermediates for the farmaceuticals or agrochemicals. This study aims at the development of the enantioselective solid catalyst with a high enantioselectivity and its high durability in the repeated use of the recovered catalyst. In this study, enantioselective catalyst was prepared by adsorbing (R,R)-tartaric acid and NaBr on a nickel surface (this process is called modification). Two types of modification methods have been developed, that is i)pre-modification (nickel catalyst is soaked in a solution of (R,R)-tartaric acid and NaBr, is washed by water, methanol and THF, and then uses for the hydrogenation reaction), and ii)in-situ-modification ((R,R)-tartaric acid and NaBr are added to the reaction media). The type of methods significantly influence the enantioselectivity and its durability.In this study, for comparing the features of the pre-modification and tho … More se of the in-situ-modification, effects of the pre-modification conditions in an aqueous solution and in an organic solvent were investigated. As the base nickel catalyst, reduced nickel was used. The reduced nickel was prepared by the reduction of nickel oxide (commercially available one or one prepared by the decomposition and calcinations of nickel hydroxide at 773 K or 1373 K) in a hydrogen stream. As a results, for the modification in an aqueous solution, the modified reduced nickel catalyst prepared from nickel oxide calcined at 1373 K gave the highest enantioselectivity of 88%. The coverage of tartaric acid and Br^- on the catalyst surface was 25% and 13%, respectively. The modified reduced nickel prepared from nickel oxide calcined at 773 K gave the enantioselectivity of 50%. The coverage of tartaric acid and Br^- on the surface was 17% and 16%, respectively. On the other hand, for the modification in an organic solvent (THF), it was revealed that the modification at a high temperature (373 K in an autoclave) and a high hydrogen pressure (9 MPa) were mandatory for attaining a high enantioselectivity and its high durability. In this case, the coverage of tartaric acid and Br^- on the surface was 30% and 38%, respectively. From these results, the coverage of tartaric acid on the surface, which was reported as a crucial factor for attaining a high enantioselectivity in the literature, was not the only factor for determining the enantioselectivity and the durability. The surface of nickel (the type of base nickel) was also very important for determining the enantioselectivity. It was also revealed that a high coverage of Br^- was important, especially for attaining a high durability of the enantioselectivity. Less