Stereoselective hydrogenation of (-)-menthone and (+)-isomenthone mixture using nickel catalysts

The catalytic hydrogenation of an optically active mixture of (-)-menthone and (+)-isomenthone was studied. The catalysts Raney nickel and Ni/SiO2 wer e used for these hydrogenations. Catalysts modified with (2R,3R)-(+)-tartar ic acid were tested as well. Various non-equilibrium mixtures of isomers we re produced by means of these reactions, especially mixtures containing the less stable menthol isomers, (+)-neomenthol and (+)-neoisomenthol. (-)-Men thol was produced during these reactions to a limited extent; the productio n of(-)-isomenthol was barely existent. Isomerization of (-)menthone and ()-isomenthone occurred during these reactions. Isomerizations among individ ual isomers were barely detectable. The catalysts used showed a very low ac tivity under the given reaction conditions.