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 were used for these hydrogenations. Catalysts modified with (2R,3R)-(+)-tartaric acid were tested as well. Various non-equilibrium mixtures of isomers were produced by means of these reactions, especially mixtures containing the less stable menthol isomers, (+)-neomenthol and (+)-neoisomenthol. (−)-Menthol was produced during these reactions to a limited extent, the production of (−)-isomenthol was barcly existent. Isomerization of (−)-menthone and (+)-isomenthone occurred during these reactions. Isomerizations among individual isomers were barely detectable. The catalysts used showed a very low activity under the given reaction conditions.