Abstract
1) The catalytic isomerization and racemi-zation of menthol isomers by means of copper chromite and Raney nickel catalyst were investigated.
2) Although Raney nickel catalyst was excellent in the racemization ability, copper chromite had be better used as the isomeri-zation catalyst.
3) In the case of catalytic isomerization and racemization the ketones, especially men-thone and isomenthone, showed considerable inhibitory action.
4) The equilibrium concentration in the catalytic isomerization corresponded to 52_??_53% menthol, 30_??_31% neomenthol, 12_??_13% isomenthol and 4_??_5% neoisomenthol at 200°C.
5) The isomerization of menthols by means of sodium mentholates was also studied. It was shown that the equilibrium menthol mixture was composed of 74_??_75% menthol, 8_??_9% neomenthol, 16_??_17% isomenthol and trace of neoisomenthol without any racemiza-tion.
6) From these data a free energy difference between equatorial and axial hydroxyl (or methyl) in menthols is calculated to be 0.5_??_0.6 Kcal./mole for hydroxyl and 1.4_??_1.5 Kcal./mole for methyl at 200°C.
