(-)-Menthol → (-)-Isopulegol

Participants

Reaction Steps

In the middle of the column at a height of 331 cm, 900 g/h of liquid L-menthol of synthetic origin were fed to the dividing wall column in the feed section of the dividing wall, which had been obtained by catalytic hydrogenation of L-isopulegol over a nickel catalyst, and comprised 99.39 GC area % L-menthol, 0.29 GC area % isopulegol, 0.25 GC area % neomenthol and 0.011 GC area % isomenthol, and also 0.044 GC area % neoisomenthol. The column was operated at top pressure 50 mbar and a return rate of 3.0 kg/h. A pressure drop of about 35 mbar (±1 mbar) was established. At the top of the column, a temperature of 120° C. was measured, and in the bottom a temperature of 135° C. (±0.5 K). The column was operated without a bottom draw and the distillate withdrawal was adjusted by means of a balance control system to 15 g/h (±1 g/h). The reflux ratio was thus about 200:1. The condenser of the column was at a temperature of 40° C. in order to prevent solids formation.

Provenance & Evidence