In a
1-l. round-bottomed flask provided with a
mechanical stirrer is placed
120 g. (0.4 mole) of crystallized sodium dichromate (or an equivalent amount of potassium dichromate), and to this is added a solution of
100 g. (54.3 cc., 0.97 mole) of concentrated sulfuric acid (sp. gr. 1.84) in 600 cc. of water. To this mixture
90 g. (0.58 mole) of menthol (crystals, m.p.
41–42°) is added in three or four portions and the mixture stirred (Note
1). Heat is evolved, and the temperature of the mixture rises to about 55° (Note
2). As soon as the reaction is complete the temperature falls. The oil is mixed with an equal volume of
ether, separated in a
separatory funnel, and washed with three
200-cc. portions of 5 per cent sodium hydroxide solution (Note
3). The
ether is then removed by distillation and the residue distilled under reduced pressure, the
menthone being collected at
98–100°/18 mm. If distilled under atmospheric pressure it boils at
204–207°. The yield is
74–76 g. (
83–85 per cent of the theoretical amount).