l-Menthone (CAS NO.: ), with other names as (+)-, could be produced through the following synthetic routes.

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. is evolved, and the temperature of the mixture rises to about 55°. 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. 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).