Organic Syntheses, Coll. Vol. 1, p.340 (1941); Vol. 9, p.52 (1929).
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.
per cent of the theoretical amount).
On addition of the menthol
a black spongy mass forms which softens as the temperature rises and finally forms a dark brown oil.
The temperature may not reach 55°, in which case the mixture may be warmed gently with a small flame. If the reaction is slow in starting, gentle heating with a small flame is advantageous.
The oil, which is dark brown before washing with sodium hydroxide
, becomes light yellow. If three washings are not sufficient to remove the dark color another portion of sodium hydroxide
solution is used.
This preparation is referenced from:
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