A
1-l. three-necked round-bottomed flask is mounted on a steam cone and is fitted with a
250-ml. separatory funnel and a
reflux condenser connected to a trap (Note
1) for absorbing gases. In the flask is placed
325 g. (198 ml., 2.73 moles) of thionyl chloride (Note
2), and to it is added, during the course of 1 hour,
125 g. (0.58 mole) of l-menthoxyacetic acid (p. 544). The flask is shaken frequently during the addition of the acid and, if necessary, is warmed to start the reaction. When all the acid has been added (Note
3), the reaction mixture is refluxed gently for 5 hours. After the reaction is complete, the excess of
thionyl chloride is removed by distillation on the
steam bath (Note
4) and the residue is distilled under reduced pressure. The yield of
l-menthoxyacetyl chloride boiling at
117–120° /3 mm. (
120–125° /5 mm.),
[α]25D −89.6°, amounts to
115–118 g. (Note
5) (
85–87%). The product turns dark on standing; it should be stored in a
glass-stoppered amber bottle.