Z-Menthoxyacetic acid

Z-Menthoxyacetic acid has been prepared only by the action of sodium menthoxide upon monochloroacetic acid.1... 

The aqueous layer is acidified, the crude Z-menthoxyacetic acid is extracted with a liberal amount of toluene, the extract is distilled to remove toluene and water, and the Z-menthoxyacetic acid is distilled under reduced pressure. The principal fraction, b.p. 160-170°/10 mm., is satisfactory for conversion to the chloride. The yield is 76-78%, based on the chloroacetic acid. The pure acid has b.p. 163-164 °/10 mm., m.p. 52-54°, and [ ]d — 91.5° (o = 2, 95% ethanol). 

Pure d-menthyl-Z-menthoxyacetate is hydrolyzed by refluxing for an hour with 1.2 mole equivalents of 5-10% ethanolic potassium hydroxide. (More vigorous hydrolysis is inadvisable since 1-menthol may thus be formed from the resolving agent by rupture of the ether linkage.) The mixture is almost neutralized to phenolphthalein with hydrochloric acid and is distilled with steam to remove first the ethanol and then the menthol. The menthol is conveniently extracted with benzene and purified by distillation under reduced pressure. It has b.p. 97-99°/10 mm., 215-2167760 mm. m.p. 42° and [aft0 + 49.5°(c = 2, 95% ethanol). The yield in this step is 80-85%. 

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