Acetyl chloride → 4-Carbomethoxy-2-methylbutanoic acid

2-Methylglutaric acid (14.6 g.) and acetyl chloride (26 ml.) are heated in the steam bath for one hour. The mixture is concentrated to dryness in vacuo and the residue evaporated twice from toluene. The residue is dissolved in methanol (4.7 ml.), heated on the steam bath for one hour and concentrated to dryness. The residue is dissolved in a mixture of ether (17 ml.), dicyclohexylamine (16.7 ml.) and hexane (83 ml.). The crystalline salt is filtered, stirred and treated with boiling ethyl acetate (75 ml.). The insoluble material is filtered off, and the filtrate is concentrated to one-third volume and chilled. The crystals are filtered and dried to yield 11.3 g. of 4-methoxycarbonyl-2-methyl butanoic acid dicyclohexylamine salt, m.p. 97°-99°. The salt is converted to the free acid by treatment with Dowex 50.