2-Bromopentane → 3-Methylhexanoic acid

Sodium metal (42.0 g, 1.827 mol) was dissolved in absolute ethanol (500 ml) under argon atmosphere. Ethyl malonate (289.3 g, 1.806 mol) was added at a stretch to the solution with stirring. Further, 2-bromopentane (262.6 g, 1.738 mol) was added dropwise at first slowly and, after sodium bromide was precipitated, in such a rate that ethanol was slowly refluxed. After 3 hour reflux, the mixture was cooled to room temperature, and 50% aqueous potassium hydroxide solution (510 g) was added dropwise slowly. The mixture was again warmed slowly and refluxed for 4 hours. After distilling off ethanol, concentrated hydrochloric acid (500 ml) was added and the mixture was refluxed for one hour. The reaction mixture was cooled to room temperature, and extracted with ether (500 ml×3). The combined ether layers were washed with brine (200 ml×2) and dried over anhydrous sodium sulfate. After distilling off ether, the residue was heated at 180° C. until carbon dioxide was no longer generated. The resulting residue was distilled under reduced pressure to give dl-3-methylhexanoic acid (172 g, 1.323 mol, 76%, b.p.: 112°-113° C./15 mmHg).