To a stirred suspension of l-valine (46.8 g, 0.4 mol) in dry THF (400 mL) was slowly added a solution of phosgene (0.8 mol)in toluene (stock solution ca. 5 m). In the closed vessel (Author’s remark: It is better to use a reflux condenser cooled to at least -15 ℃ or a dry-ice reflux condenser under ambient pressure), the mixture was stirred at 45 ℃ for 7 h in order to obtain a clear solution. The solvent was then evaporated in vacuo at room temperature. The residue was redissolved in dry THF and this solution was concentrated to dryness. The crystalline residue was dried over CaCl2 in vacuo; yield 57.0 g (quantitative).
