Methane → Asparagine methyl ester isocyanate

0.35 mol diphosgene is added dropwise over 1 hour to a mixture of 0.28 mol of the methyl ester of asparagine and 0.4 g activated charcoal in 400 mL dioxane under N2. The reaction mixture is then heated and stirred at reflux for 21/2 hours. The reaction mixture is then cooled, filtered, and concentrated to dryness by rotary evaporator, keeping exposure to moisture to a minimum. The crude product is re-dissolved in 100 mL THF, and the pH of the solution is adjusted to 5.5-6.0 by addition of pyridine. The product mixture is again filtered, and the filtrate is fractionally distilled to give asparagine methyl ester isocyanate.