4-Nitrophenol

Experimental procedure: Boc-Gly-OH (1.98 kg, 11.3 mol) and 4-nitrophenol (1.73 kg, 12.43 mol, 1.1 eq.) are dissolved in dry dioxane (25 L), a solution of DCC (2.8 kg, 13.56 mol, 1.2 eq.) in dry dioxane (10 L) is added and the mixture is stirred for 8-10 h. After cooling for 2 h, the precipitate is removed and the filtrate is used directly for next reaction without purification. The mixture of glycine (0.94 kg, 12.43 mol, 1.1 eq.) and NaHCO₃ (1.05 kg, 12.43 mol, 1.1 eq.) in H₂O (10 L) is slowly added to the solution of Boc-Gly-ONp in dioxane (25 L). The solution is stirred at about 25 °C for 7 h and then evaporated under reduced pressure. The residue is acidified to a pH 2-3 with 10% citric acid and extracted with EtOAc (3 × 20 L). The organic phase is successively washed with brine (20 L), dried, and evaporated to give Boc-Gly-Gly-OH (2.37 kg, 90%) as a white crystal.