Diphenylcarbonat (120 g, (0.56 mol, 1.0 eq.) was dissolved in 200 mL of THF, and the rest of the DPC was washed with an additional 200 mL of THF. The reaction flask was left to react for 7-9 days at room temperature. Subsequently, the reaction mixture was filtered, and volatiles was removed under reduced pressure. The residue was dissolved in 400 mL of 5 % NaHCO3 and extracted three times with 300 mL of ethyl acetate (EtOAc). The water phase was adjusted to pH 3-4 with concentrated HCl and extracted three times with 300 mL of EtOAc. The organic phase was dried under Na2SO4 overnight. The solvent was removed under reduced pressure, and the high viscous gel was obtained as the raw product. The yield of the obtained product is 37.6 % (44.1 g).