16865-11-5

2033-29-6

16865-11-5

The general procedure for the synthesis of 2,5,6-trichlorobenzimidazole using 5,6-dichloro-1H-benzo[d]imidazol-2(3H)-one as starting material was as follows: completely dry 5,6-dichloro-1,3-dihydro-benzimidazol-2-one (28.4 g, 0.14 mol) was suspended in trichlorophosphorus (POCl3, 75 mL). The reaction mixture was heated to reflux temperature, kept for 3 h and then cooled to room temperature. The reaction solution was slowly poured into crushed ice/water mixture (1.5 L) under vigorous stirring. The pH of the mixture was adjusted with sodium hydroxide (NaOH) solution to 7.0. The precipitated solid product was collected by filtration, washed with water and dried to afford 2,5,6-trichlorobenzimidazole (27.9 g, 90% yield). The crude product obtained can be used directly in the subsequent reaction without further purification.