Triethylamine → 5,6-Dichloro-1-(methylsulphonyl)-benzimidazole

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Reaction Steps

A solution of methanesulphonyl chloride (60 parts) in acetone (800 parts) was added dropwise to a suspension of 5,6-dichloro-benzimidazole (94 parts) in acetone (240 parts) containing triethylamine (50 parts). A precipitate of triethylamine hydrochloride was observed and the temperature rose to 40° C. The mixture was heated under reflux for 10 minutes and then stirred at room temperature for 20 hours. On pouring into cold water (4000 parts) a solid product precipitated out, which was filtered off, washed with water, dried and recrystallised from acetone (charcoal) to give 5,6-dichloro-1-(methylsulphonyl)-benzimidazole (61 parts) as pale yellow needles, melting point 191°-193° C.

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