Ammonia → HCID 86680256, Verbindung

A mixture of 26.6 g (100 mmol) of 2-(4-amino-6-tert-butylpyridin-3-yl)benzimidazole (employed as equimolar mixture with 2-tert-butylbenzimidazole as obtained from synthesis 18)) and 1 mol of the corresponding carboxylic acid chloride is heated for 8 to 40 h under reflux in the case of carboxylic acid chlorides which boil below 150° C. or at 150° C. to 180° C. in the case of carboxylic acid chlorides which boil above 150° C., until the 2-(4-aminopyridin-3-yl)benzimidazole derivative has reacted. The reaction mixture is allowed to cool to 80° C., optionally diluted with 100 ml of dioxane, then stirred into a mixture of 500 ml of conc. ammonia solution and 500 g of ice and stirred for a further 3 h. The solid is subsequently filtered off with suction, washed twice with 100 ml of water each time and dried in vacuo. The solid is taken up in 1000 ml of ethyl acetate, filtered through a short silica-gel column, rinsed with 500 ml of ethyl acetate, the ethyl acetate is removed in vacuo, and the brown residue is recrystallised from methanol. The solids obtained in this way are freed from low-boiling components and non-volatile secondary components by sublimation (p about 1×10−5 mbar, T about 180-220° C.). Purity according to 1H-NMR typically >99.5%.