Diethyl Ether → 1,3-Dimethyl-2-[2-(1-phenyl-3-indazolyl)vinyl]1H-imidazo[4,5-b]pyrazinium p-toluenesulfonate

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A mixture of 1,2,3-trimethyl-1H-imidazo[4,5-b]-pyrazinium p-toluenesulfonate (1.67 g, 0.050 mole) and 3-formyl-1-phenylindazole (1.11 g, 0.050 mole) is heated together in acetic anhydride (15 ml) at reflux for 30 minutes. After chilling, ether (500 ml) is added and the solid which separates is filtered off and dried. Yield 1.92 g, (72%). After recrystallization from water the yield of dye is 0.55 g (41%).

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