Sulfuric Acid → t-Butyl 2-(6-amino-3-bromo-5-hydroxy-2-pyridylazo)-5-phenyl-3-thenoate

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Reaction Steps

A solution of t-butyl 2-amino-5-phenyl-3-thenoate (8.26 g; 0.03 mole) in 2:5 acid (120 ml) (see Example 1) was chilled to -2° C. and concentrated sulfuric acid (5 ml) was added at such a rate that the temperature did not exceed 2° C.; a solution of sodium nitrite (2.16 g) in water (5 ml) was added dropwise below 2° C. The resulting diazonium solution was stirred at -2° C. to +2° C. for 45 minutes, then added in a slow stream with magnetic stirring to a cold (below 5° C.) solution of 2-amino-5-bromo-3-pyridinol (Example 2-L) (5.67 g; 0.03 mole) in pyridine (30 ml) and 2:5 acid (90 ml). The dye solution was stirred at 0° to 5° C. for 1.5 hours, then the cooling bath was removed and the mixture stirred for an additional 30 minutes. After drowning in cold water (2.5 liters), the dye was collected on a filter, washed with water and dried to yield 14.7 g of material with only traces of impurities.

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