Hydrochloric Acid → 5-Amino-1-(4-nitrophenyl)-4-(4-sulfophenylazo)pyrazole

Participants

Reaction Conditions

Reaction Steps

7.79 g (45 mmol) of sulfanilic acid was diazotized, 7.38 g (90 mmol) of sodium acetate was added, and the reaction mixture was allowed to agitate at 0 to 5° C. for a about 15 more minutes. Then, 9.2 g (45 mmol) of 5-amino-1-(4-nitrophenyl)-1H-pyrazole from Step 11.1 (dissolved in 20 mL of dimethyl-formamide) was added dropwise over a period of 30 minutes. During the addition, the reaction mixture assumed a yellow-brown color, and an increasingly thick suspension formed. The suspension was diluted with about 50 mL of cold water, and the reaction mixture was allowed to stand overnight at room temperature. The precipitate was then removed by suction filtration and washed with a small amount of cold water. The moist, crude product thus obtained (about 14 g) was then suspended in 100 mL of isopropanol, 10 mL (72 mmol) of triethylamine was added, and the mixture was heated at reflux. After about 30 minutes, the reaction mixture was cooled slightly, and to it was added dropwise 14.5 mL (112 mmol) of a 25% hydrochloric acid solution which produced a thick, ocher-yellow suspension. The suspension was cooled to 0 to 5° C. and the precipitate was removed by suction filtration and washed with a small amount of ethyl acetate. The residue was dried at 60° C. under vacuum. This gave 12.18 g (31.4 mmol), 69.7% of the theoretical) of 5-amino-1-(4-nitrophenyl)-4-(4-sulfophenylazo)pyrazole; melting point: 135-136° C. (decomp.).

Provenance & Evidence