[2-(5-Benzylamino-3-bromo-4-nitropyrazol-1-yl)ethyl]carbamic acid tert-butyl ester → Hydrogen Bromide

A mixture of [2-(5-benzylamino-3-bromo-4-nitropyrazol-1-yl)ethyl]carbamic acid tert-butyl ester (2.1 g; 4.76 mmol) in EtOH (100 ml) containing a 5% Pd/C catalyst (Engelhard type, 50% moisture, 0.4 g wet weight) was hydrogenated in an autoclave (250 ml) at 15 bar for 3 h. The catalyst was filtered off under an inert atmosphere and washed with EtOH, and the filtrate was recovered in an ethanolic solution (25 ml) containing hydrobromic acid (47%, 2 ml). The orange-colored solution was evaporated to dryness to give the 2-(2-aminoethyl)-2H-pyrazole-3,4-diamine in the hydrobromide form (3.55 HBr) as a pale pink solid (1.5 g, 92%).