2.1 Synthesis of 2-naphthylhydrazine hydrochloride
To a suspension of 2-naphthylamine (800 mg, 5.59 mmol) in hydrochloric acid (6.0 M, 6 mL), a solution of sodium nitrite (NaNO2, 578 mg, 8.38 mmol) in water (1.2 mL) was slowly added under cooling conditions in a water-ice bath (addition time was 2 min). The reaction mixture was stirred in a water-ice bath for 1 h, followed by the slow addition of stannous chloride (SnCl2, 3.71 g, 19.56 mmol) (addition time was 5 min). The resulting suspension was continued to be stirred in a water-ice bath for 3.5 h, followed by filtration. The filter cake was washed sequentially with ice water (0°C, 4 × 8 mL), room temperature water (1 × 8 mL), ice ether (0°C, 2 × 4 mL), and ether/hexane (1:1, 2 × 4 mL) and hexane (2 × 5 mL). The solid was dried to give 690 mg of the target product (Rf = 0.7, 40% ethyl acetate/hexane unfolding agent, milky white solid, 63% yield).
1H NMR (DMSO-d6, 250 MHz, δ): 7.81 (m, 2H, ArH), 7.71 (d, J = 7.7 Hz, 1H, ArH), 7.49-7.19 (m, 4H, ArH).
MS-El+ m/z: 159.1 (M-HCl+1).
