Synthesis
2-Amino-3-chloroquinoxaline (2a) was synthesized as follows: 2,3-dichloroquinoxaline was used as starting material, and the reaction was carried out at 80 °C using the method modified by Saikachi and Tagami [1]. The procedure was as follows: 2,3-dichloroquinoxaline (8.0 g, 40.2 mmol) was dissolved in 60 mL of N-methyl-2-pyrrolidinone (NMP) and heated to 80 °C. While maintaining this temperature, ammonia was passed into the solution for 3 h. The reaction process was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the crude product was poured into 100 mL of water, the precipitate was collected by filtration, dried with CaCl2 and recrystallized by chloroform to give 4.8 g (63% yield) of light yellow crystals with a melting point of 150-158 °C (literature value 137-139 °C). Nuclear magnetic resonance hydrogen spectrum (1H-NMR, CDCl3) showed: δ1.85 (broad peak, 1H, 0.5H2O), 5.53 (broad single peak, 2H, NH2), 7.47 (triple peak, 3J = 8.3,6.8,4J = 1.7 Hz, 1H, H-6), 7.63 (triple peak, 3J = 8.3,6.8,4J = 1.4 Hz, 1H, H -7), 7.69 (multiple peaks, 3J = 8.3,4J = 1.5,5J = 0.5Hz, 1H, H-8), 7.86 (multiple peaks, 3J = 8.2,4J = 1.3,5J = 0.5Hz, 1H, H-5). NMR carbon spectrum (13C-NMR, CDCl3) showed δ 125.4 (CH-6), 126.1 (CH-8), 128.1 (CH-5), 130.6 (CH-7), 137.1,137.3 (Cq-4a, Cq-3), 140.3 (Cq-8a), 148.7 (Cq-2). Mass spectra (EI 70eV, 165°C) showed: m/z (%) = 181 (30) [M+ (37Cl)], 179 (100) [M+ (35Cl)], 144 (84), 117 (23), 102 (8), 90 (26), 44 (81). The water was removed by azeotropic distillation of toluene at atmospheric pressure and the residual toluene was removed under vacuum. Elemental analysis results: C8H6ClN3 (179.61 g/mol) Calculated values: C 53.50%, H 3.37%, N 23.40%; measured values: C 53.59%, H 3.40%, N 22.96%.
References
[1] European Journal of Medicinal Chemistry, 2001, vol. 36, # 3, p. 255 - 264
[2] Bulletin des Societes Chimiques Belges, 1988, vol. 97, # 11-12, p. 919 - 926
[3] European Journal of Organic Chemistry, 2009, # 27, p. 4655 - 4665
[4] Bulletin of the Chemical Society of Japan, 1998, vol. 71, # 5, p. 1125 - 1135
[5] Polyhedron, 2013, vol. 50, # 1, p. 101 - 111
