2-Aminobenzonitrile (10.0 g, 84.6 mmol) and cyanoguanidine (7.12 g, 84.6 mmol) were heated and refluxed in 42 ml of aqueous 2N HCl solution for 2 hours. After the reaction was completed, 320 ml of deionized water and 53 ml of 2N NaOH aqueous solution were added to the yellow solution. To remove unreacted feedstock, the reaction mixture was treated with activated carbon and filtered through a short column filled with diatomaceous earth. The filtrate was cooled to 4 °C and 2,4-diaminoquinazoline precipitated as colorless needle-like crystals, which were filtered and recrystallized from water to give 2.90 g (21% yield) of the target product. Melting point: 154-155 °C (literature value: 255-257 °C).1H-NMR (250 MHz, DMSO-d6) δ (ppm): 7.94 (dd, J=8.2 Hz, 1.1 Hz, 1H, Ar-H), 7.47 (dd, J=8.3 Hz, 6.8 Hz, 1.2 Hz, 1H, Ar-H), 7.25 ( br, 2H, NH2), 7.18 (dd, J=8.4 Hz, 0.8 Hz, 1H, Ar-H), 6.99 (ddd, J=8.3 Hz, 6.8 Hz, 1.2 Hz, 1H, Ar-H), 5.98 (s, 2H, NH2).13C-NMR (75.4 MHz, DMSO-d6) δ (ppm): 162.4, 160.7, 152.4, 132.3, 124.1, 123.5, 119.7, 110.3. IR (cm-1): 3505 (s), 3389 (s), 3172 (s), 3083 (m), 2827 (w), 2744 (w), 2669 (w), 2272 (w), 1952 (w). 1690(s), 1658(s), 1633(s), 1574(s), 1512(s), 1482(s), 1418(s), 1380(s), 1341(m), 1286(s), 1253(w), 1184(w), 1157(m), 1131(w), 1080(m), 1029(m). 993(m), 940(w), 928(w), 889(m), 856(m), 798(m), 753(s), 678(m), 590(m). Elemental analysis (C8H8N4, Mr=160.18): calculated values C 59.99%, H 5.03%, N 34.98%; measured values C 59.94%, H 5.08%, N 35.13%.
