2.2 Synthesis of mono-azo sulfonamide derivatives
In step-1 10 mL of dil. HCl, 2 mmol of substituted aromatic amine F (Sulfamethiazole) and P (sulfapyridine) was dissolved. The reaction mixture was cooled to 0–5°C. On the other hand, sodium nitrite (2 mmol) was dissolved in 2 mL of Conc. H2SO4 in a round bottom flask. To this added previously prepared amine solutions drop by drop individually and reaction mixture with mechanical stirring for about 2 hours. Completion of diazotization was monitored using starch-iodide paper as an external indicator. (Starch iodide paper is that it can be used to control diazotization reactions. Diazotization reactions include Sandmeyer's reaction). [36, 37]
In Step-2 N, N-diethyl-3-methylaniline, 3-(diethylamino) phenol and Thiobarbituric acid were dissolved in 10 mL of alkaline / alcoholic KOH. The reaction mixture was cooled to 0–5°C, and diazotized amine F (1–2) and P (1–2) were added slowly with constant stirring maintaining the temperature at 0–5°C and pH between 4–5 using saturated sodium bicarbonate solution. After additional stirring for 30 min., the precipitate was filtered, washed with water and dried over anhydrous CaCl2 in a decicator. In Scheme 1, the synthesis routes used for novel sulfonamide mono-azo dyes are outlined.
Table 1 Molecular structures of the synthesized dye, melting point and yields.
![](https://myfiles.space/user_files/122228_c8a1650c59388082/122228_custom_files/img1704695315.png)
2.2.1.4-((4-(diethylamino)-2-methylphenyl)diazenyl)-N-(5-methyl-1,3,4-thiadiazol-2-yl) benzenesulfonamide (F1)
Orange solid, C20H21N6O2S2, Yield: 77% m.p. = 258–260°C. FT-IR (KBr) cm− 1 3420 (-NH) 2976 (Ar − CH), 1600 (N = N), 1375(C = N), 1256 (C–N). 1H NMR (400 MHz, DMSO-D6) δ 13.72 (s, 1H), 7.83 (dd, 4H), 7.63 (d, 1H), 7.54 (d, 1H), 6.59 (s, 1H), 3.41 (q, 4H), 2.58 (s, 3H), 2.43 (s, 3H), 1.11 (t, 6H). HR-MS (m/z) = 446.1329 [M + H]+ .
2.2.2. 4-((4,6-dioxo-2-thioxohexahydropyrimidin-5-yl)diazenyl)-N-(5-methyl-1,3,4-thiadiazol-2-yl)benzenesulfonamide (F2)
Orange solid, C13H15N7O4S3, Yield: 79% m.p. = 230–235°C. FT-IR (KBr) cm− 1 3420 (-NH) 2981 (Ar − CH), 1677 (N = N), 1347 (C = N), 1251 (C–N). 1H NMR (400 MHz, DMSO-d6) δ 12.57 (s, 2H), 7.76 (d, J = 1.8 Hz, 1H), 7.65 (s, 1H), 3.65 (s, 1H), 2.42 (s, 3H). HR-MS (m/z) = 426.0297 [M + H]+ .
2.2.3. 4-((4-(diethylamino)-2-hydroxyphenyl)diazenyl)-N-(pyridin-2-yl)benzenesulfonamide
Orange solid, C15H12N6O4S2, Yield: 74% m.p. = 225–227°C. FT-IR (KBr) cm− 1 3430 (-OH) 2818 (Ar − CH), 1595 (N = N), 1352 (C = N), 1265 (C–N). 1H NMR (400 MHz, DMSO-D6) δ 12.51 (s, 2H), 11.84 (s, 1H), 7.97 (d, 1H), 7.91 (d, 1H), 7.68 (d, 1H), 7.49 (d, 1H), 7.15 (d, 1H), 7.05 (t, 1H), 6.84 (t, 1H), 6.53 (d, 1H), 5.91 (s, 1H). HR-MS (m/z) = 405.0748 [M + H]+ .
2.2.4. 4-((4,6-dioxo-2-thioxohexahydropyrimidin-5-yl)diazenyl)-N-(pyridin-2-yl) benzenesulfonamide
Yellow solid, C21H23N5O5S, Yield: 75% m.p. = 230–235°C. FT-IR (KBr) cm− 1 3435 (-NH) 2966 (Ar − CH), 1600 (N = N), 1347(C = N), 1146 (C–N). 1H NMR (400 MHz, DMSO-D6) δ 14.14 (s, 1H), 11.97 (s, 1H), 7.98 (d, 1H), 7.91 (d, 1H), 7.75 (d, 1H), 7.71 (t, 1H), 7.44 (d, 1H), 7.16 (d, 1H), 6.85 (t, 1H), 6.53 (d, 1H), 6.00 (s, 1H), 3.45 (q, 4H), 1.13 (t, 6H). HR-MS (m/z) = 426.1902 [M + H]+ .