4-Phenylazo-3,5-pyrazolidinedione (13a). Red needles from methanol. Yield 70%; mp 278-279°C. IR
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spectrum, , cm–1: 3290, 3215 (NH), 1655 (C=O). H NMR spectrum, , ppm: 3.52 (1H, s, CH); 7.44 (5H, m,
13
Ar); 7.97 (2H, br. s, NH). C NMR spectrum, , ppm: 80.6, 122.3, 125.0, 129.1, 170.3. Mass spectrum, m/z (Irel,
%): 204 [M]+ (100), 197 (2), 194 (1.5), 176 (2), 169 (3), 145 (5.3), 127 (37), 107 (4), 105 (9), 93 (34), 92 (35),
78 (11), 77 (67), 64 (18), 65 (46.6). Found, %: C 53.12; H 4.21; N 27.36. C9H8N4O2. Calculated, %: C 52.94;
H 3.95; N 27.44.
4-(4'-Methoxyphenylazo)-3,5-pyrazolidinedione (13b). Dark-red needles from methanol. Yield 43%;
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mp 230-231°C. IR spectrum, , cm–1: 3450 (OH), 3350 (NH), 1640 (C=O). H NMR spectrum, , ppm: 3.42
(1H, s, CH); 3.73 (3H, s, CH3O); 6.91 (4H, m, Ar); 9.85 (2H, br. s, 2NH). 13C NMR spectrum, , ppm: 56.0,
80.6, 114.6, 123.3, 143.2, 159.4, 170.3. Mass spectrum, m/z (Irel, %): 234 [M]+ (75), 197 (2), 175 (3), 149 (2), 147
(3), 123 (21), 122 (100), 121 (14), 108 (14), 107 (9), 95 (13), 60 (44), 45 (68), 43 (79). Found, %: C 51.36;
H 4.25; N 22.82. C10H10N4O3. Calculated, %: C 51.28; H 4.30; N 23.92.
4-(2'-Nitrophenylazo)-3,5-pyrazolidinedione (13c). Red needles from methanol. Yield 80%; mp
309-310°C. IR spectrum, , cm–1: 3400 (OH), 3250 (NH), 1665 (C=O), 1550 (NO2). 1H NMR spectrum, , ppm:
3.41 (1H, s, CH); 6.60 (4H, m, Ar); 9.23 (2H, s, NH). 13C NMR spectrum, , ppm: 80.6, 115.9, 120.1, 123.3,
123.7, 143.8, 170.3. Mass spectrum, m/z (Irel, %): 249 [M]+ (20), 248 (100), 163 (21), 150 (5), 138 (39), 136
(10), 127 (71), 122 (16), 90 (12), 43 (37). Found, %: C 43.42; H 2.95; N 28.23. C9H7N5O4. Calculated, %: C
43.38; H 2.83; N 28.11.
4-(2'-Chlorophenylazo)-3,5-pyrazolidinedione (13d). Dark-red needles from methanol. Yield 84%;
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mp 280-281°C. IR spectrum, , cm–1: 3100 (NH), 1665 (C=O). H NMR spectrum, , ppm: 3.41 (1H, s, CH);
7.22 (4H, m, Ar); 9.62 (2H, s, 2NH). 13C NMR spectrum, , ppm: 82.4, 115.1, 122.3, 124.1, 125.1, 144.3, 170.4.
Mass spectrum, m/z (Irel, %): 238 [M]+ (100). Found, %: 45.41; H 3.15; Cl 14.75; N 23.53. C9H7ClN4O2.
Calculated, %: C 45.30; H 2.96; Cl 14.86; N 23.48.
Synthesis of Diethyl Arylazomalonate 14 (General Method). The aryl diazonium salts were prepared
by diazotization of the corresponding primary aromatic amines using sodium nitrite and hydrochloric acid. It
was coupled with the equivalent amount of diethyl malonate and the mixture was neutralized using sodium
acetate to give the required azo derivative. The dye was filtered off, washed with water, and dried.
Diethyl 2-Nitrophenylazomalonate (14a). Pale-yellow needles from ethanol. Yield 75%; mp 79-80°C.
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IR spectrum, , cm–1: 1715 (C=O), 1525 (NO2). H NMR spectrum, , ppm (J, Hz): 1.26 (6H, t, J = 6.7, 2CH3);
3.32 (1H, s, CH); 4.21 (4H, q, J = 6.7, 2CH2); 7.51 (4H, m, Ar). 13C NMR spectrum, , ppm: 22.1, 38.3, 54.0,
119.4, 123.2, 128.1, 171.4. Mass spectrum, m/z (Irel, %): 309 [M]+ (100). Found, %: C 50.52; H 4.72; N 13.65.
C13H15N3O6. Calculated, %: C 50.49; H 4.89; N 13.59.
Diethyl 2-Chlorophenylazomalonate (14b). Yellow needles from ethanol. Yield 73%; mp 60-61°C. IR
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spectrum, , cm–1: 1710 (C=O). H NMR spectrum, , ppm (J, Hz): 1.26 (6H, t, J = 6.4, 2CH3); 3.32 (1H, s,
CH); 4.25 (4H, q, J = 6.4, 2CH2); 7.62 (4H, m, Ar). 13C NMR spectrum, , ppm: 21.3, 38.1, 53.1, 122.0, 124.4,
130.2, 169.3. Mass spectrum, m/z (Irel, %): 298 [M]+ (43), 297 (69), 254 (11), 225 (35), 223 (79), 153 (18), 128
(21), 127 (61), 126 (60), 125 (100), 113 (15), 111 (38), 99 (56). Found, %: C 52.41; H 5.12; Cl 11.83; N 9.35.
C13H15ClN2O4. Calculated, %: C 52.27; H 5.06; Cl 11.87; N 9.38.
Synthesis of Arylazomalonic Acid Hydrazides (15) (General Method). The arylazo diethyl malonate
(0.01 mol) was dissolved in absolute ethanol (20 ml), the solution was treated with hydrazine hydrate
(0.03 mol), and the mixture was stirred for 2 h. The precipitated product was filtered off, washed with water, and
dried. It was crystallized from the proper solvent.
2-Nitrophenylazomalonic Acid Hydrazide (15a). Pale-yellow needles from methanol. Yield 98%; mp
258-259°C. IR spectrum, , cm–1: 3450, 3200 (NH2, NH), 1650 (C=O). 1H NMR spectrum, , ppm: 2.51 (1H, s,
CH); 7.93 (4H, m, Ar); 9.81 (4H, s, 2NH2); 13.76 (2H, br. s, 2NH). 13C NMR spectrum, , ppm: 38.2, 122.1,
124.3, 136.1, 172.1. Mass spectrum, m/z (Irel, %): 281 [M]+ (100). Found, %: C 38.51; H 4.01; N 34.77.
C9H11N7O4. Calculated, %: C 38.44; H 3.94; N 34.86.
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