8
506 Dueke-Eze et al.
Asian J. Chem.
-
1
spectroscopic analysis was carried out using MultiRam FR-
Raman Spectrometer with Nd-YAG laser which lases in the
near infrared at 1064 nm equipped for the collection of fluore-
hexane). IR (ATR, νmax, cm ): 3434, 2925, 1613, 1589, 1463,
1377, 1278, 1256, 1148, 993, 915, 845, 790, 732,578; Raman
(solid/1064 nm): 3059, 1618, 1586, 1567, 1487, 1285, 1226,
1
13
1
1188, 1032, 994, 778, 664; H NMR (300 MHz, CDCl
scence-free Raman spectra. H and C NMR were recorded
on a Varian Mercury 300 MHz NMR spectrometer and the
chemical shifts are quoted relative to the solvent peaks.
3
H
) δ :
1
3
6.91-8.49 (m, 8H), 9.41 (s, 1H), 13.40 (s, 1H); C NMR (75
MHz, CDCl ) δ : 117.21, 118.93, 119.19, 120.44, 122.54,
33.44, 133.81, 138.45, 148.92, 151.51, 161.82, 164.70. Anal.
calcd. (%) for C12 O: C, 72.72, H, 5.05, N, 14.14. Found
%) C, 72.33, H, 5.03, N, 14.00.
3
C
1
Preparation of 4-amino-pyridine Schiff bases (IA-IIIA)
10 2
H N
N-(2-Hydroxylbenzylidene)pyridin-4-amine (IA): A
degassed mixture of 4-aminopyridine (75 mg, 8.0 mmol),
(
N-(5-Nitro-2-hydroxylbenzylidene)pyridin-2-amine
2
-hydroxybenzaldehyde (98 mg, 8.0 mmol.) and p-toluene
(
IIB): Yellow solid (0.22 mg, 46 %); m.p. 182-184 ºC (1:1,
-1
ethanol-hexane). IR (ATR, νmax, cm ): 3053, 1615, 1585, 1527,
sulfonic acid monohydrate (10 mg) in dry toluene (100 mL)
under nitrogen atmosphere was refluxed under Dean-Stark
conditions for 24 h. The solvent was removed under reduced
pressure and the residue recrystallized to afford IA as a deep
yellow solid (12.80 mg, 81 %); m.p. 76.5 °C (toluene). IR
1
6
9
7
δ
1
463, 1430, 1332, 1289, 1108, 1090, 992, 895, 829, 787, 706,
39; Raman (solid): 3051, 1631, 1579, 1557, 1463, 1332, 1215,
1
94, 792, 625; H NMR (300 MHz, CDCl
3
H
) δ : 7.10-8.54 (m,
13
H), 9.53 (s, 1H), 14.56 (s, 1H); C NMR (75 MHz, CDCl
: 117.79, 118.49, 120.51, 123.60, 128.90, 129.52, 131.63,
38.76, 149.25, 155.78, 162.89, 167.63. Anal. calcd. (%) for
: C, 59.26, H, 3.70, N, 17.28. Found (%): C, 59.14,
3
)
-
1
(
ATR, νmax, cm ) 1618, 1600, 1595, 1454, 1247, 1172, 1140,
C
8
1
40, 738; Raman (solid/1064 nm): 3059, 1618, 1585, 1502,
1
487, 1453, 1403, 1364, 1334, 1284, 1188, 993, 778, 663; H
12 9 3 3
C H N O
3 H
NMR (300 MHz, CDCl ) δ : 6.95-7.05 (m, 2H), 7.14 (d, J =
H, 3.56, N, 16.96.
N-(5-Bromo-2-hydroxylbenzylidene)pyridin-2-amine
6
.6 Hz, 2H), 7.46 (t, J = 15.6 Hz, 2H), 8.61 (s, 1H), 8.65 (d,
13
3
J = 5.4 Hz, 2H), 12.57 (s, 1H ). C NMR (75 MHz, CDCl )
(
IIIB): Light-orange crystal (0.45 mg, 80.94 %); m.p. 138-
δ
1
7
1
C
: 116.10, 151.15, 155.46, 117.50, 118.64, 119.45, 132.92,
-1
1
1
8
1
6
40 ºC (1:1, ethanol-hexane). IR (ATR, νmax, cm ): 2640, 1607,
582, 1461, 1431, 1381, 1341, 1271, 1179, 1073, 991, 915,
71, 812, 783, 739, 699, 624; Raman (solid/1064 nm): 3055,
10 2
34.37, 161.29, 165.68. Anal. calcd. (%) for C12H N O: C,
2.71, H, 5.08, N, 14.13. Found (%): C, 72.62, H, 5.02, N,
3.96.
609, 1589, 1550, 1446, 1310, 1276, 1226, 1184, 994, 785,
N-(5-Nitro-2-hydroxylbenzylidene)pyridin-4-amine
1
25; H NMR (300 MHz, CDCl
3
) δ
H
: 6.89-8.49 (m, 7H), 9.34
) δ : 110.60,
19.28, 120.35, 120.65, 122.99, 135.26, 136.36, 138.56,
49.05, 156.98, 163.40. Anal. calcd. (%) for C12 OBr: C,
(
IIA): Yellow solid (14.60 mg, 75 %); m.p. 193.7-194.1 ºC
13
(
s, 1H), 13.42 (s, 1H); C NMR (75 MHz, CDCl
3
C
-1
(toluene). IR (ATR, νmax, cm ): 1620, 1610, 1572, 1540, 1460,
1
1
5
9
1
6
1
7
8
1
440, 1396, 1326, 1178, 1100, 960, 930, 863, 827, 770, 720,
60; Raman (solid/1064 nm): 1610, 1590, 1561, 1461, 1341,
9 2
H N
1.98, H, 3.24, N, 10.10. Found (%): C, 51.96, H, 3.21, N,
.88.
1
213, 1096, 995, 626; H NMR (300 MHz, CDCl
3 H
) δ : 7.09-
.22 (m, 3H), 8.30-8.44 (m, 2H), 8.56 (s, 1H), 8.717 (t, J =
1
3
.4Hz, 2H), 10.01; C NMR δ: 115.94, 118.58, 119.04, 128.95,
29.30, 129.67, 131.63, 151.44, 164.14, 166.39. Anal. calcd.
RESULTS AND DISCUSSION
Synthesis: Condensation of 4-aminopyridine with substi-
(
9 3 3
%) for C12H N O : C, 59.26, H, 3.70, N, 17.28. Found (%):
tuted 2-hydroxybenzaldehydes, in dry toluene under Dean-
Stark conditions in the presence of p-toluene sulfonic acid as
catalyst afforded the corresponding air stable Schiff bases IA-
IIIA in good yields and high purity resulting in sharp melting
point values (Scheme-I). Attempted reactions in absence of
the catalyst or using ethanol as solvent led to complicated
mixture of products that were difficult to isolate by column
chromatography. Elemental analyses data also fit well the
composition suggested for the compounds (Table-1). Charac-
C, 58.96, H, 3.67, N, 17.06.
N-(5-Bromo-2-hydroxylbenzylidene)pyridin-4-amine
(
IIIA): Orange crystals (18.60 mg, 84 %); m.p. 139.5-140.2
-1
ºC (toluene). IR (ATR, νmax, cm ): 1614, 1560, 1543, 1471,
1
1
9
8
410, 1353, 1272, 1180, 1077, 915, 864, 626; Raman (solid/
064 nm): 3057, 1587, 1566, 1478, 1437, 1382, 1280, 1187,
1
94, 784, 665; H NMR (300 MHz, CDCl
3 H
) δ : 6.96 (d, J =
.7 Hz, 2H), 7.13 (d, J = 5.4Hz, 2H), 7.48-7.54 (m, 2H), 8.54
13
3
(s, 1H), 8.66 (s, 2H), 12.57 (s, 1H ); C NMR (75 MHz, CDCl )
1
teristic IR and H NMR peaks for the Schiff bases are listed in
Table-2. The IR spectra of the compounds show no presence
of the carbonyl stretch for the aldehydic group, but reveal the
δ
1
C
: 110.88, 116.05, 119.53, 119.97, 134.80, 136.93, 151.26,
9 2
54.93, 160.27, 164.382. Anal. calcd. (%) for C12H N OBr:
C, 52.01, H, 3.27, N, 10.11. Found (%): C, 52.16, H, 3.18, N,
.82.
-1
presence of an intense band in the region v 1614-1607 cm
due to imine group (C=N) stretching vibration. The IR absor-
-1
ption bands at ν ca. 1247-1326 cm in the spectra of these
9
Preparation of 2-amino- pyridine Schiff bases (IB-IIIB)
N-(2-Hydroxylbenzylidene)pyridine-2-amine (IB): A
solution of 2-hydroxybenzaldehyde (24.5 mg, 0.20 mmol) in
ethanol (10 mL) and two drops of formic acid were added to a
stirred solution of 2-aminopyridine (18.8 mg , 0.20 mmol) in
ethanol (10 mL). The reaction mixture was refluxed for 6 h
and then allowed to cool to room temperature. The resulting
precipitate was filtered and recrystallized to afford IB as a
yellow-orange solid (0.14 mg, 35 %); m.p. 63-64 ºC (1:1, ethanol-
compounds are due to the C-O stretching vibration of the
phenolic group. Despite the C-O stretching vibration, only the
IR spectrum of the 2-aminopyridine derivatives revealed the
-1
presence of the ν(OH) stretching vibration at 3438-3434 cm
typical of the phenolic -OH. The absence of the O-H band in
the IR spectra of the Schiff bases derived from 4-aminopyridine
compounds is probably the result of resonance stabilization
1
with the keto form of the compound. The H NMR spectra of