An improved synthesis of N-substituted-2-nitroanilines

Article abstract of DOI:10.1081/SCC-120022180

The reaction of 2-chloronitrobenzene with substituted amines/ anilines in the presence of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) gives N-substituted-2-nitroanilines in good to excellent yields (>75-90%).

Full text of DOI:10.1081/SCC-120022180

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An Improved Synthesis of N-Substituted-2-nitroanilines
S. M. S. Chauhan a , Ram Singh a & Geetanjali a
a Department of Chemistry , University of Delhi , Delhi, India
Published online: 19 Aug 2006.
To cite this article: S. M. S. Chauhan , Ram Singh & Geetanjali (2003) An Improved Synthesis of N-Substituted-2-nitroanilines,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:16,
2899-2906, DOI: 10.1081/SCC-120022180
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 16, pp. 2899–2906, 2003
An Improved Synthesis of
N-Substituted-2-nitroanilines
*
S. M. S. Chauhan, Ram Singh, and Geetanjali
Department of Chemistry,
University of Delhi, Delhi, India
ABSTRACT
The reaction of 2-chloronitrobenzene with substituted amines/
anilines in the presence of DBU (1,8-diazabicyclo[5.4.0]undec-
7-ene) gives N-substituted-2-nitroanilines in good to excellent yields
(>75–90%).
Key Words: N-Substituted-2-nitroaniline; DBU; Nucleophilic aro-
matic substitution.
The 2-substituted aminoanilines are important intermediates in the
synthesis of isoalloxazines, benzimidazoles, triazoles and other biologi-
cally active nitrogen heterocycles.[1–6] The reduction of N-substituted-
*Correspondence: S. M. S. Chauhan, Department of Chemistry, University
of Delhi, Delhi, India; E-mail: smschauhan@chemistry.du.ac.in or ramchem@
indiatimes.com.
2899
DOI: 10.1081/SCC-120022180
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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2900
Chauhan, Singh, and Geetanjali
2-nitroanilines (3) gives the 2-substituted aminoanilines in high yields,
however there is no general method for the synthesis of N-substituted-
2-nitroanilines. The reaction of 2-chloro/2-fluoronitrobenzenes with sub-
stituted amines/anilines (2) in the presence of bases like anhydrous
potassium acetate[6] or potassium fluoride[7] gives poor yields in vigorous
conditions.
Bicyclic amidine, DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) is an
excellentnon-nucleophilic base and has been used in a variety of organic
reactions.[8] The reaction of 2-chloronitrobenzene (1) with substituted
amines/anilines (2) in the presence of DBU at 80ꢀC for ꢁ1 h gave
N-substituted-2-nitroanilines (3) in good to excellent yield (79–92%)
(Sch. 1). The structures of 3a–w have been confirmed by various spectro-
1
scopic data including IR, H NMR, mass spectroscopy, and elemental
analysis.
To explore the scope of this reaction, a number of N-substituted-
2-nitroanilines have been prepared (Table 1). In all the cases,
the nucleophilic substitution was successful in good to excellent yield.
The formation of N-substituted-2-nitroanilines may be explained as the
reaction of DBU with substituted amines/anilines forms a charge transfer
complex I. The nitrogen bearing the negative charge attacks the ipso
carbon having the chlorine atom in 2-chloronitrobenzene (1) forming a
Meisenheimer type ꢀ-complex. The spontaneous decomposition of ꢀ-
complex eliminates the chloride ion forming DBU.HCl which is removed
by washing with water. The reactions were performed at moderate tem-
perature (80ꢀC) within 60 min in presence of DBU overcoming the diffi-
culty of high temperature (120–180ꢀC) and longer reaction time (48 h) in
the presence of other bases. The reaction of the sterically hindered
anilines (e.g., 2,6-dimethylaniline) and deactivated anilines (e.g., chloroa-
niline) also gave good yields (Table 1). The presentmethod is more useful
for the ester substituents in chloronitrobenzene. The reaction of
1-chloro-4-methoxycarbonyl-2-nitrobenzene (1n–w) with substituted ami-
nes/anilines (2) in the presence of DBU preferentially gave nucleophilic
substitution products 3n–w as compared to two products amide (4n–w)
NHR
Cl
o
DBU, 80 C
+
RNH2
R'
NO2
2
R'
NO2
3
1
Scheme 1.

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N-Substituted-2-nitroanilines
Table 1. N-Substituted-2-nitroanilines prepared.
2901
ꢀ
Entry
R
R0
Yield (%)
M.p.a (Lit. M.p.) C
3a
3b
3c
3d
3e
3f
C6H5
20-ClC6H4
H
H
H
H
H
H
H
H
H
H
H
H
H
86
79
83
80
78
78
77
81
84
80
84
90
92
92
89
91
90
88
84
89
81
85
84
76 (75.5)[9]
115 (116–117)[7]
30-ClC6H4
90 (89)[7]
40-ClC6H4
146 (145–146)[7]
20-CH3C6H4
40-CH3C6H4
20,60-diCH3C6H3
20-OCH3C6H4
40-OCH3C6H4
40-BrC6H4
76 (76)[10]
69 (69–70)[10]
3g
3h
3i
108 (106–107)[7]
82–83 (83)[10]
87–88 (89)[10]
3j
166–168 (167)[10]
3k
3l
20-COOCH3C6H4
CH3
155–156 (155–156)[11]
37–38 (37)[10]
53
3m
3n
3o
3p
3q
3r
3s
3t
CH2CH¼CH2
CH2(CH2)2CH3
CH2(CH2)8CH3
CH2(CH2)10CH3
CH2CH¼CH2
C6H5
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
COOC2H5
COOCH3
COOCH3
44
50
53
77
120
156
40-OCH3C6H4
C6H11
88
3u
3v
3w
40-CH3C6H4
CH2C6H5
104 (106)[9]
163
102
40-BrC6H4
aReferences.
Cl
+
CH3(CH2)3NH2
2n
H3COOC
NO2
1
KF or CH3COOK
o
120-180 C/ 24-48h
NH(CH2)3CH3
+
NH(CH2)3CH3
NO2
H3COOC
NO2
CH3(CH2)3NHOC
3n
4n
Scheme 2.

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2902
Chauhan, Singh, and Geetanjali
δ-
..
. .
.
.
.
.
+
N
δ
H
N
R
N
H
I
and nucleophilic substitution products (3n–w) in the presence of other
bases like KF and potassium acetate (Sch. 2). The formation of the amide
was confirmed by various spectroscopic data including elemental analy-
1
sis, IR, H NMR, and mass spectroscopy.
In conclusion, a mild and simple procedure for the synthesis of
N-substituted-2-nitroanilines has been developed in the presence of
DBU by nucleophilic aromatic substitution.
EXPERIMENTAL
Melting points were determined on a Thomas Hoover Capillary
melting point apparatus and are uncorrected. The purities of the com-
pounds were determined on silica-coated Al plates (Merck). Infrared
spectra were recorded on Perkin Elmer 1710 spectrophotometer and
1
ꢁmax are expressed in cmÀ1. H NMR spectra were recorded on Bruker
Avance 300 spectrophotometer (300 MHz) and the chemical shifts were
expressed in ppm. EIMS spectra were recorded on Joel SX 102/DA-6000
(6 kV, 10 mA) spectrophotometer.
General Procedure for Nucleophilic Substitution
A mixture of 2-chloronitrobenzene (0.1 mol), the amine/aniline
(0.1 mol) and DBU (0.1 mol) are heated at 80ꢀC for 1 h. The reaction
mixture was allowed to cool to room temperature and partitioned
between dichloromethane and water. The organic layer was dried over
anhydrous sodium sulphate and the residue was chromatographed on
silica gel (60–120 mesh), eluting with petroleum ether (b.p. 60–80ꢀC).
2-Chloronitrobenzene was eluted first, followed by the highly colored
(orange to red) product 3.

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N-Substituted-2-nitroanilines
2903
N-Allyl-2-nitroaniline (3m). IR (KBr): 3388, 3091, 2925, 2857, 1617,
1574, 1531, 1419, 1352, 1242, 1158, 1054, 995, 925, 855, 777, 648.
1H NMR (CDCl3): 3.91–3.99 (m, 2H, NCH2), 5.11–5.61 (m, 3H,
CH¼CH2), 6.87 (dd, 1H, 6-H, J ¼ 8.0 & 1.86 Hz), 7.12–7.25 (m, 2H,
H-4 & H-5), 7.98 (dd, 1H, 3-H, J ¼ 8.21 & 1.89 Hz), 8.12 (bs, 1H, NH).
MS m/z (% base): 178 (Mþ, 28), 177 (9), 161 (17), 148 (44), 137 (11), 132
(100), 120 (47), 105 (27), 41 (9). Anal. calcd. for C9H10N2O2: C, 60.67; H,
5.66; N, 15.72. Found: C, 60.14; H, 5.38; N, 15.79.
N-Butyl-4-methoxycarbonyl-2-nitroaniline (3n). IR (KBr): 3360,
2960, 1718, 1627, 1570, 1531, 1438, 1362, 1291, 1268, 1130, 1111, 973.
1H NMR (CDCl3): 1.00 (t, 3H, CH3, J ¼ 6.9 Hz), 1.20–1.80 (m, 4H,
2 ꢂ CH2), 3.20–3.50 (m, 2H, NCH2), 3.95 (s, 3H, OCH3), 6.90
d, 1H, 6-H, J ¼ 8.0 Hz), 8.19 (bs, 1H, NH), 8.25 (dd, 1H, 5-H,
J ¼ 8.0 & 2.0 Hz) and 8.91 (s, 1H, 3-H). MS m/z (% base): 252 (Mþ,
100), 251 (100), 221 (85), 209 (65), 208 (100), 193 (5), 192 (50), 177
(38), 151 (62), 120 (100), 103 (61), 91 (38), 77 (42), 41 (42). Anal. calcd.
for C12H16N2O4: C, 57.13; H, 6.39; N, 11.10. Found: C, 57.14; H, 6.38;
N, 11.09.
N-Decyl-4-methoxycarbonyl-2-nitroaniline (3o). IR (KBr): 3374, 3093,
2926, 1718, 1625, 1570, 1533, 1439, 1360, 1289, 1224, 1155, 1116, 977.
1H NMR (CDCl3): 0.91 (t, 3H, CH3, J ¼ 7.0 Hz), 1.15–1.91 (m, 16H,
8 ꢂ CH2), 3.51–3.60 (m, 2H, NCH2), 3.99 (s, 3H, OCH3), 6.89 (d, 1H,
6-H, J ¼ 8.0 Hz), 8.09 (bs, 1H, NH), 8.15 (dd, 1H, 5-H, J ¼ 8 & 2 Hz) and
8.81 (s, 1H, 3-H). MS m/z (% base): 336 (Mþ, 34), 319 (5), 301 (19), 233
(5), 209 (100), 193 (22), 177 (7), 104 (10), 55 (9), 44 (64). Anal. calcd. for
C18H28N2O4: C, 64.26; H, 8.38; N, 8.32. Found: C, 64.24; H, 8.40;
N, 8.33.
N-Dodecyl-4-methoxycarbonyl-2-nitroaniline (3p). IR (KBr): 3361,
3101, 2921, 2852, 1709, 1631, 1572, 1527, 14400, 1416, 1368, 1311,
1
1288, 1195, 1123, 919. H NMR (CDCl3): 0.88 (t, 3H, CH3, J ¼ 6.8 Hz),
1.26–1.45 (m, 20H, 10 ꢂ CH2), 3.31–3.38 (m, 2H, NCH2), 3.89 (s, 3H,
OCH3), 6.86 (d, 1H, 6-H, J ¼ 8.42 Hz), 8.04 (dd, 1H, 5-H, J ¼ 8.0 &
2.0 Hz), 8.11 (bs, 1H, NH), 8.88 (d, 1H, 3-H, J ¼ 1.89 Hz). MS m/z (%
base): 364 (Mþ, 22), 329 (19), 301 (5), 233 (5), 209 (100), 193 (23), 177
(10), 149 (12), 95 (7), 44 (42). Anal. calcd. for C20H32N2O4: C, 65.90; H,
8.84; N, 7.68. Found: C, 65.91; H, 8.82; N, 7.67.
N-Allyl-4-methoxycarbonyl-2-nitroaniline (3q). IR (KBr): 3382, 2962,
1712, 1626, 1565, 1514, 1436, 1329, 1300, 1219, 1163, 914. 1H NMR
(CDCl3): 3.95 (s, 3H, OCH3), 4.10–4.20 (m, 2H, NCH2), 5.20-5.60 (m,
3H, CH¼CH2), 6.90 (d, 1H, 6-H, J ¼ 8.0 Hz), 8.10 (dd, 1H, 5-H, J ¼ 8.0
& 2.0 Hz), 8.20 (bs, 1H, NH), 8.90 (s, 1H, 3-H). MS m/z (% base): 236
(Mþ, 72), 219 (11), 204 (36), 189 (73), 188 (55), 163 (43), 131 (100), 129

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2904
Chauhan, Singh, and Geetanjali
(80), 103 (40), 43 (83). Anal. calcd. for C11H12N2O4: C, 55.92; H, 5.12; N,
11.85. Found: C, 55.93; H, 5.14; N, 11.84.
4-Methoxycarbonyl-2-nitro-N-phenylaniline(3r). IR(KBr):3431, 1722,
1
1664, 1621, 1566, 1525, 1435, 1356, 1114, 844, 754. H NMR (CDCl3):
3.97 (s, 3H, OCH3), 6.99 (d, 1H, 6-H, J ¼ 7.99 Hz), 7.26–7.35 (m, 5H, N-
phenyl protons), 7.49 (d, 1H, 5-H, J ¼ 7.98 Hz), 8.01 (s, 1H, 3-H), 8.19
(bs, 1H, NH). MS m/z (% base): 272 (Mþ, 85), 256 (12), 255 (20), 241
(25), 213 (9). Anal. calcd. for C14H12N2O4: C, 61.76; H, 4.44; N, 10.28.
Found: C, 61.75; H, 4.43; N, 10.26.
4-Methoxycarbonyl-N-(40-methoxyphenyl)-2-nitroaniline (3s). IR (KBr):
3343, 2925, 1722, 1627, 1567, 1515, 1432, 1357, 1286, 1214, 1125,
1
819, 757. H NMR (CDCl3): 3.90 (s, 3H, OCH3), 3.95 (s, 3H, OCH3),
6.90 (d, 1H, 6-H, J ¼ 8.75 Hz), 6.92–7.20 (m, 4H, 20, 30, 50 & 60-H),
8.00 (d, 1H, 5-H, J ¼ 8 Hz), 8.18 (bs, 1H, NH), 8.95 (s, 1H, 3-H). MS
m/z (% base): 302 (Mþ, 5), 301 (76), 287 (5), 286 (22), 259 (15), 271 (5),
195 (10), 237 (12), 182 (14), 91 (7), 77 (7), 58 (35), 43 (100). Anal. calcd.
for C15H15N2O5: C, 59.40; H, 4.98; N, 9.23. Found: C, 59.38; H, 4.97;
N, 9.25.
N-Cyclohexyl-4-methoxycarbonyl-2-nitroaniline (3t). IR (KBr): 3337,
2930, 1713, 1623, 1568, 1525, 1438, 1364, 1270, 1218, 1152, 972, 760.
1H NMR (CDCl3): 1.20–2.40 (m, 11H, C6H11), 4.00 (s, 3H, OCH3),
7.00 (d, 1H, 6-H, J ¼ 8 Hz), 8.10 (bs, 1H, NH), 8.15 (d, 1H, 5-H,
J ¼ 8 Hz), 9.00 (d, 1H, 3-H, J ¼ 1.2 Hz). MS m/z (% base): 278 (Mþ,
6), 277 (21), 261 (7), 235 (63), 195 (14), 161 (26), 119 (8), 58 (28), 56
(25), 43 (100). Anal. calcd. for C14H18N2O4: C, 60.42; H, 6.51; N, 10.06.
Found: C, 60.42; H, 6.52; N, 10.04.
N-Benzyl-4-methoxycarbonyl-2-nitroaniline (3v). IR (KBr): 3368,
2927, 1714, 1624, 1566, 1530, 1438, 1354, 1297, 1250, 1221, 1192, 1116,
1
969, 757. H NMR (CDCl3): 3.95 (s, 3H, OCH3), 4.70 (d, 2H, NCH2,
J ¼ 5.8 Hz), 6.95 (d, 1H, 6-H, J ¼ 8.0 Hz), 7.40–7.45 (m, 5H, Ar-H), 8.10
(d, 1H, 5-H, J ¼ 8 Hz), 8.15 (bs, 1H, NH), 9.00 (s, 1H, 3-H). MS m/z (%
base): 286 (Mþ, 29), 285 (100), 237 (45), 236 (63), 208 (90), 179 (32), 105
(100), 91 (100), 77 (44). Anal. calcd. for C15H14N2O4: C, 62.93; H, 4.92;
N, 9.78. Found: C, 62.92; H, 4.93; N, 9.80.
N-(40-Bromophenyl)-4-methoxycarbonyl-2-nitroaniline (3w). IR (KBr):
3313, 3097, 2942, 1716, 1617, 1584, 1564, 1523, 1433, 1354, 1283, 1213,
1148, 1071, 963, 754. 1H NMR (CDCl3): 4.00 (s, 3H, OCH3), 6.90 (d, 1H,
6-H, J ¼ 8.0 Hz), 7.20–7.70 (m, 4H, 20, 30, 50, 60-H), 8.10 (d, 1H, 5-H,
J ¼ 8.1 Hz), 8.18 (bs, 1H, NH), 9.00 (s, 1H, 3-H). MS m/z (% base):
353 (M þ 2, 100), 351 (Mþ, 100), 271 (24), 334 (15), 318 (37), 245 (25),
226 (33), 194 (81), 166 (100), 139 (52). Anal. calcd. for C14H11N2O4Br: C,
47.88; H, 3.15; N, 7.97. Found: C, 47.86; H, 3.14; N, 7.95.

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N-Substituted-2-nitroanilines
2905
4-(N-Butyl)amino-3-nitro-N-butylbenzamide (4n). M.p. 121ꢀC. IR (KBr):
3352, 3286, 2929, 2864, 1628, 1553, 1523, 1469, 1355, 1266, 1226, 1153,
1
908, 722, 680. H NMR (CDCl3): 0.87–0.95 (m, 6H, 2 ꢂ CH3), 1.31–1.72
(m, 8H, 4 ꢂ CH2), 3.28 (q, 2H, CH2), 3.39 (q, 2H, CH2), 6.00 (bs, 1H,
NH), 6.83 (d, 1H, 5-H, J ¼ 9.03 Hz), 7.91 (d, 1H, 6-H, J ¼ 9.06 Hz), 8.22
(bs, 1H, NH) and 8.43 (d, 1H, H-2, J ¼ 1.68 Hz). MS m/z (% base): 293
(Mþ, 46), 292 (63), 275 (13), 249 (89), 237 (32), 220 (100), 193 (36), 176
(9), 147 (10), 119 (27), 91 (10), 41 (9). Anal. calcd. for C14H11N2O4Br: C,
47.88; H, 3.15; N, 7.97. Found: C, 47.86; H, 3.14; N, 7.95.
ACKNOWLEDGMENTS
We are thankful to CSIR and UGC, New Delhi, India for financial
support.
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Received in the UK October 25, 2002