Regioselective copper-catalysed amination of halobenzoic acids using aromatic amines

Article abstract of DOI:10.3184/030823407X255597

Copper dipyridine dichloride (CuPy₂Cl₂) has been found to be an efficient catalyst for the synthesis of N-arylanthranilic acids from ortho halobenzoic acids and aromatic amines under microwave irradiation. Some of the advantages of this method are high chemoselectivity, ease of operation, less reaction times and high yields. (61-98%).

Full text of DOI:10.3184/030823407X255597

JOURNAL OF CHEMICAL RESEARCH 2007
OCTObER, 587–589
RESEARCH PAPER 587
Regioselective copper-catalysed amination of halobenzoic acids using
aromatic amines
Mohan Babu Maradolla, Amaravathi Mandha and Chandra Mouli Garimella*
Department of Chemistry, National Institute of Technology, Warangal-506004 India
Copper dipyridine dichloride (CuPy2Cl2) has been found to be an efficient catalyst for the synthesis of N-arylanthranilic
acids from ortho halobenzoic acids and aromatic amines under microwave irradiation. Some of the advantages of
this method are high chemoselectivity, ease of operation, less reaction times and high yields. (61–98%).
Keywords: copper dipyridine dichloride, 2-halobenzoic acids, aromatic amines, ethylene glycol, microwave irradiation
Microwave-assisted organic synthesis (MAOS) continues
to affect synthetic chemistry significantly by enabling rapid,
reproducible, and scalable chemistry development.1 Numerous
reactions have been explored under microwave conditions,
some of which have been applied to medicinal chemistry and
the total synthesis of natural products.2 Microwave irradiation
is a convenient procedure for conducting reactions in minutes
that otherwise would require hours under traditional heating.3
The exploration of microwave chemistry has been of particular
interest to us. Here, we report a regioselective copper-
catalysed amination of halobenzoic acids using aromatic
amines under microwave irradiation. The method eliminates
the need for acid protection and produces N-arylanthranilic
acid derivatives in up to 98% yield. N-Arylanthranilic acids
have received considerable attention in recent years.4,5
The first direct synthesis of N-arylanthranilic acids from
2-chlorobenzoic acid was accomplished by Ullmann.6
Since then, various copper-catalysed amination procedures
suitable to ortho-chlorobenzoic acids have been used by
others.7 The palladium-catalysed amination of aryl halides
exhibiting free carboxylic acid groups in the meta or para
position has also been explored.8 N-Arylanthranilic acids
are usually prepared from 2-chlorobenzoic acids or via
coupling of anthranilic acid and arylhalides.9 A wide range
of 2-bromobenzoic acid derivatives are readily available,
by the oxidation of 2-alkyl-1-bromobenzenes10 or lithiation
of dibromobenzenes and subsequent treatment with carbon
dioxide.11 The drawbacks of cross-coupling procedures using
bromobenzoic acids are due to their limited tolerance of
functional groups to very high reaction temperatures and low
yields were reported with sterically hindered arylamines.12
Recently, Cu/Cu2O, CuPy2Cl2 catalysed amination procedures
suitable for ortho-halobenzoic acids have been described
under high temperature,13 and long reaction times. Microwave
irradiation gives good yields and shorter reaction times.
the absence of ethylene glycol. The yields were significantly
less when 2-methoxyethanol, diethyleneglycol, ethoxyethanol
and glycerol were employed. The optimised amination
procedure was then applied to a variety of arylamines and
halobenzoic acids to evaluate the synthetic potential of this
method (Table 1). Reaction of halobenzoic acid with aromatic
amines gave the corresponding N-arylanthranilic acids in
61–98% yields. Importantly, the copper-catalysed amination
proceeds with remarkable chemo- and regioselectivity because
only the bromide adjacent to the carboxylic acid moiety is
replaced. The most striking advantage of this method is that
this reaction can be conducted at ordinary pressure in the
presence of air. No inert atmosphere is needed for conducting
the experiment which is easy to operate and shorter. We also
observed that the yields are higher with ortho-iodobenzoic
acids. Amination of dibromobenzoic acid with aniline yielded
N-phenyl-5-bromo-anthranilic acid. Aryl halide bonds located
in the aniline ring are also not affected. N-(3-Chlorophenyl)-
and N-(3-bromophenyl) anthranilic acids were obtained
through cross-coupling of halobenzoic acids with 3-chloro
and 3-bromo-anilines. Comparison of the results obtained
with 4-substituted anilines reveals that incorporation of
electron-donating groups facilitates the amination reaction.
In particular, the formation of N-(4-nitrophenyl)anthranilic
acid, proved to be slow and substantial amounts of starting
materials were recovered after 24 h.
In conclusion, we have shown that amination of halobenzoic
acids using aromatic amines proceeds microwave irradiation
with copper dipyridine dichloride (CuPy2Cl2) as a catalyst.
The best results were obtained by heating the reaction mixture
to 300 W and holding this power for 20 min. It is also possible
to perform the reaction at a lower power of 200 W but to the
slight detriment of yield. The experimental procedure is very
simple and the yields are relatively high.
Experimental
General
Results and discussion
All materials were obtained from commercial suppliers and
used without further purification. Standard distilled water was
used throughout the study. Melting points were measured on
Electrothermal 9100. NMR spectra were recorded at 293 K on a 300
MHz spectrometer (1H NMR) and 75 MHz (13C NMR). All reactions
were carried out in air. All products are known and were characterised
by comparison of NMR data with that in the literature.13
Wereportahighlyregioselectivesyntheticprocedureproviding
convenient access to a range of N-aryl anthranilic acids
containing various functional groups through the Cu-catalysed
amination of 2-halobenzoic acids. Initially, we employed
CuPy2Cl2 as the catalyst in the reaction of 2-bromobenzoic
acid, and 1-aminopyrene, using n-butanol, 2-ethoxyethanol
and ethylene glycol as solvent. Further screening of bases
(Na2CO3, K3PO4, K2CO3) showed that the best results for the
synthesis of N-(1-pyrenyl) anthranilic acid, were obtained in
the presence of potassium carbonate and catalytic amounts of
dipyridine copper chloride in ethylene glycol under microwave
irradiation at 300 W for 20 min. Ethylene glycol acts as a
ligand in stabilising or solubilising the copper complex. A
control experiment revealed that no reaction was observed in
General procedure for amination of halobenzoic acids using copper
dipyridine dichloride (CuPy2Cl2) as a catalyst under microwave
irradiation.
A mixture of 1-aminopyrene (2.0 g, 9.3 mmol), 2-bromobenzoic acid
(1.75 g, 8.8 mmol), K2CO3 (9.3 mmol), copper dipyridine dichloride
(CuPy2Cl2) (1.0 mmol), and 3 ml of 2-ethylene glycol was placed in a
10 ml glass tube. The vessel was then sealed with a septum and placed
in microwave cavity. Initial microwave temperature of 75°C was used
and a power of 300 W. Once this was reached, the reaction mixture
was held at this temperature for 20 min. The reaction mixture was
stirred continuously during the reaction. After allowing the mixture
to cool to room temperature, the reaction vessel was opened and
* Correspondent. E-mail: gvpc_2007@yahoo.co.in
PAPER: 07/4798

588 JOURNAL OF CHEMICAL RESEARCH 2007
Table 1 CuPy2Cl2 catalysed amination of 2-halo bezoic acids using aromatic amines under microwave irradiation
Entry
Halobezoic acid
Amine
Product
Yield/%
b
a
c
CO H
2
1
70
71
88
X
H N
2
N
H
CO
2
H
CH
3
CH
CO
H
H
3
3
2
2
3
80
89
91
90
86
94
N
H
H
2
N
X
CO
H
2
OCH
OCH
CO
2
3
H
2
N
N
X
H
CO
2
H
CO H
2
CN
CN
4
64
75
89
H
2
N
X
N
H
CO
H
2
COOH
COOH
CO
H
2
H
2
5
6
61
62
72
82
88
81
H
2
N
N
X
H
CO
2
H
NO
2
NO
2
CO
H
2
N
N
X
H
CO
2
H
CO H
2
Cl
Cl
7
8
80
83
94
91
96
93
X
H N
2
N
H
CO
2
H
CO H
2
Br
Br
X
H N
2
N
H
CO H
2
CO H
2
9
88
79
91
91
94
96
H
2
N
N
X
H
CO
2
H
COOH
Br
Br
10
X
H N
2
N
H
CO H
2
CO H
2
11
72
87
98
X
N
H
NH
2
CO H
2
OCH
3
OCH
3
CO H
2
12
13
67
84
79
90
90
94
H
H
N
N
2
N
H
X
i Pr
i Pr
CO
2
CO
2
H
H
OCH
3
OCH
3
CO H
2
2
N
H
X
i Bu
i Bu
CO H
2
14
89
93
96
N
H
X
COOH
NH
2
COOH
X
(a) X =Cl, (b) X = Br, (c) X = I
PAPER: 07/4798

JOURNAL OF CHEMICAL RESEARCH 2007 589
1
the contents were poured into 30 ml of water to which decolourised
charcoal was added. The mixture was filtrated through Celite.
The crude product was obtained by precipitation upon acidification
of the filtrate with diluted HCl. The residue was dissolved in 100 ml
of 5% aqueous Na2CO3. The solution was filtered through Celite, and
N-(1-pyrenyl)anthranilic acid 14 (2.75 g, 8.2 mmol) was obtained in
93% yield as an off-white solid by precipitation as described above.
N-(2-tert-Butylphenyl)anthranilic acid (13): H NMR (300 MHz,
CDCl3) δ = 1.41 (s, 9H), 6.65 (dd, J = 7.0 Hz, 7.9 Hz, 1H), 7.15
(d, J = 8.6 Hz, 1H), 7.17–7.28 (m, 4H), 7.47–7.50 (m, 1H), 8.02 (d,
J = 8.1 Hz, 1H), 9.21 (bs, 1H). 13C NMR (75 MHz, CDCl3) δ = 31.3,
35.7, 110.0, 114.8, 116.7, 126.6, 127.6, 128.1, 129.8, 133.1, 135.9,
139.4, 147.1, 151.4, 173.7. M.p. 248°C
1
N-(1-Pyrenyl)anthranilic acid (14): H NMR (300 MHz, DMSO-
d6) δ = 6.94 (dd, J = 7.4 Hz, 7.4 Hz, 1H), 7.14 (d, J = 8.3 Hz, 1H),
7.43 (dd, J = 8.0 Hz, 7.4 Hz, 1H), 8.09–8.41 (m, 10H), 10.7 (bs, 1H).
13C NMR (75 MHz, DMSO-d6): δ = 114.2, 118.1, 122.0, 122.1,
124.8, 124.9, 125.4, 125.7, 125.8, 126.4, 126.7, 127.2, 128.0, 128.2,
131.4, 131.7, 133.6, 134.6, 135.2, 148.8, 172.7. EIMS m/z 337 (M + ).
Anal. calcd. for C23H15NO2: C, 81.88; H, 4.48; N, 4.15. Found: C,
81.63; H, 4.74; N, 4.32. M.p. 268°C
Product characterisation data13
N-Phenylanthranilic acid (1): 1H NMR (300 MHz, CDCl3) δ = 6.75
(dd, J = 7.9 Hz, 8.3 Hz, 1H), 7.13 (dd, J = 7.3 Hz, 8.6 Hz, 1H),
7.20–7.50 (m, 5H), 8.05 (d, J = 7.6 Hz, 1H), 9.33 (bs, 1H). 13C NMR
(75 MHz, CDCl3) δ = 111.0, 114.7, 117.8, 123.8, 124.7, 130.0, 133.2,
135.8, 140.9, 149.5, 174.3. M.p. 182°C
N-(4-Methyl phenyl)anthranilic acid (2): 1H NMR (300 MHz,
CDCl3) δ = 2.22 (s, 3H), 6.75 (dd, J = 7.9 Hz, 8.3 Hz, 1H), 7.13
(dd, J = 7.3 Hz, 8.6 Hz, 1H), 7.20–7.50 (m, 5H), 8.05 (d, J = 7.6
Hz, 1H), 9.33 (bs, 1H). 13C NMR (75 MHz, CDCl3) δ = 19.5, 111.4,
112.8, 114.8, 116.3, 125.1, 131.9, 133.0, 134.2, 148.9, 156.1, 170.2.
M.p. 191°C
Received 19 August 2007; accepted 16 October 2007
Paper 07/4798 doi: 10.3184/030823407X255597
References
N-(4-Methoxyphenyl)anthranilic acid (3): 1H NMR (300 MHz,
CDCl3) δ = 3.83 (s, 3H), 6.68 (dd, J = 7.3 Hz, 7.3 Hz, 1H), 6.93 (dd,
J = 8.6 Hz, 8.6 Hz 3H), 7.18 (d, J = 8.6 Hz, 2H), 7.26–7.32 (m, 1H),
8.0 (d, J = 8.6 Hz, 1H)), 9.60 (bs, 1H). 13C NMR (75 MHz, DMSO-
d6) δ = 55.2, 111.4, 112.8, 114.8, 116.3, 125.1, 131.9, 133.0., 134.2,
148.9, 156.1, 170.2. M.p. 207°C
1
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N-(4-Cyanophenyl)anthranilic acid (4): 1H NMR (300 MHz,
DMSO-d6) δ = 7.13 (ddd, J = 2.0 Hz, 7.1 Hz, 7.2 Hz, 1H), 7.47 (d,
J = 8.8 Hz, 2H), 7.61–7.68 (m, 2H), 7.78 (d, J = 8.8 Hz, 2H), 8.22
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119.5, 120.7, 121.5, 133.7, 135.1, 145.8, 147.9, 171.9. M.p. 201°C
N-(4-Carboxyphenyl)anthranilic acid (5): 1H NMR (300 MHz,
CD3OD) δ = 7.00–7.06 (m, 1H), 7.37 (d, J = 8.8 Hz, 2H), 7.56–7.59
(m, 2H), 7.98 (d, J = 8.8 Hz, 2H), 8.04 (d, J = 8.3 Hz, 1H), 9.91 (bs,
1H). 13C NMR (75 MHz, CD3OD) δ = 115.3, 116.2, 117.9, 119.6,
123.5, 131.2, 132.0, 134.1, 144.6, 145.6, 167.1, 169.7. M.p. 229°C
N-(4-Nitrophenyl)anthranilic acid (6): 1H NMR (300 MHz,
CD3OD) δ = 7.22 (dd, J = 7.1 Hz, 7.8 Hz, 1H), 7.50 (m, 2H), 7.68–
7.78 (m, 2H), 8.26 (d, J = 8.1 Hz, 1H), 8.36–8.36 (m, 2H). 13C NMR
(75 MHz, CD3OD) δ = 118.1, 118.2, 118.8, 122.2, 127.1, 133.7,
135.3, 142.6, 145.4, 150.0, 171.5. M.p. 220°C
2
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N-(4-Chlorophenyl)anthranilic acid (7): 1H NMR (300 MHz,
CD3OD) δ = 6.81 (dd, J = 7.6 Hz, 7.6 Hz, 1H), 6.97–7.01 (m, 2H),
7.08 (dd, J = 1.2 Hz, 8.8 Hz, 1H), 7.21–7.27 (m, 2H), 7.43 (ddd,
J = 1.7 Hz, 7.7 Hz, 7.9 Hz, 1H), 8.11 (dd, J = 1.7 Hz, 8.1 Hz, 1H).
13C NMR (75 MHz, CD3OD) δ = 112.5, 114.4, 117.2, 117.3, 127.4,
133.4, 134.0, 135.4, 151.7, 156.0, 172.4. M.p. 198°C
N-(4-Bromophenyl)anthranilic acid (8): 1H NMR (300 MHz,
CD3OD) δ = 6.81 (dd, J = 7.6 Hz, 7.6 Hz, 1H), 6.99–7.04 (m, 2H),
7.12 (dd, J = 1.2 Hz, 8.8 Hz, 1H), 7.29–7.32 (m, 2H), 7.48 (ddd,
J = 1.7 Hz, 7.7 Hz, 7.9 Hz, 1H), 8.11 (dd, J = 1.7 Hz, 8.1 Hz, 1H).
13C NMR (75 MHz, CD3OD) δ = 112.5, 114.4, 117.2, 117.3, 127.4,
133.4, 134.0, 135.4, 151.7, 156.0, 172.4. M.p. 211°C
1
N-(2-Naphthyl)anthranilic acid (9): H NMR (300 MHz, DMSO-
d6) δ = 6.85 (ddd, J = 2.0 Hz, 7.0 Hz, 9.0 Hz, 1H), 7.35–7.49
(m, 5H), 7.73 (d, J = 2.0 Hz, 1H), 7.79–7.90 (m, 3H), 7.98 (dd,
J = 1.7 Hz, 7.9 Hz, 1H), 9.90 (bs, 1H). 13C NMR (75 MHz, DMSO-
d6) δ = 113.1, 114.2, 115.9, 117.8, 122.2, 124.3, 126.4, 126.8, 127.5,
129.2, 129.7, 131.9, 134.0, 134.2, 138.3, 146.7, 170.0. M.p. 231°C
N-Phenyl-5-bromoanthranilic acid (10): 1H NMR (300 MHz,
CD3OD) δ = 7.29–7.33 (m, 2H), 7.38–7.42 (m, 2H), 7.48–7.60
(m, 3H), 8.23 (d, J = 2.4 Hz, 1H), 13C NMR (75 MHz, DMSO-d6)
δ = 108.3, 116.7, 122.1, 122.6, 124.4, 130.2, 134.3, 137.2, 140.7,
147.0, 169.4. M.p. 241°C
5
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N-(1-Naphthyl)anthranilic acid (11): 1H NMR (300 MHz, CDCl3)
δ = 6.73 (dd, J = 7.3 Hz, 7.6 Hz, 1H), 6.85(d, J = 8.6 Hz, 1H), 7.23–
7.29 (m, 1H), 7.46–7.51 (m, 4H), 7.75 (d, J = 7.6 Hz, 1H), 7.89–7.92
(m, 1H), 8.08(m, 2H), 9.60 (bs, 1H). 13C NMR (75 MHz, CDCl3)
δ = 110.5, 114.2, 117.5, 122.8, 123.5, 126.5, 126.5, 127.1, 129.1,
130.8, 133.1, 135.5, 136.0, 136.9, 151.2, 174.2. M.p. 233°C
8
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1
N-(2-Isopropylphenyl)anthranilic acid (12): H NMR (300 MHz,
CDCl3) δ = 1.22 (d, J = 6.9 Hz, 6H), 3.21 (sept, J = 6.9 Hz, 1H), 4.68
(bs, 1H), 6.68 (dd, J = 7.2 Hz, 7.4 Hz, 1H), 6.81 (d, J = 8.2 Hz, 1H),
7.22–7.40 (m, 4H), 8.1 (dd, J = 1.7 Hz, 8.2 Hz, 1H), 9.18 (bs, 1H).
13C NMR (75 MHz, DMSO-d6) δ = 23.6, 28.4, 112.0, 113.6, 117.0,
125.7, 126.1, 127.1, 127.3, 132.5. 135.0, 137.9, 143.6, 149.8, 171.0.
M.p. 241°C
PAPER: 07/4798