Ultrasound-assisted ullmann reaction of alkyl and aromatic amines with substituted benzoic acids using copper catalyst

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Ultrasound-assisted Ullmann Reaction
of Alkyl and Aromatic Amines with
Substituted Benzoic Acids using Copper
Catalyst
Michael Ruby Raj a , Krishnaraj Arun a , Muthupandian Ashokkumar b
& Sambandam Anandan a
a Department of Chemistry, National Institute of Technology,
Tiruchirappalli, 620 015, India
b School of Chemistry, University of Melbourne, Victoria, 3010,
Australia
Version of record first published: 21 May 2012
To cite this article: Michael Ruby Raj, Krishnaraj Arun, Muthupandian Ashokkumar & Sambandam
Anandan (2012): Ultrasound-assisted Ullmann Reaction of Alkyl and Aromatic Amines with Substituted
Benzoic Acids using Copper Catalyst, Organic Preparations and Procedures International: The New
Journal for Organic Synthesis, 44:3, 271-280
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Organic Preparations and Procedures International, 44:271–280, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5452 online
DOI: 10.1080/00304948.2012.676822
Ultrasound-assisted Ullmann Reaction of Alkyl
and Aromatic Amines with Substituted Benzoic
Acids using Copper Catalyst
Michael Ruby Raj,1 Krishnaraj Arun,1 Muthupandian
Ashokkumar,2 and Sambandam Anandan1
1Department of Chemistry, National Institute of Technology, Tiruchirappalli 620
015, India
2School of Chemistry, University of Melbourne, Victoria 3010, Australia
Copper-catalyzed arylation of nucleophiles (Ullmann, Ullmann-Goldberg and Ullmann-
Hurtley) is a useful reaction in the formation of carbon-carbon and carbon-hetero bonds.1–6
However, the traditional Ullmann-type reactions suffer from reduced synthetic scope as a
result of the harsh reaction conditions such as the use of strong bases, and high temper-
atures (for aryl aminations) often required.1 Hence, currently there has been a substantial
effort in the development of new experimental procedures.1,7–10 An important breakthrough
was achieved by Taillefer and Buchwald with the discovery of versatile and efficient new
copper/ligand systems allowing the use of mild conditions (90–110◦C).11,12 This discovery
was followed by several studies to improve reaction conditions13–16 including the effect of
ultrasound.17–23 Ultrasound-assisted Ullmann condensations using electron-deficient aryl
halides with aliphatic primary amines were reported by Docampo, Pellon et al.24–27 who
also synthesized substituted 2-(alkylamino)benzoic acids in water for 2-chlorobenzoic acid
and aminothiazoles or aminobenzothiazoles. Ullmann-Goldberg condensations involving
N-aryl anthranilic acid derivatives bearing dioxolo, dioxano, cyclopentano, and imidazolo
ring systems using ultrasonic irradiation were reported by Robin et al.28 Ultrasound-induced
acoustic cavitation processes have been found useful in promoting chemical reactions.29,30
Sonochemical techniques offer specific experimental conditions to perform synthetic chem-
ical processes either within the bubble or at the bubble interface with extreme and non-
equilibrium conditions.30 Herein we report an ultrasound-assisted preparation of N-alkyl
and N-arylanthranilic acid derivatives in high yield via the Ullmann reaction of amines with
substituted benzoic acid, catalyzed by copper powder in 2-methoxyethanol. The results are
compared with the results of the conventional process (Table 1).
Received September 26, 2011; in final form February 24, 2012.
Address correspondence to Muthupandian Ashokkumar and Sambandam Anandan, Department
of Chemistry, National Institute of Technology, Tiruchirappalli 620 015, India, and School of Chem-
istry, University of Melbourne, Victoria 3010, Australia. E-mail: masho@unimelb.edu.au (MA);
sanand@nitt.edu (SA)
271

272
Anandan et al.
For comparison purpose, we performed initial screening experiments using conven-
tional heating method (Method A) using 2-chlorobenzoic acid (0.1 g, 0.63 mmol, 1 equiv.),
various substituted alkyl/aromatic amines [4-(2-aminoethyl)phenol] and 2-amino-4-chloro-
5-nitrophenol (1.28 mmol, 2 equiv.) in the presence of a base, [K2CO3 (0.5 eq.)] and
copper(I) iodide (5 mg) as catalyst. To determine a suitable solvent, a test reaction was per-
formed by conventional heating method using various solvents [dimethylacetamide (DMA),
2-ethoxyethanol, 2-methoxyethanol (at the boiling point of the respective solvents)]. Ull-
mann condensation using 2-methoxyethanol was chosen as solvent for our studies owing to
its low boiling point (i. e.∼120◦C–125◦C), moderate polarity and lesser toxicity compared
to other solvents. In Ullmann condensation reactions, either copper(I) iodide or copper
powder is used as a catalyst. To determine a suitable catalyst for our reaction, a test reac-
tion was performed by conventional heating method using 2-methoxyethanol and copper(I)
iodide or copper powder. It was found that air-stable, low-cost copper powder (3 mg) led
to good yields and was choosen as the optimal catalyst for our studies. The effect of base
concentration on the Ullmann reaction was determined using 2-methoxyethanol and copper
powder with various equivalents of K2CO3 base and it is clear that one equiv. of K2CO3 is
the optimal amount for the Ullmann reaction.
Based on aforementioned optimization processes, the Ullmann reactions were con-
ducted using conventional heating and ultrasonic irradiation methods for different sub-
strates (see Table 1) in the presence of one eq. K2CO3, 3 mg copper powder and 5 ml
2-methoxyethanol. It was noticed that under ultrasonic irradiation conditions, the reaction
times were dramatically reduced (by 2–4 h) and the yields and purity were significantly
enhanced nearly quantitative compared to the conventional heating method.
Ultrasound irradiation of 2-chlorobenzoic acid and with 4-(2-aminoethyl) phe-
nol yielded 2-(4-hydroxyphenethylamino)benzoic acid (Table 1, Entry 1), (95%) in 1
h. The conventional method requires about 5 h (85%) to afford such a high yield.
Furthermore, ultrasound irradiation of 2-chlorobenzoic acid with 4-(2-aminoethyl)-2-
methoxyphenol required 1.5 h to yield 2-(4-hydroxy-3-methoxyphenethyl amino)benzoic
acid (Table 1, Entry 2) (94%) indicating that the presence of an activating or-
tho methoxy group did not impede condensation. Similar high yields were obtained
with other substrates using of ultrasound irradiation (Table 1). In the case of ultra-
sound irradiation of 2-chlorobenzoic acid as starting substrate with 2-amino-4-chloro-
5-nitrophenol afforded 2-(5-chloro-2-hydroxy-4-nitrophenylamino)benzoic acid (Table 1,
Entry 3) in 92% in 2 h. (N-(4-amino-5-chloro-2-hydroxyphenyl)-3,4-dichlorobenzamide

Ultrasound-assisted Ullmann Reaction
273
Table 1
Condensation of 2-Halobenzoic Acids (1.0 equiv.) with Alkyl and Aromatic amines (2.0
equiv.) in 2-methoxyethanol by Conventional and Ultrasound Irradiation Processes
Aryl Halides
Amines
Product[a]
Yield[a]
(%)
A[b] B[c]
85 95
87 94
86 92
78 90
84 94
80 90
76 85
(Continued on next page)

274
Anandan et al.
Table 1
Condensation of 2-Halobenzoic Acids (1.0 equiv.) with Alkyl and Aromatic amines (2.0
equiv.) in 2-methoxyethanol by Conventional and Ultrasound Irradiation Processes
(Continued)
Aryl Halides
Amines
Product[a]
Yield[a]
(%)
A[b] B[c]
63 71
67 75
69 84
60 74
81 94
75 89
88 97

Ultrasound-assisted Ullmann Reaction
275
Table 1
Condensation of 2-Halobenzoic Acids (1.0 equiv.) with Alkyl and Aromatic amines (2.0
equiv.) in 2-methoxyethanol by Conventional and Ultrasound Irradiation Processes
(Continued)
Aryl Halides
Amines
Product[a]
Yield[a]
(%)
A[b] B[c]
90 98
79 92
[a] Yield of isolated and recrystallized products from EtOH/H2O.
[b] Conventional conditions and reaction times: 5 h (1), 6 h (2, 3, 6, 7, 13, 16), 6.5 h (8, 11), 7 h
(12), 8 h (4, 5, 14), 8.5 h (9, 10, 15).
[c] Ultrasonic irradiation (20 kHz, 750 W; 25◦C–30◦C), Reaction times: 1 h (1, 8, 11) 1.5 h (2, 6,
9, 10, 13–15), 2 h (3, 7, 12, 16) 2.5 h (4, 5).
and hexadecyl-3-amino-4-chlorobenzoate) yielded corresponding products 2-(2-chloro-4-
(3,4-dichlorobenzamido)-5-hydroxyphenylaminobenzoic acid (Table 1, Entry 4) and 2-(2-
chloro-5-hexadecyloxycarbonyl) phenylaminobenzoic acid (Table 1 Entry 5).
However, other aromatic amines required longer time presumably due to the electronic
and steric effects of activating and deactivating groups.31 The reason for the low yield in
the case of heterocyclic amines (Table 1 Entries 6, 11, 16) may be due to the competition
between the two amino groups (thiazol-2-ylamino or cyclic amino group). Through NMR
spectral studies, the presence of a cyclic amino group (6-amino) peaks at δ 1.90–0.07
(broad singlet, 2H, NH2), confirmed that the thiazol-2-ylamino group is involved in the
condensation reaction to yield the product (Table 1, Entry 6).
Furthermore, substituted 2-halobenzoic acids were condensed with various substituted
amines by ultrasound irradiation to study the effect of activating and deactivating groups.
The reduced yield of products (Table 1, 7–11) may be due to electron-deactivating bromo
group present at position 5 and the higher yield of products (Table 1, 12–16) may be the
result of electron- activating methoxy group present at position 5.
In summary, we have developed a simple, efficient, economic and environmentally
friendly method for the Ullmann condensation of substituted benzoic acids with various
amines to yield corresponding N-alkyl- or N-arylanthranilic acid derivatives in good yields
using ultrasound irradiation at room temperature. The salient features of this protocol are
mild reaction conditions, higher yields and shorter reaction times.

276
Anandan et al.
Experimental Section
Chemicals were obtained from Sigma Aldrich (USA) and Rankem (India) and used without
further purification. All solvents were used after distillation and storage over molecular
sieves as described in Vogel’s Textbook of Practical Organic Chemistry, 5th Ed. Anhydrous
Na2SO4 was used as the drying agent. High purity (99.99%) nitrogen gas was used to
maintain an inert atmosphere during the reactions, carried out in a two-neck round-bottom
flask for the conventional procedure and in a sonication cell (Sonics) for ultrasonication
method using a 20 kHz (23–47 W cm−3) horn sonifier (Sonics 750). Reactions were
monitored using TLC (Merck 60 F254, 0.25 mm) by visualizing through UV chamber.
Melting points were determined in open capillaries on a Veego melting point apparatus,
India. FT-IR spectra were recorded using a Perkin-Elmer spectrometer. Elemental analyses
were performed on a Vario EL III elemental analyzer. Mass spectra were determined by
Electrospray ionization-mass spectra (ESI-MS) recorded on a Micromass Quattro II triple
1
quadrupole mass spectrometer. H NMR spectra were recorded with a Brucker 300/500
MHz spectrometer with CDCl3 / DMSO-d6 as the solvent, chemical shifts (δ) are relative to
TMS as an internal standard. The starting samples were analyzed by gas chromatography
Table 2
Melting Points and Combustion Analysis Data of Compounds 1–16
Cmpd mp. (◦C) Physical Appearance
Analysis Data (Found)
H
C
N
1
2
3
4
5
6
7
8
9
132–133 dark brown solid
134–135 brown solid
131–132 dark brown solid
127–128 off-white solid
138–139 off-white solid
108–109 off-white solid
154–155 off-white crystal
157–158 off-white solid
153–154 brown solid
159–160 white needle crystals
130–131 white solid
70.02 (70.25) 5.88 (6.04)
66.89 (66.64) 5.96 (6.09)
50.58 (50.74) 2.94 (3.02)
53.18 (53.32) 2.90 (2.98)
69.81 (69.56) 8.20 (8.32)
5.44 (5.38)
4.88 (4.98)
9.08 (9.18)
6.20 (6.29)
2.71 (2.81)
53.39 (53.55) 5.67 (5.75) 12.45 (12.53)
53.59 (53.71) 4.20 (4.26)
52.48 (52.62) 4.40 (4.52)
45.27 (45.43) 2.28 (2.38)
60.56 (60.72) 6.95 (7.03)
42.00 (42.16) 3.53 (3.65) 10.50 (10.67)
66.89 (67.03) 5.96 (5.96)
4.17 (4.28)
3.82 (3.88)
5.28 (5.42)
2.35 (2.47)
10
11
12
157–158 light brown needle
crystals
4.88 (4.88)
13
14
15
161–162 brown needle crystals 64.34 (64.50) 6.03 (6.18)
157–158 brown needle crystals 52.36 (52.60) 3.14 (3.24)
4.41 (4.55)
5.82 (5.94)
2.56 (2.76)
161–162 off-white needle
crystals
68.18 (68.31) 8.12 (8.22)
16
133–134 off-white needle
crystals
51.26 (51.45) 4.88 (4.92) 11.96 (12.01)

Ultrasound-assisted Ullmann Reaction
277
Table 3
FT-IR, Mass and 1H NMR Spectral Data of Compounds 1–16
Cmpd
FT-IR (cm−1
)
1H NMR δH
Mass (m/z)
1
2555–2850, 1705,
3200, 3428
10.7 (s, 1H), 11.0 (bs, 1H), 9.8 (bs,
1H), 7.87 (d, J = 8.7Hz, 1H),
7.48–7.40 (m, 1H), 7.10–7.05 (m,
3H), 6.97(d, J = 8.4Hz, 1H,), 6.79
(d, J = 9Hz, 1H), 3.75–3.72 (m,
2H), 2.8–2.9 (m, 2H) ppm
12.48 (s, 1H), 10.28 (bs, 2H), 7.86
(d, J = 7.5Hz, 1H), 7.50 (s, 1H),
7.45–7.41(m, 1H), 7.37–7.29 (m,
4H), 3.86 (s, 3H), 2.63–2.58 (m,
2H), 1.25 (m, 2H) ppm
12.74 (s, 1H), 10.41 (bs, 2H), 7.85
(m, 1H), 7.56 (d, J = 10.8Hz, 1H),
7.46–7.42 (m, 2H), 7.42–7.30 (m,
1H), 6.72 (s, 1H) ppm
12.58 (s, 1H), 9.38 (bs, 1H), 8.11 (bs,
2H), 7.87 (d, J = 7.2Hz, 1H), 7.71
(s, 1H), 7.56 (dd, J = 8.4Hz, J =
8.4Hz, 2H), 7.47–7.39 (m, 3H),
7.35–7.30 (m, 2H) ppm
258 [M+H]+
2
2485–2640, 1712
3135, 3455 2843,
1046
288 [M+H]+
3
4
2755–2850, 1708
3420, 3500, 750
309 [M+H]+
2558–2876, 1655
1735, 749, 3435
451 [M+]
5
2475–2750, 1612
1725, 1167, 744,
2843, 1046, 3345
12.78 (s, 1H), 9.88 (bs, 1H),
517 [M+H]+
7.86–7.84 (d, J = 6.9Hz,1H), 7.56
(s, 1H), 7.44–7.39 (m, 3H),
7.35–7.26 (m, 2H), 2.59 (s, 2H),
1.37 (s, 28H), 0.90–0.87 (m, 3H)
ppm
12.5 (s, 1H), 10.2 (bs, 1H), 7.88 (d,
J = 2.5Hz, 1H), 7.48–7.41 (m,
1H), 7.41–7.36 (m, 2H), 7.36–7.28
(m, 1H), 2.60 (s, 4H), 1.30–1.20
(m, 2H), 0.07 (s, 2H) ppm
13.74 (bs, 1H), 9.20 (bs, 1H), 8.31
(bs, 1H), 7.89 (d, J = 2Hz, 1H),
7.67–7.62 (m, 3H), 7.47 (m, 2H),
6.75 (d, J = 9.5Hz, 1H), 3.32–3.21
(m, 2H), 2.77–2.74 (m, 2H) ppm
13.73 s, 1H), 8.2, 8.0 (bs, 2H), 7.89
(d, J = 2.5Hz, 1H), 7.67–7.62 (m,
4H), 3.32 (s, 3H), 1.90–1.92 (m,
2H), 1.20–1.25 (m, 2H) ppm
6
7
8
2585–2830, 1715
3448, 2936
306 [M+H]+
337 [M+H]+
367 [M+H]+
2557–2845, 1703
3202, 3430, 598
2482–2645,1711
3137, 3454, 2845
1045, 699

278
Anandan et al.
Table 3
FT-IR, Mass and 1H NMR Spectral Data of Compounds 1–16 (Continued)
Cmpd
FT-IR (cm−1
)
1H NMR δH
Mass (m/z)
530 [M+]
9
2560–2878, 1654
1733, 753, 3436,
700
2472–2747, 1613
1726, 1166 744,
2845 1045, 3345
698
13.64 (bs, 1H), 9.75 (bs, 1H), 9.64
(bs, 1H), 9.45 (bs, 1H), 7.84 (d, J =
2Hz, 2H), 7.67–7.58 (m, 6H) ppm
13.72 (bs, 1H), 8.32 (bs, 1H), 7.88
(m, 2H), 7.67–7.62 (m, 4H), 2.63
(s, 2H), 2.54–2.36 (s, 28H),
10
11
12
596 [M+H]+
368 [M+]
0.90–0.87 (m, 3H) ppm
2586–2832, 1714
3447, 2934 702
13.75 (s, 1H),10.2 (bs, 1H), 7.88 (d, J
= 2.5Hz, 1H), 7.67–7.62 (m, 2H),
2.65–2.60 (m, 4H), 1.90 (bs, 2H),
1.30–1.20 (m, 2H) ppm
13.43 (s, 1H), 8.31 (bs, 2H), 7.58 (d,
J = 8.5, 2H), 7.25 (d, J = 3Hz,
2H), 7.02 (dd, J = 9Hz, 8.5, 3H),
3.78 (s, 3H), 2.64–2.61 (m, 2H),
1.25 (m, 2H) ppm
13.43 (s, 1H), 8.31 (bs, 2H), 7.59 (d,
J = 9Hz, 2H), 7.25 (d, J = 3.5Hz,
2H), 7.03–7.01 (dd, J = 3Hz, 2,
3H), 3.78 (s, 6H), 2.65–2.63 (m,
2H), 1.23 (m, 2H) ppm
12.22 (s, 1H), 8.9 (bs, 1H), 8.1(bs,
2H), 7.57 (d, J = 8.7Hz, 2H,), 7.23
(d, J = 3Hz, 1H,), 7.01 (dd, J =
3Hz, J = 3Hz, 4H), 3.77 (s, 3H)
ppm
12.26 (s, 1H),8.15 (bs, 1H), 7.57 (d, J 547 [M+H]+
= 8.7Hz, 2H), 7.23 (d, J = 3Hz,
2H), 7.03 (d, J = 3Hz, 2H), 7.0 (d,
J = 3.3Hz, 1H), 3.76 (1s, 3H), 2.65
(s, 2H), 1.215 (s, 28H), 0.9–0.87
(m, 3H) ppm
13.64 (s, 1H),8.06 (bs, 1H), 7.64 (d, J
= 8.8Hz, 2H), 7.31 (d, J = 3.2 Hz,
2H), 7.10–7.07 (dd, J = 8.8 Hz,
2H), 3.39 (s, 3H), 1.90 (bs, 2H),
1.39–1.24 (m, 2H) ppm
2555–2851, 1705
3202, 3427 2844,
1045
288 [M+H]+
13
14
15
2484–2642, 1712
3136, 3455 2842,
1045
318 [M+H]+
2558–2876, 1655
1735, 751 3435,
2844 1045
481 [M+]
2475–2751, 1613
1724, 1167 744,
2842 1046, 3345,
2841
16
2585–2829, 1715
3448, 2936 2842,
1046
319 [M+]

Ultrasound-assisted Ullmann Reaction
279
using Restek capillary column (60 m length X 0.32 mm dia.) on a GC-SHIMADZU-2010
spectrometer.
General Procedure (Conventional Heating, Method A)
In a 50 ml two-neck round bottom flask, a mixture of 2-halobenzoic acids (1 equiv.),
the amines (2 equiv.), granular anhydrous potassium carbonate, copper powder and 2-
methoxyethanol was heated to reflux under an inert atmosphere at 120–125◦C for the
time indicated in Table 1. The progress of the reaction was followed until the starting
materials were no longer detectable by TLC on SiO2 [ethyl acetate/chloroform/acetic acid
(4:3:0.5 ml)]. After completion of the reaction, the reaction mixture was cooled to room
temperature and filtered (by gravity) to remove the copper catalysts. The resulting solution
was neutralized with dilute hydrochloric acid:water (1:1), and then extracted with ethyl
acetate (2 × 10 ml), followed by water wash (2 × 5 ml). The combined organic layers were
dried over Na2SO4 and evaporated under reduced pressure to afford the products which
were purified by recrystallization using EtOH/H2O mixture. The identity of the products
was established by combustion analysis, FT-IR, 1H NMR, and mass spectroscopy (Tables
2 and 3)
General Procedure (Ultrasonic Irradiation, Method B)
In a sonication cell, a mixture of 2-halobenzoic acids (1 equiv.), the amines (2 equiv.), gran-
ular anhydrous potassium carbonate, copper powder and 2-methoxyethanol was degassed
by purging by nitrogen gas for 15 min and sonicated for the time as indicated in Table 1.
The reaction temperature was controlled at 25◦C–28◦C by circulation of chilled water. The
rest of the procedure was followed as in the heating method.
Acknowledgments
The author SA thanks DST, New Delhi (Ref. No.SR/S1/PC-49/2009) for the sanction
of major research project. Also the authors (SA and MA) thank DST, New Delhi and
DEST, Australia for the sanction of INDIA-AUSTRALIAN strategic research fund for
their collaborative research.
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