A convenient and efficient synthesis of triarylamine derivatives using CuI nanoparticles

Article abstract of DOI:10.1039/c4ra00853g

We report a simple and efficient method for the synthesis of triarylamine derivatives using copper iodide nanoparticles, 1,10-phenanthroline and potassium hydroxide. Copper iodide nanoparticles enhanced the rate and ease of reaction and exhibited a high influence in the efficient synthesis of various amine derivatives. The nanoparticles also increased the yields of products and decreased the reaction times in all cases. The heterogeneous mediator was fully characterized by scanning electron microscopy and X-ray diffraction techniques.

Full text of DOI:10.1039/c4ra00853g

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A convenient and efficient synthesis of triarylamine
derivatives using CuI nanoparticles
Cite this: RSC Adv., 2014, 4, 16385
*
Javad Safaei-Ghomi, Zeinab Akbarzadeh and Abolfazl ziarati
We report a simple and efficient method for the synthesis of triarylamine derivatives using copper iodide
nanoparticles, 1,10-phenanthroline and potassium hydroxide. Copper iodide nanoparticles enhanced the
rate and ease of reaction and exhibited a high influence in the efficient synthesis of various amine
derivatives. The nanoparticles also increased the yields of products and decreased the reaction times in
all cases. The heterogeneous mediator was fully characterized by scanning electron microscopy and
X-ray diffraction techniques.
Received 29th January 2014
Accepted 17th February 2014
DOI: 10.1039/c4ra00853g
www.rsc.org/advances
the C–N coupling reaction in various systems. For example, the
synthesis of a variety of triphenylamines in good yields using
1. Introduction
CuCl mediated, 8-hydroxyquinoline as the chelating ligand and
K3PO4 as the base in DMF at 120 ꢀC has recently been
reported.47
Triarylamines are an important class of chemical compounds
due to their prominent physical, photochemical, electro-
chemical and special pharmacological properties.1 Triaryl-
amine has been widely used in many elds of chemistry
including the synthesis of natural products,2 dyes3 and poly-
mers.4–7 It also has good electron donating and hole trans-
porting abilities, therefore these compounds have broad
applications in organic electroluminescence (EL).8–11 In recent
years, organic photovoltaic functional materials with triaryl-
amine acting as an electron donor have been developed in the
eld of solar cells.12–15 Furthermore triarylamines have found
applications as photoconductors in xerographic photorecep-
tors.16–19 The synthesis of these compounds have been carried
out via N-arylation of aniline by aryl iodides under Ullman
coupling using different approaches.20 These reactions have
been developed using palladium21,22 or copper23–25 as catalysts.
The main limitations of bis-arylation reaction of substituted
anilines with two equivalents of aromatic halides are the high
temperature of reaction, low yield of triarylamines and sensi-
tivity to catalyst type. These limitations have been widely
observed in the synthesis of bromo-substituted triphenyl-
amines7 which have applications in the synthesis of polymers7
and dyes.26,27 Conventionally, the synthesis of these compounds
has been reported via two steps by arylation followed by
bromination with N-bromosuccinimide, NBS.28,29
The copper iodide-mediated synthesis of triarylamines has
also been performed using Cs2CO3 as the base in the absence of
an additive ligand.46 The ligand-free copper-catalysed Ullman
reaction was carried out using tetraethyl orthosilicate (TEOS) as
the solvent and this method requires a high temperature
ꢀ
(145 C) and long reaction time to achieve completion.
We attempted to alter the reaction of aryl iodides and aryl
amines to obtain triarylamine more conveniently and efficiently
by the use of nanoparticles. Nanoparticles can be used as suit-
able catalysts in organic reactions due to their high surface-to-
volume ratio, which provides a larger number of active sites per
unit area in comparison to their bulk counterparts.30 Copper
iodide nanoparticles (CuI NPs) have performed signicantly as
catalysts in terms of reactivity, selectivity, and improvement in
the yields of organic reactions.31–35 We applied a simple and
efficient method for the synthesis of various derivatives of tri-
arylamine, including electron withdrawing and bromo-
substituted triphenylamine, using CuI NPs and 1,10-phenan-
throline as a convenient catalytic system.
2. Results and discussion
In the N-arylation reaction, activation of aniline is facile
using a copper catalyst with chelating bidentate ligands such as
2,20-bipyridine and 1,10-phenanthroline. Ligands increase the
catalytic activity of the Cu complex by activation of the amine
and elimination of iodide.25 Different ligands have been used in
2.1. Synthesis
The synthesis of triarylamine via Ullman condensation started
from the reaction of aryl amine with aryl iodide (molar ratio
1 : 2) in the presence of potassium hydroxide as the base
mediated by CuI nanoparticles and 1,10-phenanthroline as a
catalytic system,25 in toluene as a solvent. The reaction mixture
was heated to reux under a nitrogen atmosphere (Scheme 1).
The optimized experimental conditions were obtained by
performing this reaction in different solvents and varying the
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, P.O.
Box 87317-51167, Kashan, Islamic Republic of Iran. E-mail: safaei@kashanu.ac.ir;
Fax: +98-361-5912397; Tel: +98-361-5912385
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Table 2 Synthesis of triarylamines using CuI nanoparticlesa
Scheme 1 Synthesis of triarylamine derivatives.
Entry Productb R1
R2
Time (h) Yieldc (%) Mpd (ꢀC)
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1I
H
H
4-Me
H
4-Br
4-Br
8
10
10
12
12
8
12
12
10
92
83
86
81
78
90
75
77
80
76
78
83
71
126–12737
—
83–8543
e
temperature and catalytic system. Reactions were carried out
using polar (Table 1, entries 1–3) and non-polar (Table 1, entries
4 and 5) solvents. Obviously, the non-polar solvents were more
suitable than polar solvents. The best results were obtained
using toluene. The different temperatures (with toluene as
solvent) were then investigated for this reaction in which the
maximum yields were obtained under reux conditions (Table
1, entries 5 and 6). In order to nd the best catalyst, a variety of
copper catalysts were investigated (Table 1, entries 8–10). As a
result of these experiments, we observed that the CuI nano-
particle-containing catalyst was the most effective for the
aforementioned reaction (Table 1, entry 10). A higher yield was
observed using 3 mol% CuI NPs and 3 mol% 1,10-phenan-
2-OMe 4-Br
3-OMe 4-Br
4-OMe 4-Br
4-Br
4-Br
4-Br
4-Br
4-Br
4-Br
4-Me
91–92
110–112
74–7638
4-Br
4-H
4-Me
2-OMe 12
3-OMe 12
4-OMe
140–14239
110–11240
104–10541
120–121
89–9144
9
10
11
12
13
1J
1k
1L
1m
8
95–9642
4-NO2 15
190–19245
a
Reactions conditions: aniline and iodobenzene (2 : 5), CuI
nanoparticles (3 mol%), 1,10-phenanthroline (3 mol%), potassium
b
hydroxide, toluene, reux.
All products were characterized by
throline (Table 1, entry 11). It should be noted that the reaction spectroscopic (IR, 1H NMR and 13C NMR), mass and CHN analysis.
c
Isolated yield. d Literature reference. e Viscous liquid.
did not proceed in the absence of catalyst (Table 1, entry 7).
Furthermore this reaction produced triarylamines in low yields
in the absence of 1,10-phenanthroline (Table 1, entry 13).
The increased catalytic activity of CuI nanoparticles over the triarylamines under the aforementioned conditions. The
highest yields of triarylamine were afforded by the electron
donating para-methoxy group as the substituent for aryl
commercially available bulk CuI can be attributed to their
higher surface area.
We also utilized CuI NPs in the synthesis of triarylamine halides and aniline (Table 2, entries 6 and 12). Although
derivatives with various aryl amines and aryl iodides under ortho-substituted aniline and aryl halides resulted in good
similar conditions and the results are shown in Table 2. As yields (Table 2, entries 4 and 10), the yields obtained were
seen from Table 2, excellent yields were obtained from this lower than para-substituted aniline because of steric effects.
reaction under reux and in the presence of nano copper Aryl iodides showed higher reactivity than aryl bromides in
iodide (3 mol%). Electron-withdrawing and electron- this reaction. The coupling of 1-bromo-4-iodobenzene with
aniline derivatives yielded products containing bromide on
the aromatic ring (entries 2–7 in Table 2).
donating substituents for aryl halides and aniline such as
CH3, OCH3, Br and NO2 resulted in good to excellent yields of
Table 1 Optimization of reaction conditions for the synthesis of triphenylamine
Entry
Solvent/condition
Catalytic system (mol%)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
Acetonitrile/reux
THF/reux
1,4-Dioxane/reux
Xylene/reux
CuI (15%), 1,10-phenb (15%)
CuI (15%), 1,10-phen (15%)
CuI (15%), 1,10-phen (15%)
CuI (15%), 1,10-phen (15%)
CuI (15%), 1,10-phen (15%)
CuI (15%), 1,10-phen (15%)
None
CuCl (15%), 1,10-phen (15%)
CuBr (15%), 1,10-phen (15%)
CuI NPs (5%), 1,10-phen (5%)
CuI NPs (3%), 1,10-phen (3%)
CuI NPs (2%), 1,10-phen (2%)
CuI NPs (3%)
48
48
48
32
32
48
48
32
32
8
38
35
36
65
69
49
Trace
43
51
89
Toluene/reux
Toluene/80 ꢀ
C
Toluene/reux
Toluene/reux
Toluene/reux
Toluene/reux
Toluene/reux
Toluene/reux
Toluene/reux
9
10
11
12
13
8
8
12
92
85
71
a
Isolated yield. b 1,10-Phenanthroline as chelating ligand.
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2.2. Structural analysis of CuI nanoparticles
Fig. 1 shows the XRD pattern of copper iodide nanoparticles. As
seen from this gure, all reection peaks could be indexed to
the pure cubic crystal phase of nano crystalline CuI. No specic
peaks due to any impurities were observed. This pattern is in
good agreement with the reported pattern for copper iodide
(JCPDS no. 75–0832). The crystalline size diameter (D) of the
synthesized CuI nanoparticles was calculated by the Debye–
Scherrer equation (D ¼ Kl/b cos q),36 where the FWHM (full-
width at half-maximum or half-width) is in radians and q is the
position of the maximum of diffraction peak (b ¼ 0.4723[ꢀ2q]), K
is the shape factor which usually is a value about 0.9, and l is
the X-ray wavelength. The average diameter of CuI NPs was
found to be 20 nm.
Fig. 2 SEM image of the CuI nanoparticles.
In order to conrm the particle size of the CuI nanoparticles,
the scanning electron microscopy (SEM) image is shown in
Fig. 2. This gure illustrates that CuI NPs were obtained with
diameters in the range of nanometers (20 nm) under ultrasonic
irradiation. According to the TEM image of CuI NPs, the particle
size of the nano CuI was found to be less than or equal to 20 nm
(Fig. 3).
internal standard. IR spectra were recorded on a FT-IR Magna
550 apparatus using KBr plates. EI-MS (70 eV) was performed
using
a Finnigan-MAT-8430 mass spectrometer in m/z.
Elemental analyses (C, H, N) of the samples were performed
using a LECO CHNS 923 analyser.
Powder X-ray diffraction (XRD) of CuI nanoparticles was
carried out on a Philips diffractometer (X'pert Company) with
2.3. Proposed mechanism
˚
monochromatized Cu Ka radiation (l ¼ 1.5406 A). Microscopic
The proposed mechanism for the synthesis of triarylamine
using CuI NPs chelated by 1,10-phenanthroline is shown in
Scheme 2. In the rst step, C–N coupling occurs by oxidative
addition followed by a reductive elimination reaction. These
processes are carried out on the nano copper surface. Nano-
particles of CuI have high catalytic activity owing to their high
surface area.
morphology was visualized using a SEM (LEO 1455VP). The
transmission electron microscopy (TEM) image of nano copper
iodide was obtained on a Philips EM208 transmission electron
microscope with an accelerating voltage of 100 kV.
3.2. Preparation of copper iodide nanoparticle
The nanocatalyst was produced by ultrasonic irradiation with
copper sulphate (CuSO4) as the Cu source. First, CuSO4
(1 mmol) was cleaned for 20 s in acetone under ultrasonic
irradiation followed by repeated rinsing with distilled water.
The dried substrate was then dipped slowly into a solution of
potassium iodide (1 mmol) in 40 mL of distilled water and the
mixture was sonicated for 30 min. When the reaction was
completed, the obtained grey precipitate was ltered, washed
with distilled water and dried to afford pure CuI NPs. The
prepared nanoparticles were fully characterized by SEM, TEM
and XRD analyses.
3. Experimental
3.1. Chemicals and apparatus
All reagents and solvents were purchased from Merck (Ger-
many) and Aldrich and used without further purication.
Melting points were determined on an Electrothermal 9200
apparatus. 1H NMR and 13C NMR spectra were recorded using a
Bruker Avance-400 MHz spectrometer. NMR spectra were
obtained in CDCl3 and DMSO-d6 solution and are reported as
parts per million (ppm) downeld from tetramethylsilane as
Fig. 1 XRD pattern of the CuI nanoparticles.
Fig. 3 TEM image of the CuI nanoparticles.
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Scheme 2 Proposed reaction pathway for the synthesis of triarylamine mediated by CuI nanoparticles and 1,10-phenanthroline.
3.3. General procedure for the preparation of triarylamines
derivatives
N,N-Bis(4-bromophenyl)aniline (1b). Colorless viscous
liquid. 1H NMR (400 MHz, CDCl3): d (ppm) 6.95 (d, 4H), 7.06 (m,
3H), 7.27 (d, 2H), 7.35 (d, 4H). 13C NMR (100 MHz, CDCl3): d
(ppm) 115.53, 123.82, 124.66, 125.46, 129.62, 132.22, 146.57,
The amination reaction was carried out in a two-necked round
bottomed ask under a nitrogen atmosphere. In a typical
experiment, a mixture of aniline (1 mmol), iodobenzene (2.5
mmol), CuI NPs (3 mol%), 1,10-phenanthroline (3 mol%) and
potassium hydroxide (0.43 g, 0.008 mmol) were dissolved in 10
mL of toluene and stirred under a nitrogen atmosphere at reux
for the required time. The reaction was monitored to comple-
tion using TLC with hexane as the eluent. At the end of reaction,
the mixture was then cooled to room temperature and poured
into distilled water. The products were extracted using CH2Cl2
and the organic layer was dried over anhydrous sodium
sulphate (Na2SO4). The solvent was evaporated in vacuo, the
crude products were puried by silica column chromatography
using normal hexane to afford the triarylamines. The products
were characterized by IR, NMR analysis, mass spectrum and
elemental analysis.
146.96. FT-IR (KBr): 3071, 3056, 1579, 1484, 1274, 1070 cmꢁ1
.
MS (EI, 70 eV): m/z 400 (M+), Anal. calcd for C18H13NBr2: C,
53.87; H, 3.24; N, 3.50%. Found: C, 53.61; H, 3.03; N, 3.35%.
4-Methyl-N,N-bis(4-bromophenyl)aniline (1c). White solid.
1H NMR (400 MHz, CDCl3): d (ppm) 2.32 (s, 3H), 6.91 (d, 4H),
6.96 (d, 2H), 7.09 (d, 2H), 7.31 (d, 4H). 13C NMR (100 MHz,
CDCl3): d (ppm) 20.89, 114.94, 124.92, 125.20, 130.25, 132.23,
133.86, 144.29, 146.69. FT-IR (KBr): 3033, 2922, 1578, 1483,
1276, 1070 cmꢁ1. MS (EI, 70 eV): m/z 415 (M+), Anal. calcd for
C
19H15NBr2: C, 54.70; H, 3.60; N, 3.36%. Found: C, 54.63; H,
3.49; N, 3.28%.
2-Methoxy-N,N-bis(4-bromophenyl)aniline (1d). White solid.
1H NMR (400 MHz, CDCl3): d (ppm) 3.69 (s, 3H), 6.93 (d, 4H),
7.01 (d, 1H), 7.12 (m, 3H), 7.32 (d, 4H). 13C NMR (100 MHz,
CDCl3): d (ppm) 56.48, 115.45, 122.32, 124.92, 125.65, 129.25,
132.03, 132.86, 145.12, 145.97. FT-IR (KBr): 3031, 2935, 1585,
1472, 1272, 1072 cmꢁ1. MS (EI, 70 eV): m/z 430 (M+), Anal. calcd
3.4. Spectral data for triarylamine derivatives
Triphenylamine (1a). White solid. 1H NMR (400 MHz, for C19H15NOBr2: C, 52.68; H, 3.47; N, 3.23%. Found: C, 52.51;
CDCl3): d (ppm) 7.08 (m, 9H), 7.26 (d, 6H), 13C NMR (100 MHz, H, 3.38; N, 3.21%.
CDCl3): d (ppm) 124.82, 125.46, 135.62, 147.65. FT-IR (KBr):
3-Methoxy-N,N-bis(4-bromophenyl)aniline (1e). White solid.
3031, 3016, 1590, 1454, 1276 cmꢁ1. MS (EI, 70 eV): m/z 244 (M+), 1H NMR (400 MHz, CDCl3): d (ppm) 3.72 (s, 3H), 6.90 (s, 1H),
Anal. calcd for C18H15N: C, 88.16; H, 6.12; N, 5.72%. Found: C, 6.94 (d, 4H), 7.05 (m, 3H), 7.22 (d, 4H). 13C NMR (100 MHz,
87.95; H, 6.01; N, 5.62%.
CDCl3): d (ppm) 57.84, 116.14, 120.21, 121.85, 124.36, 131.51,
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133.97, 142.65, 144.84, 152.23. FT-IR (KBr): 3033, 2950, 1523, 7.18 (d, 4H), 7.33 (d, 2H), 8.05 (d, 4H). 13C NMR (100 MHz,
1454, 1256, 1064 cmꢁ1. MS (EI, 70 eV): m/z 431 (M+), Anal. calcd DMSO-d6): d (ppm) 122.34, 125.36, 126.27, 130.58, 132.60,
for C19H15NOBr2: C, 52.68; H, 3.47; N, 3.23%. Found: C, 52.57; 139.04, 147.23, 147.69. FT-IR (KBr): 3063, 3043, 1548, 1508,
H, 3.32; N, 3.24%.
1452, 1335, 1273 cmꢁ1. MS (EI, 70 eV): m/z 348 (M+), Anal. calcd
4-Methoxy-N,N-bis(4-bromophenyl)aniline (1f). White solid. for C19H15N3O4: C, 65.32; H, 4.33; N, 12.03%. Found: C, 65.06;
1H NMR (400 MHz, CDCl3): d (ppm) 3.75 (s, 3H), 6.90 (d, 2H), H, 4.12; N, 12.15%.
6.96 (d, 4H), 7.08 (d, 2H), 7.39 (d, 4H). 13C NMR (100 MHz,
CDCl3): d (ppm) 57.98, 115.34, 126.34, 131.50, 133.73, 135.65,
4. Conclusions
145.67, 146.32, 150.07. FT-IR (KBr): 3056, 2948, 1584, 1457,
1273, 1075 cmꢁ1. MS (EI, 70 eV): m/z 431 (M+), Anal. calcd for
In this work a simple and efficient method for the amination of
C
19H15NOBr2: C, 52.68; H, 3.47; N, 3.23%. Found: C, 52.54; H,
iodobenzene using CuI NPs under reux was investigated . The
mediated system which included nano CuI as the catalyst
precursor, 1,10-phenanthroline as the ligand, KOH as the base
and toluene as the solvent resulted in good yields of triaryl-
amines. The conditions were very mild, neutral and environ-
mentally benign. Furthermore it was very effective due to the
high surface-to-volume ratio of nanoparticles. The products
were formed in excellent yields with short reaction times. This
method is also suitable for the one-step synthesis of bromo-
substituted triphenylamines.
3.35; N, 3.19%.
4-Bromo-N,N-bis(4-bromophenyl)aniline (1g). Pale green
solid. 1H NMR (400 MHz, CDCl3): d (ppm) 6.97 (d, 6H), 7.08 (d,
6H). 13C NMR (100 MHz, CDCl3): d (ppm) 115.23, 125.92, 132.43,
146.59. FT-IR (KBr): 3056, 1585, 1483, 1272, 1071 cmꢁ1. MS (EI,
70 eV): m/z 481 (M+), Anal. calcd for C18H12NBr3: C, 44.84; H,
2.49; N, 2.91%. Found: C, 44.32; H, 2.31; N, 2.89%.
1
4-Bromo-N,N-bis(phenyl)aniline (1h). White solid. H NMR
(400 MHz, CDCl3): d (ppm) 7.01 (d, 2H), 7.16 (m, 6H), 7.22 (d,
4H), 7.42 (d, 2H). 13C NMR (100 MHz, CDCl3): d (ppm) 115.35,
120.64, 124.97, 127.79, 128.44, 136.21, 146.69, 147.74. FT-IR
(KBr): 3085, 1590, 1483, 1273, 1075 cmꢁ1
.
Acknowledgements
4-Bromo-N,N-bis(4-methylphenyl)aniline (1I). Yellowish
solid. 1H NMR (400 MHz, CDCl3): d (ppm) 2.35 (s, 6H), 6.92 (d,
2H), 7.01 (d, 4H), 7.09 (d, 4H), 7.31 (d, 2H). 13C NMR (100 MHz,
CDCl3): d (ppm) 19.96, 113.07, 124.88, 126.34, 129.52, 132.65,
135.06, 145.84, 146.37. FT-IR (KBr): 3110, 2989, 1568, 1495,
1275, 1069 cmꢁ1. MS (EI, 70 eV): m/z 350 (M+), Anal. calcd for
The authors are grateful to the University of Kashan for sup-
porting this work by grant no.: 159196/XXI.
References
C
20H18NBr: C, 68.20; H, 5.11; N, 3.98%. Found: C, 68.08; H, 4.96;
N, 3.73%.
4-Bromo-N,N-bis(2-methoxyphenyl)aniline (1J). Yellowish
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Yellow
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Yellow
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2H), 7.21 (d, 4H), 7.28 (d, 2H), 7.43 (d, 4H). 13C NMR (100 MHz,
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20H18NO2Br: C, 62.52; H, 4.69; N, 3.65%. Found: C, 62.35; H,
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4-Methyl-N,N-bis(4-nitrophenyl)aniline (1M). Yellow solid.
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