Convenient and rapid diazotization and diazo coupling reaction via aryl diazonium nanomagnetic sulfate under solvent-free conditions at room temperature

Article abstract of DOI:10.1016/j.dyepig.2015.03.041

For the first time, nanomagnetic-supported sulfonic acid is used for conversion of several types of aromatic amine, containing electron-withdrawing groups as well as electron-donating groups to the corresponding azo dyes in excellent yield. The synthesis of these compounds is described by the sequential diazotization-diazo coupling of various aromatic amines with sodium nitrite, nanomagnetic supported sulfonic acid and coupling agents under solvent-free conditions at room temperature. This new method offers several advantages including short reaction time, mild reaction conditions, avoidance of harmful acids, and simple work-up procedure. More importantly, aryldiazonium salts supported on magnetic nanoparticles (aryl diazonium nanomagnetic sulfate) were sufficiently stable to be kept at room temperature in the dry state.

Full text of DOI:10.1016/j.dyepig.2015.03.041

Accepted Manuscript
Convenient and rapid diazotization and diazo coupling reaction via aryl diazonium
nanomagnetic sulfate under solvent-free conditions at room temperature
Nadiya Koukabi, Somayeh Otokesh, Eskandar Kolvari, Ali Amoozadeh
PII:
S0143-7208(15)00132-1
10.1016/j.dyepig.2015.03.041
DYPI 4732
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 9 December 2014
Revised Date: 15 March 2015
Accepted Date: 17 March 2015
Please cite this article as: Koukabi N, Otokesh S, Kolvari E, Amoozadeh A, Convenient and rapid
diazotization and diazo coupling reaction via aryl diazonium nanomagnetic sulfate under solvent-free
conditions at room temperature, Dyes and Pigments (2015), doi: 10.1016/j.dyepig.2015.03.041.
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ACCEPTED MANUSCRIPT
Highlights
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Diazotization and diazo coupling are done via aryl diazonium nanomagnetic sulfate.
Different anilines are converted to azo dyes with good to excellent yields.
The advantages of this method are short reaction time, avoidance of harmful acids.

ACCEPTED MANUSCRIPT
Convenient and rapid diazotization and diazo coupling reaction via aryl diazonium
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nanomagnetic sulfate under solvent-free conditions at room temperature
Nadiya Koukabi*, Somayeh Otokesh, Eskandar Kolvari* and Ali Amoozadeh
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Department of Chemistry, Semnan University, Semnan 3535119111, Iran
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Corresponding author: Tel.:+98 23 33383196; fax:+98 23 33354110
E-mail address: n.koukabi@semnan.ac.ir
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ABSTRACT
For the first time, nanomagnetic-supported sulfonic acid is used for conversion of several types of aromatic
amine, containing electron-withdrawing groups as well as electron-donating groups to the corresponding azo
dyes in excellent yield. The synthesis of these compounds is described by the sequential diazotization–diazo
coupling of various aromatic amines with sodium nitrite, nanomagnetic supported sulfonic acid and coupling
agents under solvent-free conditions at room temperature. This new method offers
several
advantages
including
short
reaction
time,
mild
reaction
conditions, avoidance of harmful acids, and simple work-up procedure. More importantly, aryldiazonium salts
supported on magnetic nanoparticles (aryl diazonium nanomagnetic sulfate) were sufficiently stable to be kept
at room temperature in the dry state.
Keywords Aryl diazonium nanomagnetic sulfate; Azobenzene; Diazo coupling; Nanomagnetic particles;
Solvent-free condition
1. Introduction
Azobenzene, with two phenyl rings linked by N=N double bond, serves as the parent molecule for
abroad class of aromatic azo compounds. The strong absorption of band these compounds can be
tailored by ring substitution to fall anywhere from the ultraviolet to red-visible regions, allowing
chemical fine-tuning of color. This property, combined with the fact that the azo groups are relatively
robust and chemically stable, has prompted extensive study of azobenzene based structures as dyes
[1]. Approximately 10,000 different dyes and pigments are used industrially, and over 0.7 million
tones of synthetic dyes are produced annually worldwide [2]. Azoic dyes are the most important
group of all synthetic dyes that are used extensively for textile dyeing [3], paper printing and color
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photography and as additives in petroleum products. In addition, azobenzene moiety is an important
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structural motif in biological systems [4]. The photo response of azo compounds modifies the activity
of enzymes and polypeptides, also is used for more accurate diagnosis of Alzheimer, s disease [5].
Moreover, azobenzenes recently have been targeted for potential applications in areas of nonlinear
optics [6], optical storage media [7], chemosensory [8, 9], liquid crystals [1], photochemical
molecular switches [10], molecular shuttles [11], nanotubes [12], in the manufacture of protective eye
glasses and filters [13] and as optical switch for in vivo experiments [14].
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The synthesis of aromatic azo components has been attracting increasing interest over the past decade
because of their utility in various applications. In recent years, several methods have been reported for
synthesis of these components [15-17]. Although remarkable developments have been achieved in this
field, the search for mild conditions could represent a useful tool in organic chemistry. The most
important methods for the preparation of aromatic azo have focused on diazotization-azo coupling
reaction. The main limitation of this process is their environmental incompatibility. Since, use of
strong liquid acids for diazotization reaction (such as H2SO4, HCl) causes permanent damage to the
environment and their use is contrary to the principles of green chemistry. In addition, these liquid
acids require special processing in the form of neutralization, which involves costly and inefficient
catalyst separation from homogeneous reaction mixture, and then results in an unrecyclable waste.
The need for a ―green‖ approach to chemical processing has stimulated the use of recyclable strong
solid acids as replacements for unrecyclable liquid acid catalysts [18-21].
Magnetic nanoparticles have emerged as a highly valuable substrate for the attachment of
homogeneous inorganic and organic containing catalysts. They have advantages such as readily
available, high surface area and most importantly magnetically recoverable, which facilitates reaction
work-up and rapid sample processing, and reduces solvent consumption [22, 23].
We have previously report synthesis of nanomagnetic-supported sulfonic acid (nano--Fe2O3-SO3H)
and its applications as viable alternative to unrecyclable homogenous catalysts in organic synthesis
[24-26]. Recently, we have used this catalyst for the synthesis of aryl iodides [27]. As part of our
ongoing research program to explore catalytic properties of nanomagnetic-supported sulfonic acid, we
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herein report a new process for diazotization and diazo coupling reaction of aromatic amines using
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nano--Fe2O3-SO3H (Scheme 1).
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Scheme 1.
2. Experimental
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2.1. General
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Nano-γ-Fe2O3-SO3H was prepared by the reaction of chlorosulfonic acid with nano maghemite
previously [24]. All reagents were purchased from Merck and Aldrich and used without further
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purification. Melting points were recorded on electro thermal 9100 apparatus and are uncorrected. H
NMR and C NMR spectra were obtained with a Bruker Avance spectrometer (1H NMR 300, 400
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MHz and 13C NMR 75, 100 MHz) in pure deuteriated chloroform and DMSO using TMS as an
internal standard. The IR spectra were recorded on a Perkin-Elmer model 783 spectrophotometer
(Waltham, MA, USA). UV-Vis spectra were obtained as CH2Cl2 or DMSO solutions (5*10-5 M) on a
Shimadzu UV-1650PC spectrophotometer.
2.2. Typical procedure for the preparation of N,N-dimethyl-4-(phenyldiazenyl)aniline
Aniline (2 mmol, 0.1863 g), nanomagnetic-supported sulfonic acid (-Fe2O3-SO3H) (1.3 g), NaNO2 (4
mmol, 0.276 g) and 0.2 mL of H2O were homogenized by grinding in a mortar with a pestle for a few
minutes. The diazotization reaction lasted approximately 5-10 minutes. Dimethylaminobenzene (2
mmol, 0.2424 g) was added to the diazonium salt and grinding continued for 10 min. After
completion of the reaction, the mixture was triturated with acetone (30 mL). In the presence of a
magnetic stirrer bar, catalyst moved on to the stirrer bar steadily and the reaction mixture turned clear
within 10 s. The catalyst was isolated by simple decantation. After evaporation of the solvent by
rotary evaporator, the crude product was purified by recrystalization in EtOH/H2O, 9:1. N,N-
dimethyl-4-(phenyldiazenyl)aniline was obtained in 94% yield (0.423 g), mp 108–9 ºC, literature
107–9 ºC [28]. Recyclability of the catalyst was tested in this reaction, after completion of the
reaction, the mixture was triturated with acetone and the catalyst was easily removed with an external
magnet, after being washed with acetone and ethanol and dried at 70oC to be used in the next cycles.
This process was repeated three times without significant loss of activity.
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CAUTION! Although we did not experience any problems, diazonium salts are known to be
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explosive. Care must be exercised in handling them, especially when they are subjected to grinding.
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2.3. The spectral data of some representative products
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1-(p-tolyldiazenyl)naphthalen-2-ol (Table 2, 3a): (0.225 g, 86%), as an orange red solid,
(recrystallized from ethanol:water, 9:1). IR (KBr) cm-1: 3433.06, 3030, 2920, 1620.09, 1496.66, 1265,
1203, 810, 748. UV (λmax in CH2Cl2): 483 nm. 1H NMR (CDCl3): δH 15.98 (NH, s), 8.66 (1H, d, J=8.4
Hz), 7.79 (1H, d, J=9.2 Hz), 7.74 (1H, d, J=8 Hz), 7.69 (1H, d, J=8 Hz), 7.60 (1H, d, J=8.4 Hz), 7.44
(1H, d, J=8.4 Hz), 7.34 (2H, d, J=8 Hz), 6.96 (1H, d, J=9.2 Hz), 2.44 (CH3, s). 13C NMR: 21.3,
129.79, 168.4, 143.59, 130.19, 119.1, 138.36, 121.64, 124, 125.3, 128, 128.5, 128.6, 129.7, 130.1,
133.5, 138.36, 138.86, 143.59, 168.4. Anal. Calcd for C17H14N2O: C, 77.84; H, 5.38; N, 10.68%.
Found: C, 77.58; H, 5.48; N, 10.38%.
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1-(phenyldiazenyl)naphthalen-2-ol (Table 2, 3e): (0.196 g, 79%), (recrystallized from ethanol:water,
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9:1). IR (KBr) cm-1: 3434, 1617, 1447, 1261, 1207, 839, 751. H NMR (Acetone-d6): 16.05 (NH, s),
8.37 (1H, d, J=8 Hz), 7.58 (2H, d, J=8.4 Hz), 7.56 (1H, d, J=9.2 Hz), 7.42 (1H, d, J=8 Hz), 7.36 (1H,
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d, J=8 Hz) 7.21 (1H, d, J=8 Hz), 7.11 (2H, d, J=7.2 Hz), 6.68 (1H, d, J=9.2 Hz). C NMR: 118.6,
121.73, 124.02, 125.7, 127.4, 128, 128.8, 129.5, 130.08, 133.4, 140, 144.8, 177.87. Anal. Calcd for
C16H12N2O: C, 77.40; H, 4.87; N, 11.28%. Found: C, 77.25; H, 4.94; N, 11.18%.
1-((4-chlorophenyl)diazenyl)naphthalen-2-ol (Table 2, 3f): (0.268 g, 95%), as a maroon solid,
(recrystallized from ethanol:water, 9:1). IR (KBr) cm-1: 3432, 1621, 1485.09, 1253.64, 1211.21,
1089.71, 819.69, 748.33. UV (λmax in CH2Cl2): 480 nm. 1H NMR (CDCl3): 15.89 (NH, s), 8.55 (1H, d,
J=8 Hz), 7.74 (1H, d, J=9.2 Hz), 7.69 (2H, t of d, J=6.8, 2 Hz), 7.62 (1H, d, J=8 Hz), 7.46-7.39 (2H,
m), 6.89 (1H, d, J=9.2 Hz). 13C NMR: 119.9, 121.7, 124.3, 125.8, 128.1, 128.69, 128.65, 128.9,
129.73, 130.22, 133, 133.36, 140.1, 164, 170. Anal. Calcd for C16H11ClN2O: C, 67.97; H, 3.92; N,
9.91%. Found: C, 68.19; H, 3.90; N, 10.01%.
1-((4-bromophenyl)diazenyl)naphthalen-2-ol (Table 2, 3g): (0.304 g, 93%), as a dark red solid,
(recrystallized from ethanol:water, 9:1). IR (KBr) cm-1: 3437, 1620.09, 1483.16, 1251.72, 1209.28,
1070.42, 817.76, 748.33. UV (λmax in CH2Cl2): 483 nm. 1H NMR (CDCl3): 16.1 (NH, s), 8.54 (1H, d,
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J=7.2 Hz), 7.74 (1H, d, J=8.8 Hz), 7.61-7.57 (6H, m), 7.42 (1H, d, J=6.4 Hz), 6.87 (1H, d, J=9.2 Hz).
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13C NMR: 121.1, 121.9, 122.9, 125.6, 127.1, 129.3, 129.8, 130.1, 131.4, 133.8, 134.5, 141.4, 145.2,
172. Anal. Calcd for C16H11BrN2O: C, 58.74; H, 3.39; N, 8.56%. Found: C, 58.40; H, 3.53; N, 8.5%.
4-((4-chlorophenyl)diazenyl)-N,N-dimethylaniline (Table 2, 3h): (0.2337 g, 90%), (recrystallized
from ethanol:water, 9:1). IR (KBr) cm-1: 1598.88, 1519.80, 1365.51, 1135.99, 838.98. UV (λmax in
CH2Cl2): 421 nm. 1H NMR (CDCl3): 7.86 (2H, d, J=8), 7.78 (2H, t, J=7.6 Hz), 7.42 (2H, d, J=8 Hz),
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6.75 (2H, d, J=8.8 Hz), 3.09 (6H, t, J=20 Hz). C NMR: 40.2, 111.4, 123.4, 125, 129, 134.9, 152.5.
Anal. Calcd for C14H14ClN3: C, 64.74; H, 5.43; N, 16.18%. Found: C, 64.82; H, 5.41; N, 16.12%.
1-(4-((2,4-dihydroxyphenyl)diazenyl)phenyl)ethanone (Table 2, 3j): (0.218 g, 85%), as a brown solid,
(recrystallized from acetone). IR (KBr) cm-1: 3263.33, 3178.47, 1658.67, 1596.95, 1481.23, 1249.79,
1118.64, 840.91. UV (λmax in DMSO): 410 nm. 1H NMR (CDCl3): 13.85 (NH, s), 7.97-8.1 (3H, m),
7.83-7.87 (2H, m), 7.77 (1H, d, J=8.8 Hz), 6.6 (1H, d, J=8 Hz), 6.4 (OH, 1H) 2.5 (3H, s). 13C NMR:
26.5, 108.8, 103.9, 117.7, 125.8, 129.1, 122.9, 138.9, 157, 153, 162.1, 197. Anal. Calcd for
C14H12N2O3: C, 65.62; H, 4.72; N, 10.93%. Found: C, 65.84; H, 4.78; N, 10.72%.
N,N-dimethyl-4-((2-(trifluoromethyl)phenyl)diazenyl)aniline (Table 2, 3k): (0.267 g, 91%),
(recrystallized from acetone). IR (KBr) cm-1: 1604.66, 1521.73, 1402.15, 1373.22, 1317.29, 1309.58,
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1265.22, 1153.35, 1137.92, 1126.35, 1103.21, 1051.13. UV (λmax in CH2Cl2): 430 nm. H NMR
(CDCl3): 7.92 (2H, d of d , J=7.2, 2 Hz), 7.87 (2H, t, J=8.4), 7.59 (1H, t, J=7.2 Hz), 7.42 (1H, t, J=7.4
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Hz), 6.75 (2H, d of d, J=7.2, 2 Hz) 3.1 (6H, t, J=20). C NMR: 40.23, 116.2, 122.8, 125.6, 125.8,
126.2, 128.4, 132.3, 144, 150.3, 152.9. Anal. Calcd for C15H14F3N3: C, 61.43; H, 4.81; N, 14.33%.
Found: C, 61.64; H, 4.72; N, 14.23%.
Sodium 4-((2-hydroxynaphthalen-1-yl)diazenyl)benzenesulfonate (Table 2, 3n): (0.2905 g, 83%),
(recrystallized from acetone). IR (KBr) cm-1: 3423.41, 1620.09, 1506.30, 1398.3, 1122.49. UV (λmax
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in DMSO): 446 nm. H NMR (DMSO-d6): 15.8 (1H, s), 8.52 (1H, d, J=7.6), 7.93 (1H, d, J=9.2 Hz),
7.79-7.71 (5H, m), 7.60 (1H, d, J=6.4 Hz), 7.44 (1H, d, J=6.4 Hz), 6.88 (1H, d, J=8.4 Hz). 13C NMR:
119.7, 123, 125.7, 127.5, 128.7, 129.4, 132.38, 130.5, 130.5, 130.8, 130.9, 134.3, 141.8, 149.1, 159,
171.5. Anal. Calcd for C16H11N2NaO4S: C, 54.86; H, 3.16; N, 8.01%. Found: C, 54.80; H, 3.17; N,
8.06%.
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1-(4-((4-(dimethylamino)phenyl)diazenyl)phenyl)ethanone (Table 2, 3o): (0.248 g, 93%),
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(recrystallized from acetone). IR (KBr) cm-1: 2918.10, 1670.24, 1606.59, 1523.66, 1365.51, 1267.14,
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1161.07, 946.98, 831.26, 821.62. UV (λmax in CH2Cl2): 480 nm. H NMR (CDCl3): 8.06 (2H, d,
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J=8.4), 7.89 (4H, t, J=8.4 Hz), 6.76 (2H, d, J=9.2 Hz), 3.11 (6H, t, J=20 Hz) 2.64 (3H, s). 13C NMR:
26.7, 40.2, 111.4, 122.1, 125.5, 129.3, 136.9, 143.7, 152.9, 155.9, 197.5. Anal. Calcd for C16H17N3O:
C, 71.89; H, 6.41; N, 15.72%. Found: C, 71.79; H, 6.78; N, 15.46%.
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1-((4-hydroxyphenyl)diazenyl)naphthalen-2-ol (Table 2, 3p): (0.2245 g, 85%), (recrystallized from
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ethanol:water, 9:1). IR (KBr) cm-1: 3424, 1598, 1458, 1279, 1216, 844, 744. H NMR (Acetone-d6):
14.97 (NH, s), 9.22 (OH, s) 8.82 (1H, d, J=8.4 Hz), 7.95 (2H, d, J=8.8 Hz), 7.94 (1H, d, J=9.6 Hz),
7.86 (1H, d, J=7.6 Hz), 7.86 (1H, d, J=7.6 Hz), 7.63 (1H, d, J=7.6 Hz), 7.46 (2H, d, J=7.6 Hz), 7.15
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(1H, d, J=9.6 Hz), 7.08 (1H, d, J=8.8 Hz). C NMR: 116.37, 120.6, 121.45, 123.38, 124.5, 127.9,
128.3, 128.41, 132.38, 135.24, 143, 143.6, 155.61, 160.06, 172. Anal. Calcd for C16H12N2O2: C,
72.72; H, 4.58; N, 10.60%. Found: C, 72.92; H, 4.38; N, 10.58%.
1-((4-nitrophenyl)diazenyl)naphthalen-2-ol (Table 2, 3q): (0.258 g, 88%), as a dark red solid,
(recrystallized from ethanol:water, 9:1). IR (KBr) cm-1: 3384, 1632, 1516, 1448, 1352, 1245, 1205,
805, 749. 1H NMR (CDCl3): 16.15 (NH, s), 8.51 (1H, d, J=8 Hz), 8.39 (2H, d, J=9.2 Hz), 8.01 (2H, d,
J=9.2 Hz), 7.93 (1H, d, J=8.8 Hz), 7.71 (1H, d, J=7.6 Hz) 7.62 (1H, d, J=8 Hz), 7.53 (1H, d, J=8 Hz),
6.72 (1H, d, J=8.8 Hz). Anal. Calcd for C16H11N3O3: C, 65.53; H, 3.78; N, 14.33%. Found: C, 65.60;
H, 3.67; N, 14.34%.
2-((2-hydroxynaphthalen-1-yl)diazenyl)benzoic acid (Table 2, 3r): (0.225 g, 77%), as an orange red
solid, (recrystallized from acetone). IR (KBr) cm-1: 1712.67, 1604.66, 1558.38, 1504.37, 1396.37,
1257.50, 1110.92, 748.33. UV (λmax in DMSO): 483 nm. 1H NMR (CDCl3): 16.4 (NH, s), 8.28 (1H, d,
J=8 Hz), 8.178 (1H, d, J=7.2 Hz), 7.96 (1H, d, J=8 Hz), 7.55-7.47 (3H, m), 7.40-7.34 (2H, m), 7.05
(1H, d of d, J=7.2, 7.6 Hz), 6.51 (1H, d, J=9.6). Anal. Calcd for C17H12N2O3: C, 69.86; H, 4.14; N,
9.58 %. Found: C, 69.66; H, 4.51; N, 9.38%.
2-((2,4-dihydroxyphenyl)diazenyl)-5-methylbenzoic acid (Table 2, 3s): (0.250 g, 92%), as a dark red
solid, (purified by short column chromatography using n-hexane and ethyl acetate, 8:2). IR (KBr)
cm-1: 2923.88, 1620.09, 1427.23, 1380.94, 1265.22, 1211.21. UV (λmax in DMSO): 405 nm. 1H NMR
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(CDCl3): 7.85-7.81 (3H, m), 7.31-7.33 (2H, m), 6.47 (2H, br, s), 2.35 (3H, s). Anal. Calcd for
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C14H12N2O4: C, 61.76; H, 4.44; N, 10.29%. Found: C, 62.2; H, 4.67; N, 10%.
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4-((4-nitrophenyl)diazenyl)benzene-1,3-diol (Table 2, 3t): (0.225 g, 87%), as an orange red solid,
(recrystallized from ethanol:water, 9:1). IR (KBr) cm-1): 3467.92, 1602.42, 1526.61, 1503.24,
1342.03, 1271.31, 1140.41. UV (λmax in DMSO): 428 nm. 1H NMR (CDCl3): 8.71 (1H, t, J= 1.8 Hz,),
8.28-8.32 (1H, m), 8.23 (1H, t, J= 7.2 Hz), 7.95 (2H, d, J= 8.7 Hz), 7.69, (1H, t, J= 8.1 Hz), 6.99 (2H,
d, J= 8.7 Hz), 5.37 (OH, br, 1H). 13C NMR: 163.66, 157.03, 150.97, 149.07, 132.82, 130.54, 127.19,
121.60, 109.81, 103.44. Anal. Calcd for C16H12N2O4S: C, 58.53; H, 3.68; N, 8.53%. Found: C, 58.38;
H, 3.79; N, 8.66%.
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3. Results and discussion
Arene diazonium salts are highly useful intermediates in organic synthesis due to their rich reactivity
and diverse transformations. Usually, they are synthesized around 10 ºC, and to avoid their
decomposition, are handled below 0 ºC. In this new method, diazotization and diazo coupling reaction
of aniline derivatives with electron withdrawing groups as well as electron-donating groups were
examined under solvent-free conditions at room temperature. First, in order to optimize the
conditions, different ratios of aniline and sodium nitrite were studied in the presence of various
quantities of nano--Fe2O3-SO3H as a catalyst (Table 1, Entries 1-7). The best amount of catalyst was
0.65 g (Table 1, Entry 6). It should be emphasized that the presence of the catalyst is critical to a
successful outcome, since no product was formed in the absence of the catalyst (Table 1, Entry 8).
Table 1
The process was carried out in two steps: the aromatic amine (1 mmol), nanomagnetic-supported
sulfonic acid (0.65 g), sodium nitrite (2 mmol), and 0.1 mL of water were homogenized by grinding in
a mortar with a pestle for a few minutes. Then the reaction mixture is ground for 5–10 min until the
gas evolution completely stops. Then, coupling reagent was added to the diazonium salt and grinding
continued for 10 min. the whole process of diazotization and diazo coupling took 10–20 minutes. The
crude product was extracted with acetone or ethanol, and after evaporation of the solvent, the crude
product was purified by recrystallization or short column chromatography. It is important to mention
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that our new conditions also provide a fast and facile work-up; after completion of the reaction, the
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mixture was triturated with hot ethanol or acetone. Within a few seconds, after stirring was stopped,
the reaction mixture turned clear and the catalyst was deposited on the magnetic bar, which was easily
removed with an external magnet, after being washed with acetone and dried in air, the nano-γ-Fe2O3-
SO3H catalyst could be used at least three times without significant loss of activity. As is indicated in
Table 2, electron-deficient, -neutral and -rich aryl amines were all successfully transformed to the
corresponding azo dyes. Also, the various coupling reagents were employed in this reaction and high
yields were obtained.
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Table 2
The intrinsic instability of diazonium compounds limits the applications of them. So in order to
investigate the stability of the diazonium salts prepared by this method, some aryldiazonium salts
supported on nanomagnetic-supported sulfonic acid were stored in a desiccator at room temperature.
After the specified times in Table 3, coupling reagent was added to each salt and the reaction mixture
was ground at room temperature. The products were extracted and the yields of azo dyes
compared with the product provided with the corresponding fresh diazonium salts. As shown in
Table 3, aryl diazonium nanomagnetic sulfates with electron-withdrawing groups on the aromatic
rings were more stable than those with electron-donating groups because of the instability of the
resulting aryl cation.
Table 3
Table 4 compares the efficiency of our method with other published results. As indicated in Table 4,
the main advantage of this research is the creation of diazonium salts that are relatively stable at room
temperature (Compared with rows 1-7). Other benefits of this method are the fast reaction time, clean
and environmentally benign catalyst. Furthermore, easy isolation of the catalyst from the reaction
mixture was enabled by use of an external magnet.
Table 4
4. Conclusion
This synthetic method combines several advantages: 1) First, aryl diazonium nanomagnetic sulfate is
easily prepared in large quantities from aniline derivatives; 2) both reaction steps (diazotization–azo
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coupling) take place at room temperature; 3) the leaving group N2 does not interfere with the reaction
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mixture; 4) the coupling reaction proceed with high chemo selectivity. 5) Easy magnetic separation of
the catalyst eliminates the requirement of catalyst filtration after completion of the reaction. In the
absence of a magnetic field, the catalyst disperses in the same manner as any nanoparticle. However,
in the presence of a magnetic field, it can be selectively precipitated. This property enables it to be
readily removed from the reaction vessel by a simple magnetic separation and may enable it to be re-
dispersed and re-used again. 6) The whole process of diazotization-diazo coupling reaction take 10-20
minutes, thus the time factor is another advantage. For these reasons, we wish to report an efficient,
rapid, and one pot procedure for the synthesis of azo dyes employing aryl diazonium nanomagnetic
sulfates in the presence of activated aromatic compounds at room temperature.
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4. Acknowledgements
The authors gratefully acknowledge Semnan University Research Council for financial supporting
this work.
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Captions
Scheme 1. One-pot diazotiation-diazo coupling reaction of aryl amines via aryl diazonium
nanomagnetic sulfate.
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Table
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Table 1
Effect of reagent and catalyst amounts on the synthesis of N,N-dimethyl-
4-(phenyldiazenyl)aniline
Entry
Sodium nitrite : aniline
Yield (%)a
-Fe2O3-SO3H (g)
1
2
3
4
5
6
7
8
1:1
1:1
1:1
2:1
2:1
2:1
4:1
2:1
0.45
0.55
0.65
0.45
0.55
0.65
0.65
-
40
50
55
70
80
94
85
Trace
a Isolated yields.
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Table 2
Diazotization and diazo coupling reaction of aromatic amines by nanomagnetic-supported sulfonic acid under solvent-free
conditions at room temperature a,b
Product
number
Entry
Substrate
Coupling reagent
Product
Time (min)
Yield (%)
1
10
86
3a
2
3
4
5
6
7
20
15
20
10
15
10
81
94
85
79
95
93
3b
3c
3d
3e
3f
3g
8
9
10
20
90
89
3h
3i
10
11
10
20
85
91
3j
3k
12
13
10
10
90
94
3l
3m
14
15
16
20
10
20
83
93
85
3n
3o
3p
17
10
88
3q
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18
20
77
3r
19
20
20
10
92
87
3s
3t
a The yields refer to the isolated pure products.
1
b The products were characterized from their spectral data (IR, H NMR, 13C NMR, UV, CHN and mp) and compared with
authentic samples [28-31].
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Table 3 The stability of some aryl diazonium nano magnetic sulfates at room temperaturea,b
Yield (%)a after
Diazonium salt
Product
30 min
1 day
2 days
3 days
86
65
55
50
3a
79
88
61
76
50
70
50
65
3e
3q
a
The yields refer to the isolated pure products after adding 2-Naphthol into their corresponding
diazonium salts within the specified time.
b
Each yield of the product was compared with the product provided with the corresponding fresh
diazonium salt.
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Table 4 Comparison of diazotization of aromatic amines by nano-γ-Fe2O3-SO3H with the reported values.
Entry
1
2
3
4
5
6
7
8
Condition
Time (min)
30
20-40
20-40
-
120
45-60
6-7
Yield (%)
90
Ref.
[32]
[31]
[30]
[33]
[34]
[35]
[36]
[29]
PTSA/MeCN/10-25 ºC
SiO2-IL-ONO/HCl//0-5 ºC
IL-ONO/HCl/0-5 ºC
H2SO4/0-5 ºC
Activated clay with HCl /0-5 ºC
HCl(conc.)/0 ºC
Nano-BF3.SiO2/Solvent-free/r.t
Fe(HSO4)3/SiO2/H2O/r.t
wet SSA/Solvent-free/r.t
γ-Fe2O3-SO3H/Solvent-free/ r.t
74-92
71-90
25-80
30-85
65-85
77
80-97
55-86
77-95
3-20
20-30
10-20
9
10
[37]
This work
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13