An environmentally friendly approach to the green synthesis of azo dyes in the presence of magnetic solid acid catalysts

Article abstract of DOI:10.1039/c4ra13562h

A solvent-free, efficient and green approach for the synthesis of azo dyes has been developed by the diazo coupling reactions of aromatic amines with β-naphthol in the presence of sulfonic acid functionalized magnetic Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂-SO₃H) by a grinding method at room temperature. This green methodology aims to overcome the limitations and drawbacks of the previously reported methods such as low temperature, use of acids, alkalis and toxic solvents, instability of diazonium salts at room temperature, modest yields, and long reaction times. Moreover, the attractive advantages of the process include mild conditions with excellent conversions, simple product isolation process, inexpensive procedure and recyclability of the magnetic catalyst. This journal is

Full text of DOI:10.1039/c4ra13562h

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PAPER
An environmentally friendly approach to the green
synthesis of azo dyes in the presence of magnetic
solid acid catalysts
Cite this: RSC Adv., 2015, 5, 17738
Javad Safari* and Zohre Zarnegar
A solvent-free, efficient and green approach for the synthesis of azo dyes has been developed by the diazo
coupling reactions of aromatic amines with b-naphthol in the presence of sulfonic acid functionalized
3 4 3 4 2 3
magnetic Fe O nanoparticles (Fe O @SiO -SO H) by a grinding method at room temperature. This
green methodology aims to overcome the limitations and drawbacks of the previously reported methods
such as low temperature, use of acids, alkalis and toxic solvents, instability of diazonium salts at room
temperature, modest yields, and long reaction times. Moreover, the attractive advantages of the process
include mild conditions with excellent conversions, simple product isolation process, inexpensive
procedure and recyclability of the magnetic catalyst.
Received 31st October 2014
Accepted 26th January 2015
DOI: 10.1039/c4ra13562h
www.rsc.org/advances
their corresponding bulk materials. As the diameter of the
particle decreases to the nanometer scale, external surface area
1
. Introduction
11–13
In recent years, organic colour chemistry has been undergoing becomes available for chemical transformations.
Among
very exciting developments as a result of the opportunities these, solid acid systems and magnetically recyclable catalysts
presented by dye applications in modern technology elds such are unique due to their inherent properties such as biocom-
as linear and non-linear optics, reprography, electronic devices, patibility, thermal stability against degradation, easy renew-
1
sensors and biomedical uses. Azo dye compounds are the most ability and recovery by magnetic separation, higher catalytic
widely used class of synthesized organic dyes due to their activity due to the higher loading of active sites and large
1
4–16
versatile applications in different elds such as dyeing textile surface area.
Moreover, various solid acids have been used
2
3
17,18

bers,
biological–pharmacological
activities,
organic for the preparation of azo dyes compounds.
synthesis and as materials with excellent optic and photo- satisfactory yields of products are usually obtained, some of
electric properties. Azo dyes are generally synthesized in two these synthetic methods are not environmentally friendly and
Although
4
5
steps: the diazotization of aromatic primary amines, followed by suffer from one or more drawbacks such as control of the
the coupling reaction between diazonium salts and activated reaction temperatures, difficult purication, unsatisfactory
6,7
aromatic compounds (phenols or aromatic amines). The yields, and long reaction time. Therefore, the development of
formation of diazonium salts starts with the protonation of clean, high-yielding, mild, and green approaches is still a
nitrous acid under strongly acidic conditions and the azo challenge for diazotization and diazo coupling reactions.
ꢀ
coupling is carried out at low temperature (0–5 C) in the
The aim of this protocol is to highlight the synergistic effects
6
presence of nucleophilic coupling components. The main of the combined use of the grinding method and application of
limitations of this synthetic method are low temperature, use of recyclable strong solid acid nanocatalysts with inherent
acid–base catalyst, instability of aryl diazonium salts at room magnetic properties for the development of a new, eco-
temperature, modest yields, and long reaction times. However, compatible strategy for the synthesis of azo dyes. We prepared
the main limitation of such synthetic processes is its environ- Fe O nanoparticles by the co-precipitation method and
3 4
mental incompatibility. The acidic and basic effluents from the subsequently coated them with tetraethoxysilane (TEOS) via a
laboratory and industry result in permanent damage to the silanization process. The graing of chlorosulfonic acid on the
6
,7
environment and disturb the ecological balance.
Recently, solid acids have resolved these problems and Fe
improved activity and selectivity.
Fe
3
O
O
4
@SiO
@SiO
2
MNPs afforded sulfonic acid-functionalized
3
4
2
nanoparticles (Fe @SiO -SO H). Therefore, we
3
O
4
2
3
6
–10
In this regard, nano- now wish to explore a convenient and green one-pot procedure
structure solid acids exhibit higher activity and selectivity than for diazotization and diazo coupling reactions using
Fe O @SiO -SO H as a procient, mild, environmentally friendly,
3
4
2
3
non-toxic and powerful magnetic nanostructure solid acid catalyst
with good stability (Scheme 1). To the best of our knowledge, the
use of a magnetic solid acid catalyst for the synthesis of azo
Laboratory of Organic Compound Research, Department of Organic Chemistry, College
of Chemistry, University of Kashan, P.O. Box: 87317-51167, Kashan, I. R. Iran. E-mail:
Safari@kashanu.ac.ir; Fax: +98 361 5912397; Tel: +98 361 591 2320
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3 4 2 3
Scheme 1 One-pot method for diazotization and diazo coupling reactions using Fe O @SiO -SO H under solvent-free conditions.
compounds has not been reported previously. The ndings of this other hand, the band in this region became much broader. All
research may have implications for an effective synthesis on a these observations conrm that the sulfonic groups have
21
larger scale in dyeing and medical industries (Scheme 1).
functionalized the surface of the MNPs.
Fig. 2 presents the XRD-diffraction patterns of the Fe
3 4
O
MNPs, Fe
Fig. 2(a) shows the XRD pattern of Fe
3
O
4
@SiO
2
and Fe
3
O
4
@SiO
2
-SO
3
H nanocomposites.
nanoparticles, pre-
3
O
4
2
. Results and discussion
senting the characteristic peaks of cubic structure. In Fig. 2(b),
it can be seen that the diffraction peaks of Fe @SiO are
similar to those of the parent Fe O nanoparticles, which
2
.1. Characterization of the Fe
The rst step entails the synthesis of highly stable Fe
SO H MNPs. The magnetite Fe nanoparticles were prepared suggest that the phase structure of MNPs was well retained aer
using Massart's procedure and Fe @SiO nanocomposites forming outer SiO2 shells. Fig. 2(c) shows six characteristic
3 4 2 3
O @SiO -SO H MNPs
3
O
4
2
3 4 2
O @SiO -
3
4
3
3 4
O
19
3
O
4
2
20
were prepared according to the St ¨o ber method. The reaction of peaks, which reveal a cubic iron oxide phrase (2q ¼ 30.35, 35.95,
OH groups on Fe O @SiO with chlorosulfuric acid led to 43.45, 53.70, 57.25, 62.88, 71.37, 74.46); these are related to their
3
4
2
Fe O @SiO -SO H nanocomposites (Scheme 2). The number of corresponding indices of (2 2 0), (3 1 1), (4 0 0), (3 3 1), (4 2 2), (3
3
4
2
3
+
H
sites of magnetic solid acid was determined by pH-ISE 3 3), (4 4 0) and (5 3 1). It is implied that the resultant nano-
conductivity titration (Denver Instrument Model 270) and particles are pure Fe O with a spinel structure and that the
3
4
+
ꢀ
found to be 1.25 H sites per 1 g of solid acid at 25 C (pH 2.30). graing process did not induce any phase change of Fe O for
3
4
ꢀ
Fig. 1 shows the Fourier transform infrared (FTIR) pattern of the Fe O @SiO -SO H. The weak broad band at 2q from 20 to
3
4
2
3
ꢀ
ꢀ
ꢀ
the Fe
3 4 2 3
O @SiO -SO H nanocomposites. The Fe–O stretching 27 in the Fe O @SiO and the broad peaks at 2q from 18 to 27
3 4 2
ꢁ
1
vibration near 589 cm and O–H deformed vibration near 1630 in the Fe O @SiO -SO H shown in Fig. 2(b) and (c), respectively,
3
4
2
3
ꢁ
1
22,16
cm were observed for the magnetic nanocomposites. The are ascribed to amorphous silica.
appearance of the peaks at 1195 and 1131 cm is ascribed to
The components of the Fe O @SiO -SO H nanocomposites
3 4 2 3
the stretching of the S–O bonds. A peak appeared at about 3320 were analysed, by using an energy dispersive spectrometer
ꢁ1
ꢁ
1
3
cm due to the stretching of OH groups in the SO H. On the
3 4
Scheme 2 Preparation steps for fabricating sulfonic acid-functionalized magnetic Fe O nanoparticles.
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3 4 2 3
Fig. 1 The FT-IR spectrum of Fe O @SiO -SO H nanocomposites.
3 4 2 3
Fig. 3 The EDS of Fe O @SiO -SO H nanocomposites.
(
EDS), as shown in Fig 3. The presence of S, Si, O, and Fe signals
in Fig. 3 indicates that the iron oxide nanostructure has been
coated by SO H groups.
The thermo gravimetric analysis (TGA) curves of the nano
particles and Fe @SiO -SO H nanocomposites show
3
Fe
3
O
4
3
O
4
2
3
the mass loss of the organic materials as they decompose upon
heating (Fig. 4). The initial weight loss from the magnetic
ꢀ
nanostructures up to 126 C is due to the removal of physically
Fig. 2 Powder XRD patterns: (a) Fe
Fe @SiO -SO H nanocomposites.
3 4 3 4 2
O , (b) Fe O @SiO and (c)
Fig.
4
TGA curve of (a) Fe
O
3 4
3 4 2 3
and (b) Fe O @SiO -SO H
3
O
4
2
3
nanocomposites.
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3 4 3 4 2 3 4 2 3
Fig. 5 The SEM image of (a) Fe O (b) Fe O @SiO , (c) Fe O @SiO -SO H before the reaction and (d) after the reaction.
nanocomposites are spherical with particle size of about 120
nm. Fig. 5(c) shows that Fe @SiO -SO H nanocomposites are
3
O
4
2
3
nearly spherical with nano dimension ranging from 120 to 150
nm in size and have smoother surface.
The magnetic property of the nanostructures was studied by
VSM, as shown in Fig. 6. The magnetization curve for Fe
3 4
O
nanoparticles, Fe O @SiO and Fe O @SiO -SO H are shown in
3
4
2
3
4
2
3
Fig. 6. The saturation magnetization of Fe O @SiO and
3
4
2
Fe O @SiO -SO H nanocomposites were found to be 45.87 and
3
4
2
ꢁ
3
1
2
2.67 emu g , respectively, which are much lower than that of
bare Fe O MNPs (67.22 emu g ) due to the coated silica shell.
3 4
ꢁ
1
Fig. 6 Magnetization curves for the Fe
3 4 3 4 2 3
O , Fe O @SiO and Fe -
2
.2. Diazotization and diazo coupling reactions on
O
4
@SiO -SO H nanocomposites at room temperature.
2
3
Fe @SiO -SO H under solvent-free conditions
3
O
4
2
3
Diazonium salts are very important intermediates in the
synthesis of organic compounds, especially azo dyes. However,
the poor thermal stability of diazonium salts, strong acidic
conditions, and the difficulty to separate the acidic catalysts
from the reaction medium limit the application of these
compounds. We tried to solve these problems by developing a
green and facile procedure for the synthesis of azo dyes in the
presence of a magnetic solid acid catalyst.
adsorbed solvent and surface hydroxyl groups. The TGA curve of
the Fe @SiO -SO H was divided into several regions corre-
3
O
4
2
3
sponding to different ranges of mass loss. The rst region,
ꢀ
which occurred below 160 C, displayed a mass loss that was
attributable to the loss of adsorbed solvent or trapped water
from the magnetic nanocomposites. The weight loss at higher
ꢀ
temperature (250–500 C) could be mainly attributed to the
evaporation and subsequent decomposition of SO
3
H moieties.
3 4 2 3
Initially, the efficiency of Fe O @SiO -SO H as acidic catalyst
The occurrence of further mass losses at higher temperature
in the diazotization reaction, followed by diazo coupling with b-
naphthol, was explored via a model reaction. 4-Bromoaniline
was selected as a model substrate and the reaction parameters,
such as amount and type of catalyst, stability of diazonium salt
at room temperature, reaction time of diazotization, yield of
resulted azo dyes and also reusability of solid acid catalyst, were
23
resulted from the decomposition of silica shell.
Fig. 5 shows the SEM images of the relative magnetic
nanostructures. It can be seen from Fig. 5(a) that Fe O nano-
3
4
particles have a mean diameter of about 30 nm. The SEM image
shown in Fig. 5(b) demonstrates that most of Fe O @SiO
2
3
4
Table 1 Comparison of efficiency of various catalysts for the synthesis of azo dyes
Stability of diazonium
Entry
Catalyst (g)
salt at r.t
Time of diazotization
Yield of azo dyes (%)
1
2
3
4
5
6
7
8
9
Fe
Fe
Fe
Fe
Fe
3
3
3
3
3
O
O
O
O
O
4
4
4
4
4
@SiO
@SiO
@SiO
@SiO
@SiO
2
2
2
2
2
-SO
-SO
-SO
-SO
-SO
3
3
3
3
3
H (0.2)
H (0.4)
H (0.5)
H (0.6)
H (0.7)
24 months
24 months
24 months
24 months
24 months
2 days
2 days
—
—
—
20 s
20 s
20 s
20 s
65
85
90
88
82
45
80
—
—
—
20 s
Silica phosphoric acid (0.5)
Silica sulfonic acid (0.5)
Silica gel (0.5)
Fe
Fe
35 min
10 min
No reaction
No reaction
No reaction
3
O
O
4
@SiO
2
(0.5)
1
0
3
4
(0.5)
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3 4 2 3
Table 2 The synthesis azo dyes in the presence of Fe O @SiO -SO H by grinding method under solvent-free conditions
ꢀ
Entry
R
Time (min)
Product
Yield (%)
MPrep./MPLit. ( C)
1
2
3
4
5
6
7
8
9
H
25
30
30
25
20
20
15
15
10
10
10
15
2a
2b
2c
2d
2e
2f
2g
2h
2i
88
83
85
90
90
90
85
85
90
92
91
88
132–134/131–133 (ref. 24)
244–246/245 (ref. 25)
164–165/166 (ref. 25)
2-NO
2-Cl
4-NO
4-Br
4-Cl
4-CH
4-CH
4-OH
4-OMe
4-CH CH
4-NH
2
2
252–254/254–256 (ref. 24)
157–160/157–159 (ref. 24)
168–170/169–171 (ref. 24)
244–246/245 (ref. 25)
130–132/130–132 (ref. 24)
191–193/191–193 (ref. 26)
137–138/136–137 (ref. 27)
133–134/133–134 (ref. 28)
301–302/300–302 (ref. 29)
3
3
CH
2
10
11
12
2j
2k
2l
3
2
O
2
examined. As shown in Table 1, the results show that Fe O @ ltration; however, the magnetite-supported catalyst can be
3
4
2 3
SiO -SO H nanocomposites were the best among the tested separated from the reaction system by an external permanent
catalysts in terms of the reaction time of diazotization and magnet. This will circumvent time-consuming and laborious
synthesis of azo-dyes with excellent yields and short reaction separation steps.
times (Table 1, entry 3). In addition, other solid acids, such as
Aer establishing the optimal conditions, in order to prove
silica phosphoric acid and silica sulfonic acid, yielded azo dyes the generality of this method, different types of aromatic amine
with lower yields (Table 1, entries 6–7). Moreover, the rate of derivatives with electron-withdrawing groups as well as
diazotization in the presence of Fe O @SiO -SO H was much electron-donating groups, were converted to the corresponding
3
4
2
3
higher than the other catalysts. The small size of nanoparticles azo dyes in high yields by the grinding method under solvent-
and large surface to volume ratio in Fe @SiO -SO H can be free conditions at room temperature (Table 2). It is important
3
O
4
2
3
the reason for the greater stability of the diazonium salt in that the reaction requires a small amount of water for the
comparison to that supported on the bulk acid catalyst. There formation of moist conditions and the addition of water must
was no reaction in the presence of silica gel, Fe
3
O
4
@SiO
2
and be carried out in a stepwise manner to ensure good yields.
The structure of azo dyes was deduced from their high-
Fe (Table 1, entries 9–11). Interestingly, in the synthesis of
3 4
O
1
azo dyes, most of the immobilized catalysts are separated by eld H NMR, IR, R , and UV spectral data. Moreover, their
f
1
Fig. 7 H NMR spectra of 1-(4-chlorophenyl azo)-2-naphthol (2f) in (a) CDCl
3
and (b) CDCl
3
+ D
2
O.
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. Conclusions
In summary, we have developed a highly efficient green method
for the diazotization and subsequent azo-coupling for the
preparation of azo dyes. This new protocol has some advantages
over traditional methods, which include the rapid and solvent-
free synthesis of diazonium salts in high conversion at room
temperature, long-term stability of diazonium salts supported
Fig. 8 Recyclability of Fe
O
3 4
@SiO
2
-SO
3
H for the one-pot synthesis of on Fe O @SiO -SO H, no use of toxic solvents, acid catalysts,
3
4
2
3
2e.
short reaction times in synthesis of azo compounds and recy-
clability of the magnetic catalyst.
1
1
melting points were compared with previous reports.
H
4
. Experimental
NMR spectra for compound 2f is given in Fig. 7. In the H
NMR spectra in Fig 7(a), the signals of aromatic protons can
be seen at d ¼ 6, 88–8.56 ppm. The signal at around d ¼ 16.11
ppm is related to the OH proton corresponding to the
N–H/O proton, which is involved in the relevant intra-
molecular hydrogen bond. The presence of this signal
conrmed the formation of the desired products in this
reaction. To prove the presence of the OH group, we have
investigated the hydrogen–deuterium exchange protocol for
4.1. Chemicals and apparatus
Chemical reagents in high purity were purchased from Merck
and Aldrich and were used without further purication. Melting
points were determined in open capillaries using an Electro-
1
13
thermal Mk3 apparatus and are uncorrected. H NMR and
C
NMR spectra were recorded with a Bruker DRX-400 spectrom-
eter at 400 and 100 MHz, respectively. FT-IR spectra were
obtained with potassium bromide pellets in the range 400–4000
ꢁ
1
compound 2f (Fig. 7(b)). In this method, a drop of D O is
placed in the NMR tube containing the CDCl solution of the
3
2
cm with a Perkin-Elmer 550 spectrometer. Nanostructures
were characterized using a Holland Philips Xpert X-ray powder
diffractometer (XRD, CuKa, radiation, l ¼ 0.154056 nm), at a
compound 2f. Aer shaking the sample and sitting for a few
minutes, the OH hydrogen is replaced by deuterium, causing
it to disappear from the spectrum at d ¼ 16.11 ppm and a new
peak appears around d ¼ 4.89 ppm, corresponding to DOH.
ꢀ
ꢁ
1
ꢀ
ꢀ
scanning speed of 2 min from 10 to 100 (2q). Scanning
electron microscopy (SEM) was performed using a FEI Quanta
200 SEM operated at a 20 kV accelerating voltage. The samples
ꢀ
Azo dyes are usually synthesized around 0–10 C, because
for SEM were prepared by spreading a small drop containing
nanoparticles onto a silicon wafer, drying almost completely in
air at room temperature for 2 h, and then transferring onto SEM
conductive tapes. The transferred sample was coated with a thin
layer of gold before measurement. The purity of the compounds
synthesized was monitored by TLC, visualized with ultraviolet
ꢀ
temperatures above 5 C cause the decomposition of diazo-
nium salts and conversion to side products before coupling
reactions. This is the main reason for the modest yield of the
products. To overcome this limitation, we decided to use
Fe @SiO -SO H as a solid acid catalyst to be able to do the
reaction at room temperature. Moreover, the stability of
diazonium salts supported on solid acid nanocatalyst at
room temperature signicantly increased the efficiency of
azo dyes synthesis.
1
2
3
O
4
2
3
1
13
light. The known products were characterized by H and
C
NMR, IR data and melting point and compared with the
reported values. All the yields refer to isolated products aer
purication.
Aer completion of the reaction, the separated catalyst can
be reused aer washing with acetone and ethanol and drying at
4
.2. Preparation of the magnetic Fe
Fe nanoparticles were synthesized using a chemical co-
precipitation method described in previous reports. In brief,
0 mmol of FeCl $6H O and 10 mmol of FeCl $4H O were
3 4
O nanoparticles
ꢀ
70 C. We showed that the catalyst could be reused for the next
3 4
O
cycle without great loss of catalytic activity (Fig 8). However,
aer 4 times of reuse, Fe @SiO -SO H got aggregated (as
30
3
O
4
2
3
2
3
2
2
2
shown in SEM image Fig. 5(d)), due to which the active func-
tional groups became unavailable. As a result, the catalyst got
lost in the chemical reaction and the efficiency of recovery
decreased gradually.
dissolved in 75 ml of distilled water in a three-necked round
bottomed ask under Ar atmosphere for 30 min. Then, 10 ml of
NaOH (10 M) was added into the solution within 30 min with
vigorous mechanical stirring under continuous Ar atmosphere
bubbling. Aer being rapidly stirred for 1 h, the mixture was
heated to 85 C for 1 h. The black precipitate formed was iso-
lated by magnetic separation, exhaustively washed with double-
distilled water and ethanol until neutrality and then dried at
Titration was used to determine the acid loading of the
recovered catalysts. 100 mg of recycled catalyst was stirred in 20
ml of 0.1 N NaOH solution for 30 min in an Erlenmeyer ask.
The excess amount of base was then neutralized by the addition
of 0.1 N HCl solution to the equivalence point of titration. The
ꢀ
ꢀ
+
60 C in vacuum.
amount of acid sites on a solid acid surface was 1.24 H sites per
1
g of solid acid. Thus, the magnetite solid acid catalyst is stable
4.3. Silica coated MNPs (Fe
3 4 2
O @SiO )
in the diazotization and diazo coupling reactions. This result
clearly conrms that there is no leaching of SO
occurring during the course of the reaction.
3
H groups The Fe O @SiO nanocomposites were prepared according to
3
4
2
20
the modied St ¨o ber method. The details are as follows: 0.50 g
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3
of the freshly made Fe
3
O
4
nanoparticles as described above (dd, 1H, J ¼ 8.3, 6.8 Hz, Ar-H), 7.50–7.56 (m, 3H, Ar-H), 7.67 (d,
3
3
were homogeneously dispersed in a mixture of 50 ml of ethanol, 1H, J ¼ 9.5 Hz, Ar-H), 7.77–7.83 (dd, 1H, J ¼ 8.3, 6.8 Hz, Ar-H),
3
3
9
ml of deionized water, and 1.0 ml of 28 wt% concentrated 8.31 (d, 1H, J ¼ 8.4 Hz, Ar-H), 8.43 (d, 2H, J ¼ 8.3 Hz, Ar-H),
ammonia aqueous solution (NH $3H O), followed by the addi- 16.75 (s, 1H, OH).
3
2
ꢀ
tion of 0.50 ml of TEOS. Aer vigorous stirring at room
Compound 2c. Red powder; MPrep. ( C): 164–165; MPLit.
temperature for 16 h under Ar atmosphere, the magnetic ( C): 166; MF: C17H N O ): MWextract (amu): 282.72; UV-Vis:
12 2 3
ꢀ
25
ꢁ1
nanocomposites (Fe
3
O
4
@SiO
2
) were isolated by magnetic
l
max CHCl
3
¼ 488 nm; IR (KBr) n (cm ): 3451 (OH), 1605
1
decantation to remove the unbounded silica particles and dried (C]C), 1500 (N]N), 1245 (C–O), 1085 (C–Cl); H NMR (CDCl
3
+
ꢀ
at 60 C in vacuum aer being washed with de-ionized water DMSO-d
6
, 400 MHz) d (ppm): 7.05–7.03 (m, 4H, Ar-H), 7.44 (t,
3
3
and ethanol.
1H, J ¼ 8.0 Hz, Ar-H), 7.58 (t, 1H, J ¼ 8.0 Hz, Ar-H), 7.70 (d, 1H,
3 3 3
J ¼ 8.4 Hz, Ar-H), 7.75 (d, 1H, J ¼ 9.2 Hz, Ar-H), 7.83 (d, 2H, J
3
4.4. General procedure for the synthesis of Fe O @SiO -
¼ 9.2 Hz, Ar-H), 8.75 (d, 1H, J ¼ 8.4 Hz, Ar-H), 16.01 (s, 1H, OH).
3
4
2
ꢀ
SO H MNPs
Compound 2d. Red powder; MPrep. ( C): 252–254; MPLit.
3
ꢀ
24
(
C): 254–256; MF: C16
acetate; 10 : 1 (v/v)): 0.28; MWextract (amu): 293.28; UV-Vis: lmax
11 3 3 f
H N O ; R (in petroleum ether–ethyl
A 500 ml suction ask was equipped with a pressure equalizing
dropping funnel, containing chlorosulfonic acid and gas inlet
tube for conducting HCl gas over adsorbing the solution water.
A ask was charged with Fe
and dispersed in dry CH Cl
Then, chlorosulfonic acid (0.4 ml in dry CH
dropwise manner to a cooled (ice-bath) solution of Fe
over a period of 1 h, upon which HCl gas evolved from the
reaction vessel immediately. Aer the addition was completed,
the mixture was shaken for 30 min, Fe O @SiO -SO H was
ꢁ
1
CHCl
3
¼ 490 nm; IR (KBr) n (cm ): 3434 (OH), 1594 (C]C),
1
1
503 (N]N), 1332 (NO ), 1201 (C–O); H NMR (CDCl , 400 MHz)
2
3
3
O
4
@SiO
by ultrasonic bath for 30 min.
Cl ) was added
@SiO
2
2
nanocomposites (500 mg)
3
3
d (ppm): 6.81 (t, 1H, J ¼ 7.8 Hz, Ar-H), 7.43 (t, 1H, J ¼ 7.8 Ar-H),
2
2
3
3
7
.59 (m, 3H, Ar-H), 7.73 (d, 1H, J ¼ 7.2 Hz, Ar-H), 7.91 (d, 1H, J
2
2
3
3
¼
7.2 Hz, Ar-H), 8.10 (d, 1H, J ¼ 8.0 Hz, Ar-H), 8.51 (d, 1H, J ¼
3
O
4
3
8
.0 Hz, Ar-H), 8.54 (dd, 1H, J ¼ 8.1 Hz, Ar-H), 16.12 (s, 1H, OH);
1
3
3
C NMR (CDCl , 100 MHz) d (ppm): 112.33, 115.64, 117.08,
1
1
19.14, 119.52, 120.28, 121.85, 124.87, 127.20, 128.55, 130.19,
34.05, 137.46, 142.57.
Compound 2e. Orange red powder; MPrep. ( C): 157–160;
3
4
2
3
collected using a normal magnet and washed with CH
methanol, before being dried in an oven at 60 C.
2
Cl
2
and
ꢀ
ꢀ
ꢀ
24
MPLit. ( C): 157–159; MF: C H CN O; R (in petroleum ether–
16
11
l2
f
ethyl acetate; 10 : 1 (v/v)): 0.47; MW
(amu): 282.72; UV-Vis:
extract
ꢁ
4
.5. Typical procedure for the diazotization and azo
coupling reactions
-Bromoaniline (2 mmol), Fe
1
l
CHCl ¼ 486 nm; IR (KBr) n (cm ): 3445 (OH), 1620 (C]
max
3
1
C), 1486 (N]N), 1253 (C–O), 1090 (C–Cl); H NMR (CDCl
3
, 400
4
3
O
4
@SiO
2
-SO
3
H MNPs (0.5 g) and
3
MHz) d (ppm): 6.88 (d, 1H, J ¼ 9.6 Hz, Ar-H), 7.44–7.46 (m, 3H,
sodium nitrite (4 mmol, 0.276 g) were ground in a mortar with a
pestle for a few minutes. Then, a few drops of water was grad-
ually added to this and the grinding continued further for 10
min to obtain a homogeneous mixture. Then, b-naphthol (2
mmol) was added to the diazonium salt and the grinding
continued for a longer time. The progress of the reaction was
monitored by TLC (petroleum ether–ethyl acetate 10 : 1). The
crude product was extracted with acetone (3 ꢂ 10 ml) and the
solid acid was magnetically separated. The solvent was evapo-
rated by rotary evaporator and the crude product puried by
recrystallization in EtOH.
3
3
Ar-H), 7.55 (d, 1H, J ¼ 7.2 Hz, Ar-H), 7.57 (d, 1H, J ¼ 7.2 Hz, Ar-
3
H), 7.68–7.75 (m, 4H, Ar-H), 8.56 (d, 1H, J ¼ 8.1 Hz, Ar-H), 16.11
13
2 3
(s, 1H, OH, D O exchangeable); C NMR (CDCl , 100 MHz) d
(ppm): 115.43, 116.90, 118.45, 119.22, 120.18, 120.66, 122.88,
125.20, 128.00, 128.45, 141.22, 144.95, 147.84, 154.16.
ꢀ
Compound 2f. Bright red powder; MP
( C): 168–170;
rep.
ꢀ
24
11 2 f
MPLit. ( C): 169–171; MF: C16H N OBr; R (in petroleum
ether–ethyl acetate; 10 : 1 (v/v)): 0.45; MWextract (amu): 327.18;
ꢁ1
UV-Vis: lmax CHCl
3
¼ 485 nm; IR (KBr) n (cm ): 3434 (OH),
1
3
1618 (C]C), 1496 (N]N), 1142 (C–O); H NMR (CDCl , 400
3
3
MHz) d (ppm): 6.88 (d, 1H, J ¼ 9.6 Hz, Ar-H), 7.42 (t, 1H, J ¼ 7.6
3
Hz, Ar-H), 7.55–7.61 (m, 6H, Ar-H), 8.54 (d, 1H, J ¼ 9.6 Hz, Ar-
4.6. Selected spectroscopic data of representative products
3
13
H), 8.56 (d, 1H, J ¼ 8.0 Hz, Ar-H), 16.10 (s, 1H, OH); C NMR
ꢀ
Compound 2a. Dark red needles; MPrep. ( C): 132–134; MPLit. (CDCl
, 400 MHz) d (ppm): 119.92, 120.03, 120.75, 121.77,
3
ꢀ
24
(
12 2
C): 131–133; MF: C16H N
O; MWextract (amu): 248.28; UV- 124.55, 125.97, 128.18, 128.72, 128.99, 130.27, 132.68, 133.37,
Vis: lmax CHCl ¼ 480 nm; IR (KBr) n (cm ): 3435 (OH), 1619 140.36, 144.05, 171.50.
ꢁ
1
3
1
ꢀ
(
(
C]C), 1457 (N]N), 1205 (C–O); H NMR (CDCl , 400 MHz) d
Compound 2g. Red powder; MPrep. ( C): 244–246; MPLit.
3
3
3
ꢀ
25
ppm): 6.70 (d, 1H, J ¼ 9.2 Hz, Ar-H), 7.09 (t, 1H, J ¼ 7.2 Hz, Ar- ( C): 245; MF: C18
16 2 f
H N O; R (in petroleum ether–ethyl acetate;
3
H), 7.23 (d, 1H, J ¼ 8.0 Hz, Ar-H), 7.33 (m, 3H, Ar-H), 7.41 (d, 10 : 1 (v/v)): 0.90; MWextract (amu): 276.34; UV-Vis: lmax CHCl
3
¼
3
3
ꢁ1
1
H, J ¼ 8.0 Hz, Ar-H), 7.54 (m, 3H, Ar-H), 8.35 (d, 1H, J ¼ 8.0 475 nm; IR (KBr) n (cm ): 3235 (OH), 1620 (C]C), 1504 (N]N),
1
3
Hz, Ar-H), 16.04 (s, 1H, OH).
11 430 (C–O); H NMR (CDCl
3
3
, 400 MHz) d (ppm): 1.43 (t, 3H, J
ꢀ
3
Compound 2b. Red powder; MPrep. ( C): 244–246; MPLit. ¼ 8.5 Hz, CH
), 2.52 (q, 2H, J ¼ 8.5 Hz, CH
), 6.83 (d, 1H, J ¼
3
2
ꢀ
25
3
3
(
C): 245; MF: C16
H
11
N
3
O
3
; R
f
(in petroleum ether–ethyl 7.2 Hz, Ar-H), 6.85 (d, 1H, J ¼ 9.2 Hz, Ar-H), 7.20 (t, 1H, J ¼ 8.2
3
acetate; 10 : 1 (v/v)): 0.13; MWextract (amu): 293.28; UV-Vis: lmax Hz, Ar-H), 7.23 (t, 1H, J ¼ 8.2 Hz, Ar-H), 7.30–7.82 (m, 5H, Ar-H),
ꢁ
1
3
CHCl ¼ 490 nm; IR (KBr) n (cm ): 3443 (OH), 1609 (C]C), 8.58 (d, 1H, J ¼ 7.5 Hz, Ar-H), 16.09 (s, 1H, OH).
3
1
ꢀ
1
569 (NO
2
), 1480 (N]N), 1315 (NO
2
), 1186 (C–O); H NMR
Compound 2h. Red powder; MPrep. ( C): 130–132; MPLit.
3
ꢀ
24
(CDCl
3
, 400 MHz) d (ppm): 6.70 (d, 1H, J ¼ 9.5 Hz, Ar-H), 7.42 ( C): 130–132; MF: C17
14 2
H N O; MWextract (amu): 262.31; UV-
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Paper
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ꢁ
1
Vis: lmax CHCl
3
¼ 470 nm; IR (KBr) n (cm ): 3420 (OH), 1615
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(
(
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Chem., 2011, 335, 46.
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3
3
2
H, J ¼ 8.0 Hz, Ar-H), 7.44 (t, 1H, J ¼ 7.2 Hz, Ar-H), 7.59 (t, 1H, 11 R. Karimian, F. Piri, B. Karimi and A. Moghimi, Chin. J.
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13
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C
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3
1
1
25.36, 127.82, 128.20, 129.22, 130.75, 139.10, 141.25, 144.69, 13 A. Bamoniri, B. F. Mirjalili and S. Nazemian, Curr. Chem.
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This study is part of Zohre Zarnegar's PhD thesis entitled: “The 16 A. Mobaraki, B. Movassagh and B. Karimi, Appl. Catal., A,
preparation of magnetic iron oxide nanostructures and their
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