Nano-CuFe2O4-supported sulfonic acid as a novel and recyclable nanomagnetic acid for diazotization of aromatic amines: efficient synthesis of various azo dyes

Article abstract of DOI:10.1007/s13738-016-0818-x

Abstract: A novel heterogeneous sulfonic acid functionalized nanomagnetic CuFe₂O₄ was successfully prepared and characterized by analyzing different obtained data including Fourier transform infrared spectroscopy, X-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, dynamic light scattering and vibrating sample magnetometer. Then the novel acidic reagent was examined in synthesis of various azo-containing compounds from coupling of aryl diazonium ferrite sulfate salts with aromatic and non-aromatic compounds. The procedure starts by diazotization of aromatic amines with NaNO₂ and wet CuFe₂O₄–SO₃H and then coupling reaction of aryl diazonium ferrite sulfate salts with appropriate reagent. The prepared nano-solid acid showed high activity in synthesis of variety of aryl diazonium salts. In addition the as-prepared aryl diazonium ferrite sulfate salts are stable at room temperature for many hours and reacted efficiently in coupling reactions of aryl diazonium salts. All the azo dyes are synthesized in high yields and simple reaction conditions at room temperature. Moreover, the nanomagnetic solid acid was easily recovered from the reaction mixture and reused five runs without significant loss of activity. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s13738-016-0818-x

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0818-x
ORIGINAL PAPER
Nano‑CuFe2O4‑supported sulfonic acid as a novel and recyclable
nanomagnetic acid for diazotization of aromatic amines: efficient
synthesis of various azo dyes
Firouzeh Nemati1 · Ali Elhampour1 · Mahshid B. Natanzi1 · Samaneh Sabaqian1
Received: 17 September 2015 / Accepted: 14 January 2016
© Iranian Chemical Society 2016
Abstract A novel heterogeneous sulfonic acid functional-
ized nanomagnetic CuFe2O4 was successfully prepared and
characterized by analyzing different obtained data includ-
ing Fourier transform infrared spectroscopy, X-ray powder
diffraction, field emission scanning electron microscopy,
energy-dispersive X-ray spectroscopy, thermogravimetric
analysis, dynamic light scattering and vibrating sample
magnetometer. Then the novel acidic reagent was examined
in synthesis of various azo-containing compounds from
coupling of aryl diazonium ferrite sulfate salts with aro-
matic and non-aromatic compounds. The procedure starts
by diazotization of aromatic amines with NaNO2 and wet
CuFe2O4–SO3H and then coupling reaction of aryl diazo-
nium ferrite sulfate salts with appropriate reagent. The pre-
pared nano-solid acid showed high activity in synthesis of
variety of aryl diazonium salts. In addition the as-prepared
aryl diazonium ferrite sulfate salts are stable at room tem-
perature for many hours and reacted efficiently in coupling
reactions of aryl diazonium salts. All the azo dyes are syn-
thesized in high yields and simple reaction conditions at
room temperature. Moreover, the nanomagnetic solid acid
was easily recovered from the reaction mixture and reused
five runs without significant loss of activity.
Introduction
Compounds containing azo groups linked to methine or
aromatic-sp2 hybridized-C atoms are the most important
group of pharmaceutically important materials in the lit-
erature [1]. These compounds have received much attention
and have wildly used in many practical applications such
as coloring fiber, photoelectronic applications, printing sys-
tems, optical storage technology and in analytical chemis-
try [2]. Many azo compounds have been applied as chro-
mogenic reagents for the determination of several metal
ions [3]. The synthesis of azo dyes is usually carried out at
low temperature in two steps: diazotization of arylamines
with sodium nitrite in the presence of aqueous Bronsted
acid, followed by reaction with electron-rich compounds or
enol-type coupling components. The former is an interest-
ing type of compound since they potentially have several
tautomeric forms in solution and solid state [4]. The main
limitation of such synthetic processes is their environmen-
tal incompatibility. The acidic effluents produce perma-
nent damage to the environment and disturb the ecological
balance.
One of the most important aims of “green chemistry” is
to find alternative catalysts or reagents being readily availa-
ble, inexpensive, selective, recyclable and environmentally
benign [5]. In this context, supported heterogeneous acid
catalysts have been actively investigated instead of harmful
homogeneous acids such as H2SO4, HF, and H3PO4 [6].
Recently, magnetic nanoparticles have increasingly
attracted interest as a support, due to their lack of toxicity,
high thermal and mechanical stability, and adaptability for
large-scale production and low price [7]. Remarkably, mag-
netic separation of the magnetic nanoparticles is more effi-
cient than conventional filtration, simple, effective and eco-
nomical and industrial applications. Among their various
Keywords Nanomagnetic-supported sulfonic acid ·
Diazonium salt · Azo dye · Aromatic amine
* Firouzeh Nemati
fnemati_1350@yahoo.com; fnemati@semnan.ac.ir
1
Department of Chemistry, Semnan University,
Semnan 35131-19111, Iran
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J IRAN CHEM SOC
Scheme 1 Preparation of
CuFe2O4–SO3H nanoparticles
magnetic nanoparticles, mixed metal oxide nanoparticles
became the strong candidates in the past few years and the
improvements of modern organic synthesis are followed
[8–10]. Hence, because of high catalytic activity of mixed
metal oxide nanoscale, they are preferable than individual
component oxides in diverse reactions [11, 12]. To this end,
nanoscale copper ferrite particles are of great interest as a
result of their efficient recycling, high stability, cleaning
reaction profile and unique magnetic property [13].
Loading of H+
The loading of H+ for the acidic magnetic nanoparticles
was determined using potentiometric titration and it found
to be 2.5 mmol/g.
General procedure for synthesis of aryldiazoium ferrite
sulfate salts
Aryl diazonium salts are important intermediates that
can be readily converted into a diverse functionality group
[14]. High activity of diazonium group (–N2+) cases aryl
diazonium salts possess sufficient potential energy to react
spontaneously with generally low transition state barri-
ers [15]. However, the key factors in the operation of such
transformations are the easy availability, stability and safety
of diazonium salts. So many researchers have investigated
how to use them in a safer and more sustainable ways [16].
Therefore, considering the points above and in con-
tinuation of our studies in design of heterogeneous nano-
catalysts [17–19] and successful attempt for the stabiliza-
tion of aryl diazonium salts [20, 21], the aim of this work
is to report the preparation and characterization of novel
magnetic nano-acid, a superior heterogeneous acid, in the
synthesis of aryl diazonium ferrite sulfate salts. Then the
diazonium salts, ArN+2 −OSO3CuFe2O4, as stable precur-
sors were used for the efficient synthesis of various azo
compounds from diazo coupling of aryl diazonium ferrite
sulfate salts with active aromatic and non-aromatic com-
pounds under solvent-free grinding condition (Scheme 1).
An aromatic amin (1 mmol), nano-CuFe2O4–SO3H (0.8 g)
and a few drops of water (0.2 mL) ground in a mortar with
a pestle to afford a homogeneous mixture, then NaNO2
(2 mmol) was added. The reaction mixture was ground
smoothly for 5–10 min. During this time the starting amine
was consumed that was established by TLC monitoring.
General procedure for synthesis of azo compounds
The as-synthesized aryl diazonium salt was added to active
compound (1 mmol) and the mixture was ground at room
temperature for appropriate time; the color of the reaction
will change [for the preparation of salt of 2-hydroxynaph-
thalene-1,4-dione and naphthol, we mixed 1 mmol from the
former compounds with 0.8 mL water and NaOH (0.1 g,
2.5 mmol) in the other vessel and then added to the aryl
diazonium salts]. After completion of the reaction (TLC),
the mixture was washed by distilled water (50 mL) and the
nano-CuFe2O4–SO3H was separated using an external mag-
net. The solid products were filtrate and washed with EtOH.
The most of the product were recrystallized from appro-
priate solvents and gave corresponding products in high
yields. Some of them need purification with short column
chromatography.
Experimental
CAUTION! Although aryldiazoium ferrite sulfate salts
are stable in the dry state, and we did not experience any
problems, the operation needs to be conducted carefully,
especially when they are subjected to grinding.
Spectroscopic data and physical properties of some
selected compounds:
Preparation of nano‑CuFe2O4–SO3H
Firstly, the nano-CuFe2O4 particles were prepared accord-
ing to literature report [22]. Then, in a flask, equipped with
a constant-pressure dropping funnel and a gas inlet tube
for conducting HCl gas over an adsorbing solution, nano-
CuFe2O4 (1 g) was charged. Then, neat chlorosulfonic acid
(3.3 mmol) was added drop-wise over a period of 0.5 h at
0–5 °C. HCl gas immediately evolved from the reaction
vessel. After that, the mixture was shaken for 1 h at room
temperature and nano-CuFe2O4–SO3H was collected as a
brown solid (1.25 g).
N,N-Dimethyl-4-[(2-nitrophenyl)diazenyl]aniline
(8a) 1H NMR (400 MHz, CDCl3) δ: 17.90 (d, 2H,
J = 9.2 Hz); 7.87 (d, d, 1H, J = 4 Hz, J = 1.2 Hz);
7.74 (d, d, 1H, J = 4 Hz, J = 1.2 Hz); 7.64 (t, d,
1H, J = 4 Hz, J = 1.2 Hz); 7.47 (t, d, 1H, J = 4 Hz,
J = 1.2 Hz); 6.76 (d, 2H, J = 9.2 Hz); 3.14 (s, 6H, Me);
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J IRAN CHEM SOC
1-(Phenyldiazenyl)naphthalen-2-ol (10a): 1H NMR
(400 MHz, CDCl3) δ: 16.31 (s, 1H); 8.59 (d, 1H,
J = 8.4 Hz,); 7.8 (s, 1H,); 7.6 (s, 1H,); 7.4 (s, 1H); 7.64–
7.57 (m, 2H); 8.59 (t, 2H, J = 7.52 Hz); 7.43 (t, d, 1H,
J = 7.6 Hz, J = 1.2 Hz); 7.34 (t, 1H, J = 7.6 Hz); 6.9 (d,
1H, J = 9.2);
135.36, 135.49, 140.90, 141.07, 175.82, 179.29, 179.58,
181.85; Calcd for C16H9N2O3Cl: C, 61.44; H, 2.88; N,
8.96; found: C, 61.04, H, 2.92; N, 8.76.
Results and discussion
2-[(4-Nitrophenyl)diazenyl]malononitrile (2b): bright
red color; UV–Vis (DMSO) λmax1 (π–π*):478 nm;
FTIR (KBr, cm−1): υ 3222, 2229, 1598, 1342, 1510; 1H
NMR (400 MHz, DMSO): δ 8.25 (2H, d, J = 9.2 Hz),
7.61 (2H, d, J = 9.2 Hz), 13C NMR (100 MHz, DMSO):
δ 88.9; 109.8, 114.2, 117.1, 125.9, 144.3, 147.1; Anal.
Calcd for C9H5N5O2: C, 50.23; H, 2.32; N, 32.55; found:
C, 50.12; H, 2.45; N, 32.41.
Characterization of nano‑CuFe2O4–SO3H
FT‑IR and UV spectra
The infrared spectra of CuFe2O4 and CuFe2O4–SO3H are
depicted in Fig. 1. In Fig. 1a the band observed at 574 cm−1
indicated the Fe–O stretching vibration [23]. The charac-
teristics peaks from the OSO3H group of chlorosulfonic
acid were observed at 3300, 1581, 1288 and 1064 cm−1
that corresponding to O–H, S=O and S–O groups, which
clearly indicates the presence of –OSO3H group over mag-
netic surface [24].The absorption spectra of CuFe2O4 and
CuFe2O4–SO3H in comparison with the unprotonated indi-
cator (4-nitroaniline) are presented in Fig. 2, which con-
firms the presence of SO3H groups and acidity strength of
magnetic nano-CuFe2O4–SO3H [25].
Ethyl 2-cyano-2-(4-nitrophenyl)acetate (5b): yellow
color; UV–Vis (DMSO) λmax1 (π–π*):494 nm; FTIR
1
(KBr, cm−1): υ 3215, 2200, 1699; H NMR (400 MHz,
DMSO): δ 12.61 (0.52 H, s), 8.30 (2H, t, J = 8.8 Hz),
7.76–7.64 (2H, m), 4.33 (2H, q, J = 7.2 Hz), 1.31 (3H,
t, J = 7.2 Hz); 13C NMR (100 MHz, DMSO): δ 14.56,
62.50, 108.22, 111.33, 116.56, 126.11, 143.75, 160.70;
Anal. Calcd for C11H10N4O4: C, 50.38; H, 3.81; N,
21.37; found: C, 50.22, H, 3.65; N, 21.26.
2-[(4-Chlorophenyl)diazenyl]cyclohexane-1,3-dione (8b)
brown color; UV–Vis (DMSO) λmax1 (π–π*):387 nm;
1H NMR (400 MHz, DMSO): δ 7.48 (2H, d, J = 8.8 Hz),
7.387(2H, d, J = 8.8 Hz), 2.60 (4H, s), 1.13 (6H, s).
6-Amino-5-[(4-bromophenyl)diazenyl]-1,3-dimethylpy-
rimidine-2,4(1H,3H)-dione (15b) Orange color; UV–Vis
FE‑SEM, EDX and DLS analysis
FE-SEM images of CuFe2O4 and CuFe2O4–SO3H are
shown in Fig. 3, which shows uniform-sized magnetic nan-
oparticles with somewhat spherical morphology and it has
marked tendency to form large clusters. The nanoparticles
that almost entirely separable from each other are appar-
ent. It can be observed that there is no change in the shape
of CuFe2O4 MNPs after being functionalized with sulfonic
acid and the surface morphology is also retained (Fig. 3c).
The elemental compositions of the CuFe2O4 from EDX
1
(DMSO) λmax1 (π–π*):378 nm; H NMR (400 MHz,
DMSO): δ 10.27 (1H, s br), 9.63 (1H, s br), 7.46 (2H,
d, J = 7.2 Hz), 7.10(2H, d, J = 7 Hz), 3.4 (3H, s), 3.2
(3H, s).
2-Hydroxy-3-(p-tolyldiazenyl)naphthalene-1,4-di-
one (17b) red color; UV–Vis (DMSO) λmax1 (π–
π*):429 nm; FTIR (KBr, cm−1): υ 3600–3200 (br),
1
1697; H NMR (400 MHz, DMSO): δ 8.21 (1H, d,
J = 7.6 Hz), 8.1 (1H, d of d, J = 7.4 Hz, J = 0.8 Hz),
7.96–7.85 (2H, m), 7.67 (2H, d, J = 8 Hz), 7.33 (2H,
d, J = 8.4 Hz), 2.35 (3H, S); 13C NMR (100 MHz,
DMSO): δ 21.16, 118.29, 127.47, 130.79, 134.53,
135.46, 137.80, 139.51, 175.73; Anal. Calcd for
C17H12N2O3: C, 69.86; H, 4.10; N, 9.58; found: C, 69.
71; H, 4.29; N, 9.41.
2-[(4-Chlorophenyl)diazenyl]-3-hydroxynaphthalene-
1,4-dione (18b) red color; UV–Vis (DMSO) λmax1
(π–π*):379 nm; FTIR (KBr, cm−1): υ 3600–3200 (br),
1699;1H NMR (400 MHz, DMSO): δ 14.98 (0.23 H, s,
br), 14.83 (0.23 H, s br), 8.23–8.12 (m, 2H), 7.99–7.80
(m, 4H), 7.60 (2H, d, J = 8.4 Hz); 13C NMR (100 MHz,
DMSO): δ 79.66, 119.66, 127.52, 128.13, 130.23,
131.32, 131.49, 133.65, 134.03, 134.43, 134.83, 135.16,
Fig. 1 The FTIR spectra of a nano-CuFe2O4 and b nano-CuFe2O4–
SO3H
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J IRAN CHEM SOC
Fig. 2 Absorption spectra of a
indicator b nano-CuFe2O4 and c
nano-CuFe2O4–SO3H
Fig. 3 The FEG-SEM–EDS
analysis of a, b nano-CuFe2O4
and c, d nano-CuFe2O4–SO3H
analysis also exhibited in Fig. 2b and show the presence
of Cu, Fe and O elements. The presence of sulfur peak in
addition of Cu, Fe and O in Fig. 2d, clearly indicate the
successful functionalization of CuFe2O4. According to
DLS results the size distribution of particles were signifi-
cantly narrow (Fig. 4).
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J IRAN CHEM SOC
Fig. 4 Distribution of hydro-
dynamic diameter for the nano-
CuFe2O4
Fig. 5 The magnetization
curves of nano-CuFe2O4 and
nano-CuFe2O4–SO3H
Fig. 6 XRD patterns of a nano-
CuFe2O4 and b nano-CuFe2O4–
SO3H
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J IRAN CHEM SOC
Fig. 7 TGA of nano-CuFe2O4–SO3H
VSM analysis
Thermo‑gravimetric analyses (TGA)
The saturation magnetization of CuFe2O4 and CuFe2O4–
SO3H was 33.85 and 24.11 emu/g, respectively. Obvi-
ously, after the preparation of CuFe2O4–SO3H, its magnetic
response was affected due to coating with non-magnetic
materials [26] (Fig. 5). Nonetheless, this magnetic property
is enough and the CuFe2O4–SO3H could be completely and
quickly separated from the reaction mixture when an exter-
nal magnetic force was applied.
The thermal stability of the CuFe2O4–SO3H was observed
by TG analysis (Fig. 7). In the TG curve of acidic MNPs,
the first weight loss below 150 °C is due to remove of
trapped solvent molecules from the lattice. Another weight
loss of approximately 9 % beginning from 150 up to
700 °C can be attributed to the decomposition of sulfonic
acid groups from the CuFe2O4 surface. Thus, the catalyst
was stable sufficiently and could be used in organic reac-
tions at elevated temperatures.
X‑ray diffraction spectrum (XRD)
Preparation of stable aryl diazonium ferrite sulfate
salts
The XRD spectrum of CuFe2O4 clearly matches well with
the literature data (Fig. 6). Six peaks at 18.3, 30.3, 35.6,
42.8, 57.1 and 62.98 can be assigned to the (101), (200),
(211), (221), (303) and (224) diffraction peaks of CuFe2O4
spinel, respectively (Fig. 6a) [27]. Notably, the same peaks
were also observed in CuFe2O4–SO3H XRD spectra, which
indicate the structural stability of CuFe2O4 with SO3H
modification. The crystallite size of the nanoparticles was
calculated to be around 29 nm from the XRD results using
the Debye–Scherrer equation.
After the successful characterization of heterogeneous mag-
netic acid, the acid activity of CuFe2O4–SO3H was exam-
ined for its ability to produce the stable aryl diazonium fer-
rite sulfate salts from aromatic amines. In order to optimize
the amount of solid acid, different quantity of CuFe2O4–
SO3H used to confirm its effects in prepare of diazonium
salts. As shown in Scheme 2, a mixture of 4-nitroaniline
(1 mmol), CuFe2O4–SO3H (0.8 g), water (0.2 mL) and
Scheme 2 The model reaction
for optimization of synthesis
of stable aryldiazonium ferrite
sulfate salt
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J IRAN CHEM SOC
sodium nitrite (2 mmol) in grinding condition, gave an
excellent yield of stable 4-nitro benzene diazonium ferrite
sulfate salt (99 %) at room temperature (Scheme 2).
diazonium ferrite sulfate salts with electron-withdrawing
groups or electron-donating groups also reacted effectively.
The Steric effects of ortho substituents had little influence
on the yields and reaction times. In addition, it was observed
that the reaction of phenolic compounds have higher yields
in basic media. The diazonium salts with an electron-with-
drawing substituent provided better results in comparison to
those having electron-donating substituent.
Coupling of stable aryl diazonium ferrite sulfate salts
with active compounds: synthesis of azo dyes
Coupling with active aromatic compounds
The reaction of stable aryl diazonium ferrite sulfate salts with
a number of active aromatic compounds was investigated
and results depicted in Table 1. All the reactions were carried
out under solvent-free condition at room temperature in mild
and heterogeneous conditions. The corresponding azo dyes
were obtained in good to high yields. The reactions were
completed within 10–15 min, with good isolated yields. Aryl
Coupling with active non‑aromatic compounds
After the successful synthesis of azo dyes from the reac-
tion of stable aryl diazonium ferrite sulfate salts with
active aromatic compounds, we decided to investigate
the efficiency of coupling of these diazonium salts with
non-aromatic active compounds. For this purpose, a
Table 1 Condensation of aryl
Entry
G
Active aromatic compounds Product Yield % Mp (Lit) °C
Color
diazonium ferrite sulfate salts
with various active aromatic
compounds
1
H
N,N-Dimethylaniline
N,N-Dimethylaniline
Phenol
1a
2a
3a
4a
5a
6a
7a
8a
9a
10a
11a
82
95
75
90
90
85
83
85
85
87
82
110–113 [28] Yellow
2
p-NO2
p-Et
218–220 [29] Deeply colored
3
270 [29]
Yellow
4
p-NO2
Phenol
207–210 [29] Brown
300–303 [30] Brown
5
p-SO3H N,N-Dimethylaniline
6
p-Cl
β-Naphthol
β-Naphthol
N,N-Dimethylaniline
Aniline
75 [31]
Red
7
o-NO2
o-NO2
p-NO2
H
280–282 [32] Orange
130–132 [29] Orange
198–203 [33] Orange
130–131 [29] Red
8
9
10
11
β-Naphthol
Phenol
p-Cl
188–190 [34] Black
Table 2 Condensation of
aryl diazonium ferrite sulfate
salts with non-aromatic active
compounds
Entry
G
Active methylene compounds Product Yield % Mp (Lit) °C
Color
1
H
Malononitrile
Malononitrile
Malononitrile
Malononitrile
Ethyl cyanoacetate
Dimedone
1b
92
99
95
85
98
90
80
87
85
80
88
75
77
75
78
73
75
80
136–138 [36]
141–143
Red
2
p-NO2
p-Cl
m-Cl
p-NO2
p-NO2
m-NO2
p-Cl
H
2b
Yellow
Yellow
Yellow
Yellow
Red
3
3b
184.5–186 [36]
170–173 (dec.) [37]
179–180
4
4b
5
5b
6
6b
157–158 [38]
124–125 [38]
216–219 [38]
119 [40]
7
Dimedone
7b
Yellow
Brown
Yellow
8
Dimedone
8b
9
Dimedone
9b
10
11
12
13
14
15
16
17
18
H
Barbituric acid
Barbituric acid
Barbituric acid
Uracil
10b
11b
12b
13b
14b
15b
16b
17b
18b
317–318.5 (dec.) [39] Orange
p-Me
p-Br
p-NO2
p-Me
p-Br
194–196 [40]
245–248 [41]
310–313 [42]
259.7–261.7 [42]
238–239
Yellow
Yellow
Orange
Yellow
Yellow
Red
Uracil
Uracil
2-Pyridine Uracil
258–259 [42]
237–237.5
p-Me
p-Cl
2-Hydroxy quinoline
2-Hydroxy quinoline
Red
208–209
Red
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J IRAN CHEM SOC
Scheme 3 Synthesis various azo dyes using nano-CuFe2O4–SO3H
Fig. 8 The stability of aryl
diazonium ferrite sulfate salts
at room temperature (reaction
condition: aryl diazonium ferrite
sulfate salts, malononitrile)
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J IRAN CHEM SOC
Fig. 8, the addition of malononitrile to the stored diazonium
ferrite sulfate salts (they stored in a desiccator at room tem-
perature) provided almost the same yield of product as that
from freshly prepared salt. Obviously, because of the insta-
bility of aryl cation, the aryl diazonium salts with electron-
withdrawing group has the higher stability [43].
Recycling of the nanomagnetic solid acid
To explore the extent of recyclability of our acidic nano-
magnetic particles, its recyclability was tested by recy-
cling of CuFe2O4–SO3H in the coupling reaction of
malononitrile and 4-nitrophenyl diazonium ferrite sul-
fate. In each cycle the MNPs was separated magnetically
and washed several times with water and ethylacetate to
ensure the organic and inorganic reagents do not remain
on the surface of magnetic nanoparticles. Then, the recov-
ered MNPs reused in subsequent runs. It was found that
the performance of MNPs retains for a minimum four
reaction cycles and displayed almost high catalytic per-
formance with over 89 % product yield. Moreover, the
XRD pattern of recycled catalyst showed that the nano-
CuFe2O4–SO3H was the similar to the initial one after
four runs (Fig. 9).
Fig. 9 Recyclability of CuFe2O4–SO3H after four runs
Conclusions
series of active non-aromatic compounds involves dime-
done, barbituric acid, uracil, malononitrile, 2-hydroxy
quinoline and ethyl cyanoacetate were selected and the
coupling reaction of stable aryl diazonium ferrite sulfate
salts were examined. We mixed the diazonium salt and
active compounds in stochiometric amounts in a mortar
and ground the mixture with the help of a pestle until the
completion of the reaction. The corresponding results are
summarized in Table 2. As it can be seen in Table 2, our
method was highly efficient and general in the synthesis
of diverse azo compounds; a series of active non-aromatic
compounds including malononitrile, ethyl cyanoacetate,
dimedone, barbituric acid and uracil coupled efficiently
and the desired products were produced in high yields
and purity (Scheme 3). Also the reaction times were short.
Fortunately, the coupling of aryl diazonium ferrite sulfate
salts with 2-hydroxynaphthalene-1,4-dione gave the cor-
responding azo compounds in excellent yields (17e, 18e)
that is different from previously reported procedure [35].
In conclusion, we have prepared a new nanomagnetic solid
acid catalyst via grafting of sulfonic acid groups on nano-
CuFe2O4 magnetic particles. The catalyst is stable under
air atmosphere and can readily be recovered by an exter-
nal magnet field. This new heterogeneous catalyst showed
many advantages including simple synthesis, easy mag-
netic separation, excellent reusability, high loading of H+
and tolerability of a broad range of functional groups.
Acknowledgments The authors gratefully acknowledge Semnan
University Research Council for financial support of this work.
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