Magnetically recyclable nano copper/chitosan in O-arylation of phenols with aryl halides

Article abstract of DOI:10.1002/aoc.5042

Interaction of chitosan (CS) with Fe₃O₄, followed by embedding Cu nanoparticles (NPs) on the magnetic surface through adsorption of Cu²⁺, and its reduction to Cu^o via NaBH₄, offers a reusable efficient catalyst (Fe₃O₄/CS-Cu NPs) that is employed in cross-coupling reactions of aryl halides with phenols, which affords the corresponding diaryl ethers, with good to excellent yields. The catalyst is completely recoverable from the reaction mixture by using an external magnet. It can be reused four times, without significant loss in its catalytic activity.

Full text of DOI:10.1002/aoc.5042

Received: 28 January 2019
DOI: 10.1002/aoc.5042
Revised: 14 May 2019
Accepted: 14 May 2019
F U L L P A P E R
Magnetically recyclable nano copper/chitosan in
O‐arylation of phenols with aryl halides
Seyed Ali Mousavi Mashhadi | Mohamad Z. Kassaee
| Esmaiel Eidi
Department of Chemistry, Tarbiat
Interaction of chitosan (CS) with Fe O , followed by embedding Cu nanoparti-
Modares University, P.O.Box 14155‐175,
Tehran, Iran
3 4
2+
cles (NPs) on the magnetic surface through adsorption of Cu , and its reduc-
o
tion to Cu via NaBH , offers a reusable efficient catalyst (Fe O /CS‐Cu NPs)
4
3 4
Correspondence
Mohamad Z. Kassaee, Department of
Chemistry, Tarbiat Modares University, P.
O.Box 14155‐175. Tehran, Iran.
Email: kassaeem@modares.ac.ir
that is employed in cross‐coupling reactions of aryl halides with phenols,
which affords the corresponding diaryl ethers, with good to excellent yields.
The catalyst is completely recoverable from the reaction mixture by using an
external magnet. It can be reused four times, without significant loss in its cat-
alytic activity.
KEYWORDS
chitosan, magnetic, nanocatalyst, O‐arylation, recyclable
1
| INTRODUCTION
the synthesis of Fe O /CS‐Cu NPs, and its application as
3
4
a green, effective and reusable magnetic nanocatalyst in
Ullmann cross‐coupling of phenols with aryl halides,
under mild conditions.
Nano iron oxide (Fe O NPs) shows superb properties,
with many applications.
3
4
[
1,2]
It is often treated with vari-
ous materials, including precious metals, carbon, silica,
[
3–9]
biopolymers, chitosan (CS) and cellulose systems.
CS
2
| EXPERIMENTAL
2.1 | Preparation of Fe O /CS NPs
3 4
is the second most abundant polysaccharide that is
synthesized by deacetylation of chitin and applied in
[10]
many fields.
The CS‐coated Fe O NPs are desired for
3
4
their safety, non‐toxicity, availability, biocompatibility,
To CS (1.5 g) dissolved in 100 ml of 0.05 M acetic acid
solution, FeCl ·6H O (0.0065 mol) and FeCl ·4H O
biodegradability, low immunogenicity and antibacterial
[11–16]
3
2
2
2
activity.
The CS itself is applied in industry, biomed-
(
4
0.0033 mol) were added. This solution was stirred for
hr at 80°C, under N atmosphere. Then, 25% NH OH
icine, pharmaceuticals, metal chelating, food processing,
[17–19]
2
4
etc.
Diaryl ethers have many useful applications,
(
6 ml) was dropped into the reaction mixture, and strring
continiued for 30 min. After cooling the reaction mixture
to room temperature, Fe O /CS NPs were separated by an
and are prepared using Ullmann synthesis through reac-
tion of aryl halides with sodium or potassium aryl oxides
[20–24]
3 4
catalyzed by copper reagents.
This procedure has
external magnet and washed with distilled water, then
with ethanol several times, and then dried under vacuum
several drawbacks, such as elevated temperatures and
stoichiometric amounts of copper. New methods for prep-
aration of diaryl ethers under relatively mild reaction
(
Scheme 1).
[25–30]
conditions are desired.
Environmentally friendly
magnetic nanocatalysts provide high surface areas, and
are generally characterized by easy product purification
and recycling. Copper as a catalyst holds the advantage
of low cost for industrial applications. Here, we report
2.2 | Preparation of Fe O /CS‐Cu NPs
3
4
For preparation of Fe O /CS‐Cu NPs, a solution of Fe O /
3
4
3 4
CS NPs (500 mg) was dispersed in water for 30 min under
Appl Organometal Chem. 2019;e5042.
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© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5042

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MOUSAVI MASHHADI ET AL.
3 4
SCHEME 1 Preparation of magnetic Fe O /Cs NPs
sonication. Then an aqueous solution of CuCl (50 mg in
2
5
ml) was dropped over a period of 10 min, at room
temperature, and then stirred for 4 hr at 60°C. The Cu
II) precursor was reduced by addition of hydrazine
(
hydrate. The mixture was stirred for 3 hr. Afterwards,
Fe O /CS‐Cu NPs were separated by an external magnet,
washed thoroughly with water and ethanol, and then
dried under vacuum at room temperature overnight
3
4
SCHEME 3 O‐Arylation of phenols with aryl halides over Fe
CS‐Cu NPs
3 4
O /
(Scheme 2).
microscopy (SEM) and energy‐dispersive X‐ray spectros-
copy (EDX; Figures 1–6, respectively).
2
.3 | General procedure for Fe O /CS‐Cu
3
4
NPs catalyzed O‐arylation of phenols with
aryl halides
3.1 | Fourier transform‐infrared analysis
A comparison is made between FT‐IR spectra of CS,
Fe O /CS NPs and Fe O /CS‐Cu NPs (Figure 1). In that
of CS, the broad band at 3411 cm is related to the
A mixture of phenol (1 mmol), aryl halide (1.1 mmol),
3
4
3 4
K CO (138.205 mg, 1.0 mmol) and Fe O /CS‐Cu NPs
2
3
3
4
−1
(20 mg) in dimethylsulfoxide (DMSO) was stirred at
stretching vibrations of N–H and O–H groups (Figure 1
1
20°C for 15 hr. After completion of the reaction [moni-
−
1
a). Peaks appearing at 2922 and 2858 cm are character-
tored by thin‐layer chromatography (TLC)], cooling to
room temperature was followed by separating the catalyst
from the reaction mixture with a magnet, and quenching
the reaction mixture with water, and extracting with
ethyl acetate. Solvent was removed with a rotary evapora-
tor under reduced pressure. The residue was purified by
column chromatography on silica gel to afford the desired
product (Scheme 3).
istic of C–H stretching vibrations of CH and CH, respec-
2
−
1
tively. The band at 1605 cm
corresponds to N–H
bending vibration, and the absorption bands at about
−
1
1
089 and 1014 cm are related to the stretching vibra-
tions of different C–O–C bands. In the FT‐IR spectrum
−
1
of Fe O /CS NPs, the peak at 594 cm corresponds to
3
4
the stretching vibrations of Fe–O groups that indicates
magnetic Fe O NPs is coated by CS (Figure 1b). The
3
4
FT‐IR spectrum of Fe O /CS‐Cu NPs reveals the presence
3
4
of all the peaks corresponding to Fe O /CS NPs, and the
changes in the region 1000–1350 cm relate to C–N
3
4
−1
3
| RESULTS AND DISCUSSION
vibrations and point to Cu conjugation with CS.
Here we discuss synthesis of Fe O /CS‐Cu NPs and its
3
4
application as a heterogeneous catalyst in coupling of aryl
halides with phenols. The catalyst is fully characterized
by Fourier transform‐infrared (FT‐IR), X‐ray diffraction
3.2 | X‐ray diffraction analysis
(
XRD), thermogravimetric analysis (TGA), vibrating‐
The crystal structures of NPs are determined by XRD.
°
°
sample magnetometry (VSM), scanning electron
There are six diffraction peaks at 2θ about 35.1 , 41.4 ,
°
°
°
5
0.5 , 63.0 , 67.3 and 74.2 with indexes (2 2 0), (3 1 1),
(
4 0 0), (4 2 2), (5 1 1) and (4 4 0) lattice planes that are
in agreement with standard patterns of inverse cubic spi-
nel magnetite (Fe O ) crystal structure (Figure 2a). Also,
3
4
there are the small and weak broad bands in the range
°
of 21–29 that are indications of CS. In the XRD pattern
of Fe O /CS‐Cu NPs, three additional peaks appear at
3
4
°
°
°
SCHEME 2 Preparation of magnetic nanocatalyst Fe
3
O
4
/CS‐Cu NPs
2θ of 50.7 , 59.3 and 88.8 , that correspond to (1 1 1), (2

MOUSAVI MASHHADI ET AL.
3 of 7
FIGURE 3 Magnetization curve of Fe
recycled catalyst after last run. CS, chitosan; NP, nanoparticle
3
O
4
/CS‐Cu NPs and
FIGURE 1 Comparison between Fourier transform‐infrared (FT‐
IR) spectra of (a) CS, (b) Fe
3 4 3 4
O /CS NPs, and (c) Fe O /CS/Cu NPs.
CS, chitosan; NP, nanoparticle
0
0) and (2 2 0) planes, respectively. They are attributed to
the structure of face centered cubic (fcc) copper crystal
Figure 2b).
(
3.3 | Magnetic properties
The magnetic hysteresis loops of Fe O /CS‐Cu NPs are
3
4
analyzed at room temperature by VSM. The magnetization
curves indicate that the sample is super‐paramagnetic. The
saturation magnetization (MS) value of Fe O /CS‐Cu NPs
3
4
is 12 emu/g. This reduction in MS value can be related to
the existence of organic layer and Cu NPs on the surface
of Fe O NPs. This property facilitates magnetic separation
3
4
with a conventional magnet (Figure 3).
3.4 | Thermogravimetric analysis
FIGURE 4 Thermogravimetric analysis (TGA) and Differential
The organic content and the thermal stability on the sur-
face of the magnetic NPs are determined by TGA whose
thermal analysis (DTA) of Fe
nanoparticle
3 4
O /CS‐Cu NPs. CS, chitosan; NP,
3 4 3 4
FIGURE 2 Comparison between X‐ray diffraction (XRD) patterns of (a) Fe O /CS NPs and (b) Fe O /CS/Cu NPs. CS, chitosan; NP, nanoparticle

4
of 7
MOUSAVI MASHHADI ET AL.
3 4
FIGURE 5 Scanning electron microscopy (SEM) images of Fe O /CS‐Cu NPs. CS, chitosan; NP, nanoparticle
In order to evaluate the catalytic applicability of the
nanocatalyst, it is used in a synthesis of diaryl ether by
cross‐coupling reactions of various substituted aryl
halides with phenols. To optimize the reaction condi-
tions, some parameters such as solvent, catalyst amount,
reaction time and temperature are probed for the cou-
pling of phenol with iodobenzene as a model reaction.
Initially, the effect of quantity of catalyst on reaction is
examined with different catalyst amounts (5, 10, 15, 20
a
TABLE 1 Optimization of the reaction conditions
Catalyst Temperature
Time Yield
FIGURE 6 Energy‐dispersive X‐ray (EDX) spectrum of Fe
CS‐Cu NPs. CS, chitosan; NP, nanoparticle
3
O
4
/
b
Entry (mg)
(°C)
Solvent (hr)
(%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
0
10
10
10
15
15
20
20
20
20
20
20
20
20
20
25
110
100
110
120
100
120
80
DMSO
DMF
10
10
–
40
12
78
–
thermogram shows the initial weight loss is below 200°C,
which is attributed to the removal of physically adsorbed
solvent and water. Also, the mass loss at the temperature
range 210–400°C is due to the decomposition of CS,
grafted on the surface of the magnet (Figure 4).
Toluene 12
DMSO
–
13
13
15
15
15
15
15
15
15
DMSO
DMSO
DMSO
DMSO
DMSO
–
88
85
87
90
91
–
3.5 | Scanning electron microscopy
90
The size and morphology of the Fe O /CS‐Cu NPs are
100
110
120
120
120
120
120
120
3
4
shown by SEM (Figure 5). It shows uniformly dispersed
spherical particles, along with weak agglomerations.
0
1
2
3
4
5
H
2
O
22
35
65
95
95
3
.6 | Energy‐dispersive X‐ray analysis of
Toluene 15
elements
DMF
15
15
15
DMSO
DMSO
The EDX analysis of the catalyst is carried out to examine
the existence of copper, iron and other elements. The
presence of Cu, Fe, O, N and C is established in 8.72%,
16
a
2 3
Reaction conditions: phenol (1.0 mmol), iodobenzene (1.1 mmol), K CO
8
4.34%, 4.95%, 0.42% and 1.58% by weight, respectively
(1.0 mmol).
b
(Figure 6).
Isolated yield.

MOUSAVI MASHHADI ET AL.
5 of 7
and 25 mg). The coupling reaction proceeds smoothly
with 20 mg of catalyst to give diphenyl ether in good
yield. The reaction does not proceed in the absence of
the catalyst. To determine the effects of media on the
reaction, several solvents [dimethylformamide (DMF),
proceed smoothly with very good efficiency to form the
desired products in high yields. However, the steric hin-
drance greatly affects the activity of the substrates and
the reaction gives lower yield, owing to the larger steric
effect of the group on the phenol (Table 2). Finally, the
excellent catalytic performance of Fe O /CS‐Cu NPs for
DMSO, toluene, H O] are screened. Among them, the
2
3 4
reaction in DMSO produces 95% of the coupled product
and hence it is used as the solvent of choice. The effect
of temperature is studied by carrying out cross‐coupling
the reaction is attributed to the large surface area of the
nanocatalyst, which facilitates the appropriate interaction
of the reactant and product molecules.
of phenol with iodobenzene at 80, 90, 100, 110 and
To check leaching of the Cu NPs, after completion of
reaction, the catalyst is separated from the solution by
an external magnet, analysis of the aqueous phases of
reaction mixture using inductively coupled plasma analy-
sis show that the leaching of copper is negligible and the
catalyst is mainly heterogeneous in nature.
To investigate the reusability of the catalyst, after com-
pletion of the model reaction it was easily removed by an
external magnet and washed repeatedly with water and
ethanol, and dried under vacuum. Then, the catalyst
was reused directly for the next run. The isolated yields
for four successive runs demonstrated the practical recy-
clability of the prepared catalyst and good stability of
the catalytic system (Figure 7).
o
1
8
20 C, where the yield of diphenyl ether appeared to be
5%, 87%, 90%, 91% and 95%, respectively. In addition,
the product yield increases with the increase of the reac-
tion time from 10 to 15 hr. Therefore, the optimum time
for reaction is selected to be 15 hr. The nature of the base
has crucial importance on the yield of the coupling reac-
tions. Both Cs CO3 and K CO3 appeared as effective
2
2
bases. The latter was chosen as it was much cheaper.
Based on these results, the reaction is best catalyzed by
2
0 mg of Fe O /CS‐Cu NPs using K CO as the base,
3
4
2
3
and DMSO as the solvent at 120°C (Table 1). To extend
the scope of this study, the above optimized conditions
were employed for an Ullmann‐type coupling reaction
between a variety of aryl halides and phenols over the
Fe O /CS‐Cu NPs catalyst. Phenol derivatives with both
A possible mechanism is proposed for the synthesis of
[31,32]
diaryl ether that is consistent with the literature.
Firstly, Fe O /CS‐Cu NPs inserts in the aryl halide bond
3
4
electron‐donating and electron‐withdrawing groups
3
4
a,b
TABLE 2 O‐arylation of phenols with aryl halides catalyzed by Fe
3 4
O /CS‐Cu NPs
a
2 3
Reaction conditions: phenols (1 mmol), aryl halide (1.1 mmol), K CO (1.0 mmol).
b
Isolated yield.

6
of 7
MOUSAVI MASHHADI ET AL.
diaryl ether product, and completes the catalytic cycle of
this reaction (Scheme 4).
In order to evaluate the efficiency of the catalyst, a
comparison of the catalytic activity of Fe O /CS‐Cu NPs
3
4
with several reported Cu‐catalysts in the literature is
made, which shows our catalyst is superior in terms of
reaction conditions, reaction time and product yield
(
Table 3).
4
| CONCLUSIONS
Magnetically recyclable nano copper/CS is used in O‐
arylation of phenols with aryl halides.
Hence, the highly active and sustainable Fe O /CS‐Cu
3
4
FIGURE 7 Reusability of the magnetic nanocatalyst for the
catalyst was successfully prepared and characterized by
several techniques, including FT‐IR, XRD, SEM, TGA,
EDX and VSM. Interesting features of the present meth-
odology include simple preparation, mild conditions, easy
removal of the catalyst after the reaction, and substantial
improvements in the reaction rates and yields. The cata-
lyst is easily recyclable and reused at least four times
without any significant loss in its performance.
model reaction
via oxidative addition reaction (I). Subsequently, reaction
of I through nucleophilic substitution proceeds via reac-
tion with phenol, giving intermediate II. Eventually,
reductive elimination on intermediate II releases the
ORCID
Mohamad Z. Kassaee
30X
https://orcid.org/0000-0003-3489-
1
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