Imidazolium chloride immobilized on copper acetylacetonate-grafted magnetic chitosan as a new metal/ionic liquid bifunctional catalyst for selective oxidation of benzyl alcohols in water

Article abstract of DOI:10.1039/c6ra18100g

Copper acetylacetonate and 1-methyl-3-propylimidazolium chloride as an ionic liquid (Fe₃O₄/CS/Cu/IL) were immobilized on chitosan magnetite nanoparticles via covalent attachment. The prepared heterogeneous catalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray powder detection (XRD), thermogravimetric/differential thermal analyses (TG/DTA), vibrating sample magnetometry (VSM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and energy dispersive X-ray (EDX) spectroscopy. The Fe₃O₄/CS/Cu/IL exhibits superior catalytic activity for the oxidation of various benzyl alcohols to the corresponding carboxylic acids using TBHP as an oxidant. The catalyst could be simply recycled with the assistance of an external magnet and reused for five runs without significant loss of activity.

Full text of DOI:10.1039/c6ra18100g

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Page 1 of 23
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Imidazolium Chloride Immobilized on Copper Acetylacetonate-Grafted
Magnetic Chitosan as New Metal/Ionic Liquid Bifunctional Catalyst for
Selective Oxidation of Benzyl Alcohols in Water
Kobra Azizi, Naghmeh Esfandiary, Meghdad Karimi, Elahe Yazdani and Akbar Heydari*
Chemistry Department, Tarbiat Modares University, P. O. Box 14155ꢀ4838 Tehran, Iran
Fax: (+98)ꢀ21ꢀ82883455, Phone: (+98)ꢀ21ꢀ82883444, email: heydar_a@modares.ac.ir
Abstract
Copper acetylacetonate and 1ꢀmethylꢀ3ꢀpropylimidazolium chloride as an ionic liquid
(Fe3O4/CS/Cu/IL) were immobilized to chitosan magnetite nanoparticles via covalent
attachment. The prepared heterogeneous catalyst was characterized by Fourier transform infrared
spectroscopy (FTꢀIR), Scanning electron microscopy (SEM), Xꢀray powder detection (XRD),
Thermogravimetric/Differential thermal analyses (TG/DTA), Vibrating sample magnetometry
(VSM), Inductively coupled plasma atomic emission spectroscopy (ICPꢀAES) and Energy
dispersive XꢀRay (EDX). The Fe3O4/CS/Cu/IL exhibits superior catalytic activity for the
oxidation of various benzyl alcohols to the corresponding carboxylic acids using TBHP as an
oxidant.
The catalyst could be simply recycled with the assistance of an external magnet and reused for
five runs without significant loss of activity.
Keywords: Magnetic, Chitosan, Catalyst, Bifunctional, Water
Introduction
Oxidation of benzylic position is one of the most significant and beneficial procedures in organic
chemistry as the aldehydes and carboxylic acids are versatile intermediates in a diversity of

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transformations. In the past, potassium permanganate or potassium dichromate were used in
stoichiometric quantities as oxidants in these reactions.1
2
3
During the last decades, RuCl3/H5IO6, TEMPO/NaOCl, and Chromiumꢀcatalyzed oxidation
of primary and secondary alcohols to the acids and ketones with periodic acid (H5IO6) have been
described. 4 A twoꢀstep process involving Swern oxidation in the first step, then oxidation of the
resulting aldehyde with sodium chlorite (NaClO2) is another option. 5, 6
In 2007, aerobic oxidation in 1ꢀButylꢀ3ꢀmethylimidazolium trifluoromethanesulfonate
[bmim]OTf as ionic liquid converted various activated primary alcohols into their corresponding
acids or aldehydes by using VO(acac)2 and Copper(II) 2ꢀethylhexanoate in good to excellent
yields (Eq 1).7
Later, various alcohols were transformed into the corresponding carboxylic acids and ketones in
good yields with tꢀBuOOH in the presence of Bi2O3 as catalyst (Eq 2). 8 Also, aerobic oxidation
of benzyl alcohols to carboxylic acids in the presence of Pd/C along with NaBH4 in aqueous
ethanol or methanol by using K2CO3 or KOH as base at room temperature was reported (Eq 3).9
Tetrapropylammonium perruthenate (TPAP) could catalyze direct oxidation of primary alcohols
to carboxylic acids through stabilized aldehyde hydrates in acetonitrile.10
Recently, Nꢀheterocyclic carbene (NHC)–silver catalyst was able to oxidize benzyl alcohols to
11
aldehydes or carboxylic acids in the presence of BnMe3NOH or KOH under dry air. Photo
oxidation of benzyl alcohols under visible light irradiation led to produce carboxylic acids using
2ꢀchloroanthraquinone as an organocatalyst.12
13
Most of these methods involve toxic metals
and their applicability is limited in terms of
substrate range, harsh conditions, using strong bases and so on alternative methods are still
desirable.

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The search for efficient catalysts that combine the advantages of both homogeneous and
heterogeneous catalysts is one of the most exciting challenges of catalysis research. Then we
decided to synthesize benzoic acid, with the highest possible yield, by oxidizing benzyl alcohol
using a semiheterogeneous system (Eq 4).14
Scheme 1: Reactions toward benzoic acids
Chitosan is a linear aminopolysaccharide of glucosamine and Nꢀacetylglucosamine units and is
obtained by alkaline deacetylation of chitin extracted from the exoskeleton of crustaceans such
as shrimps and crabs, as well from the cell walls of some fungi.15 Recently, much attention has
been paid to chitosan as a potential polysaccharide resource because of its unique
physiochemical characteristics and biological activities.16 Owing to its high biodegradability,
nontoxicity, and antimicrobial properties, chitosan is widelyꢀused as an antimicrobial agent
either alone or blended with other natural polymers.17 These properties have led to its increased
utility in specific applications such as antibacterial/antiꢀbiofouling coatings, controlled release
coatings and microcapsules, nanofiltration, drug delivery hydrogels, gene delivery and tissue

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engineering scaffolds.18ꢀ20 Within the past decade, green chemistry has attained the status of a
major scientific discipline due to safer solvents, energy efficient which lead to the development
of cleaner and more benign chemical processes.21 Immobilized ILs have attracted considerable
interest due to their extended advantages such as their easy recovery and reusability,
22
noncorrosive and nonꢀhazardous nature, low cost and operational simplicity. In extension to
our recent works we have now prepared new bifunctional catalyst including copper
acetylacetonate and ionic liquid supported on magnetic chitosan. This catalyst system shows
additive effect and serves as a superb catalyst. Chitosan is an excellent adsorbent for metal
removal in nearꢀneutral solutions because of the large number of NH2 groups. Interaction
between NH2 group of chitosan molecules and carbonyl group of Copper acetylacetonate led to
imine bond formation then Copper acetylacetonateꢀgrafted magnetic chitosan was obtained. A
supported ionic liquid bearing imidazole groups was synthesized by anchoring 1ꢀ
propyltrimethoxysilaneꢀ3ꢀmethylimidazolium chloride onto chitosan. First, imidazole was
treated with 3ꢀchloropropyltrimethoxysilane to give 3ꢀ(3ꢀ trimethoxysilylpropyl)imidazole, and
was further treated with magnetic chitosan to produce the supported zwitterion. The reason
behind the incorporation of 1ꢀmethylimidazole in the catalyst system is that an ionic liquid can
dissolve many polar and nonꢀpolar organic and inorganic molecules and also has good catalytic
activity. Magnetic modified chitosan immobilized copper acetylacetonatate and ionic liquid
(Fe3O4/CS/Cu/IL) was prepared as a novel catalyst. The combination of the metal and zwitterion
sites in the same molecule could make the catalyst behave as a bifunctional catalyst hence
facilitating its recovery and reuse. Thus, the interesting structural and chemical features as well
as the good results obtained, led us to explore the ability of this catalyst in oxidation of benzyl
alcohols in water. This catalyst was very effective and had several advantages such as being cost

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effective, high yielding, involving shorter reaction times, no byꢀproducts formation and most
importantly its easy usage with negligible reduction in catalytic activity. On the other hand, when
water is used as the reaction medium, a repulsive hydrophobic interaction arises between the
small organic molecules and water. Small organic molecules due to their insolubility in water are
forced to form aggregates in order to decrease the organic surface area exposed to water. The
combined effect of hydrophobic interaction and hydrogen bonding at the boundary accelerates
the reaction and thus gives high yields. Herein, we report a new cooperative catalytic system
comprising a bifunctionalized magnetic chitosan (MC) with a transition metal catalyst, Copper
acetylacetonate, and a general ionic liquid, 1ꢀpropyltrimethoxysilaneꢀ3ꢀmethylimidazolium
chloride. This bifunctional catalyst might find promising applications in green chemistry, as it
can not only reduce costs and waste by saving separation/purification steps but also using water
as solvent. The carboxylic acids were isolated by extraction with sufficient purity without the
need for further chromatographic purification thus rendering this protocol both cost and time
efficient.
Experimental
All purchased chemicals were of analytical grade and used without further purification. Chitosan
(ACROS, USA), acetic acid and ethanol were purchased from Merck. FTꢀIR spectra were
obtained over the region 400ꢀ4000 cmꢀ1 with NICOLET IR100 FTꢀIR with spectroscopic grade
KBr. The powder Xꢀray spectrum was recorded at room temperature by model: Philips XꢀPert
1710 difractometer using Co Kα (α =1.78897Å) voltage: 40 Kv, current: 40 mA and the data
were collected from 10◦ to 90◦ (2θ) with a scan speed of 0.02/s. The morphology of catalyst was
studied with scanning electron microscopy using SEM (Philips XL 30 and Sꢀ4160) with gold
coating equipped with energy dispersive Xꢀray spectroscopy. The magnetic properties of

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Fe3O4@CS@Cu(acac)2@IL
nanoparticle
was
measured
with
vibrating
sample
magnetometer/Alternating Gradient Force Magnetometer (VSM/AGFM, MDK Co, Iran,
www.mdkꢀmagnetic.com). Thermogravimetric/differential thermal analyses (TG/DTA) was
performed on a thermal analyser with a heating rate of 10 °C minꢀ1 over a temperature range of
25–800 °C under flowing compressed N2 and O2 and thermogravimetric analyses (TG) was done
with a heating rate of 20 °C minꢀ1 over a temperature range of 25–1100 °C under flowing
compressed N2.
Synthesis of Fe3O4/CS/Cu/IL (a):
Scheme 2 illustrates the preparation of the Fe3O4/CS/Cu/IL bifunctional catalyst. Chitosan, a
linear polymer of (1ꢀ4)ꢀlinked 2ꢀaminoꢀ2ꢀdeoxyꢀgucopyranose, containing free amines provides
a facile immobilization of the metal complex to its surface.
Fe3O4 nanoparticles are prepared by chemical coꢀprecipitation of Fe3+ and Fe2+ ions with molar
ratio 2:1, in presence of chitosan, followed by the hydrothermal treatment. Unfortunately,
chitosan is only soluble in acidic aqueous solutions with pH values lower than 6.5.Then 1.5 g of
chitosan is dissolved in 100 mL of 0.05 M acetic acid solution; to which FeCl3.6H2O (3.51 g)
and FeCl2.4H2O (1.29 g) are added. The resulting solution is mechanically stirred for 6 h at 80 ◦C
under N2 atmosphere. Consequently, 6 mL of ammonia solution 25% (Merck) is injected drop
wise into the reaction mixture with constant stirring. After 30 min, the mixture is cooled to room
temperature and chitosan coated over magnetic nanoparticles are separated by an external
magnet, first washed with distilled water, then ethanol (Industrial Grade), and finally dried under
vacuum at room temperature in 12 h.
Magnetic nanoparticles Fe3O4 were chosen as the core magnetic support because of their simple
synthesis, low cost, and relatively large magnetic susceptibility. The presence of the crossꢀlinked

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chitosan polymer layer not only prevents the agglomeration but also protects the Fe3O4 core from
oxidation.
As synthesized magnetic chitosan (Fe3O4/CS) was subsequently used for the immobilization of
copper acetylacetonate by using amino groups of the chitosan.
Copper acetylacetonate was immobilized on the magnetic chitosan via Schiff condensation at
NH2 moiety. 0.5 g of modified magnetic chitosan was treated with 0.1 g of Cu(acac)2 in 25 ml of
ethanol (Merck, 99.9% purity) under refluxing condition for 24 h. Then Magnetic nanoparticles
were washed using ethanol (Industrial Grade) 3 times to remove not reacted Cu(acac)2.
Finally the synthesized Fe3O4/CS/Cu(acac)2 was treated with 1ꢀpropyltrimethoxysilaneꢀ3ꢀ
methylimidazolium
chloride
(synthesized
before
from
the
reaction
of
1
3ꢀchloropropyltrimethoxysilane (IPTMS) and methylimidazol: H NMR (500 MHz, CDCl3): δ:
0.51ꢀ0.55 (2H, m), 1.83ꢀ2.07 (2H, m), 3.57 (9H, s), 4.17 (3H, s), 4.33ꢀ4.37 (2H, m), 7.52ꢀ7.81
(2H, m), 10.47 (1H, m)) in ethanol (Merck, 99.9% purity) under reflux for 24 h to give magnetic
modified chitosan immobilized copper acetylacetonate and ionic liquid (Fe3O4/CS/Cu/IL)
catalyst (Scheme 2). The solid material was separated by external magnate and thoroughly
washed with ethanol (Industrial Grade) and dried under vacuum in 12 h at room temperature.
The loading of the catalyst was determined by ICPꢀAES which was found to be 0.31 mmol Cu/g.

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Scheme 2: Preparation of Fe3O4/CS/Cu/IL bifunctional catalyst
Typical Procedure
The reactions were carried out in a 25 mL round flask equipped with a condenser and a magnetic
stirrer. Into the flask were placed 30 mg of the catalyst (including: 1 mol% Cu, 0.5 mol % ionic
liquid), 1 mmol of benzyl alcohol, 2 mL of deionized water, and 2 mmol TBHP. The resulting
mixture was vigorously stirred at 60 °C for 4 h under Ar. After completion the reaction, the
catalyst was separated by external magnet. The reaction mixture was purified by extraction. The
recovered catalyst was washed with ethanol (Industrial Grade) and deionized water and then
dried under a vacuum in 12 h at room temperature. The catalyst was then reused for the next
reaction.
Result and Discussions
The crystalline structure of Fe3O4/CS/Cu/IL NPs and phase purity were determined by
powder Xꢀray diffraction (XRD) as shown in Fig 1. The XRD pattern of MNPs indexed
to the spinal phases of iron oxide and six peaks (2θ = 30.1, 35.5, 43.2, 53.5, 57.0 and
62.8) are related to their corresponding indices (220), (311), (400), (422), (511) and (440),
respectively. The positions of all diffraction peaks matched well with those from the
JCPDS card (NO. 75-0033). As amorphous chitosan has an amorphous structure is
difficult to see the diffraction peaks. This result proves that chitosan coating and
immobilization of copper and ionic liquid have not altered the structure of magnetic
nanoparticles.

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Figure 1: The Xꢀray diffraction pattern of Fe3O4/CS/Cu/IL
For discovering the surface, morphology and the size of nanoparticles, we used scanning electron
microscopy. Figure 2 are properly magnified (20ꢀ40 KX) SEM micrographs indicating surfaces
of particles. The result pictures show uniform and minuscule nanoparticles. The approximate size
of particles is examined about 30ꢀ50 nm.

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(Magnified 40000 x)
Figure 2: SEM images of Fe3O4/CS/Cu/IL (Magnified 20000 x)
TGA technique is very helpful to understand the degradation temperatures, moisture content and
percentage of inorganic and organic components in material. Figure 3 shows the TGA

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spectra
of
pure
Fe3O4,
Fe3O4@Chitosan,
Fe3O4@Chitosan@Cu(acac)2
and
Fe3O4@Chitosan@Cu(acac)2@Ionic Liquid which indicates that around 13% of the chitosan gets
o
disintegrated between 200ꢀ400 C. The variation in thermal events proved the formation of the
new materials. According to the spectra, the quantity of Cu(acac)2 was 2%. At the end of the
experiment around 18% of the Fe3O4@Chitosan@Cu (acac)2@Ionic Liquid gets decomposed
and in comparison to Fe3O4@Chitosan@Cu (acac)2, ionic liquid quantity was measured 3%.
Figure 3: TGA of Fe3O4, Fe3O4@Chitosan, Fe3O4@Chitosan@Cu (acac)2 and
Fe3O4@Chitosan@Cu(acac)2@Ionic Liquid
TGA/DTA with a heating rate of 10 °C minꢀ1 over a temperature range of 25–800 °C under
flowing compressed N2 and O2 indicates the change in weight of material with change in
temperature. As it has shown in Fig 4. Fe3O4@Chitosan@Cu(acac)2@Ionic Liquid containing
moisture is heated, with increase in temperature moisture get evaporated that result in decrease in

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the weight of sample correspond to the moisture (endothermic). Combustion of the sample and
o
decomposition of the surface around 200ꢀ600 C (exothermic with weight loss), led to decrease
in the sample weight.
Figure 4: TGA/DTA of Fe3O4@Chitosan@Cu(acac)2@Ionic Liquid
In order to deduce the composition of the nanoparticles, energyꢀdispersive Xꢀray spectroscopy
(EDS) analysis was carried out (Fig. 5). The EDS spectrum depicts no other peaks except those
for Fe3O4/CS/Cu/IL (Fe, Si, O, C, N, Cl, and Cu) indicating the high purity of the composites.
The results of this analyses of the Fe3O4/CS/Cu/IL are given in the following table. Weight
percent of the elements of Fe3O4/CS/Cu/IL nanoparticles are 3.22%(C), 0.84%(N),
5.87%(O), 0.52%(Si), 0.93%(Cl), 1.96%(Cu) and 86.66%(Fe) , respectively (Table 1).

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This implied that copper and ionic liquid was on the surface of the covered chitosan on
Fe3O4 NPs.
Figure 5: EDX pattern of Fe3O4/CS/Cu/IL
Table 1: Quantitative results of EDX analysis of Fe3O4/CS/Cu/IL
Element
Line
Ka
Ka
Ka
Ka
Ka
Ka
La
Int
W%
3.22
0.84
5.87
0.52
0.93
86.66
1.96
A%
11.54
2.59
C
N
185.0
49.3
O
939.3
137.5
169.9
1735.3
104.1
15.79
0.80
Si
Cl
Fe
Cu
1.13
66.81
1.33

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Bare nanocrystals of Fe3O4 owner high saturation magnetization 73.7 emu/g at room
temperature.23 The results of VSM shows that the saturation magnetization value in Fe3O4/CS
decreased to 50emugꢀ1 due to the coated chitosan polymer and in the case of Fe3O4/CS/Cu(acac)2
closed to 43 emugꢀ1 and finally reached to 37 emugꢀ1 in Fe3O4/CS/Cu(acac)2/IL NPs (Fig. 6)
Figure 6: Magnetization curves of Fe3O4/CS, Fe3O4/CS/Cu and Fe3O4/CS/Cu/IL
The FTꢀIR spectra of magnetic nanoparticles (Fe3O4), chitosan, and magnetic nanoparticles
coated by chitosan (Fe3O4@chitosan) are shown in Fig.7.
The FTꢀIR spectrum of pure chitosan were characterized by the following absorption bands: the
(NH) of backbone polymer arising at 3435 (stretching characteristic), 1639 cmꢀ1 (bending

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vibration) and C–O stretching vibration of alcoholic group at 1065 cmꢀ1. The spectrum of
Fe3O4@CS compared with Fe3O4, the presence of chitosan on magnetic nanoparticles covered
the vibration of Fe3O4. The band shifted are significant. Electrostatic interaction between the
negatively charged Fe3O4 NPs surface and the positively protonated chitosan donates the IR
spectrum change. The spectrum of the Fe3O4@Chitosan@Cu (acac)2 catalyst showed a
characteristic band at 1707 cmꢀ1 (C=N) and the absorption at 1581 cmꢀ1 is due to (CH2)3HC=Nꢀ
stretching which is a characteristic absorption due to acethylacetonte crosslinking with chitosan.
The peaks at 1576 cmꢀ1 is related to C=N stretching vibrations. It is worth mentioning that in
Cu(acac)2 anchored magnetic chitosan, the C=N stretching frequency is shifted to upper
wavelength at ca.1707 cmꢀ1 indicating that C=N bond is coordinated to copper through the lone
pair of nitrogen in the Schiffꢀbase.
Also appeared peaks around 1370ꢀ1400 cmꢀ1 corresponding to CH3 group vibrations. These
observations indicate that Cu(acac)2 has been successfully supported on the magnetic chitosan.
The FTꢀIR spectra of Fe3O4@Chitosan@Cu (acac)2@IL, a broad peak around 1584 cmꢀ1
corresponds to the C–N , CꢀC stretching vibrations of imidazole ring in the structure of catalyst.

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Figure 7: FTꢀIR spectra of Fe3O4@Chitosan@Cu (acac)2@IL
We developed a clean and single step method for the synthesis of benzoic acids. In completion of
liquid phase reaction which contains both oil or solid and water phases, a coꢀsolvent or a phase
transfer catalyst is required to promote the reaction. The oxidation of benzyl alcohol to benzoic
acid by TBHP was chosen as a probe reaction. The oxidation reactions were carried out under
the solvent water with TBHP (70 % aq.) at r.t, a high conversion of benzyl alcohol was obtained
when Fe3O4@Chitosan@Cu (acac)2@IL was used as a catalyst. It is interesting to notice that the
activity of the catalyst in water increased when ionic liquid was supported on chitosan. This fact
highlights the importance of supporting the zwitterions to stabilize catalyst in water medium. The
higher activity of catalyst can be attributed to a cooperative effect between copper and IL.
To begin, benzyl alcohol was treated with various oxidants. As shown from the results
summarized in Table 2, the reaction proceeded smoothly in other oxidants, such as hydrogen

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peroxide, urea hydrogen peroxide, metaꢀchloroperoxybenzoic acid, sodium hypochlorite. The
isolated yields were significantly influenced by the oxidant employed. Among the oxidants
tested, tertꢀButyl hydroperoxide (TBHP) was proven to be the best compared to the others (Entry
6ꢀ10). A slightly better yield of benzoic acid resulted with increasing the temperature from r.t to
o
o
40 and then to 60 C. (Entry 11, 12). Upon raising the temperature from 60 to 100 C, the
reaction rate and yield of the reaction did not change. After that, amount of the catalyst was also
optimized. The effect of catalyst loading on the oxidation of benzyl alcohol is shown in this
table. No benzoic acid was obtained without the use of a catalyst (Entry 17). When the catalyst
loading was less than 20 mg, the yield of the product was relatively lower. A yield of 95% was
obtained when 30 mg catalyst was applied (entry 15), and the yield was not apparently improved
further when the catalyst loading was more than 30 mg. Thus the optimal reaction conditions
were considered including benzyl alcohol (1 mmol), TBHP (2 mmol), 30 mg catalyst (including:
1 mol% Cu, 0.5 mol % ionic liquid) at 60
(Entry 15).
̊C for 4 h in deionized water under Ar atmosphere
TBHP serves as a source of reactive oxygen radicals (e.g., tBuO•), which would act upon the
benzyl alcohol to generate benzaldehyde in situ. Then in the next step benzaldehye could convert
to benzoic acid.
Our investigation implicated that the reaction proceeds via a radical mechanism as employing
K2CO3 or Et3N as additives did not change product yield and also, the benzoic acid formation
was suppressed in the presence of ascorbic acid.

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Table 2. Optimization of the reaction conditions a
Entry
Catalyst
Oxidant
Temp.( °C)
Yield (%)
mg
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Fe3O4
Fe3O4@CS
Cu(acac)2
10
10
10
10
10
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
H2O2
r.t.
r.t.
r.t
N.D.b
N.D.b
35b
Cu(acac)2
Fe3O4@CS@Cu(acac)2
r.t
45b,c
20 b
40 b
35 b
30 b
20 b
N.D.b
45 b
50 b
50 b
75 b
95 b
95 b
20 b
N.D.b
r.t.
r.t.
r.t.
r.t.
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 10
Fe3O4@CS@Cu(acac)2@IL 20
Fe3O4@CS@Cu(acac)2@IL
Fe3O4@CS@Cu(acac)2@IL 40
Fe3O4@CS@Cu(acac)2@IL
Fe3O4@CS@Cu(acac)2@IL 30
mCPBA
UHP
NaClO
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
ꢀ
r.t.
r.t.
40
60
100
60
60
60
60
60
30
ꢀ
a Condition: 1 mmol of benzyl alcohol, 2 mL of deionized water, and 2 mmol TBHP, 12 h
b GC yield
c In the presence of TBAB
Benzylic alcohols, including with either electron withdrawing (b, d, f) or electronꢀdonating
groups (c, e, g), were oxidized to the benzoic acids in quantitative yield. Furfuryl alcohol was the
only problematic substrate that the major product was furfural.

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Scheme 2: Oxidation of benzyl alcohols in the presence of Fe3O4/CS/Cu/IL bifunctional catalyst,
Isolated Yields
The proposed mechanism for the oxidation in the presence of catalyst is shown in Scheme 3.
O
OH
H2O +
+
OH
Cl
N
N
O
N
N
O
O
Aldehyde to Acid
Si
O
N
TBHP
Cl
O
O
O
Si
Cl
H
N
O
O
O
N
O
N
O
H2O +
OH
O
Si
O
N
Alcohol to Aldehyde
Cl
O
O
N
HO
Si
O
O
O
TBHP
Scheme 3: Plausible mechanism

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DOI: 10.1039/C6RA18100G
In the first step by using of Cu and TBHP, activated benzyl alcohol in the presence of imidazole
moiety produced benzaldehyde and tertꢀbutanol. In the second step, benzaldehyde was activated
and oxidized to benzoic acid.
This method is efficient and environmentally benign. Compared with the previously reported,
offering significantly improved yields and purity of the desired products. Additionally, no
chlorinated solvent is required.
After accomplishing the reaction, superparamagnetic nanocatalysts were separated from the
medium, as usual with applying an external magnet, then washed and dried under vacuum at
room temperature in 12 h and used for next reaction. Reusing nanocatalysts were repeated till the
results were not satisfied. In this way, the catalytic recycle ability of synthesized nanocatalyst
was examined. It showed excellent result for just 5 times and after that we were witness about its
deterioration catalytic activities (Fig. 8). Also, there is no change in the structure of the catalyst
after the reaction: all of the observed XRD peaks are the same as the recorded pattern of primary
catalyst. Regarding recyclability of the catalyst, the image obtained (Fig. 10) do not reveal
significant changes in the Fe3O4/CS/Cu/IL morphology even after the fifth run (Fig. 10).
Figure 8: Activity lost as a function of the number of reused times of the catalyst in the synthesis
of benzoic acid

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DOI: 10.1039/C6RA18100G
Figure 9: XRD pattern of the reused catalyst before using in the 6th run
Figure 10: SEM image of the catalyst after the 5th run

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DOI: 10.1039/C6RA18100G
Conclusion:
In summary, functional magnetic nanoprticles that combines catalytically active Copper
acetylacetonate and 1ꢀpropylꢀ3ꢀmethylimidazolium chloride as ionic liquid (Fe3O4/CS/Cu/IL)
was successfully prepared by imine band formation and silylanization.
We have disclosed a new catalyst system which proves to be very effective not only in reducing
the reaction time, but also in increasing the yield of the product. It involves simple procedure, is
environment friendly and also incorporates special features like reagent economy, easy workup
and easy handling.
Acknowledgment:
We are thankful to Tarbiat Modares University and National Elite Foundation of I.R. Iran for
partial support of this work.
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