Integration of aqueous biphasic with magnetically recyclable systems: Polyethylene glycol-grafted Fe3O4 nanoparticles catalyzed phenacyl synthesis in water

Article abstract of DOI:10.1016/j.catcom.2016.01.036

The present work trends to define an efficient phenacyl catalytic synthesis method employing a new nano-magnetite-supported organocatalyst. Polyethylene glycol (PEG) was bonded successfully onto silica coated ferrite and the resultant nanoparticles (PEG@SiO₂@Fe₃O₄) characterized by fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), thermal gravimetric analysis (TGA), vibrating sample magnetometry (VSM), energy dispersive X-ray analysis (EDAX) and X-ray diffraction (XRD) that exhibited a good catalytic activity in the reaction. The nanoparticles could be easily separated from the reaction mixture by an external magnet and reused in seven reaction cycles without significant loss of activity.

Full text of DOI:10.1016/j.catcom.2016.01.036

Integration of aqueous biphasic with magnetically recyclable systems:
Polyethylene glycol-grafted Fe3O4 nanoparticles catalyzed phenacyl synthesis
in water
Atefeh Amini, Soheil Sayyahi, Seyyed Jafar Saghanezhad, Narges Taheri
PII:
DOI:
Reference:
S1566-7367(16)30037-1
doi: 10.1016/j.catcom.2016.01.036
CATCOM 4581
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
11 December 2015
28 January 2016
30 January 2016
Please cite this article as: Atefeh Amini, Soheil Sayyahi, Seyyed Jafar Saghanezhad,
Narges Taheri, Integration of aqueous biphasic with magnetically recyclable systems:
Polyethylene glycol-grafted Fe3O4 nanoparticles catalyzed phenacyl synthesis in water,
Catalysis Communications (2016), doi: 10.1016/j.catcom.2016.01.036
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ACCEPTED MANUSCRIPT
Integration of aqueous biphasic with magnetically recyclable systems: Polyethylene
glycol –grafted Fe O nanoparticles catalyzed phenacyl synthesis in water
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Atefeh Amini , Soheil Sayyahi *, Seyyed Jafar Saghanezhad , Narges Taheri
1
Department of Chemistry, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran
2
ACECR-Production Technology Research Institute, Ahvaz, Iran
Email:sayyahi.soheil@gmail.com
Abstract
The present work trends to define an efficient phenacyl catalytic synthesis method employing
a new nano-magnetite- supported organocatalyst. Poly ethylene glycol (PEG) was bonded
successfully onto silica coated ferrite and the resultant nanoparticles (PEG@SiO @Fe O )
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characterized by fourier transform infrared spectroscopy (FT-IR), atomic force microscopy
AFM), thermal gravimetric analysis (TGA), vibrating sample magnetometry (VSM), energy
(
dispersive X-ray analysis (EDAX) and X-ray diffraction (XRD) that exhibited a good
catalytic activity in the reaction. The nanoparticles could be easily separated from the
reaction mixture by an external magnet and reused in seven reaction cycles without
significant loss of activity.
Keywords: Magnetically recyclable nanocatalyst; PEG-grafted nanoparticles; Phenacyl
derivatives
1
. Introduction
In recent years, magnetic nanoparticles have attracted a great deal of interest from academic
and industrial stand point due to their unique properties including high surface area, and
superparamagnetism [1-7], indicating those particles do not show magnetic interaction
without an external magnetic field. This allows surface modification of nano-magnetite
materials with homogeneous metals, organoligands, organocatalysts, enzymes and N-
heterocyclic carbenes employing them as catalyst [8]. Also, by using magnetic separation,
time-consuming and tedious filtration/separation/ isolation protocols can be significantly
simplified into a one/two-step method catalyst recovery and reuse [9]. Therefore,
magnetically recoverable catalysts were used in a wide range of reactions, such as Suzuki,
Heck, Sonogashira, Hiyama, alkyne-azide cycloaddition, hydrogenation, reduction, oxidation,
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arylation, alkylation, epoxidation of alkenes, multicomponent synthesis, Fenton-like reaction,
etc [10].
PEGs and PEG aqueous solutions have been widely used in many different kinds of reaction
systems. Their low-toxicity, low volatility, and biodegradability represent important
environmentally benign characteristics, which are particularly attractive when combined with
their relatively low cost as a bulk commodity chemical. In addition, aqueous PEG solutions
may often be substituted for expensive and toxic phase transfer catalysts (PTCs) [11]. Since
the polyethylene oxide chains have the ability to form complexes with metal cations, PEG
can be served as a PTC catalysts, as well as crown ethers [12, 13].
Phenacyl derivatives are important intermediates for the synthesis of valuable molecules
applied to heterocyclic chemistry on account of the fact that many of them are subunits of
natural and synthetic products [14-17].
Recently, we reported the use of Fe O nanoparticle-bonded β-cyclodextrin as a novel and
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efficient magnetically retrievable catalyst for the ring opening of epoxides [18].
Taking into account all these, we decided to modify magnetite with PEG and investigate the
efficieny of the resulting MNPs for catalyzed synthesis of phenacyl derivatives via
nucleophilic substitution reactions.
2
. Experimental
2
.1.General
All chemicals were purchased from Sigma Aldrich and Merck companies and used as
received without further purification. Fe O and SiO @ Fe O were prepared according to the
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2
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reported methods [19, 20]. AFM images were obtained using a Nano Wizard II instrument.
ꢁꢂꢃꢄꢃꢅꢆꢇꢈꢇꢂꢉꢃꢇꢂꢊꢋꢌꢍꢎꢌꢏꢋꢐꢂꢑꢄꢐꢋꢌꢂꢄꢈꢒꢌꢎꢓꢋꢄꢂꢉꢈꢒꢔꢂꢃꢂꢔꢋꢃꢒꢈꢄꢓꢂꢌꢃꢒꢋꢂꢎꢍꢂꢕꢖꢂC/min using a BAHR,
ꢀ
ꢗ
SPA 503. Magnetism analysis was performed on a vibrating sample magnetometer (4 inch,
Daghigh Meghnatis Kashan Company, Kashan, Iran) at room temperature. XRD patterns of
samples were taken on a PANalytical X-ray diffractometer Model X'Pert Pro. Thin-layer
chromatography was carried out on aluminum-backed 0.2 mm thick silica gel 60 F254 plates.
2
.2.Synthesis of PEG@SiO @Fe O
2 3 4
First of all, SiO @Fe O (0.5 g) was dispersed in dry toluene (20 mL), sonicated for 15 min,
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4
and then (3-chloropropyl) triethoxysilane (1.5 mL, 6.25 mmol) was added. The whole
mixture was stirred and refluxed for 48 h under nitrogen atmosphere. The solid materials
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were filtered off, washed with acetone and dried under reduced pressure. Then, triethyl amine
(
1.0 mL) and PEG300 (2.0 mL) was added to a suspension of Linker-SiO @Fe O (1.0 g) in
2 3 4
benzen (5.0 mL).
The mixture was stirred at room temperature for 24 h. The resultant MNPs were removed by
an external magnet and washed several times with ethanol and dried well to generate
PEG@SiO @Fe O .
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2
.3.General procedure for the synthesis of phenacyl thiocyanates/azides catalyzed by PEG-
grated Fe O
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A magnetically stirred solution of α-bromo ketone (1.0 mmol) and NaX (2.0 mmol) in water
5.0 mL), PEG@SiO @Fe O (50 mg) was added. The resulting suspension was stirred under
(
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4
reflux conditions for the time shown in table 1. After completion of the reaction that
confirmed by TLC, the MNPs were removed magnetically and solid was filtered off, washed
with water and subjected to flash chromatography. The desired phenacyl derivatives obtained
in 82% to 94% isolated yields.
3
. Results and discussions
The strategy used to prepare PEG@SiO @Fe O is shown in scheme 1, which consists of two-
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step synthetic procedure. First, (3-chloropropyl) triethoxysilane has been used as linker where
SiO @Fe O nanoparticles functionalized by refluxing in toluene. Then, linker terminal
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groups (-CH Cl) were reacted with PEG in benzene containing triethyl amine.
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Schem 1. Preparation of PEG@SiO @Fe O magnetite nanoparticles
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The FT-IR analysis of the nanoparticles has been used to demonestrate the successful
grafting of PEG chains on the SiO @Fe O surface (Figure 1a). Accordingly, the peaks could
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-1
be attributed to: (a) Fe-O vibration at ~580 cm (b) typical Si-O-Si streching of silica shell
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-1
and C-O streching of the ether groups in PEG chains at ~1050-1150 cm (c) Si-OH groups, -
-1
-1
OH groups in PEG chain and adsorbed water at ~3400 cm (broad) and ~1650 cm (d) -CH -
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groups in linker and PEG chains at ~2850-2950 cm . AFM images of PEG@SiO @Fe O
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indicated the nano-scale of this organic-inorganic hybrid material and confirmed grafting of
PEG chains onto the nanoparticles (Figure 1b).
(a)
(b)
Fig. 1. (a) FT-IR spectra of the bare Fe O , SiO @Fe O and PEG-grated Fe O
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nanoparticles. (b) AFM images of PEG@SiO @Fe O nanoparticles
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The TG analysis was studied and showed a weight loss with approximately of 36%ꢂꢘꢋꢒꢉꢋꢋꢄꢂ
ꢙꢖꢖꢂꢃꢄꢐꢂꢚꢖꢖꢂ
ꢗC (Figure 2). This can be attributed to the presence of the organic moieties
(
Linker and PEG chains) on the surface of Fe O nanoparticles.
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Fig. 2. TGA-DTA measurement for PEG@SiO @Fe O nanoparticles
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Also, room temperature magnetic properties of PEG-grated Fe O nanoparticles were
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investigated (Figure 3). As can be seen from the diagrams, the saturation magnetization value
decrease from 60 emu/g in the neat Fe O to about 18 emu/g in the case of PEG-grated Fe O .
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This is due to the coating of the magnetite particles with non-magnetic materials; SiO shell,
2
linker moiety and PEG chains.
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Fig. 3. Room-temperature magnetization curves of Fe O (upper) and PEG@SiO @Fe O
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(lower)
The data from EDAX analysis are consistent with our expectations and confirms the presence
of carbon, oxygen, iron and silicon elements (Figure 4, left). Moreover, the crystalline
structure of PEG-grated Fe O nanoparticels was studied in the 2θ ꢌꢋꢓꢈꢎꢄꢂꢎꢍꢂꢖ-ꢛꢖꢂ
ꢗ
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4
exhibitesꢂꢊꢋꢃꢜꢇꢂꢃꢒꢂꢝꢖꢞꢟꢚ
ꢚꢝꢞꢖꢙꢂꢠꢚꢝꢞꢕ ꢗ) , where is closely match with the corresponding standard Fe O pattern (JCPDS
3 4
ꢗ
ꢂꢠꢝꢖꢞꢡ ꢗꢢ ꢣꢂꢝꢡꢞꢤꢛ ꢗꢂ ꢠꢝꢡꢞꢛ ꢗꢢ ꢣꢂꢟꢝꢞꢡꢕ ꢗꢂ ꢠꢟꢝꢞꢟ ꢗꢢ ꢣꢂꢡꢟꢞꢖꢝ ꢗꢂ ꢠꢡꢝꢞꢛ ꢗꢢ ꢣꢂꢡꢤꢞꢟꢟ ꢗꢂ ꢠꢡꢤꢞꢡꢗ
ꢗ
no. 19-0629 shown in parantheses) (Figure 4, right) [21].
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Fig. 4. EDAX (left) and XRD (right) patterns of PEG@SiO @Fe O nanoparticles
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Our previous work in immobilizing PEG onto polymer resin and using it as heterogeneous
catalyst[22], encouraged us to investigate the capacity of PEG-grated Fe O for affecting
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phenacyl derivatives synthesis. For this purpose, several experiments were designed and the
best result was obtained when 2-bromo-1-(4-bromophenyl) ethanone (1 mmol) treated with
aqueous solution of NaN (2.0 mmol) and the MNPs (0.025 g) under reflux conditions. After
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5 min the expected product, 2-azido-1-(4-bromophenyl) ethanone, was produced in 93%
yield. The reaction in the presence of Fe O as the catalyst did not complete even after 2
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4
hours, while the reaction in the presence of PEG as a heterogeneous catalyst achieved the
product in almost 40 minutes. Accordingly, we sought to establish the scope and generality of
this protocol for the synthesis of azide, thiocyanate, cyanide, acetate and iodide phenacyl
derivatives (Table 1).
Table 1. PEG@SiO @Fe O catalyzed nucleophilic reaction of α-bromo acetophenone
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derivatives with azide, thiocyanate, cyanide, acetate and iodide ions
a
Entry
Substrate
X
Time (min) Yield (%)
1
2
3
4
N3
45
40
60
90
85
84
75
80
SCN
CN
OAc
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5
I
40
85
6
7
8
9
N3
SCN
CN
OAc
I
35
45
75
75
35
93
90
78
82
90
1
0
1
1
1
1
1
1
2
3
4
5
N3
SCN
CN
OAc
I
35
35
50
60
30
94
87
80
78
85
1
1
1
1
2
6
7
8
9
0
N3
SCN
CN
OAc
I
45
35
90
90
60
88
82
80
77
85
a
b
Isolated yield; All products are known and the structure were established by comparison of
their physical and spectral data with those of authentic samples[14, 23, 24]
In an ideal methodology, products synthesized in pure form without formation of byproducts,
something which has been observed in our method, and in all cases, the substitution proceeds
efficiently with good to high overall yields.
It should be mentioned that, the PEG part of the catalyst can chelate the counter ion (cation)
of the anion so that the nucleophile can freely attack in an S 2 fashion to yield the product
N
(Scheme 2).
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Scheme 2. Postulated catalytic activity of the catalyst
Finally, we checked the recovery and reusability of the catalyst by separating the MNPs with
a NbFeB magnet and washing with ethanol (Figure 5). Pleasingly, the catalyst did not suffer
from a significant change in structure or decrease in reactivity after seven successive runs in
the synthesis reaction of 2-azido-1-(4-bromophenyl)ethanone (93% yield to 82% yield). For
the leaching test, whether some of PEG chains separate from the silica-coated magnetite
surface and acts as a homogeneous catalyst, fresh catalyst was added to a solution of 2-
bromo-1-(4-bromophenyl) ethanone and NaN in ethanol. The resulting mixture was stirred
3
for 15 min under reflux conditions. Then, the catalyst was removed magnetically and let the
reaction to proceed. As it shown, no further conversion has been detected after separation of
the nanoparticles.
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80
60
40
20
0
0
5
10 15 20 25 30 35 40 60
Time(min)
Fig. 5. Recovery and reusability of the catalyst and leaching test results
Conclusion
This synthetic methodology has been successfully applied to convert phenacyl bromide into
the corresponding form of azide, thiocyanate, cyanid, acetate and iodide in the presence of
nano-magnetite-supported poly ethylene glycol (PEG-grated Fe O ). It should also be
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mentioned that this procedure offers several advantages including facile work-up procedure,
short reaction times, good to high yields of the products, recyclable catalyst, and eco-friendly
reaction medium.
Acknowledgments
We thank the Mahshahr Branch, Islamic Azad University for financial support. Also, we are
grateful to Dr. Bijan Nekoueishahraki for helpful comments on the manuscript.
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Integration of aqueous biphasic with magnetically recyclable systems: Polyethylene glycol –
graftedFe O nanoparticles catalyzed phenacyl synthesis in water
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Soheil Sayyahi*, Atefeh Amini, Narges Taheri
Department of Chemistry, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran
Email:sayyahi.soheil@gmail.com
PEG-grated Fe O catalyzed nucleophilic reaction of α-bromoacetophenone derivatives
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Graphical abstract
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Highlights




Synthesis and fully characterization of PEG@SiO @Fe O nanoparticles
2 3 4
Performance of the catalysts was evaluated in the synthesis of phenacyl derivatives
Facile work-up procedure, short reaction times, good to high yields of the products
The catalyst is recyclable and stable under the reaction conditions
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