Vitamin B1 supported on silica-encapsulated γ-Fe 2O3 nanoparticles: Design, characterization and application as a greener biocatalyst for highly efficient acylation

Article abstract of DOI:10.1039/c3ra46437g

A new magnetic catalyst was synthesized by the immobilization of vitamin B₁ (thiamine hydrochloride) on the surface of silica-encapsulated γ-Fe₂O₃ nanoparticles. Its capability was evaluated in the acylation of alcohols and phenols with acetic anhydride under solvent-free conditions and afforded the desired products in high yield. This novel magnetic organocatalyst could be separated from the reaction vessel by use of an external magnet and recovered 5 times without a significant loss of its activity. The amount of loaded vitamin B₁ on the silica-encapsulated γ-Fe₂O₃ was assigned by TGA and confirmed by back titration. Availability, cheapness and low toxicity are reasons associated with the utilization of vitamin B₁ as a catalyst. The catalyst has been characterized by FT-IR, XRD, SEM, VSM and TG/DTA. The Royal Society of Chemistry.

Full text of DOI:10.1039/c3ra46437g

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Vitamin B supported on silica-encapsulated
1
g-Fe O nanoparticles: design, characterization
2
3
Cite this: RSC Adv., 2014, 4, 8812
and application as a greener biocatalyst for
highly efficient acylation
Kobra Azizi and Akbar Heydari*
A new magnetic catalyst was synthesized by the immobilization of vitamin B
1
(thiamine hydrochloride) on
the surface of silica-encapsulated g-Fe nanoparticles. Its capability was evaluated in the acylation of
2 3
O
alcohols and phenols with acetic anhydride under solvent-free conditions and afforded the desired
products in high yield. This novel magnetic organocatalyst could be separated from the reaction vessel
by use of an external magnet and recovered 5 times without a significant loss of its activity. The amount
Received 6th November 2013
Accepted 9th December 2013
1 2 3
of loaded vitamin B on the silica-encapsulated g-Fe O was assigned by TGA and confirmed by back
DOI: 10.1039/c3ra46437g
titration. Availability, cheapness and low toxicity are reasons associated with the utilization of vitamin B
as a catalyst. The catalyst has been characterized by FT-IR, XRD, SEM, VSM and TG/DTA.
1
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illustrative examples of MNPs, and are noteworthy in regard to
the medical and pharmaceutical elds, due to their biocom-
Introduction
5
Thiamine hydrochloride (vitamin B
1
) named as the “thio- patibility and biodegradability.
vitamin” is a water-soluble vitamin found in the vitamin B
Recently, appreciable attempts have been devoted towards
complex. Vitamin B (VB ) consists of pyrimidine and thiazole the development of magnetic nanoparticles (MNPs) and
1
1
rings linked by a methylene bridge (Fig. 1). The use of VB1 upgrading their applicability in many diverse areas. The accu-
analogs as powerful catalysts for various organic trans- rate surface functionalization of MNPs is critical because it
1
formations has been reported.
controls their physicochemical effects, colloidal suspension
6
Vitamin B
1
is an essential cofactor in all living systems steadiness and biological fate. The xation of active biomole-
where it functions to stabilize the acyl carbanion synthon and cules via covalent attachment to a silica surface for biotechno-
catalyzes the nonenzymic decarboxylation of pyruvate to a-ace- logical processes is a remarkable synthetic approach.
tolactate and acetoin in mildly basic aqueous solutions. In the
2
7
3
In order to reduce the problems of using mineral acid
1
960's, Ronald Breslow, proposed that vitamin B could be used catalysts (e.g. H
as a catalyst in biochemical acyloin condensations and serves as clays, zeolites, sulfated metal oxides and heteropolyacids, we
2
SO and HCl) and solid acid catalysts such as
4
1
8
a coenzyme for three important types of transformations (a) are interested in the design of ‘greener’ heterogeneous catalysts.
nonoxidative decarboxylations of a-keto acids (b) oxidative So we envisioned a novel renewable and environmentally safe
4
decarboxylations of a-keto acids (c) formation of acyloins.
Brønsted acid catalyst (vitamin B supported on a magnetic
1
Magnetite (Fe
3
O
4
) and maghemite (g-Fe
2
O
3
), are two main surface). Aer characterization of the catalyst, its activity was
evaluated for the acylation of alcohols and phenols. In the
present work, to effectively utilize the catalytic properties of VB ,
1
we have developed an efficient procedure to tether VB on a
1
magnetic surface.
Results and discussion
Synthetic Modus Operandi and characterization of
Fig. 1 Structure of Vitamin B1 (VB1).
g-Fe O @SiO coated with vitamin B
2
3
2
1
FT-IR spectra. FT-IR appears to be the best technique to
conrm the modication of Fe O @SiO . To evaluate the best
possible conditions for the loading of vitamin B on silica,
1
2
3
2
Chemistry Department, Tarbiat Modares University, P.O. Box 14155-4838, Tehran,
Iran. E-mail: heydar_a@modares.ac.ir; Fax: (+98)-21-82883455; Tel: (+98)-21-
8
2883444
multifarious solvents and bases were investigated. The FT-IR
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peaks of the nanoparticles did not change in the absence of a the last step. Also, the broad peak of the hydroxyl group hasn't
base, which means that vitamin B was not attached on the been observed in this spectrum conrming hydroxyl groups are
1
silica. Our results conrmed that, by adding base, the silica is linked to silica surface (d).
capable of covalently binding to vitamin B . In this study,
Scanning electron microscopy (SEM). The morphology of
various solvents were tested under basic conditions to investi- nano g-Fe @SiO @vitamin B was evaluated using scanning
gate the effect of solvent on the enhancement of vitamin B electron microscopy (SEM). The SEM image of the supported
1
2
O
3
2
1
1
loading. The FT-IR peaks clearly changed in the presence of catalyst showed uneven-sized particles due to deposition of the
triethylamine with methanol as the solvent. Then the reaction silica on magnetic nanoparticles (Fig. 3).
was done at different temperatures. The FT-IR peaks of the
X-ray diffraction (XRD). Average size was calculated by using
system exhibited distinguishable changes in the presence of Scherrer's formula D ¼ 0.9l/b cos q to be about 80 nm, D is the
ꢀ
˚
triethylamine as the base in methanol at 80 C. We propose that average crystalline size, l is the X-ray wavelength (a ¼ 1.78897 A),
the ammonium salt produced from the reaction of triethyl- b is the angular line width of half-maximum intensity and q is
1
amine and vitamin B catalyzed the formation of covalent Bragg's angle in degrees (Fig. 4). Diffraction peaks at around
ꢀ
ꢀ
ꢀ
ꢀ
binding between silica and thiamine. Substitution includes the 35.5 , 43.1 , 54 , 62.8 , corresponding to the (311), (400), (440)
O nucleophile of silica attacking the electrophilic C in the and (511) are identied from the XRD pattern. It is apparent that
hydroxyethyl side chains of thiamine displacing a water the diffraction peaks of our magnetic silica nanoparticles match
molecule.
2 3
to the standard pattern for crystalline maghemite (g-Fe O ) with
9
FT-IR spectra of Fe O @SiO , vitamin B , Fe O @SiO @thi- an inverse spinel structure and also conrming that the nano-
2
3
2
1
2
3
2
amine and Fe O @SiO @vitamin B are depicted in Fig. 2. The particles are coated with silica.
2
3
2
1
ꢁ
1
spectrum of Fe O @SiO (a), shows a band around 461 cm
Vibrating sample magnetometry (VSM). The magnetic
which can be attributed to the stretching vibrations of the Fe–O possession of the g-Fe @SiO @vitamin B was measured by
bond in the g-phase Fe . Also, the bands around 804 and the vibrating sample magnetometry (VSM). Magnetization (emu g
2
3
2
2
O
3
2
1
ꢁ1
2
O
3
1
)
ꢁ
strong band at 1089 cm , are associated to vibrations of the as a function of applied eld (Oe) is depicted in Fig. 5 with the
symmetric stretching of Si–O–Si and asymmetric of Si–O–Si, conned eld from ꢁ10 000 to 10 000 Oe.
respectively in the spectrum of Fe
2
O
3
@SiO
2
conrming that
2 3
Bare nanocrystals of g-Fe O have a high saturation
ꢁ
1
10
silica is well coated on the g-phase Fe O . The spectrum of magnetization of 68 emu g at room temperature which
supported g-Fe O @SiO with thiamine (c) also shows small decreased to 15 emu g for g-Fe O @SiO @vitamin B , none-
bands around 2900 cm that are related to asymmetric and theless it is enough to remove this catalyst from the reaction
symmetric C–H stretching. The signals located at 3416 cm can vessel with an ordinary magnet.
2
3
ꢁ
1
2
3
2
2
3
2
1
ꢁ
1
ꢁ1
be attributed to the N–H stretching and conrmed that thia-
2 3 2
VSM shows the hysteresis loops of the g-Fe O @SiO @vita-
mine was tethered on a silica surface through its hydroxyl min B
1
at room temperature. The zero remanence and coercivity
group. In the spectrum (c) for thiamine functionalized of magnetization curve demonstrate that these silica nano-
ꢁ1
g-Fe
2 3 2
O @SiO , the peak at 1626 cm can be ascribed to the particles have super paramagnetic properties. With the
C]N or C]C bands stretching frequency. The spectrum of the g-Fe O @SiO @vitamin B dispersed in CH Cl an external
2
3
2
1
2
2
supported g-Fe O @SiO with vitamin B1 revealed an asym- magnetic eld can easily gather the nanoparticles in less than
2
3
2
metric and symmetric C–H band stretching frequency at around one minute (Fig. 6), and then with a slight shake they can
ꢁ
1
2
900 cm and the N–H stretching frequency was shied to a promptly be re-dispersed, the results show that the particles
ꢁ
1
higher wavelength at 3430 cm and its intensity decreased display good magnetic characteristics and that they can be
indicating that NH had been converted to its chloride salt in applied as a magnetic catalyst.
Thermo-gravimetric analysis (TGA) and differential thermal
2
analysis (DTA). Piccaluga and co-workers have reported DTA
measurements of g-Fe O @SiO (ref. 11) that showed an
2
3
2
ꢀ
endothermic peak at a low temperature (lower than 200 C) due
ꢀ
to water elimination and exothermic signal over 600 C.
Fig. 2 FT-IR spectra of g-Fe
2
O
3
@SiO
2
coated with vitamin B
1
.
2 3 2 1
Fig. 3 SEM analysis of the g-Fe O @SiO @vitamin B .
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2 3 2 1
Fig. 4 The X-ray diffraction patterns of the g-Fe O @SiO @vitamin B .
Fig. 7 Thermogravimetric and differential thermogravimetric of g-
Fe O @SiO coated with vitamin B .
2 3 2 1
Through the TGA analysis, the vitamin B
1
content of
ꢁ
1
g-Fe
The acidity of vitamin B
g-Fe was conrmed by the back-titration method. Thus,
triplicate ꢂ100 mg samples, were added to 5 mL of 0.1 N NaOH
solution. To ensure that all of the vitamin B was reacted with
2
O
3
@SiO
2
was evaluated to be 0.2 mmol g
.
1
loaded on the silica-encapsulated
2 3
O
1
NaOH, an excess amount of NaOH was used. The mixture was
sonicated for 10 minutes. To each vessel, was added two drops
of phenolphthalein pH-indicator. Back-titration was accom-
plished by titrating the unreacted base in solution with stan-
dardized 0.1 N HCl solutions to the rst permanent cloudy pink
colour. This was subtracted from the primary amount of base to
Fig. 5 Magnetization curve of g-Fe
2
O
3 2
@SiO @vitamin B
1
.

nd the amount of base that actually reacted with the vitamin
as an acid and hence the quantity of supported vitamin B on
B
1
1
ꢁ
1
the MNPs. The acidity value was obtained as 0.2 mmol g by
adding 0.8 mL HCl.
Total number of moles of NaOH added to the sample:
0.1 mmol, total volume of HCl added to each vessel: 0.8 mL,
number of moles of consumed HCl: 0.08 mmol, average
number of moles of excess NaOH le aer the reaction was
Fig.
6
Visualization of the g-Fe
2
O
3
@SiO
2
@vitamin B
1
collection
process using a magnetic bar: (A) before the reaction without a magnet
bar (B) during stirring with a magnet bar (C) collection on the magnet complete: 0.02 mmol.
bar after reaction.
Thus:
2 3 2
Thermogravimetric analysis (TGA/DTA) of g-Fe O @SiO coated
with vitamin B
1
is depicted in Fig. 7.
The formation of phenyl acetate from phenol was complete
ꢀ
1
The endothermic peak below 200 C showed a weight loss of in the presence of vitamin B (0.2 mol%) as the catalyst in less
this catalyst of 5% that can be assigned to the release of phys- than one hour but the main problem of this reaction was the
isorbed molecules on the surface of g-Fe O @SiO . There are loss of catalyst at the end of the reaction.
2
3
2
two exothermic peaks accompanied with a mass loss of 5.5% in
the temperature range of 200–600 C in the DTA curve of the acetylation reaction of phenol was carried out in the pres-
To survey the efficacy of vitamin B in this transformation,
1
ꢀ
2 3 2 1 2 3 2
g-Fe O @SiO coated with vitamin B . These peaks were mainly ence of g-Fe O @SiO which did not result in the absolute
attributed to the decomposition of organic groups graed to the conversion of phenol to the corresponding acetate even aer
ꢀ
g-Fe
2
O
3
@SiO
2
surface. The peak higher than 600 C most 2 h. This was emblematic of the necessity of vitamin B
1
in this
probably corresponds to a phase transition in which the transformation.
1
1
amorphous phase is converted to a crystalline phase. In this
The acetylation of phenol in the presence of various amounts
of catalyst was investigated. The conversion of phenol to phenyl
temperature range, XRD shows the starting point of the a-Fe O
2
3
formation. Also the transition g- to a-Fe O gives an exothermic acetate improved when the amount of catalyst increased from
2
3
12
DTA trace, that in the present case, is superimposed on the 5 mg to 10 mg however, amounts greater than 10 mg of catalyst
amorphous to g-Fe
2
O
3
transition trace.
had no signicant inuence in this conversion. Thus, the
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2 3 2 1
optimal amount of g-Fe O @SiO coated with vitamin B was
10 mg (0.2 mol%) which resulted in a 98% yield of phenyl
acetate aer 1 h at room temperature under solvent-free
conditions. Hence, the reaction was also investigated in the
presence of several organic solvents such as acetone, acetoni-
trile and dichloromethane as well as trying solvent-free condi-
2
tions. In H O, the formation of phenyl acetate did not go to
completion, so the optimal conditions of the reaction were
selected to be without solvent, at room temperature and in the
presence of 10 mg catalyst.
The supported organocatalyst was tested in the acetylation of
alcohols and phenols to survey its efficacy.
2 3 2 1
Scheme 1 Preparation of g-Fe O @SiO @vitamin B .
was recorded at room temperature on a Philips X'pert 1710
˚
diffractometer using Co Ka (a ¼ 1.78897 A) voltage: 40 kV,
ꢀ
ꢀ
current: 40 mA, and the data were collected from 10 to 90 (2q)
ꢀ
ꢁ1
with a scan speed of 0.02 s . The morphology of the catalyst
was studied with scanning electron microscopy using SEM
(
Philips XL 30 and S-4160) with gold coating equipped with
energy dispersive X-ray spectroscopy. The magnetic properties
of the vitamin B functionalized silica-coated magnetic nano-
1
particles were measured with a vibrating sample magnetom-
eter/alternating gradient force magnetometer (VSM/AGFM,
MDK Co., Iran, http://www.mdk-magnetic.com). Thermogravi-
metric/differential thermal analyses (TG/DTA) was performed
The reaction proceeded efficiently with high product yields
and the catalyst could be recovered for at least ve consecutive
runs. Fig. 8 shows that the catalytic system of g-Fe
coated with vitamin B worked well as phenyl acetate was
produced with a high yield aer the h run. If vitamin B had
been adsorbed on the surface of the silica, aer the initial run
this catalyst wouldn’t be active in the subsequent runs. The Preparation of vitamin B supported on g-Fe O @SiO
2
O
3
@SiO
2
ꢀ
ꢁ1
on a Thermal Analyzer with a heating rate of 20 C min over a
1
ꢀ
temperature range of 25–1100 C under owing compressed N .
2
1
1
2
3
2
binding between vitamin B and silica should be covalent.
(Scheme 1)
1
(a) Preparation of Fe
3
O
4
MNPs. 5 mmol FeCl
3
2
$6H O and
2
.5 mmol FeCl $4H O salts were dissolved in 100 mL deionized
2 2
Experimental
water under vigorous stirring (800 rpm) then NH OH solution
4
(
25%, w/w, 30 mL) was added to the above mixture at room
temperature until the pH was raised to 11. The addition of
NH OH solution followed to maintain the reaction pH between
All purchased solvents and chemicals were of analytical grade
and used without further purication. FT-IR spectra were
ꢁ
1
obtained over the region 400–4000 cm on a NICOLET IR100
4
1
1 and 12 at which point a black suspension was formed. The
FT-IR with spectroscopic grade KBr. The powder X-ray spectrum
resulting black dispersion was continuously stirred for 1 h at
room temperature and then reuxed for 1 h.
(
b) The surface modication of g-phase Fe O by tetraethyl
2 3
orthosilicate (TEOS). Coating of a layer of silica on the surface of
the g-Fe nanoparticles was achieved by adding ethanol
40 mL) to puried nanoparticles which were then heated for 1 h
2 3
O
(
ꢀ
at 40 C. Subsequently, tetraethyl orthosilicate (TEOS, 10 mL)
was charged to the reaction vessel, and the mixture was
continuously stirred for 24 h. The silica-coated nanoparticles
were collected by a magnet, followed by washing ve times with
ꢀ
EtOH, diethyl ether and drying at 100 C in vacuum for 12 h. The
ꢀ
prepared nanoparticles at this stage are heated at 300 C in a
Fig. 8 Activity lost as a function of the number of reused times of
furnace for 3 h to convert Fe
g-Fe @SiO nanoparticles.
3 4 2
O @SiO to sustainable
2 3 2 1
the g-Fe O @SiO coated with vitamin B for the synthesis of
phenylacetate.
O
3
2
2
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(
c) Preparation of g-Fe
2
O
3
@SiO
2
coated with thiamine. Various derivatives of alcohols and phenols were converted to
Thiamine hydrochloride (1 mmol) was added to 1 g of the their corresponding acetates with high yields under solvent-free
former suspension of g-Fe @SiO
nanoparticles in methanol conditions. Recyclability of the catalyst was observed up to
2
O
3
2
in the presence 1.2 mmol triethylamine and reuxed for 8 h. 5 times without signicant loss of its catalytic activity.
The residue was collected by a magnet, followed by washing
several times with methanol, water and ethanol to remove tri-
ethylamine and any unreacted vitamin to obtain
Acknowledgements
g-Fe O @SiO @thiamine.
We acknowledge Tarbiat Modares University for partial support
2
3
2
(
d) Preparation of g-Fe
2
O
3
@SiO
2
@vitamin B
1
. To replace of this work. This article is dedicated to the memory of Pilot. Ali
the acid functionality previously neutralized by triethylamine, Akbar Shirudi.
was added 2 mL HCl (1 M) in diethylether and stirred for 3 h at
ꢀ
0
C. The magnetic nanoparticles were washed with diethyl
Notes and references
ꢀ
ether and distilled water, then dried for 24 h at 80 C in an oven.
The desired catalyst was formed.
1
2
M. Lei, L. Ma and L. Hu, Tetrahedron Lett., 2009, 50, 6393.
(a) J. H. Park, P. C. Dorrestein, H. Zhai, C. Kinsland,
F. W. McLafferty and T. P. Begley, Biochemistry, 2003, 42,
Application of the catalyst in acylation of alcohols and
phenols
12430; (b) R. A. W. Frank, F. J. Leeper and B. F. Luisi, Cell.
To a stirred mixture of the alcohol or phenol (1 mmol) and
Mol. Life Sci., 2007, 64, 892.
(
(
CH
3
CO)
2
O (1.2 mmol) was added g-Fe
2
O
3
@SiO
2
@vitamin B
1
3 (a) E. Yatco-Manzo, F. Roddy, R. G. Yount and D. E. Metzler,
J. Biol. Chem., 1959, 234, 733; (b) Chem. & Ind., B. I. F.,
London, 1956, p. 28, Review.
4 T. C. Bruice and S. Benkovic, Bioorganic Mechanism, W. A.
Benjamin, Inc., New York, 1966, p. 2.
10 mg ¼ 0.2 mol%) and stirring was continued at room
temperature for the appropriate time (TLC). Aer completion of
the reaction, CH Cl was added to the mixture to remove the
catalyst by an external magnet. Water (10 mL) was added and
the phases were separated. The organic phase was washed with
saturated NaHCO3 solution, brine, dried (Na SO ) and
2
2
5 L. H. Reddy, J. L. Arias, J. Nicolas and P. Couvreur, Chem.
Rev., 2012, 112, 5818.
2
4
concentrated to give the pure product. The catalyst was washed
with methanol and dried to reuse. The catalyst could be recycled
6 W. Wu, Q. He and C. Jiang, Nanoscale Res. Lett., 2008, 3, 397.
7 A. Stamatis, G. Malandrinos, I. S. Butler, N. Hadjiliadis and
M. Louloudi, J. Mol. Catal. A: Chem., 2007, 267, 120.
8 A. Kong, P. Wang, H. Zhang, F. Yang, S. P. Huang and
Y. Shan, Appl. Catal., A, 2012, 417–418, 183–189.
5
times without a measurable loss of activity. The desired pure
products were characterized by comparison of their physical
data with those of known compounds.
9
Z. Ma, Y. Guan and H. Liu, J. Magn. Magn. Mater., 2006, 301,
69–477.
4
Conclusion
10 H. Zhu, D. Yang, L. Zhu, H. Yang, D. Jin and K. Yao, J. Mater.
1
In summary, vitamin B was found to be a green and biocom-
Sci., 2007, 42, 9205–9209.
patible organocatalyst for the acetylation of hydroxyl groups. 11 G. Ennas, A. Musinu, G. Piccaluga and D. Zedda, Chem.
The catalyst was easily separated from the reaction mixture by Mater., 1998, 10, 495–502.
using an external magnet and thus supporting the catalyst on 12 O. Clause, L. Bonneviot and M. Che, J. Catal., 1992, 138, 195–
magnetic nanoparticles increased the efficiency of the method. 205.
8816 | RSC Adv., 2014, 4, 8812–8816
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