Sol-gel derived LaFeO3/SiO2 nanocomposite: Synthesis, characterization and its application as a new, green and recoverable heterogeneous catalyst for the efficient acetylation of amines, alcohols and phenols

Article abstract of DOI:10.1007/s13738-013-0377-3

LaFeO₃/SiO₂ nanocomposite was synthesized by the sol-gel process from metal nitrates and tetraethyl orthosilicate (TEOS) as the SiO₂ source. The nanocomposite product was characterized by XRD, FT-IR, SEM, and surface area measurements and was used as a heterogeneous catalyst for the efficient acetylation of amines, alcohols and phenols to the corresponding acetates using acetic anhydride under solvent-free conditions. Among the various substrates, acetylation of amines was preceded rapidly, so that an amine group could be selectively acetylated in the presence of alcoholic or phenolic hydroxyl groups by the appropriate choice of reaction time. The catalyst can also be reused several times without the loss of activity. In addition, the catalytic activity of the LaFeO₃/SiO₂ nanocomposite was higher than that of the pure LaFeO₃ nanoparticles. The method is high yielding, clean, cost effective, compatible with the substrates having other functional groups and very suitable for the practical organic synthesis.

Full text of DOI:10.1007/s13738-013-0377-3

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0377-3
ORIGINAL PAPER
Sol–gel derived LaFeO /SiO nanocomposite: synthesis,
3
2
characterization and its application as a new, green
and recoverable heterogeneous catalyst for the efficient
acetylation of amines, alcohols and phenols
Saeed Farhadi
•
Kosar Jahanara Asma Sepahdar
•
Received: 14 August 2013 / Accepted: 1 November 2013
Ó Iranian Chemical Society 2013
Abstract LaFeO /SiO nanocomposite was synthesized
3
organic transformation [3–13], but most of them are homo-
geneous and non-recoverable. In addition, many of these
methods have certain drawbacks, such as long reaction time,
involvement of toxic and expensive reagents, use of addi-
tional reagents, requirement of special effort for catalyst
preparation, need to use special apparatus, moderate yields,
and side reactions. With growing environmental concerns,
much attention has been directed towards this transformation
using heterogeneous catalysts [14, 15]. Heterogeneous cat-
alysts can be easily recovered from reaction mixture by
simple filtration and can be reused several times, making the
process more economically and environmentally viable. In
this context, heterogeneous catalysts such as HClO –SiO
2
by the sol–gel process from metal nitrates and tetraethyl
orthosilicate (TEOS) as the SiO source. The nanocom-
2
posite product was characterized by XRD, FT-IR, SEM, and
surface area measurements and was used as a heterogeneous
catalyst for the efficient acetylation of amines, alcohols and
phenols to the corresponding acetates using acetic anhy-
dride under solvent-free conditions. Among the various
substrates, acetylation of amines was preceded rapidly, so
that an amine group could be selectively acetylated in the
presence of alcoholic or phenolic hydroxyl groups by the
appropriate choice of reaction time. The catalyst can also be
reused several times without the loss of activity. In addition,
the catalytic activity of the LaFeO /SiO nanocomposite
4
2
[16], montmorillonites [17–19], metal oxides [20–22],
H SO –SiO [23], zeolites [24, 25], HBF –SiO [26],
3
2
was higher than that of the pure LaFeO nanoparticles. The
3
2
4
2
4
2
method is high yielding, clean, cost effective, compatible
with the substrates having other functional groups and very
suitable for the practical organic synthesis.
MoO –Al O [27], NaHSO –SiO [28], sulphated zirconia
3 2 3 4 2
[29], (NH4)2.5H0.5PW O [30], silica-bonded cobalt(II)
12 40
salen [31], silica-bonded N- and S-propyl sulfamic acids [32,
3], poly(4-vinylpyridinium) perchlorate [34], polystyrene-
3
Keywords Lanthanum orthoferrite Á Silica matrix Á
Sol–gel process Á Nanocomposite Á Heterogeneous
catalyst Á Acetylation Á Solvent-free conditions
supported GaCl3 [35], borated zirconia modified with
ammonium metatungstate [36] and rice husk [37] have been
applied for the acetylation of alcohols and phenols. How-
ever, each of these catalysts has advantages and limitations.
In recent years, transition metal mixed oxides with perov-
Introduction
skite-type structure (ABO ) have attracted considerable atten-
3
tion as promising catalytic materials for organic
transformations due to their high thermal and hydrothermal
stability and relatively low cost compared with their conven-
tional noble metal counterparts [38–43]. However, the potential
catalytic applications of them are greatly limited by their low
surface areas. One possible way of circumventing this problem
is to disperse these oxides in a medium that possesses a high-
specific surface area. The sol–gel technique has been widely
used as an appropriate method for preparing various nano-
structured materials and nanocomposites [44, 45]. In
Acetylation is an efficient route for protecting the functional
groups of alcohols, phenols and amines during oxidation,
peptide coupling and glycosidation reactions [1, 2].
Numerous catalytic systems are available for this important
S. Farhadi (&) Á K. Jahanara Á A. Sepahdar
Department of Chemistry, Lorestan University,
68135-465 Khorramabad, Iran
e-mail: sfarhadi48@yahoo.com
123

J IRAN CHEM SOC
comparison with traditional method, the sol–gel method offers
the advantage of good chemical homogeneity and high purity.
In addition, sol–gel derived nanocomposite can be obtained at a
temperature much lower than that necessary for the melting of
an oxide mixture. Silica-based nanomaterials have been
reported to be promising supports for a number of catalytically
active species because of their high surface area and stable well-
ordered pore structures [46–48].
Catalyst preparation and characterization
LaFeO
FeO was synthesized on the basis of sol–gel method as
follows. A mixture of TEOS (23.5 mL; SiO content:
/SiO nanocomposite containing 40 % w/w La-
3
2
3
2
6.3 g), ethanol (50 mL) and water (10 mL) was prepared
in a 250-ml beaker. The mixture was stirred at room
temperature for 1 h. Then, a mixture of Fe(NO
)
3
Á9H
O
2
3
In this paper, perovskite-type lanthanum orthoferrite
(7 g) and La(NO ) O, (7.5 g) dissolved in water
3
2
Á6H
2
(
LaFeO ) nanoparticles embedded in silica matrix (abbre-
3
(40 mL) was added. The resulting mixture was stirred for
1 h and allowed to gel at room temperature within
5 days. After gelation, it was dried and calcined at 300,
400 and 500 °C for 4 h and washed with hot water
viated as LaFeO /SiO nanocomposite) were easily pre-
3
2
pared via a sol–gel process and its catalytic activity was
evaluated for the acetylation reaction with acetic anhydride
as a protecting agent. The results indicate that the LaFeO3/
SiO2 nanocomposite is a selective and highly efficient
recyclable catalyst for the acetylation of alcohols, phenols
and amines to the corresponding acetates under solvent-
free conditions. To the best of our knowledge, this is the
first report of the catalytic reaction of organic compounds
over a perovskite-type mixed oxide-silica nanocomposite.
(80 °C) three times to give ca. 10 g of the LaFeO
/SiO
3 2
nanocomposite. On the basis of the solid mass obtained at
the end of the preparation at 500 °C and the initial
amount of two metal nitrates employed, we could esti-
mate that the prepared material, LaFeO
40 % (w/w) of LaFeO . A SiO sample not including
LaFeO was also prepared, following the procedure
/SiO , contained
3
2
3
2
3
described above but without adding the two metal
nitrates. In addition, pure LaFeO3 nanoparticles were
prepared according to the previous method by us and its
Experimental
catalytic activity was compared with LaFeO nanoparti-
3
General
cles embedded in an inert matrix [49].
The reagents used in the synthesis of LaFeO embedded in
3
General procedure for the acetylation reaction
silica
matrix
were
Fe(NO ) Á9H O
(98 %),
on LaFeO
3
/SiO
2
nanocomposite
/SiO nanocomposite (0.25 g)
2
3
3
2
La(NO ) Á6H O (99 %) and tetraethyl orthosilicate
3
2
2
Si(OC H ) (TEOS[99.5 %), which were purchased from
To a mixture of the LaFeO
3
2
5 4
Merck chemical Co. All chemicals and solvents were
and acetic anhydride (2 mmol), alcohol, phenol and/or
amine (2 mmol) were added. The mixture was stirred, and
the progress of the reaction was monitored by TLC. After an
appropriate time when the reaction was completed, 10 mL
of ethyl acetate and/or diethyl ether was added and the
mixture was filtered to separate the catalyst. The catalyst
was washed with ethyl acetate (2 9 7.5 mL) for recycling.
The combined organic phases were washed with 10 %
solution of sodium hydrogen carbonate and dried over
purchased from Merck in the highest purities available
1
([98 %) and used as received. H-NMR spectra were
recorded on a Bruker 500 MHz instrument. GC–MS ana-
lysis was carried out on a Shimadzu QP 5050 GC–MS
instrument. The LaFeO /SiO nanocomposite was charac-
3
2
terized by a Bruker D8 Advance X-ray diffractometer
˚
using CuKa radiation (k = 1.5406 A). Infrared spectra
were recorded on a Shimadzu system FT-IR 8400 spec-
trophotometer using the KBr pellet method. The particle
size and morphology of the LaFeO /SiO nanocomposite
MgSO . The solvent was removed to afford the product. If
4
further purification was needed it was passed through a
short column of silica gel. All products were characterized
1
on the basis of GC–MS, FT-IR and H-NMR spectral data
3
2
were investigated by LEO-906E transmission electron
microscope (TEM) with an accelerating voltage of 80 kV.
In the process of preparation of the TEM specimen, a small
amount of the powders was dispersed in ethanol in an
ultrasonic bath for 30 min, and few drops the resulting
suspension were placed onto a carbon coated copper grid.
The specific surface area of the catalyst was calculated by
the Brunauer–Emmett–Teller (BET) method using N2
adsorption–desorption experiments carried out at -196 °C
on a surface area analyzer (Micromeritics ASAP 2010).
Before each measurement, the sample was degassed at
and comparison with those of authentic samples or reported
data. The results are summarized in Tables 1–5.
Results and discussion
Characterization of LaFeO /SiO nanocomposite
3 2
Figure 1 shows the XRD patterns of the LaFeO
/SiO gels
2
3
2
00 °C for 1 h.
heat-treated at 300–500 °C temperature range for 4 h.
1
23

J IRAN CHEM SOC
3 2
Table 1 The effect of LaFeO /SiO nanocomposite amount on the
reaction of benzyl alcohol with acetic anhydride
a
Entry Catalyst (g) Solvent Time (min) Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
0.05
0.10
0.15
0.20
0.25
0.30
0.25
0.25
0.25
0.25
0.10
0.15
–
–
25
25
25
25
18
18
30
30
14
–
18.5
42
–
–
76
–
90
–
88
Acetonitrile
Toluene
35
15
Dichloromethane 30
26
0
1
2
3
Acetone
30
30
30
30
40
b
c
–
–
–
15
Trace
Trace
Reaction conditions: benzyl alcohol (2 mmol); acetic anhydride
2 mmol) without solvent at r.t. or with solvent (10 mL) under re-
fluxing conditions
(
a
Isolated yield
b
3
Unsupported LaFeO (0.10 g) used as the catalyst, without solvent
at r.t.
c
2
SiO used as the catalyst, without solvent at r.t.
Fig. 1 XRD patterns of LaFeO
3 2
/SiO samples calcined at different
From the Fig. 1a, it is clear that the gel sample calcined at
00 °C is amorphous, with one broad reflection centered at
temperatures for 4 h: a 300 °C, b 400 °C, and c 500 °C
3
approximately 2h = 22.5°, which is characteristic of dif-
fraction of the amorphous SiO matrix. As can be seen in
2
Fig. 1b and c, heating beyond 300 °C resulted in a gradual
crystallization of the samples. Increase of heat-treated
temperature to 400 and then 500 °C was resulted in an
increase in crystallinity. All peaks indexed as (2 2 0), (3 1
1
), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) in XRD patterns were
assigned to the LaFeO3 phase (ICCD Card File No.
-0669), no other crystalline phases were detected in the
5
calcined samples. In the XRD patterns, broad humps are
present at approximately 2h = 22.5°, which can be attrib-
uted to the amorphous phase of SiO matrix. This means
2
that the materials consist of the LaFeO nanoparticles and
3
an amorphous phase of SiO . Further, the diffraction peaks
2
of the LaFeO phase are markedly broadened due to the
3
Fig. 2 FT-IR spectrum of the LaFeO
at 500 °C
3 2
/SiO nanocomposite prepared
small size effect of the particles. The average particle size
can be calculated by X-ray diffraction line broadening
using the Debye–Scherrer equation [50]: d = (0.9k)/
(
h1/2cosh), where d represents the grain size; k is the
The XRD analysis confirmed that high crystalline
LaFeO /SiO nanocomposite was completely formed by
˚
wavelength of the X-ray (CuK , 1.5406 A); h is the dif-
a
3
2
fraction angle of the peak; and h1/2 stands for the full width
at half height of the peaks. The average particle size cal-
culated using the most intense peak (3 1 1) at 2h = 36.90°
is approximately 15 nm. This value is consistent with the
TEM observations (discussed below).
calcining the dried gel at 500 °C for 4 h, for further con-
firmation of its structure the FT-IR spectrum of this sample
was recorded. As shown in Fig. 2, the bands centered at
-
1
1,078 and 800 cm
correspond to the stretching and
bending vibrations of Si–O–Si bonds of the silica network
123

J IRAN CHEM SOC
formed via the hydrolysis and polycondensation reactions
aggregating, which was expected to improve the catalytic
activity of the LaFeO3 dispersed in the SiO2 matrix.
Meanwhile, the shape of the hysteresis loop confirms that
the nanocomposite sample under study is basically
mesoporous.
of the Si(OEt) precursor [51]. In addition, two sharp bands
4
-
1
that appeared around 570 and 425 cm are related to the
Fe–O stretching and O–Fe–O bending vibrations of the
FeO6 octahedron group in the perovskite-type LaFeO3
structure, respectively [52]. This finding proves the for-
mation of the perovskite-type LaFeO in the silica network
3
The acetylation reaction over the LaFeO /SiO
2
3
in agreement with the XRD data.
nanocomposite
In Fig. 3, the TEM image of the LaFeO /SiO nano-
3
2
composite obtained by calcining the corresponding gel at
The activity of the as-prepared LaFeO /SiO nanocom-
3
2
5
00 °C was presented. The dark and semi-spherical parti-
posite as a novel heterogeneous catalyst in the acetylation
of alcohols, phenols and amines was investigated. At the
outset, we carried out the optimization reactions to find out
the best conditions using benzyl alcohol as a model sub-
strate. A mixture of benzyl alcohol (2 mmol) and acetic
anhydride (2 mmol) in the presence of various amounts of
the catalyst was stirred at room temperature under solvent-
free conditions. The progress of the reaction was monitored
by TLC. The isolated yield of benzyl acetate was increased
from 14 to 90 % with the increase of the amount of catalyst
from 0.05 to 0.25 g per 2 mmol of alcohol, but further
increasing did not improve the yield (Table 1, entries 1–6).
The appropriate amount of catalyst in the reaction mixture
was 0.25 g per 2 mmol of alcohol used, which resulted in
the best yield (Table 1, entry 5). In order to choose the best
medium, the reaction was also studied in some organic
solvents such as acetonitrile, toluene, acetone and dichlo-
romethane under refluxing conditions (Table 1, entries
7–10). As can be seen in Table 1, the best results in terms
of reaction time and product yield have been achieved
without the use of any solvent (18 min, 90 %). Therefore,
we have continued the reactions under solvent-free
conditions.
cles in the TEM image are LaFeO nanoparticles. From the
3
TEM image, we observe that LaFeO is present as nano-
3
particles homogeneously distributed in the silica matrix
with the particles size up to 25 nm. As can be seen, a large
amount of the LaFeO3 nanoparticles is embedded in
amorphous SiO matrix. The LaFeO nanoparticles possess
2
3
a narrow size distribution in a range from 10 to 25 nm, and
the mean particle diameter is about 17 nm. This value is
consistent with the average size of the crystallites calcu-
lated from the XRD pattern using the Scherrer equation
(
discussed above).
The catalytic activity of a heterogeneous nanocatalyst is
also dependent on its surface properties. N adsorption–
2
desorption isotherms were conducted to investigate the
surface area of the LaFeO /SiO nanocomposite. As shown
3
2
in Fig. 4, the surface area of the LaFeO /SiO nanocom-
3
2
posite calculated by the BET method is 166.40 m /g,
2
which is much higher than that of the pure LaFeO nano-
3
2
particles (38.5 m /g) [49]. The high-specific surface area of
the nanocomposite product also indicated the possibility of
its application as an efficient catalytic material. The iso-
therm curve is close to Type IV of the IUPAC classification
with an evident hysteresis loop in the 0.5–1.0 range of
relative pressure, indicating that the existence of the SiO2
network prevented the LaFeO3 nanoparticles from
In an experiment, the pure (unsupported) LaFeO3
nanoparticles were used as the catalyst for the acetylation
Fig. 3 TEM image of the LaFeO
00 °C
3
/SiO
2
nanocomposite prepared at
Fig. 4 Nitrogen adsorption–desorption isotherm curve for the
LaFeO /SiO nanocomposite prepared at 500 °C
5
3
2
1
23

J IRAN CHEM SOC
Table 2 Results of acetylation
of alcohols, phenols and amines
with acetic anhydride over
b
Time Yield
Entry Substrate
Product
c
(
min) (%)
3 2
LaFeO /SiO nanocomposite
OH
OAc
1
2
3
18
12
10
90
92
91
OH
OAc
t-Bu
t-Bu
OH
OAc
MeO
OMe
MeO
OMe
OH
OAc
4
5
6
12
18
18
88
86
90
OH
OAc
F
F
Cl
Cl
OH
OAc
Cl
Cl
Cl
Cl
OH
OAc
7
8
9
19
22
20
88
86
85
OH
OAc
F3C
F3C
NO2
NO2
OH
OAc
OAc
NO2
NO2
OH
1
1
1
0
1
2
20
22
20
86
85
85
OH
OAc
CN
CN
CHO
CHO
OH
OAc
COMe
COMe
OH
OAc
OAc
1
1
3
4
20
16
87
92
OH
OH
OAc
1
5
6
16
12
90
92
OH
OH
OAc
OAc
1
1
1
7
8
15
14
90
92
Cl
Cl
OH
OAc
OMe
OMe
OMe
OMe
123

J IRAN CHEM SOC
Table 2 Results of acetylation
of alcohols, phenols and amines
with acetic anhydride over
b
Time Yield
c
Entry Substrate
Product
(
min) (%)
3 2
LaFeO /SiO nanocomposite
19
20
21
OH
OAc 25
86
86
85
OH
OAc
25
25
OH
OAc
OH
OAc
2
2
2
3
30
22
78
87
OH
OAc
OH
OAc
OH
OH
OAc
OAc
d
2
2
2
2
4
5
6
7
32
35
25
42
88
86
88
82
Me
OH
Me
OAc
O
N
OH
O N
OAc
2
2
OH
OAc
2
2
8
9
40
32
85
84
SH
SAc
Reaction conditions: substrate
2 mmol), acetic anhydride (one
equiv. per OH or NH group),
catalyst (0.25 g) under solvent-
free conditions and at RT
30
NH
2
NHAc
6
90
(
2
3
1
2
MeO
Et
NH
2
MeO
Et
NHAc
5
94
a
All products were
characterized on the basis of
3
NH2
NHAc
NHAc
5
5
94
91
1
GC–MS, IR and H-NMR
spectral data
33
Cl
NH
2
Cl
and comparison with those of
authentic samples or reported
data
NO2
NO2
3
3
4
5
8
88
NH2
NHAc
b
Isolated yield on the basis of
the weight of the pure product
obtained
OH
OH
H N
AcHN
HO
6
6
90
90
2
c
The reaction was carried out
on a 20 mmol scale of benzyl
alcohol
36
HO
NH2
NHAc
of benzyl alcohol under similar conditions. The result
LaFeO (0.10 g) used in the reaction was approximately
3
revealed that LaFeO in the supported state is more active
3
the same as the amount of the LaFeO estimated to be
3
than the neat form (Table 1; entry 11). The amount of
present in 0.250 g of 40 % LaFeO /SiO nanocomposite.
3
2
1
23

J IRAN CHEM SOC
3 2
Table 3 Results of the protection of benzyl alcohol with various anhydrides over LaFeO /SiO nanocomposite
CH OH
CH OAc
2
2
LaFeO /SiO nanocomposite
3
2
(
RCO) O Solvent-free
,
,
r. t.
2
b
Anhydride
Time (min)
Ac
2
O
(EtCO)
2
O
(iso-PrCO)
2
O
2
(PhCO) O
18
90
25
85
33
85
40
76
a
Yield (%)
Reaction conditions: benzyl alcohol (2 mmol), anhydride (2 mmol), catalyst (0.25 g)
a
Isolated yield of the corresponding acylated product
b
2
2
equiv of (PhCO) O was used
Benzyl acetate was the only product observed in both the
compound under similar conditions (Table 2, entry 23).
Among the various alcohols studied, secondary benzylic
alcohols were found to be most reactive, giving the cor-
responding acetylated products within shorter reaction
times. As we can see from Table 1, functional groups such
as –OMe, –CHO, –COMe, –CN and –NO2 remained
unchanged under the reaction conditions. In addition, the
conversion of benzyl alcohol into benzyl acetate on a
20-mmol scale proceeded just, as well as the 2-mmol
reaction (32 min, 88 %) (Table 2, entry 24).
cases. Using pure SiO support as a catalyst,\5 % product
2
was detected from GC analysis of the reaction mixture after
3
0 min (Table 1; entry 12), suggesting that the catalytic
activity of the LaFeO /SiO nanocomposite derives mainly
2
3
from the LaFeO nanoparticles. The essential role played
3
by the nanocomposite catalyst is evident from the extre-
mely low yield of benzyl acetate (\5 %) found in the
absence of it (Table 1, entry 13).
The generality of this protocol is shown by utilizing
various primary, secondary and tertiary alcohols, as well as
an allylic alcohol and diols (Table 2). The results in
Table 2 show that all substrates were selectively converted
to the corresponding acetates in high yields without any
evidence of the formation of side products. The acetylation
of a wide range of ring-substituted primary benzyl alcohols
having various electron-donating and electron-withdrawing
groups was investigated with acetic anhydride over LaFe-
O /SiO nanocomposite. These alcohols and also primary
The acetylation of phenols was also investigated under the
present experimental conditions. Phenol, substituted phenols
with electron-donating and electron-withdrawing groups, a-
naphthol and thiophenol were acetylated in high yields albeit
within longer reaction times in comparison with alcohols
(Table 2, entries 25–29). The excellent activity of the La-
FeO /SiO nanocomposite was demonstrated by the high
3
2
yields obtained for para-nitrophenol with a strong electron-
withdrawing group (Table 2, entry 27).
3
2
aliphatic alcohols were efficiently converted to their cor-
responding acetates with excellent yields, and the nature of
the substituents had no significant effect on the reaction
times and yields (Table 2, entries 1–13). In addition, var-
ious secondary alcohols were converted in high yields to
their corresponding acetates (Table 2, entries 14–18). The
a,b-unsaturated primary alcohol such as cinnamyl alcohol
was selectively converted to the corresponding acetate, and
the carbon–carbon double bond remained intact under the
reaction conditions (Table 2, entry 19). In addition, non-
benzylic primary alcohols were converted with high
selectivity to their corresponding acetates with high effi-
ciency under the same reaction conditions (Table 2, entries
Under the optimized conditions, primary aromatic
amines containing various electron-donating and -with-
drawing groups were also treated with acetic anhydride.
Excellent results were obtained in each case affording the
corresponding acetylated derivatives in 88–94 % yields in
5–8 min at room temperature under solvent-free conditions
(Table 2, entries 30–34). Selective acetylation of –NH2
group in the presence of –OH group was observed at room
temperature with one equivalent of acetic anhydride
(Table 2, entries 35 and 36). Thus, acetylation of amino
alcohols and amino phenols produced the corresponding
acetamides as sole products; the hydroxyl moiety remained
untouched. This might be due to more nucleophilicity of
2
0 and 21). A sterically hindered tertiary alcohol such as
–NH group than –OH group. The selective acetylation of a
2
triphenylmethanol also can be acetylated with high yield,
but it takes a longer reaction time (Table 2, entry 22). As
shown by GC–MS analysis, there was no elimination
product in the reaction mixture. The efficiency of the cat-
alyst can be seen clearly in the acetylation of a di-hydroxy
primary NH over a primary OH by this process is of
2
considerable synthetic importance and it is difficult to
achieve with many other reagents.
The activity of LaFeO /SiO nanocomposite as a gen-
3
2
eral catalyst was tested via the protection of benzyl alcohol
123

J IRAN CHEM SOC
Table 4 Recyclability of the catalyst
makes the carbonyl group in (PhCO) O less electrophilic
2
due to the resonance effect.
Cycle
a
Yield (%)
0
1st
90
2nd
88
3rd
85
4th
80
The recycling ability of the catalyst was tested in the
acetylation of benzyl alcohol. After completion of the
reaction, ethyl acetate was added and the mixture was fil-
tered to separate the catalyst. The recycled catalyst was
dried and used in further runs. No appreciable decrease in
activity of the catalyst was observed even after fourth run
90
Reaction conditions: benzyl alcohol (2 mmol), acetic anhydride
(
2 mmol), under solvent-free conditions at r.t.
a
Yields are for isolated pure product
(Table 4).
The nature of the recovered catalyst was also investi-
gated by the XRD analyses. As shown in Fig. 5, the XRD
pattern of the recovered catalyst did not show any signifi-
cant change after fourth cycle compared to the fresh cat-
alyst in Fig. 1, an indication that the structure of the
LaFeO /SiO nanocomposite was quite stable under the
3
2
reaction conditions and was not affected by the reactants.
In addition, the XRD pattern of the recovered catalyst
revealed the absence of characteristic peaks of organic
impurities.
To elucidate the advantages of the present method, we
have compared the obtained results in the acetylation of
3
Fig. 5 XRD pattern of the recovered LaFeO catalyst after the fourth
run
benzyl alcohol with acetic anhydride over the LaFeO /SiO
2
3
nanocomposite with some reported heterogeneous catalysts
in the literature (Table 5). It is clear that with respect to the
with other anhydrides under same reaction conditions
Table 3). In comparison with acetic anhydride, the reac-
(
reaction conditions, substrate:Ac O mole ratio, reaction
2
tions with higher anhydrides took longer times at room
temperature. However, the reactions were completed in
time, and/or product yield, the present method is more
suitable and/or superior. We can see that the reaction in the
presence of most these catalysts required longer time for
completion. Other advantages of the catalyst in this work in
comparison with other previously reported catalysts are
easy preparation, no moisture sensitivity, no explosive and
expensive, and it has very low toxicity.
1
8–40 min under solvent-free conditions affording the
corresponding acylated derivatives, providing excellent
yields (76–90 %). It seemed that the rate of acylation was
influenced by the steric and electronic factors of anhydrides
i
and followed the order Ac O [ (EtCO) O [ ( Pr-
2
2
CO) O [ (PhCO) O. The longer times required for the
The mechanism for the acetylation of various substrates
to their corresponding acetates using the LaFeO /SiO
2
2
2
i
reaction with (EtCO) O and ( PrCO) O were mainly due to
2
2
3
the steric effect of the alkyl groups of these anhydrides.
The longer reaction time and the requirement of two
equivalents of (PhCO) O against one equivalent of Ac O
nanocomposite has been proposed in Scheme 1 [27, 28].
As shown in the Scheme 1, at the initial stage, the carbonyl
group of acetic anhydride is coordinated to the unsaturated
La(III) and Fe(III) ions on the surface of the nanocom-
posite as Lewis acidic sites and then it was activated. The
2
2
were due to the combined effect of the steric and electronic
factors of the phenyl group in (PhCO) O. The phenyl group
2
Table 5 Comparison of the result obtained for the acetylation of benzyl alcohol in the present work with those obtained by some reported
heterogeneous catalysts
Entry Heterogeneous catalyst Conditions
2
Alcohol:Ac O (mole ratio) Catalyst (g) Time (min) Yield (%) Ref.
1
2
3
4
5
6
7
Mont. KSF
SiO /H SO
Solvent-free, r.t.
CH Cl , r.t.
1:2
1:2
0.1
60
90
90
91
93
92
94
90
[20]
2
2
4
2
2
0.2
240
120
10
[22]
FER zeolite
Solvent-free, 75 °C 1:1.5
Solvent-free, r.t.
0.15
0.05
0.5
[24]
Sulphated ZrO
2
1:1
[28]
(NH
Rice husk
LaFeO /SiO
4
)
2.5
H0.5PW12
O
40
Solvent-free, r.t.
1:1
60
[29]
Solvent-free, 80 °C 1:3
Solvent-free, r.t. 1:1
0.3
60
[37]
3
2
0.25
18
This work
1
23

J IRAN CHEM SOC
Acknowledgments The authors gratefully acknowledge the Lore-
stan University Research Council and Iran Nanotechnology Initiative
Council (INIC) for their financial support.
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