Sulfonated rice husk ash (RHA-SO3H): A highly powerful and efficient solid acid catalyst for the chemoselective preparation and deprotection of 1,1-diacetates

Article abstract of DOI:10.1016/j.catcom.2013.02.022

Rice husk ash (RHA), as a source of amorphous silica, was treated with chlorosulfonic acid and sulfonated rice husk ash (RHA-SO₃H) as a highly powerful solid acid catalyst was obtained and characterized with a variety of techniques including IR, TGA, SEM, XRD, pH analysis, Hammett acidity function and BET method. This solid acid showed excellent catalytic activity for the protection and deprotection of aldehydes with Ac₂O at room temperature under solvent free conditions. The procedure gave the products in excellent yields in very short reaction times and good to high yields. Also this catalyst can be reused for several times without loss of its catalytic activity.

Full text of DOI:10.1016/j.catcom.2013.02.022

Catalysis Communications 36 (2013) 31–37
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Sulfonated rice husk ash (RHA-SO3H): A highly powerful and efficient
solid acid catalyst for the chemoselective preparation and deprotection
of 1,1-diacetates
⁎
Farhad Shirini , Manouchehr Mamaghani, Mohadeseh Seddighi
Department of Chemistry, College of Science, University of Guilan, Rasht, zip code: 41335, Post Box: 1914, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 January 2013
Received in revised form 21 February 2013
Accepted 25 February 2013
Available online 4 March 2013
Rice husk ash (RHA), as a source of amorphous silica, was treated with chlorosulfonic acid and sulfonated rice
husk ash (RHA-SO3H) as a highly powerful solid acid catalyst was obtained and characterized with a variety
of techniques including IR, TGA, SEM, XRD, pH analysis, Hammett acidity function and BET method. This solid
acid showed excellent catalytic activity for the protection and deprotection of aldehydes with Ac2O at room
temperature under solvent free conditions. The procedure gave the products in excellent yields in very short
reaction times and good to high yields. Also this catalyst can be reused for several times without loss of its
catalytic activity.
Keywords:
Rice husk ash
Sulfonated rice husk ash
Solid acid
© 2013 Elsevier B.V. All rights reserved.
Protection
Solvent-free condition
1,1-Diacetates
1. Introduction
organic solvents, expensive catalyst, use of excess amounts of the acyl-
ating agents, harsh reaction conditions and non-recoverability of the
Protection and deprotection of functional groups are often
necessary during a multistep organic synthesis in order to obtain
chemoselectivity. Aldehydes are often present in organic molecules
so development of economical, efficient and mild procedures for the
protection of them is very important for synthetic organic chemistry.
Among various procedures for protection of aldehyde, preparation of
1,1-diacetates from the reaction of aldehydes and acetic anhydride is
the most common route due to the stability of the products in the
neutral and basic conditions [1,2]. 1,1-Diacetates are also important
for the preparation of other compounds, for example in reaction with
appropriate nucleophiles they can be converted to other useful func-
tional groups [3]. On the other hand α,β-unsaturated diacetates are
important starting materials for Diels–Alder reactions [4]. A variety of
catalysts including FeCl3 [2], sulfuric acid [5], Zn-montmorillonite [6],
Bi(NO3)3·5H2O [7], In(OTf)3 [8], P2O5/Al2O [9], CuSO4·5H2O [10], Silica
sulfuric acid [11], HClO4-SiO2 [12], Al(HSO4)3 [13], SO42−/SnO2 [14],
[Hmim]HSO4 [15] and [bmpy]HSO4 ionic liquid [16], silica-bonded
S-sulfonic acid [17], saccharin sulfonic acid [18], N-sulfonic acid
poly(4-vinylpyridinium) chloride [19], ZSM-5-SO3H [20] have been
reported for the promotion of the acetylation of aldehydes with acetic
anhydride. Although these methods are an improvement, most of
them suffer from disadvantages such as long reaction times, need of
catalyst. Therefore, introduction of efficient and economical catalysts
that solve these drawbacks is desirable.
Replacement of conventional, toxic and polluting Bronsted and
Lewis acid catalysts with eco-friendly reusable heterogeneous catalysts
is an area of current interest. In this context, there has been renewed in-
terest in the synthesis of solid acid catalysts for organic reactions. Solid
acid catalysts have many advantages compared to traditional liquid
acids such as their efficiency, operational simplicity, easy recyclability
and recoverability, non-corrosive nature and friendly to the environ-
ment, all factors which are important in industry. Therefore, solid acid
catalysts can play a significant role in the development of clean technol-
ogies. Among various supports that can be used for the preparation
of the above mentioned catalysts (silica, montmorillonite, organic
polymer and zeolite), silica is one of the more extensively used cases,
because it has many advantages such as ease of handling, commercially
available, low cost, high mechanical and thermal stability and
non-corrosiveness.
Recently utilization of waste materials has been found to be of in-
creasing interest. Rice husk, the outer covering of rice grains obtained
during the milling process, is one of the main agricultural residues. It
mainly consists of cellulose, hemicelluloses, lignin, silica and minor
other mineral composition [21]. Societies often dispose of the rice
husk waste using open burning that leads to environmental pollution
and damages to the land and the surrounding area in which it was
dumped. In recent years, the application of rice husk as an energy
⁎
Corresponding author. Tel./fax: +98 131 3233262.
E-mail address: shirini@guilan.ac.ir (F. Shirini).
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.02.022

32
F. Shirini et al. / Catalysis Communications 36 (2013) 31–37
source for biomass power plants, rice mills and brick factories is
increasing due to its high calorific power [22]. In this combustion,
rice husk ash (RHA) is produced. RHA possesses excellent pozzolanic
activity due to its high surface area and high silica content [23,24], so
it is used in cement, concrete and white ware production and the
preparation of lightweight aggregate [25,26]. Also, it has been
employed as adsorbent for heavy metals, purifying biodiesel and pro-
ducing zeolites and silica powders [27–29]. Although useful, the
reported method for the preparation of pure silica from rice husk
ash needs various stages and a long time [29]. On the basis of these
points it can be concluded that, at the same conditions, the use of
RHA as a support for the preparation of catalysts is better than the
use of silica which is prepared via precipitation method during
various stages and long time.
Scheme 1. Preparation of the catalyst (RHA-SO3H) catalyzed by RHA-SO3H.
2.4. General procedure for the preparation of 1,1-diacetate
Aldehyde (1 mmol) was added to a mixture of RHA-SO3H (10 mg)
and acetic anhydride (1.5 mmol) and the resulting mixture was stirred
at room temperature. After completion of the reaction (monitored by
TLC), dichloromethane (20 mL) was added and the catalyst was sepa-
rated by filtration. The organic phase was washed with 10% aqueous
solution of sodium bicarbonate (2 × 20 mL) and dried over Na2SO4.
The solvent was removed under reduced pressure to afford the desired
product. The solid crude product was purified by recrystallization from
cyclohexane. The spectral (IR, 1H and 13C NMR) data of fluorene-
3-carbaldehyde as a new compound is presented below:
2. Experimental
2.1. Instrumentation
Table 3, Entry 20: IR (neat) ν = 1765 cm−1 1H NMR (CDCl3,
;
The 1H NMR (400 MHz) and 13C NMR (100 MHz) were run on a
Bruker Avance DPX-400 FT-NMR spectrometer (δ in ppm). The chemical
composition of RHA was analyzed using X-ray fluorescence (XRF) spec-
trometer (Model Magix Pro, Philips). The FT-IR spectra were run on a
VERTEX 70 Brucker company (Germany). Thermogravimetric analyses
(TGA) were performed on Polymer Laboratories PL–TGA thermal analy-
sis instrument (England). Samples were heated from 25 to 600 °C at
ramp 10 °C/min under N2 atm. The adsorption–desorption isotherms
and the specific surface area (SBET) were determined from nitrogen ad-
sorption studies using Micro neotype StarII system. Scanning electron
microphotographs (SEM) were obtained on a SEM-Philips XL30. X-ray
diffraction (XRD) measurements were performed at room temperature
on diffractometer Model XRD 6000, PHILIPS Xpert pro using Co–Kα
radiation (K = 1.7890 Å) with the beam voltage and a beam current
of 40 kV and 30 mA, respectively.
400 MHz): δ = 2.17 (s, 6H, CH3), 2.95 (S, 2H, CH2), 7.35–7.84 (m,
8H, ArH, CH) ppm; 13C NMR (CDCl3, 100 MHz): δ = 20.9, 36.9, 90.1,
119.9, 120.2, 123.4, 125.1, 125.5, 126.9, 127.2, 133.7, 140.9, 143.3,
143.5, 143.6, 168.9 ppm.
2.5. General procedure for the deprotection of 1,1-diacetates
A mixture of 1,1-diacetate (1 mmol), RHA-SO3H (30 mg) in acetoni-
trile (2 mL) was stirred vigorously at 60 °C. After completion of the re-
action (monitored by TLC), the organic solvent was evaporated. Then
the reaction mixture was diluted by ethyl acetate (20 mL) and filtered
to separate the catalyst. The organic phase was washed with 10% aque-
ous solution of sodium bicarbonate (2 × 10 mL) to remove excess of
Ac2O and dried over Na2SO4. The solvent was evaporated under reduced
pressure. The resultant product was passed through a short column of
silica gel (n-hexane-EtOAc, 9:1) to afford the pure aldehyde.
2.2. Preparation and chemical composition of RHA
3. Results and discussion
The rice husk sample was obtained from an Iranian type of rice,
named as Hassani. It was burned at 600 °C for 1 h to obtain RHA.
The X-ray fluorescence (XRF) analysis showed a high value of silica
content for the sample (up to 80%). Other composition such as
Al2O3, Fe2O3, SO3, P2O5, K2O, Na2O and CaO are also present in RHA
as a very small proportion of metallic elements (Table 1).
3.1. Catalyst characterization
3.1.1. FT-IR analysis
The infrared spectra of RHA and RHA-SO3H are shown in Fig. 1. In
the case of RHA, the peaks at 3460 and 1640 cm 1 are respectively
2.3. Catalyst preparation (RHA-SO3H)
A 50 mL suction flask charged with 3.0 g of RHA and 10 mL CHCl3,
was equipped with a constant-pressure dropping funnel containing
chlorosulfonic acid (0.7 mL) and a gas inlet tube for conducting HCl
gas into water as an adsorbing solution. Chlorosulfonic acid was
added drop wise over a period of 20 min while the reaction mixture
was stirred in an ice bath (0 °C). After addition was completed the
mixture was stirred for an additional 2 h at room temperature to re-
move HCl. Then, the mixture was filtered and the filtrate was washed
with methanol (20 mL) to remove the remaining HCl and the solid
residue was dried at 70 °C for 1 h to afford RHA-SO3H (3.6 g) as an
earthy powder (Scheme 1).
Table 1
Chemical composition of RHA conducted by X-ray fluorescence analysis (wt%).
SiO2
Al2O3
0.25
Fe2O3
0.38
SO3
P2O5
0.44
K2O
1.25
Na2O
0.96
CaO
0.82
Cl
LOIa
80.82
0.39
1.99
12.70
a
Loss on ignition.
Fig. 1. FT-IR spectra of RHA and RHA-SO3H.

F. Shirini et al. / Catalysis Communications 36 (2013) 31–37
33
appeared around 2θ equal to 26° clearly indicated that silica of rice
husk ash was mainly in the amorphous form [31]. The peak intensities
of RHA-SO3H are remained almost unchanged compared to RHA pat-
tern that indicate an ordered mesoporosity of the supports even after
modification.
3.1.3. Thermal analysis
The thermal stability of RHA and RHA-SO3H was determined by
Thermogravimetric analysis (TGA) and differential thermogravimetry
(DTG) curves, as shown in Fig. 3. The results indicate that RHA showed
a weight change below 100 °C due to the loss of the physically adsorbed
water and then had a steady weight loss at the temperature lower than
600 °C, which could be ascribed to the loss of terminal groups such as
\OH terminal groups [32].
The TGA and DTG analysis of RHA-SO3H show two-stage decompo-
sition, completely different from RHA. The first weight loss below
100 °C can be due to desorption of water and the second weight loss
started at 170 °C can be attributed to the decomposition of covalently
bounded \SO3H groups [30]. These results indicate that the catalyst is
stable up to around 170 °C. It is important to note that, on the basis of
Fig. 3 (b and c), it can be concluded that the grafted \SO3H groups in-
crease the tendency of the absorption of water on the surface of the
catalyst.
Fig. 2. XRD patterns of RHA in comparison with RHA-SO3H.
attributed to the stretching and bending modes of the SiOH groups and
the adsorbed water. The strong peaks at 1100, 801 and 468 cm 1 are
assigned to asymmetric stretching, symmetric stretching and bending
modes of SiO2, respectively [29].
The RHA-SO3H is also characterized. The broad band around
1100 cm 1 is assigned to stretching modes of Si\O and S_O bands
which are overlapped together. The bands in 588 and 855 cm 1 corre-
spond to the S\O stretching vibrations. The spectrum also shows a
relatively broad band around 2700 to 3600 cm 1 due to OH stretching
absorption of the SO3H group [30].
3.1.4. Surface area and pore distribution measurements
N2 adsorption–desorption measurements (BET and BJH methods),
which have been a powerful tool for nano- or mesoporous material
characterization, were performed to obtain more insights into the mod-
ified porous silica materials. The N2 adsorption–desorption isotherm of
RHA and RHA-SO3H (Fig. 4a) showed that both samples exhibited type
IV isotherms according to the literature, which indicates that the sam-
ples are mesoporous materials. Furthermore, the hysteresis loop of
both samples showed H3 categories, which should be a result of
3.1.2. Powder X-ray diffraction
Fig. 2. represents the X-ray diffraction (XRD) patterns of the RHA
and RHA-SO3H. As can be seen in the RHA pattern, a broad peak
Fig. 3. (a) TGA curves of RHA and RHA-SO3H, (b) DTG curves of RHA and RHA-SO3H and (c) TGA–DTG curve of RHA-SO3H.

34
F. Shirini et al. / Catalysis Communications 36 (2013) 31–37
Fig. 4. The N2 adsorption–desorption isotherm (a), and pore size distribution (b) of RHA and RHA-SO3H.
slit-like pores [33]. These results also prove that the textural properties
of RHA were substantially maintained over sulfonic acid function-
alization. Table 2 shows the specific BET surface areas, pore volumes
and pore diameters for RHA and RHA-SO3H. A decrease in the surface
area was observed for RHA and RHA-SO3H from 57 to 40 m2/g, respec-
tively. This suggests that sulfonic acid may be well confined in the pores
of RHA, and indicates an ordered mesoporosity of the support even after
modification. The curves of pore size distribution evaluated from
desorption data by utilizing the BJH model are also shown in Fig. 4b.
3.1.6. pH analysis of catalyst
To 25 mL of an aqueous solution of NaCl (1 M) with a primary
pH 5.2, RHA-SO3H (0.5 g) was added and the resulting mixture was
stirred for 2 h at room temperature after which the pH of solution
decreased to 1.3. This is equal to a loading of 2.5 mmol H+/g [34].
3.1.7. Hammett acidity
The Hammett acidity method is an effective way to measure the
acidity strength of an acid in organic solvents, using UV–vis technique
[35]. The Hammett function is defined as:
3.1.5. SEM analysis
ꢀ
h
i ꢁ
H0 ¼ pKðIÞaq þ log ½Iꢀs= IHþ
:
The samples of RHA and RHA-SO3H were analyzed by scanning elec-
tron microscopy (SEM), as represented in Fig. 5. The pictures show that
RHA has a porous and irregular shape, thus its high specific surface area
can be explained [31]. These images also show that the primary mor-
phology of RHA is changed after modification with chlorosulfonic acid.
Indeed, the comparison of the RHA and RHA-SO3H indicated that the
particles are aggregated after modification.
s
Where the pK (I)aq is the pKa value of aqueous solution of indicator,
and [IH+
and [I]s are the molar concentrations of protonated and
unprotonated forms of the indicator in the solvent, respectively.
According to Lambert–Beer's Law, the value of [I]s/[IH+]s can be deter-
mined and calculated through UV–visible spectrum.
]
s
For this purpose, 4-nitroaniline (pK(I)aq = 0.99) as the basic indi-
cator and CCl4 as the solvent were chosen. As can be seen in Fig. 6, the
maximal absorbance of the unprotonated form of the indicator was ob-
served at 329 nm in CCl4. When RHA-SO3H as a solid acid catalyst was
added to the indicator solution, the absorbance of the unprotonated
form of the indicator decreased, which indicated that the indicator
was partially in the form of [IH+]. These results listed in Table 3, show
the acidity strength of RHA-SO3H.
Table 2
Pore structure parameters of RHA and RHA-SO3H derived from the N2 adsorption–
desorption isotherms.
Sample
SBET (m2/g)
VBJH (cm3/g)
DBJH (nm)
RHA
RHA-SO3H
57
40
0.19
0.16
10.4
11.6
Fig. 5. SEM images of (a) RHA and (b) RHA-SO3H, respectively.

F. Shirini et al. / Catalysis Communications 36 (2013) 31–37
35
were also protected as acetates. In these cases higher amount of catalyst
was needed due to the strong electron donation of OH group and high
steric hindrance (Table 4, entries 16–17).
Cinnamaldehyde, as an α,β-unsaturated aldehyde, was also acetylat-
ed in high yield using this procedure without the isomerization of double
bond (Table 4, entry 18). Furthermore, polycyclic aromatic aldehydes
such as 2-naphthaldehyde and fluorene-3-carbaldehyde also pro-
vided the desired acylals in very good yields (Table 4, entries 19–20).
This method was also found to be useful for the protection of
benzenedicarbaldehydes, phthaldialdehyde and terephthaldialdehyde,
that gave the tetraacetylated products in good yield (Table 4, entries
21–22). Furthermore, using this method pentanal as an aliphatic alde-
hyde was also converted to its corresponding acylal in high yields at am-
bient temperature and under solvent-free condition (Table 4, entry 23).
Dimethylaminobenzaldehyde failed to give the corresponding
1,1-diacetates which may be due to the electron-donating of dimethyl-
amino group (Table 4, entry 24).
Fig. 6. Absorption spectra of 4-nitroaniline (indicator) (a) and RHA-SO3H (catalyst)
(b) in CCl4.
To evaluate the chemoselectivity of the method we also investi-
gated the acylation of ketones. Under this catalytic system, acylation
of acetophenone was not successful and no product was obtained
(Table 4, entries 25–26). This observation indicates the chemo-
selectivity of the protocol and that aldehydes are more reactive than
ketones due to higher electrophilicity of aldehyde in comparison to
ketones.
Also we investigated the application of RHA-SO3H as catalyst for
deprotection of acylals to their corresponding aldehydes. For this pur-
pose, the acylals were treated with 30 mg of catalyst in acetonitrile at
60 °C. In this condition, the corresponding aldehydes were obtained
in good to high yields, as results are summarized in Table 3. We
found that nitro derivatives (Table 4, entries 13–14) gave lower yields
(b50%) in acetonitrile after 1 h, whereas in refluxing toluene they
were quantitatively deprotected after 5 min. This may be due to the
strong electron-withdrawing effect of the nitro substituent, which
requires a high refluxing temperature.
To check the reusability of the catalyst, the reaction of 4-
chlorobenzaldehyde and acetic anhydride under the optimized reaction
conditions was studied again. When the reaction completed, dichloro-
methane was added and the catalyst was separated by filtration. The re-
covered catalyst was washed with dichloromethane, dried and reused
for the same reaction. This process was carried out over three runs
and all reactions were led to the desired products without any changes
in terms of the reaction time and yield which clearly demonstrates prac-
tical recyclability of RHA-SO3H. Further pH analysis of the recovered
catalyst showed loading of 2.4 mmol H+/g. This result suggests that
the nature of the catalyst remains intact after each run and leaching of
the acid species did not occur during the course of the reaction.
In order to show the efficiency of the present method, we
have compared our results obtained from the acetylation of 4-
chlorobenzaldehyde with acetic anhydride catalyzed by RHA-SO3H
with other results reported in the literature. As can be seen in Table 5,
this method avoids disadvantages of other procedure such as long reac-
tion times, low yields and excess reagents. This comparison also clarifies
an important point about the catalyst. As it can be seen FeCl3, Al2O3 and
P2O5 are also able to catalyze this type of reactions, but in higher
amounts than there are in RHA-SO3H. As reported in the literature,
100 mg of FeCl3 and 50 mg of P2O5/Al2O3 are needed for the promotion
of the acetylation of aldehydes (Table 5, entries 1 and 4), while the
available amounts of Fe, Al and P in RHA are 0.38, 0.25 and 0.44 wt.%,
respectively. So their concentration in the catalyst is very low and is
Table 3
Calculation of Hammett acidity function (H0) for RHA-SO3H.
Entry
Catalyst
Amax
[I]s
%
[IH+
0
]
s
%
H0
1
2
–
2.3803
0.7549
100
31.71
–
RHA-SO3H
68.29
0.65
Condition for UV–visible spectrum measurement: solvent: CCl4, indicator: 4-nitroaniline
(pK (I)aq = 0.99), 1.44 × 10−4 mol/L; Catalyst: RHA-SO3H, 20 mg, 25 °C.
3.3. Catalytic activity
On the basis of the information obtained from the above mentioned
studies, we anticipated that RHA-SO3H can be used as an efficient cata-
lyst for the promotion of the reactions which need the use of an acidic
catalyst to speed up. So we were interested to investigate the applicabil-
ity of the reagent in the acetylation of aldehydes using acetic anhydride.
For optimization of the reaction conditions, conversion of 4-
chlorobenzaldehyde with acetic anhydride to its corresponding 1,1-
diacetate was chosen as a model reaction and the various conditions
including amount of the catalyst and acetic anhydride, solvent and tem-
perature were examined. Finally the optimal reaction condition for this
reaction was as follows: 1 mmol aldehyde, 1.5 mmol acetic anhydride
and 10 mg RHA-SO3H as catalyst at room temperature and solvent
free condition, as shown in Scheme 2. The preparation of 1,1-diacetate
from 4-chlorobenzaldehyde was also carried out in the absence of the
catalyst and in the presence of rice husk ash but the reactions did not
proceed even after 1 h. These results indicated that the catalyst is nec-
essary to produce the products. Any further increase in the amount of
the catalyst or temperature did not improve the reaction time and yield.
To reveal the generality of this method, we next explored the proto-
col with a variety of aromatic, aliphatic and heterocyclic aldehydes
under the optimal conditions. The results were presented in Table 4. It
was observed that under similar conditions, a wide range of aromatic al-
dehydes containing electron-withdrawing as well as electron-donating
groups such as Cl, Br, F, CH3, OCH3 and NO2 is easily protected with
acetic anhydride in short reaction times with good to excellent isolated
yields (Table 4, entries 1–14). It should be noted that the reaction con-
ditions were mild enough to induce any damage to the acid sensitive
moieties like methoxy group (Table 4, entries 10–12) and acid-
sensitive substrates like furfural (Table 4, entry 15). When the reaction
was extended towards hydroxybenzaldehydes, the hydroxyl groups
Scheme 2. The protection and deprotection of aldehydes catalyzed by RHA-SO3H.

36
F. Shirini et al. / Catalysis Communications 36 (2013) 31–37
Table 4
Acylation of aldehydes and deprotection of acylals catalyzed by RHA-SO3H.
Entry
Substrate
Product
Protection
Deprotection
Time
(min)
Yield
(%)
m.p. (°C)
Found
Time
(min)
Yield
(%)
Reported
1
2
3
4
5
6
7
8
C6H5CHO
C6H5CH(OAc)2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
94
93
92
95
90
97
96
93
93
89
95
83
95
93
43–45
57–59
66–68
82–84
72–74
81–83
52–54
64–66
Oil
75–77
Oil
61–63
66–68
124–126
43–44 [16]
58–60 [17]
64–65 [15]
81–83 [16]
83 [12]
4
5
4
4
5
4
3
3
2
3
3
4
5
5
91
92
89
92
88
94
95
90
91
90
92
94
87a
89a
2-ClC6H4CHO
3-ClC6H4CHO
4-ClC6H4CHO
3-BrC6H4CHO
4-BrC6H4CHO
4-FC6H4CHO
2-CH3C6H5CHO
3-CH3C6H5CHO
2-CH3OC6H5CHO
3-CH3OC6H5CHO
4-CH3OC6H5CHO
3-NO2C6H4CHO
4-NO2C6H4CHO
2-ClC6H5CH(OAc)2
3-ClC6H5CH(OAc)2
4-ClC6H5CH(OAc)2
3-BrC6H5CH(OAc)2
4-BrC6H5CH(OAc)2
4-FC6H5CH(OAc)2
2-CH3C6H5CH(OAc)2
3-CH3C6H5CH(OAc)2
2-CH3OC6H5CH(OAc)2
3-CH3OC6H5CH(OAc)2
4-CH3OC6H5CH(OAc)2
3-NO2C6H4CH(OAc)2
4-NO2C6H4CH(OAc)2
84 [12]
51–53 [17]
65–67 [19]
Oil [12]
73–74 [15]
Oil [15]
64–65 [16]
65–67 [15]
124–126 [15]
9
10
11
12
13
14
15
0.5
1
87
90
52–54
52–53 [15]
1
5
94
16b,c
101–103
101–102 [15]
93b,c
17c,d
1.5
1
94
91
93
91–93
90–92 [15]
84–86 [15]
101 [12]
5
2
5
94c,d
18
83–85
92
19
0.5
102–104
90
20
0.5
2.5
92
89
130–132
100–102
–
1
91
21c
96–98 [19]
10d
87c,e
22c
23
1.5
1
90
91
0
172–174
172–174 [17]
8d
89c,e
Oil
Oil [15]
5
88
24
–
1 h
–
–
–
–
–
–
–
–
25
26
C6H5COCH3
C6H5CHO
+
–
1 h
0.5
0
C6H5CH(OAc)2
+
100
+
–
C6H5COCH3
–
a
b
c
The reaction was performed in refluxing toluene.
20 mg of the catalyst was used.
3 mmol acetic anhydride was used.
50 mg of the catalyst was used.
d
e
60 mg of the catalyst was used.

F. Shirini et al. / Catalysis Communications 36 (2013) 31–37
37
Table 5
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Comparison of the results of the acylation of benzyl alcohol catalyzed by RHA-SO3H
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In conclusion, in the study we have introduced RHA-SO3H a highly
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1,1-diacetates. All reactions are carried out in very short reaction time.
Furthermore, the methodology has several advantages such as high
reaction rates, no side reactions, ease of preparation and handling of
the catalyst, simple experimental procedure, cleaner reactions, use of
inexpensive and reusable catalyst with lower loading and solvent free
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Acknowledgments
We are thankful to the University of Guilan Research Council for
the partial support of this work.