Tin exchanged heteropoly tungstate: An efficient catalyst for benzylation of arenes with benzyl alcohol

Article abstract of DOI:10.1016/j.molcata.2011.01.008

The partial exchange of tin with the protons of 12-tungstophosphoric acid (TPA) results in a highly active heterogeneous catalyst for benzylation of arenes with benzyl alcohol as benzylating agent. The catalysts were characterized by X-ray diffraction, Laser-Raman and FT-IR of pyridine adsorption. The catalytic activity depends significantly on the extent of tin exchanged with the protons of heteropoly tungstate. The characterization results suggest the presence of Lewis acidic sites by the exchange of tin. The catalyst with partial exchange of Sn showed high benzylation activity, which in turn related to variation in acidity of the catalysts. The catalyst is highly active for benzylation reaction irrespective of the nature of substituted arenes and benzyl alcohols. These catalysts are highly active compared to other acid catalysts used for benzylation of different arenes. The catalyst is easy to separate from reaction mixture and exhibit consistent activity upon reuse. The plausible reaction mechanism based on the role of both Lewis and Bronsted acid sites of the catalyst was discussed.

Full text of DOI:10.1016/j.molcata.2011.01.008

Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Tin exchanged heteropoly tungstate: An efficient catalyst for benzylation of
arenes with benzyl alcohol
Ch. Ramesh Kumar, K.T. Venkateswara Rao, P.S. Sai Prasad, N. Lingaiah∗
Catalysis Laboratory, Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Uppal Road, Hyderabad, AP 500 607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The partial exchange of tin with the protons of 12-tungstophosphoric acid (TPA) results in a highly
active heterogeneous catalyst for benzylation of arenes with benzyl alcohol as benzylating agent. The
catalysts were characterized by X-ray diffraction, Laser-Raman and FT-IR of pyridine adsorption. The
catalytic activity depends significantly on the extent of tin exchanged with the protons of heteropoly
tungstate. The characterization results suggest the presence of Lewis acidic sites by the exchange of
tin. The catalyst with partial exchange of Sn showed high benzylation activity, which in turn related
to variation in acidity of the catalysts. The catalyst is highly active for benzylation reaction irrespective
of the nature of substituted arenes and benzyl alcohols. These catalysts are highly active compared to
other acid catalysts used for benzylation of different arenes. The catalyst is easy to separate from reaction
mixture and exhibit consistent activity upon reuse. The plausible reaction mechanism based on the role
of both Lewis and Bronsted acid sites of the catalyst was discussed.
Received 22 November 2010
Received in revised form 4 January 2011
Accepted 6 January 2011
Available online 16 January 2011
Keywords:
Arene
Benzyl alcohol
Benzylation
Tungstophosphoric acid
Tin
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
alysts such as supported metal triflates [5,6], zeolites [7,8], clay
materials [9,10] and mesoporous solid acid catalysts [3,11] are
Benzylation of arenes is an important reaction in the synthe-
sis of diarylmethane derivatives, which are useful intermediates
in organic and polymer synthesis [1]. Diphenylmethane and sub-
stituted diphenylmethanes are industrially important compounds
used as pharmaceutical intermediates and fine chemicals [2]. These
diarylmethane derivatives have interesting biological and physio-
logical properties. Benzylnaphthalenes are useful as intermediates
for organic synthesis in the field of additives for lubricants, dyes
and anti oxidants [3]. The common synthetic method for diaryl-
methane derivatives has been the Friedel–Crafts type alkylation of
arenes with benzyl halides using Lewis acid or Bronsted acids as
catalysts.
In recent times, a switch from alkyl halide to alcohol, ester or
olefins as alkylating agent using late d-block and f-block metal
catalysts have been reported [4]. Rare earth metal triflates, Ir/Sn
bimetallic complexes [4], are reported for the Friedel–Crafts alky-
lation. These homogeneous catalysts are not desirable as they are
required in stoichiometric quantities, generate waste and involve
multi step procedure for their preparation.
reported. Many of these catalysts are not selective and require
longer reaction times to obtain reasonable yields.
Heteropoly acids (HPAs) are promising catalysts with strong
acidity used as catalysts for various types of reactions, particu-
larly in selective oxidation and acid-catalyzed reactions [12–14].
The major disadvantage of HPAs as catalysts lies in their low ther-
mal stability, low surface area (1–10 m2/g) and solubility in polar
media. The advantage of HPAs is that they can be made as heteroge-
neous acid catalysts with high thermal stability by supporting them
on suitable supports and/or by exchanging the protons present in
HPAs with metal ions [15].
In this paper, tin exchanged 12-tungstophosphoric acid
(SnxTPA) catalysts with varying Sn content were prepared and eval-
uated for benzylation of arenes with benzyl alcohols. The catalyst
activities were correlated to the extent of Sn exchanged, which
results in the variation of Lewis and Bronsted acidity. Benzylation
of different arenes with benzyl alcohol, substituted benzyl alcohols
and secondary benzyl alcohols were carried to reiterate the scope
of the catalysts.
There exist few studies where heterogeneous catalysts are used
for Friedel–Crafts alkylation [5–10]. However, in most of the cases
the benzylating agents are benzyl chlorides. Heterogeneous cat-
2. Experimental
2.1. Catalyst preparation
∗
A series of tin-exchanged 12-tungstophosphoric acid (SnxTPA)
catalysts were prepared with varying tin content. In a typical
Corresponding author. Tel.: +91 40 27193163; fax: +91 40 27160921.
E-mail address: nakkalingaiah@iict.res.in (N. Lingaiah).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.01.008

18
Ch. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
method required amount of TPA was dissolved in distilled water
and to this solution calculated amount of SnCl2 was added with
continuous stirring. The resultant mixture was stirred for 3 h and
the excess water was evaporated on a water bath at 100 ◦C. The
dried catalyst masses were kept for further drying in an air oven
and finally calcined at 300 ◦C for 2 h. The catalysts are denoted as
(d)
(c)
(b)
SnxTPA, where x indicates number of Sn atoms in H3PW12O40
.
2.2. Characterization of catalysts
(a)
X-ray diffraction (XRD) patterns of the catalysts were recorded
on Rigaku Miniflex diffractometer using Cu K␣ radiation (1.5406 A)
˚
at 40 kV and 30 mA. The measurements were obtained in steps of
0.045◦ with account time of 0.5 s and in the 2Â range of 10–80◦.
The Fourier Transform Infrared (FT-IR) spectra were recorded
on a Bio-rad Excalibur series spectrometer using KBr disc method.
The nature of the acid sites (Bronsted and Lewis) of the catalyst
samples was determined by FT-IR spectroscopy with chemisorbed
pyridine. The pyridine adsorption studies were carried out in the
diffuse reflectance infrared Fourier transform (DRIFT) mode. The
ratio of Bronsted and Lewis acidities was estimated from the IR
peak intensity corresponding to these acid sites.
The total acidity of the catalysts was measured by tempera-
ture programmed desorption of ammonia (TPD-NH3). In a typical
experiment, 0.1 g of catalyst was loaded and pretreated in He gas at
300 ◦C for 2 h and cooled to room temperature. The adsorption of
NH3 is carried out by passing a mixture of 5% NH3 balanced He gas
over the catalyst for 1 h at 100 ◦C. The catalyst surface was flushed
in He gas at 100 ◦C for 2 h to flush off the physisorbed NH3. The
TPD of the catalysts was carried in a He gas flow at a flow rate of
30 ml/min with a temperature ramp of 10 ◦C/min. The NH3 desorp-
tion was monitored using thermal conductivity detector (TCD) of a
gas chromatograph.
1500 1400 1300 1200 1100 1000 900 800 700
600
500
-1
Wavenumber (cm)
Fig. 1. FT-IR spectra of (a) TPA, (b) Sn0.5TPA, (c) Sn1TPA, and (d) Sn1.5TPA catalysts.
heteropoly tungstate. There was no change in the patterns with
variation in tin content suggests the existing of Keggin ion struc-
ture of tin containing heteropoly tungstate. The XRD results are in
support of the observations made from FT-IR.
Raman spectra of SnxTPA catalysts are presented in Fig. 3. Het-
eropoly tungstate shows characteristic Raman bands at 1006, 992
and 905 cm−1 related to Keggin ion of TPA [17,18]. The present cat-
alyst showed the symmetric vibration of W Ot band at 1006 cm−1
with a shoulder at 992 cm−1 [19]. The Raman results endorse the
XRD and FT-IR results, which suggest the presence of intact het-
eropoly tungstate Keggin ion structure even after exchange of tin.
Pyridine adsorption on the surface of solid acid allows one to
distinguish different acid sites. FT-IR pyridine adsorption spectra of
SnxTPA catalysts are shown in Fig. 4. The spectra showed pyridine
adsorption bands at 1635, 1607, 1536, 1442, and 1421 cm−1. The
band at 1635, and 1536 cm−1 were related to Bronsted acid sites
[20–22]. Pyridine molecules bonded to Lewis acid sites showed
the vibrations at 1607, 1442, and 1421 cm−1 [20,21]. The band at
1486 cm−1 is a combined band originating from pyridine bonded to
both Bronsted and Lewis acid sites [20]. The pyridine adsorption FT-
IR spectra suggest the presence of both Lewis and Bronsted acidity.
Confocal Micro-Raman spectra have been recorded at room
temperature in the range of 100–4000 cm−1 using a Horiba Jobin-
Yvon LabRam HR spectrometer with a 17 mW internal He–Ne
(Helium–Neon) laser source of excitation wavelength 632.8 nm.
The catalyst samples in powder form (about 5–10 mg) were usually
loosely spread onto a glass slide below the confocal microscope for
Raman measurements.
2.3. General alkylation reaction procedure
The alkylation reaction was carried-out in a 50 ml two-necked
round bottom flask provided with a reflux condenser. In a typical
run, 10 g of anisole and 3.37 g of benzyl alcohol (15:5 molar ratios)
along with 0.1 g catalyst were taken in flask. The reaction was car-
ried out at a reaction temperature of 120 ◦C. The reaction mixture
was withdrawn at different intervals and analyzed by a gas chro-
matography (VARIAN GC-3800) equipped with a SE-30 column and
flame ionization detector. The identification of products was made
from GC–MS (SHIMADZU-2010) analysis.
(d)
(c)
(b)
3. Results and discussion
3.1. Characterization
FT-IR patterns of SnxTPA are shown in Fig. 1. The catalysts
showed four characteristic bands in the region of 1100–500 cm−1
.
The main peaks observed at 1081, 981, 888, and 800 cm−1, were
related to the asymmetric stretching vibrations of P–O, W Ot,
W–Oc–W, and W–Oe–W respectively of characteristic Keggin ion
[16]. This indicates that the Keggin structure remained unaltered
during the exchange of TPA protons with tin.
(a)
10
20
30
40
50
60
70
80
2Theta
Fig. 2 shows the X-ray diffractograms of the catalysts. The XRD
pattern suggests the presence cubic structure of highly crystalline
Fig. 2. XRD pattern of (a) TPA, (b) Sn0.5TPA, (c) Sn1TPA, and (d) Sn1.5TPA catalysts.

Ch. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
19
(d)
(c)
(b)
(c)
(b)
(a)
(a)
800
900
1000
Raman shift (cm )
1100
1200
1700
1600
1500
1400
1300
-1
-1
Wavenumber (cm )
Fig. 3. Raman spectra of (a) Sn0.5TPA, (b) Sn1TPA, and (c) Sn1.5TPA catalysts.
Fig. 4. FT-IR spectra of pyridine adsorbed on (a) TPA, (b) Sn0.5TPA, (c) Sn1TPA, and
(d) Sn1.5TPA catalysts.
The ratio of Bronsted and Lewis acid sites was calculated from the
intensities of absorbance at 1536 and 1442 cm−1 and presented in
Table 1. Bronsted acidity is well known for heteropoly acids due to
the presence of protons. The Lewis acidity arises with the exchange
of TPA protons by tin. Lewis acidity is associated to the coordinately
unsaturated Sn+2 species in the catalyst. The B/L acidity ratio var-
ied with the content of Sn exchanged. Partially exchanged catalysts
showed high Bronsted acidity compared to fully exchanged cata-
lyst. The mobility of residual protons for the partially substituted
HPAs is high and results in increased Bronsted acidity along with
Lewis acidity [23].
peak related to the strong acidic sites of the catalysts. The amount
of strong acid sites is relatively more for Sn1HPW12O40 (Sn1TPA)
catalyst. The high temperature desorption peak is shifted towards
lower temperature with increase in the exchangeable Sn. The fully
exchanged catalyst Sn1.5PW12O40 (Sn1.5TPA) showed desorption
peak which is shifted marginally to lower temperature with less
intensity due to absence of residual protons. The heteropoly acids
exchanged partially with metal ions generally exhibit more acidity
due to the mobility of residual protons [21].
The ammonia TPD results are shown in Fig. 5. The patterns
showed a strong desorption peak around 550–600 ◦C and a small
hump in between 200 and 250 ◦C. The high temperature desorption
3.2. Catalytic activity for benzylation
Initially, SnxTPA catalysts were tested for their activity for the
benzylation of anisole with benzyl alcohol and the results are
shown in Table 2. This model reaction carried to optimize the reac-
tion conditions, catalyst loading and reaction temperature.
Table 1
Variation in Bronsted to Lewis acidity of SnxTPA catalysts.
S.no.
Catalyst
B/L ratio (I1536/I1442)
1.
2.
3.
Sn0.5TPA
Sn1TPA
Sn1.5TPA
1.10
1.27
1.10
The activity results suggest that Sn1TPA catalyst showed near
complete conversion of benzyl alcohol with high selectivity to alky-
lated products. The high activity resulted with the exchange of Sn
Scheme 1. Plausible reaction mechanism for benzylation of arene with benzyl alcohol over Sn1HTPA catalyst.

20
Ch. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
results in high mobility of residual protons, leading to increased
Bronsted acidity. The intact Keggin structure even after exchange
of protons with tin allows in generating Lewis acid sites along with
their Bronsted acidic sites. The presence of both Bronsted and Lewis
acidity might be responsible for high catalytic activity even at short
reaction times. The FT-IR, XRD, Raman and acidity measurements
support the reasons mentioned for the high benzylation activity of
the catalysts.
The plausible reaction mechanism is presented in Scheme 1. The
participation of both Lewis and Bronsted acid sites of the catalysts
was elucidated for the benzylation of arenes with benzyl alcohol.
The plausible mechanism and the catalyst characteristics supports
the high activity of the catalysts due to the generation of new Lewis
acidic sites with the presence of tin and Bronsted acidity because
of the mobile nature of residual protons of heteropoly tungstate.
The scope of the present catalyst system was evaluated for the
benzylation of different arene with variety of benzyl alcohols and
the results are presented in Table 3. Benzylation of electron rich
arenes such as anisole, toluene, xylenes, cresols and mesitylene
with benzyl alcohol are presented. In all the cases benzyl alcohol
conversion is near 100% with quantitative yield to the correspond-
ing benzyl arene within short reaction times. The di-substituted
arenes underwent benzylation relatively at longer reaction times.
The alkylation products are predominantly ortho/para substituted
ones. The para selectivity is relatively more in most of the cases.
In Table 4, benzylation of variety anisoles with benzyl alcohol
and substituted benzyl alcohols are presented. Both electron-
rich (4-methyl benzyl alcohol and 4-methoxy benzyl alcohol) and
electron-poor benzyl alcohol could react with anisole and gave cor-
responding diarylmethanes in high yields. When benzyl alcohol
reacted with substituted anisoles such as 4-methyl anisole, 4-fluoro
anisole, and 4-bromo anisole the product is ortho benzylated one,
with complete conversion of benzyl alcohol. The reaction of substi-
tuted benzyl alcohols such as 4-methyl benzyl alcohol, 4-methoxy
benzyl alcohol and 2-bromo benzyl alcohol with anisole forms cor-
responding benzylated products with para isomer as major product
in an hour.
Fig. 5. Ammonia TPD profiles of (a) Sn0.5TPA, (b) Sn1TPA, and (c) Sn1.5TPA catalysts.
with the protons of TPA. The catalytic activities of the SnxTPA cat-
alysts are related to their physico-chemical properties. Among all
the catalysts Sn1TPA showed highest activity. This catalyst exhib-
ited higher acidity with more B/L ratio. The partial exchange of Sn
Table 2
Benzylation of anisole with benzyl alcohol over SnxTPA catalysts.
S.no. Catalyst Reaction time (min) Conversiona (%) Yield (%)
o-
p-
Ether
1.
2.
3.
4.
TPA
Sn0.5TPA 30
Sn1TPA 30
Sn1.5TPA 30
45
93
94
100
89
36.61 42.43 14.12
34.46 40.09 19.28
45.05 54.08
–
32.59 35.46 21.11
Reaction conditions: Benzyl alcohol (3.376 g), anisole (10 g), catalyst weight (0.1 g),
The reaction of substituted anisoles (4-methyl anisole and
4-bromo anisole) with substituted benzyl alcohols (4-methyl
and reaction temperature 120 ◦C.
a
Conversion with respect to benzyl alcohol.
o-
p-
Ether
100
80
60
40
20
0
100
80
60
40
20
0
0
1
2
3
4
Number of recycles
Fig. 6. Reusability data of Sn1TPA catalyst for benzylation of anisole.

Ch. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
21
Table 3
Benzylation of different substituted arenes over Sn1TPA catalyst.
S.no.
Arene
Alcohol
Time (min)
Product
Selectivity (o-:p-)
1.
2.
3.
30
30
60
45:55
–
–
4.
5.
60
75
31:69a
–
6.
7.
60
60
31:69b
–
8.
9.
45
60
–
45:54c
10.
11.
75
30
24:76d
29:71e
Reaction conditions: Benzyl alcohol (3.376 g), arene (10 g), catalyst weight (0.1 g), and reaction temperature 120 ◦C.
a
3-benzyl-4-chloro-1-methylbenzene:2-benzyl-4-chloro-1-methylbenzene.
2-benzyl-1,3-dimethylbenzene:1-benzyl-2,4-dimethylbenzene.
2-benzyl-6-methyl phenol:4-benzyl-2-methyl phenol.
3-benzyl-4-methyl phenol:2-benzyl-4-methyl phenol.
b
c
d
e
1-benzyl-2,3-dimethoxybenzene:4-benzyl-1,2-dimethoxybenzene.
benzyl alcohol, 4-methoxy benzyl alcohol, and 2-bromo
benzyl alcohol) produced the corresponding benzylated
products in good yields with complete conversion of benzyl alcohol
within 60 min of reaction time irrespective of substitution in benzyl
alcohol.
Benzylation of anisole and substituted anisole with secondary
alcohols are presented in Table 5. It is noteworthy to mention that
the present catalytic system is highly effective even when sec-
ondary benzyl alcohols were used as benzylating agents. Anisole
reacted smoothly with 1-phenylethanol and diphenylmethanol
yielding corresponding ortho and para products with high para
selectivity. Where as, substituted anisoles (4-fluoro and 4-methyl
anisole) gave selectively only one isomer (ortho) within short reac-
tion time.
PhNO2 [24,25]. There are no details of solid acid catalysts used
for benzylation of naphthalene with benzyl alcohol and secondary
benzyl alcohols. The results suggest that benzylation of naphtha-
lene with different substituted alcohols underwent smoothly with
high conversion of alcohol with good selectivity towards the cor-
responding benzylated naphthalenes.
3.3. Comparison of the catalytic activity of Sn1TPA with reported
catalysts
The present catalyst Sn1TPA was compared with the reported
catalysts for the benzylation of anisole with benzyl alcohol. The
comparative results are shown in Table 7. When compared to
other catalysts, present catalyst showed complete conversion of
benzyl alcohol within 30 min with selectivity towards p- and o-
isomers. Where as the other reported solid acid catalysts took
about 90–540 min to get a similar conversion. The reported
H3PO4–WO3–Nb2O5 heteropoly acid catalysts showed good activ-
Benzylation of naphthalene with different benzyl alcohols and
secondary alcohols are studied and the results are summarized in
Table 6. Benzylation of naphthalene is very important and carried
by complex catalytic systems such as AlCl3-CH3NO2 and AlCl3-

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Ch. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
Table 4
Benzylation of substituted anisoles with variety of benzyl alcohols over Sn1TPA catalyst.
S.no.
Arene
Alcohol
Time (min)
Major product
Rigio isomer (o-:p-)
1.
2.
30
–
–
150
3.
4.
45
60
–
38:62
5.
6.
30
30
20:80
43:57
7.
8.
9.
60
60
60
–
–
–
10.
11.
12.
30
30
30
–
–
–
Reaction conditions: Benzyl alcohol (3.376 g), arene (10 g), catalyst weight (0.1 g), and reaction temperature 120 ◦C.
ity only when the heteropoly acid is decomposed to its intermediate
species. These results reiterate the high activity and selectivity of
SnHPW12O40 catalyst for benzylation reactions.
was dried in oven at 120 ◦C for 1 h and reused for benzylation
of anisole with benzyl alcohol. The catalyst recycles activity
data was shown in Fig. 6. From the figure it was found that
conversion of benzyl alcohol almost same without any sig-
nificant loss in activity even after fourth cycle. The catalyst
exhibited consistent selectivity towards benzylated product bar-
ring a marginal selectivity towards ether in the first cycle. The
reusability results clearly demonstrated the efficiency of the
catalyst.
3.4. Reusability of the catalyst
In order to find the reusability of SnHPW12O40 catalyst, after
the reaction the catalyst was separated from the reaction mixture
by simple filtration and washed with ethyl acetate. The catalyst

Ch. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
23
Table 5
Benzylation of anisole and substitution anisole with secondary alcohols over Sn1TPA catalyst.
S.no.
Arene
Alcohol
Time (min)
Major product
Rigio isomer (o-:p-)
1.
15
30:70
2.
3.
15
15
–
–
4.
15
13:87
5.
15
–
6.
15
–
Reaction conditions: Benzyl alcohol (3.376 g), arene (10 g), catalyst weight (0.1 g), and reaction temperature 120 ◦C.
Table 6
Benzylation of naphthalene with variety of benzyl alcohols and secondary alcohols over Sn1TPA catalyst.
S.no.
Arene
Alcohol
Time (min)
Major product
Rigio isomer (1-:2-)
22:78
1.
15
2.
3.
15
15
39:61
18:82
4.
15
20:80
17:83
5.
15
Reaction conditions: Benzyl alcohol (3.376 g), naphthalene (11.85 g), catalyst weight (0.1 g), and reaction temperature 120 ◦C.

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Ch. Ramesh Kumar et al. / Journal of Molecular Catalysis A: Chemical 337 (2011) 17–24
Table 7
Comparison of the catalytic activity of Sn1TPA with other reported solid acids catalysts.
Catalyst
Reaction temp. (◦C)
Time (min.)
Conversiona (%)
Selectivity (%)
o-
Ref.
p-
Ether
–
12.8
–
0.3
5.2
20.3
–
Other
Sn1TPA
120
Reflux
Reflux
80
160
160
80
30
540
180
180
<360
90
100
99.2
–
45
54
–
–
2.0
–
Present work
[26]
[27]
[28]
[29]
Nb2O5 + H3PO4
SiO2–Si–SCF3
H3PO4–WO3–Nb2O5
Niobiumphosphate
Nb2O5/Al2O3
TPA-PANI
85.2b
100b
93.4b
34.3
29.2
24.6
–
–
100
–
100
100
98
53.1
44.9
76.4
7.4
6.3
–
[30]
[2]
240
a
Conversion with respect to benzyl alcohol.
Benzylated product yield.
b
4. Conclusions
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In summary, tin exchanged TPA catalysts are prepared with
retention of Keggin ion structure. The SnxTPA catalysts showed high
benzylation activity and their activity depends on the extent of tin
content. The presence of Sn generated Lewis acidity, which affected
the overall catalytic activity. The catalyst with partial exchange of
tin Sn1TPA showed highest activity due to the presence of more
number of both Lewis and Bronsted acidic sites. The role of both
Lewis and Bronsted acidic sites of the catalysts for benzylation
are explained by the plausible reaction mechanism. The catalysts
showed excellent benzylation activity within short reaction times
with high selectivity compared to other reported catalysts. The
catalyst is easy to recover and exhibits consistent activity and selec-
tivity for benzylation reaction. The reported catalyst is active for the
benzylation reaction irrespective of the nature of substituted arene
and benzyl alcohols.
Acknowledgement
The authors RK and KTVR thank Council of Scientific and Indus-
trial Research (CSIR), India for the award of Junior and Senior
Research Fellowships respectively.
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