Silica-supported methanesulfonic acid - An efficient solid Bronsted acid catalyst for the Pechmann reaction in the presence of higher n -alkanes

Article abstract of DOI:10.1139/v11-055

A cost-effective and efficient solid Bronsted acid catalyst was synthesized by loading methanesulfonic acid (MSA) on silica and was used for the acid-catalyzed Pechmann reaction to test the catalytic activity and its reusability. Derivatives of 4-methylcoumarin were synthesized in good yields within short reaction times in the presence of environmentally friendly higher n-alkanes as solvents. The regeneration study of the spent catalyst showed satisfactory results.

Full text of DOI:10.1139/v11-055

6
63
Silica-supported methanesulfonic acid — An
efficient solid Brønsted acid catalyst for the
Pechmann reaction in the presence of higher
n-alkanes
J. Joshi, M.K. Mishra, and M. Srinivasarao
Abstract: A cost-effective and efficient solid Brønsted acid catalyst was synthesized by loading methanesulfonic acid
(
MSA) on silica and was used for the acid-catalyzed Pechmann reaction to test the catalytic activity and its reusability. De-
rivatives of 4-methylcoumarin were synthesized in good yields within short reaction times in the presence of environmen-
tally friendly higher n-alkanes as solvents. The regeneration study of the spent catalyst showed satisfactory results.
Key words: silica supported solid acids, methanesulfonic acid, Brønsted acidity, Pechmann reaction, derivatives of 4-methyl-
coumarin.
Résumé : On a synthétisé un catalyseur acide de Brønsted efficace et rentable d’un point de vue coût en recouvrant de la si-
lice avec de l’acide méthanesulfonique (AMS) et on l’a utilisé catalyseur acide pour la réaction de Pechmann dans le but
d’évaluer son activité catalytique et la possibilité de le réutiliser. On a synthétisé des dérivés de la 4-méthylcoumarine avec
de bons rendements, avec des temps de réaction relativement courts, dans des solvants à base d’alcanes supérieurs écologi-
ques. L’étude de régénération du catalyseur utilisé a donné des résultats satisfaisants.
Mots‐clés : acides solides supportés par de la silice, acide méthanesulfonique, acidité de Brønsted, réaction de Pechman, dé-
rivés de la 4-méthylcoumarine.
[
Traduit par la Rédaction]
Introduction
Coumarins are heterocyclic natural products finding appli-
cations as pharmacologically and biologically active com-
Methanesulfonic acid (CH SO H; MSA) is a strong
Brønsted acid (pK = –1.9) and has been reported as a poten-
3
3
11,12
pounds.
Coumarins are usually synthesized by acid-
a
catalyzed Pechmann reaction of activated phenols and a-keto
esters using homogeneous Brønsted
1
–3
tial acid catalyst for various acid-catalyzed reactions. MSA
is very cheap, has a lower tendency to oxidize organic com-
pounds, is far less corrosive and toxic than widely used fluoro-
substituted alkanesulfonic acids, like triflic acid and 1,1,2,2-
tetrafluoroethanesulfonic acid, and the mineral acids. The
problems associated with recovery and reuse of MSA from
homogeneous conditions makes its application limited. To
overcome these problems, a supported form of MSA could
be the best alternative. The supported fluoro-substituted al-
kanesulfonic acids (triflic acid, 1,1,2,2-tetrafluoroethanesulfonic
acid, etc.) have been synthesized and used for various acid-
13
14–16
17,18
and Lewis
acid
catalysts. It is to be noted that the homogeneous acids are
corrosive, required in excess, and nonreusable, sometimes re-
sult in the formation of side products, and generate acidic
waste. Various solid acid catalysts such as Amberlyst ion-
19
20
21
exchange resins, zeolites, montmorillonite K-10, sul-
22
fated zirconia, benzylsulfonic acid functionalized meso-
23
24
25
porous Zr-TMS, metal ion-exchanged ZAPO-5, W/ZrO2,
26
Nafion resin / silica nanocomposites, polyaniline sulfate
27
salt, etc., have been found to be the best alternatives to homo-
geneous acids. However, most of the solid acids require ei-
4
–10
catalyzed organic transformations.
However, supported
20–25,27
ther a longer reaction time
or a higher reaction
to achieve maximum yield. The syntheses
using some of the solid acids are not cost-effective because
MSA, which could be a cost-effective and eco-friendly solid
acid catalyst, and an attractive alternative to supported fluoro-
substituted alkanesulfonic acids for acid-catalyzed transfor-
mations, has not been reported in the literature. The present
work was aimed at developing silica-supported MSA as a
cost-effective, eco-friendly, and reusable solid acid catalyst.
The synthesized catalyst was used for the Pechmann reaction
to synthesize derivatives of 4-methylcoumarin.
22,24,27
temperature
27
of either tedious methods of synthesizing the catalysts or
the use of large amounts of catalysts.1
9,20,26
In addition, the
solid acid catalyzed Pechmann reactions are usually carried
out using nonpolar solvents like tetrahydrofuran (THF), tol-
uene, etc.,1
9,20
which are volatile, hazardous, and nonrecover-
able. To the best of our knowledge, there is no report
Received 4 September 2010. Accepted 4 February 2011. Published at www.nrcresearchpress.com/cjc on 23 June 2011.
J. Joshi, M. Mishra, and M. Srinivasarao. Department of Chemical Engineering and Shah-Schulman Center for Surface Science and
Nanotechnology, Faculty of Technology, Dharmsinh Desai University, College Road, Nadiad – 387 001, Gujarat, India.
Corresponding author: M.K. Mishra (e-mail: manishorgch@gmail.com).
Can. J. Chem. 89: 663–670 (2011)
doi:10.1139/V11-055
Published by NRC Research Press

664
Can. J. Chem. Vol. 89, 2011
available on the application of higher n-alkanes as nonpolar
solvents in heterogeneous catalysis. Hence, an attempt was
also made in the present work to use higher n-alkanes as en-
vironmentally friendly nonpolar solvents for Pechmann reac-
tions.
Lewis) in the samples was characterized by FT-IR study of
the pyridine-adsorbed samples. For this the sample (0.2 g)
was activated at 120 °C for 2 h. The activated sample was
cooled in a desiccator under vacuum and was exposed to pyr-
idine (25 mL) vapor for 12 h. The pyridine-adsorbed sample
was degassed under vacuum for 15 min to remove physically
adsorbed pyridine from the sample. The FT-IR spectra of the
samples adsorbed with pyridine (mixed with KBr in a 1:20
Experimental
Chemicals
–1
wt ratio) were recorded in the range of 400–4000 cm . The
Tetraethylorthosilicate, ethyl acetoacetate, and pyrogallol
were procured from s.d. Fine Chemicals, India. Hydrochloric
acid, methanol, n-hexadecylamine (HDA), resorcinol, nitro-
benzene, petroleum ether, n-butylamine, and acetonitrile
were from Merck, USA. n-Octadecane, n-hexadecane, n-
dodecane, phloroglucinol, methoxyphenol, and m-cresol
were procured from National Chemicals, India. Methanesul-
fonic acid was procured from Loba Chemie, India.
amount of acidity and the strength of the acid sites in the
samples were measured by potentiometric titration.8 The
sample (0.05 g) was suspended in acetonitrile and stirred for
3
h. The suspension was titrated with 0.05 N n-butylamine in
acetonitrile at 0.05 mL/min. The electrode potential variation
was measured using a potentiometric titrator (Chemito, In-
dia). The TGA-DTA of the samples was carried out by a Shi-
madzu DTG-60H, by heating the sample in the range of 50–
1
000 °C with a heating rate of 10 °C/min under nitrogen
Synthesis of silica-supported methanesulfonic acid (SiO –
3
2
flow (30 cm /min). The amount of MSA loaded on the silica
MSA) solid acid catalyst
was calculated from the TGA results (WMSA) using the fol-
The silica support was synthesized by hydrolysis of tetrae-
thylorthosilicate (TEOS) using HDA as the template. The pH
of the TEOS (20 g) and methanol (50 mL) solution was ad-
justed in the range of 2–3 by adding a few drops of concen-
trated hydrochloric acid. Water (7.2 mL) was then added to
the acidic TEOS solution with stirring and the solution was
kept for 30 min. The HDA solution, prepared by dissolving
HDA (2.4 g, 0.01 mol) in methanol (50 mL), was added to
the TEOS solution with vigorous stirring and the solution
was aged for 5 days at room temperature. The gel was fil-
tered and washed with methanol to remove surfactant tem-
plate, which was confirmed by FT-IR analysis of the dried
silica. The gel was dried at room temperature for 24 h and
then at 120 °C for 12 h. To load a nominal amount of MSA
lowing equation:8
½1ꢀ
WMSA ¼ ðWSiOꢁMSAÞ=FWMSA
where WSiO–MSA = weight loss (mg/g) of SiO –MSA catalyst
2
from 25 to 500 °C, WSiO = weight loss (mg/g) of SiO sup-
2
port from 25 to 500 °C, and FWMSA = molecular weight of
CH SO H. Percentage of sulfur in the catalysts was also ana-
3
3
lyzed by CHNS/O elemental analysis (PerkinElmer 2400) to
estimate the amount of methanesulfonic acid loaded on the
silica.
Catalytic activity of SiO –MSA for synthesis of 4-
2
methylcoumarin derivatives by the Pechmann reaction
The derivatives of 4-methylcoumarin were synthesized by
(
~1 mmol MSA / g of silica) on the silica support, 10 g of
the SiO –MSA catalyzed Pechmann reaction of a phenol
2
dried silica gel was treated with MSA solution (5 mL of
MSA in 50 mLof carbon tetrachloride) at room temperature
with stirring for 24 h. The gel was filtered and washed with
methanol and then with petroleum ether to remove free MSA.
The gel was dried at room temperature for 24 h and later at
(resorcinol, phloroglucinol, pyrogallol, m-methylphenol, m-
methoxyphenol, or phenol) and ethyl acetoacetate (Scheme 1).
The reaction was carried out by adding preactivated (at 120 °C
for 1 h) catalyst to the mixture of phenol and ethyl acetoace-
tate, with or without solvent, at constant temperature under
stirring. After the completion of reaction, the reaction mix-
ture was cooled and methanol (~10 mL) was added to dis-
solve the product. The reaction mixture was filtered to
separate the catalyst and the product was crystallized by cool-
ing the filtrate.
1
20 °C for 6 h.
Characterization of SiO –MSA catalyst
2
The catalyst was characterized by N adsorption–desorption
2
isotherm, FT-IR, FT-IR of the pyridine-adsorbed sample, po-
tentiometric titration, thermal analysis (TGA-DTA), and
CHNS/O elemental analysis. The Brunauer–Emmett–Teller
Characterization of the products
(
BET) surface area and average pore diameter of the samples
were measured by N adsorption–desorption isotherm studies
The products were recrystallized in ethanol–water (95:1)
2
using a Quantachrome NOVA 1000e surface area analyzer.
The sample was degassed under vacuum at 120 °C for 4 h
prior to adsorption measurement, to evacuate the physisorbed
moisture. The surface area was determined by using the BET
equation, and the average pore diameter of the samples was
measured by the Barrett, Joyner, and Halenda method
solution and the isolated yields were calculated. The products
1
were characterized by melting point and by FT-IR and H
NMR spectroscopy, and the data were matched with those re-
ported in the literature. Melting points were measured by a
melting point apparatus (Choudhary Instruments, India) and
are uncorrected. Infrared spectra were recorded on a FT-IR
spectrophotometer (Shimadzu IRPrestige-21) in KBr with
(
BJH).28 The loading of MSA over the silica support was
–1 1
confirmed by FT-IR study using a FT-IR spectrophotometer
Shimadzu IRPrestige-21) with a diffuse reflectance scanning
disc technique by mixing the sample with dried KBr (in a
transmittance in cm . H NMR spectra were determined on
a NMR spectrometer (Bruker Avance DPX, 200 MHz) as di-
(
methyl sulfoxide (DMSO-d ) solutions. Chemical shifts (d)
6
–
1
1
:20 wt ratio) in the range of 400–4000 cm with a resolu-
were expressed in ppm downfield from the internal standard
tetramethylsilane.
–1
tion of 4 cm . The type of surface acidity (Brønsted or
Published by NRC Research Press

Joshi et al.
665
Scheme 1. SiO2 – methanesulfonic acid (MSA) catalyzed Pechmann reaction of phenols and ethyl acetoacetate to synthesize derivatives of 4-
methylcoumarin.
Table 1. Physicochemical and catalytic properties of SiO2 support and SiO2 – methanesulfonic acid (MSA) catalyst.
Loading of MSA
(µmol/g)
Type of acid sitea
Brønsted
acidity
band area
(A/cm)
—
5.3
Lewis
acidity
band area
(A/cm)
—
Nil
Yield of 7-hydroxy-
4-methylcoumarin
SBET
(m /g)
373
362
DP
(Å)
31
31
Acid site
2
NMSAb
—
WMSAc
—
(µmol n-butylamine / g)d (wt %)e
Sample
SiO2 support
SiO2–MSA
—
1200
0
94
1000
1200
Note: SBET, BET surface area; D , average pore diameter; NMSA, the amount of MSA loaded on silica calculated from the sulfur content; WMSA, amount of
P
MSA loaded on silica calculated from TGA analysis.
a
IR study of pyridine-adsorbed sample.
b
Calculated from sulfur wt % obtained by CHNS/O analysis.
c
By TGA analysis.
By potentiometric titration with n-butylamine.
d
e
Resorcinol (10 mmol), ethyl acetoacetate (20 mmol), catalyst (0.25 g), 160 °C, 12 h.
2
7
-Hydroxy-4-methylcoumarin
the silica support (373 m /g), which is attributed to the load-
ing of MSA on the silica surface (Table 1).
2
5
–1
mp: 185–190 °C (lit. mp 188 °C). FT-IR (KBr, cm ):
1
3
1
1
159 (n ), 1674 (n ). H NMR (DMSO-d ) d: 10.54 (s,
H, –OH), 7.56 (d, 1H, Ar–H), 6.79 (d, 1H, Ar–H), 6.72 (s,
The FT-IR spectrum (Fig. 1) of SiO2 exhibits a broad band
in the range of 2800–3750 cm (nO–H, for –OH groups of
silica and adsorbed water) including small peaks at 3650
OH
C=O
6
–1
H, Ar–H), 6.12 (s, 1H, –C=CH–), 2.36 (s, 3H, –CH ).
3
–
1
(
n
O–H
, for free silanols ≡Si–OH) and 1630 cm (dO–H, for
5,7-Dihydroxy-4-methylcoumarin
adsorbed water). In the FT-IR spectrum of SiO –MSA the
2
29
–1
–1
mp: 283–285 °C (lit. mp 284–285 °C). FT-IR (KBr, cm ):
peak for silanols (3650 cm ) disappeared and the broadness
1
3
1
159 (n ), 1670 (n ). H NMR (DMSO-d ) d: 10.5 (s,
H, –OH), 10.3 (s, 1H, –OH), 6.3 (s, 1H, Ar–H), 6.2 (s, 1H,
of the band in the –OH region increased. This spectral
change indicates that MSA is bonded with free silanols of
silica by the reaction of MSA and silanols. A similar obser-
OH
C=O
6
Ar–H), 5.9 (s, 1H, –C=CH–), 2.5 (s, 3H, –CH ).
3
4
vation was also reported for silica-supported triflic acid. The
–1
7,8-Dihydroxy-4-methylcoumarin
FT-IR spectrum of SiO –MSA shows a peak at 1337 cm
2
30
–1
mp: 242–245 °C (lit. mp 242–244 °C). FT-IR (KBr, cm ):
for the n
stretching mode of the –SO H group and a small
S=O
3
1
–1
3
1
231 (n ), 1648 (n ). H NMR (DMSO-d ) d: 10.0 (s,
H, –OH), 9.4 (s, 1H, –OH), 7.1 (d, 1H, Ar–H), 6.8 (d, 1H,
peak at 1425 cm for the d
bending mode of the –CH
C–H
OH
C=O
6
3
–1
group.31 A peak for SO deformation was found at 554 cm .
2
Ar–H), 6.1 (s, 1H, –C=CH–), 2.3 (s, 3H, –CH ).
The FT-IR spectrum of pyridine-adsorbed catalyst (Fig. 2)
3
–1
shows peaks at 1489, 1554, 1620, and 1635 cm . The peak
at 1554 cm– is a characteristic peak of adsorbed pyridine on
Brønsted acid sites, showing the presence of a significant
amount of Brønsted acidity. There is no peak in the range of
1440–1450 cm for adsorbed pyridine on Lewis sites. Thus,
the catalyst has predominantly Brønsted acidity showing
5.3 A/cm peak area of the band at 1554 cm– (Table 1). The
1
Results and discussion
Characterization of SiO –MSA
The physicochemical characteristics of the silica and the
supported catalyst are given in Table 1. The average pore di-
ameter for the samples was 31 Å. The SiO –MSA had a
slightly lesser BET surface area (362 m /g) compared with
2
–
1
1
2
2
reaction of the –SO H group of MSA and silanols results in
3
Published by NRC Research Press

666
Can. J. Chem. Vol. 89, 2011
Scheme 2. Interaction of methanesulfonic acid (MSA) with the silanol of silica and generation of Brønsted acid sites.
Fig. 1. FT-IR spectra of silica support and SiO2 – methanesulfonic
acid (MSA) catalyst.
Fig. 2. FT-IR spectrum of pyridine adsorbed SiO2 – methanesulfonic
acid (MSA) catalyst.
SiO support
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
2
SiO -MSA
2
1
425
337
1
630
1
3
650
3
349
815
80 554
9
1
210
1
060
1000
445
0
4
000
3500
3000
2500
cm
2000
1500
500
–
1
loaded over silica (NMSA), calculated from the sulfur content
formation of protonated silanols, which hold methanesulfo-
nate ions on the silica surface (Scheme 2). The protonated si-
lanols bonded with methanesulfonate ions on the silica
surface act as Brønsted acid sites.
(
3.2 wt %, obtained from CHNS/O elemental analysis), corre-
sponds to 1000 µmol/g (Table 1), which is in close agree-
ment with WMSA
.
The characterization results confirmed that a significant
amount of MSA was loaded over silica by surface reaction
of MSA with silanols, generating predominantly Brønsted
acidity. This catalyst can be used as a solid Brønsted acid
for acid-catalyzed reactions.
The initial electrode potential (E ), obtained by potentio-
i
metric titration with n-butylamine, indicates that the catalyst
2
5
possesses very strong acid sites (E = 612 mV) compared
i
with those of the silica support (Fig. 3). The total number of
acid sites in the catalyst was found to be 1200 mmol n-butyl-
amine / g of catalyst (Table 1).
TGA-DTA profiles of SiO support and SiO –MSA cata-
Catalytic activity of SiO2–MSA for the Pechmann
reaction to synthesize 4-methylcoumarin derivatives and
the effect of reaction parameters
2
2
lyst are given in Figs. 4a and 4b showing two-stage weight
loss in SiO –MSA. The weight loss that occurred from 50 to
2
1
50 °C corresponds to the removal of adsorbed water. The
SiO –MSA catalyst was found to be active for the Pechmann
2
second stage weight loss in the range of 300–450 °C is at-
tributed to the decomposition of loaded MSA. The amount
reaction giving 94% yield of 7-hydroxy-4-methylcoumarin at
160 °C after 12 h (Table 1). No product formation was ob-
served with pure silica without loading MSA. The reaction
temperature was optimized by carrying out the reaction in
of MSA loaded on silica, calculated from TGA analysis
8
(
WMSA), was 1200 µmol/g (Table 1). The amount of MSA
Published by NRC Research Press

Joshi et al.
667
Fig. 5. Yield (wt %) of 7-hydroxy-4-methylcoumarin at different
catalyst loading (6.5–1.3 wt %). (Reaction conditions: resorcinol –
ethyl acetoacetate molar ratio = 2, 0.25 g catalyst, 160 °C, 12 h)
Fig. 3. Potentiometric titration curves of SiO2 – methanesulfonic acid
(MSA) catalyst and SiO2 support.
Fig. 4. TGA-DTA profile of (a) silica support and (b) SiO2 –
methanesulfonic acid (MSA) catalyst.
Fig. 6. Yield (wt %) of 7-hydroxy-4-methylcoumarin with time in
solvent-free conditions and in the presence of various solvents. (Re-
action conditions: 10 mmol resorcinol, 20 mmol ethyl acetoacetate,
8
8
8
7
7
7
.4
.2
.0
.8
.6
.4
20
(
a)
3
mL solvent, 0.25 g catalyst, 160 °C)
1
0
0
TGA
DTA
-
10
-20
1000
200
400
600
800
Temperature (°C)
1
1
0.5
0.0
20
(
b)
1
0
0
9
9
8
8
7
7
.5
.0
.5
.0
.5
.0
TGA
DTA
the range of 90–180 °C keeping all other parameters the
same (see Supplementary data, Fig. S1). The maximum yield
of 7-hydroxy-4-methylcoumarin (94%) was obtained after
1
2 h at 160 °C. The yield was observed to be slightly de-
creased (90% after 12 h) at 180 °C. Therefore, 160 °C was
selected as the optimized reaction temperature.
To demonstrate the efficiency of the catalyst, the reaction
was carried out by varying the catalyst loading (6.5, 3.9, 2.6,
and 1.3 wt %) under similar reaction conditions. The yield of
-10
-20
1000
200
400
600
800
7
-hydroxy-4-methylcoumarin was observed to be steady
Temperature (°C)
(94%) up to a catalyst loading of 2.6 wt % (Fig. 5). It shows
that the catalyst is very efficient and required in only a small
quantity to achieve the maximum yield. However, the reac-
tion kinetics were affected by the catalyst loading. It was
Published by NRC Research Press

668
Can. J. Chem. Vol. 89, 2011
Table 2. The reaction conditions and yield of 7-hydroxy-4-methylcoumarin reported with various solid acid catalysts and SiO2 – methanesulfonic
acid (MSA) catalyst.
Sample
No.
1
2
3
Reaction
time (h)
2
4
Yield
(wt %)
95
77–80
96
Solid acid
Amberlyst ion-exchange resins
Zeolite
Montmorillonite
Reaction temp. (°C)
Reflux temp.
120 / Reflux temp.
Solvent
Toluene
None/toluene
Ref.
19
20
21
K-10
150
4
None
K-10
KSF
KSF
SO4/ZrO2
Benzylsulfonic acid functionalized
mesoporous Zr–TMS
Metal (Ga , In , La , and Ce )
ion-exchanged ZAPO-5
W/ZrO2
Nafion resin / silica nanocomposites
Polyaniline sulfate salt
SiO2–MSA catalyst
Reflux temp.
150
Reflux temp.
170
8
5
Toluene
None
Toluene
None
94
88
90
91
86
10
3–24
20
4
5
22
23
150
None
3
+
3+
3+
3+
6
175
6
None
90
24
7
8
9
Reflux temp.
Reflux temp.
150/170
6
2
6
2
Toluene
Toluene
None
80
80–97
72
25
26
27
—
1
0
160
n-Hexadecane/n-octadecane
99
also observed that the higher the catalyst amount, the faster
the initial rate (see Supplementary data, Fig. S2.
Nitrobenzene and higher n-alkanes (n-dodecane, n-hexa-
decane, and n-octadecane) were used as polar and nonpolar
wards the catalyst surface, facilitating the adsorption of the
reactant molecules on the catalyst surface for the reaction. It
appears that the bulk diffusion of the reactants from solvent
to catalyst surface and the surface adsorption are made easier
by higher n-alkanes. After the surface reaction, the product
(7-hydroxy-4-methylcoumarin) formed on the surface is des-
orbed and tends to come into the n-alkane (the nonpolar sol-
vent) as the solubility of the product is significant in the
nonpolar solvent. The solubilization of product in n-alkane
facilitates the removal (desorption) of the product molecules
from the catalyst surface, making surface sites free, as well
as the bulk diffusion of the product molecules from the cata-
lyst surface to the bulk of the solvent. The lesser yield in the
polar medium (nitrobenzene) may also be attributed to the
higher solubility of the polar reactants in the solvent, which
reduces the bulk diffusion rate of the reactant molecules
from solvent to catalyst surface.
solvents, respectively, to study the effect of solvent on SiO –
2
MSA catalyzed synthesis of 7-hydroxy-4-methylcoumarin. In
nitrobenzene, the yield was significantly reduced (50% after
1
4 h) compared with the yield (94% after 14 h) obtained in
solvent-free synthesis (Fig. 6). The lesser yield in the polar
medium has been attributed to cleavage of the product19 and
the reduction in the number of available active sites owing to
22
bonding of nitrobenzene molecules with active sites. Non-
polar solvents such as toluene, cumene, THF, etc.,1
9,20
have
been widely used for synthesis of 7-hydroxy-4-methylcoumarin
and toluene has been found to be one of the best nonpolar
solvents.19 However, toluene is a hazardous, nonseparable,
nonreusable, and volatile aromatic, which limits its high-
temperature applications. In the present work, higher n-alkanes
The yield of 7-hydroxy-4-methylcoumarin and the reaction
conditions reported with the other solid acid catalysts were
(
n-dodecane, n-hexadecane, and n-octadecane) were used as
nonpolar solvents, which are nonhazardous, less volatile, and
easily recoverable. The higher n-alkanes improved the activ-
ity of the catalyst by decreasing the reaction time (2–8 h) to
achieve a maximum yield (>94%). n-Hexadecane and n-
octadecane were more effective than n-dodecane, giving the
maximum yield within 2 h. The enhanced activity of the cat-
alyst in higher n-alkanes may be attributed to the higher non-
polar nature of the medium and the insolubility of reactant
molecules in n-alkanes, which drives polar reactant mole-
cules towards the catalyst surface for adsorption and chemical
reaction. As the chain length of the n-alkane chain is in-
creased, the reaction time to achieve maximum yield of the
product was observed to be reduced as it enhances the cata-
compared with the SiO –MSA catalyst (Table 2). It can be
2
observed that SiO –MSA in the presence of higher n-alkanes
2
as solvents gives the highest yield (99%) in the shortest time
(2 h) at relatively lower temperature in comparison with the
other catalysts.
The SiO –SA catalyst showed significant activity for the
2
synthesis of derivatives of 4-methylcoumarin (Table 3). How-
ever, the activated phenols (resorcinol, phloroglucinol, and
pyrogallol) were found to be more reactive, giving 99%,
7
8%, and 70% yields of the corresponding coumarin deriva-
tives. No product formation was observed under the given
reaction conditions with less reactive phenols (m-methoxy-
phenol, m-methylphenol, and phenol). The reactivity of vari-
ous phenols for the Pechmann reaction has already been
reported.12
lytic activity of the SiO –MSA. This effect was explained on
2
the basis of increasing nonpolar behavior of the n-alkanes
with increasing chain length. The longer chain n-alkane mol-
ecules (n-hexadecane and n-octadecane) have strong van der
Waals interactions, which does not allow the polar reactant
molecules to stay in the bulk of the solvent. This forces the
reactant molecules to come out from the bulk of n-alkane to-
Regeneration study of spent SiO2–MSA
The spent catalyst, recovered from the reaction mixture (in
n-octadecane) was regenerated by washing with methanol
Published by NRC Research Press

Joshi et al.
669
Table 3. Yield (wt %) of 4-methylcoumarin derivatives synthesized by the Pechmann
reaction using SiO2 – methanesulfonic acid (MSA) catalyst.
Phenol
4-Methyl coumarin derivative
Isolated yield (wt%)a
a
Phenol substrate (10 mmol), ethyl acetoacetate (20 mmol), n-octadecane (3 mL; solvent), catalyst
(
0.25 g), 160 °C, 2 h.
Table 4. Regeneration study of spent SiO2 – methanesulfonic acid
MSA) catalyst.
(
2 × 10 mL) then with petroleum ether (10 mL), followed by
(
drying at 120 °C for 2 h (see Supplementary data, Fig. S3).
The regenerated catalyst was reused for three cycles under
similar reaction conditions as with fresh catalyst. The regen-
erated catalysts showed similar activity to fresh catalyst giv-
ing 94%–96% yield (Table 4). The CHNS/O elemental
analysis of regenerated catalyst showed a slight loss of
MSA, giving 984 µmol MSA/g catalyst (Table 4).
Reaction
cycle
Yield (wt %) of 7-hydroxy- Amount of MSA
4-methylcoumarina
b
(NMSA, µmol/g)
Fresh catalyst 99
1000
—
I
97
96
94
II
III
—
984
In conclusion, a cost-effective, efficient, and reusable
2
a
Phenol substrate (10 mmol), ethyl acetoacetate (20 mmol), n-octadecane
SiO –MSA solid acid catalyst was synthesized and used for
(3 mL, solvent), catalyst (0.25 g), 160 °C, 2 h.
b
the synthesis of 4-methylcoumarin derivatives by the Pech-
mann reaction. The higher n-alkanes were used as nonpolar
solvents for the Pechmann reaction and found to be the best
alternative to conventional nonpolar solvents.
Calculated from sulfur wt % obtained by CHNS/O analysis.
Published by NRC Research Press

670
Can. J. Chem. Vol. 89, 2011
(
(
12) Tyagi, Y. K.; Kumar, A.; Raj, H. G.; Vohra, P.; Gupta, G.;
Supplementary data
Supplementary data are available with the article through
the journal Web site (www.nrcresearchpress.com/cjc).
Kumari, R.; Kumar, P.; Gupta, R. K. Eur. J. Med. Chem. 2005
4
0 (4), 413. doi:10.1016/j.ejmech.2004.09.002.
13) Von Pechmann, H.; Duisberg, C. Ber. Dtsch. Chem. Ges. 1883
6 (2), 2119. doi:10.1002/cber.188301602117.
1
Acknowledgement
(
(
14) Russell, A.; Frye, J. R. Org. Synth. 1941 21, 22.
15) Woods, L. L.; Sapp, J. J. Org. Chem. 1962 27 (10), 3703.
doi:10.1021/jo01057a519.
The authors are thankful to H.M. Desai, Vice-Chancellor,
Dharmsinh Desai University (DDU), Gujarat, India, for pro-
viding necessary facilities and Professor D.O. Shah, Found-
ing Director, Shah-Schulman Center for Surface Science and
Nanotechnology (SSCSSN), DDU, for valuable technical dis-
cussions. They are also thankful to Shimadzu Application
Lab, Mumbai, for thermal analysis and to CSMCRI, Bhavna-
gar, for NMR analysis.
(
(
(
(
(
16) Sugino, T.; Tanaka, K. Chem. Lett. 2001 30 (2), 110. doi:10.
1
246/cl.2001.110.
17) Smitha, G.; Sanjeeva Reddy, Ch. Synth. Commun. 2004 34
21), 3997. doi:10.1081/SCC-200034821.
18) Wang, L.; Xia, J.; Tian, H.; Qian, C.; Ma, Y. Int. J. Chem. B
003 42, 2097.
(
2
19) Sabou, R.; Hoelderich, W. F.; Ramprasad, D.; Weinand, R. J.
Catal. 2005 232 (1), 34. doi:10.1016/j.jcat.2005.02.002.
20) Hoefnagel, A. J.; Gunnewegh, E. A.; Downing, R. S.; van
Bekkum, H. J. Chem. Soc. Chem. Commun. 1995 (2): 225.
doi:10.1039/c39950000225.
References
(
1) Ge, F.-Y.; Yan, X.-L.; Yan, F.-Y.; Pan, H.-Y.; Chen, L.-G. J.
Fluoresc. 2005 15 (6), 829. doi:10.1007/s10895-005-0016-1.
2) Luong, B. X.; Petre, A. L.; Hoelderich, W. F.; Commarieu, A.;
Laffitte, J.-A.; Espeillac, M.; Souchet, J.-C. J. Catal. 2004 226
(
(21) Li, T.-S.; Zhang, Z.-H.; Yang, F.; Fu, C.-G. J. Chem. Res. (S)
1998, 38. doi:10.1039/a703694i.
(
2), 301. doi:10.1016/j.jcat.2004.05.025.
(22) Tyagi, B.; Mishra, M. K.; Jasra, R. V. J. Mol. Catal. A: Chem.
2007 276 (1–2), 47. doi:10.1016/j.molcata.2007.06.003.
(23) Selvakumar, S.; Chidambaram, M.; Singh, A. P. Catal.
Commun. 2007 8 (5), 777. doi:10.1016/j.catcom.2006.08.
039.
(24) Gopalakrishnan, S.; Viswanathan, K. R.; Vishnu Priya, S.;
Herbert Mabel, J.; Palanichamy, M.; Murugesan, V. Micro-
porous Mesoporous Mater. 2009 118 (1–3), 523. doi:10.1016/
j.micromeso.2008.09.030.
(
(
(
3) Zinin, A. I.; Malysheva, N. N.; Shpirt, A. M.; Torgov, V. I.;
Kononov, L. O. Carbohydr. Res. 2007 342 (3–4), 627. doi:10.
1
4) de Angelis, A.; Flego, C.; Ingallina, P.; Montanari, L.; Clerici,
M. G.; Carati, C.; Perego, C. Catal. Today 2001 65 (2–4), 363.
doi:10.1016/S0920-5861(00)00592-7.
016/j.carres.2006.10.009.
5) Chidambaram, M.; Curulla-Ferre, D.; Singh, A. P.; Anderson,
B. G. J. Catal. 2003 220 (2), 442. doi:10.1016/S0021-9517
(
03)00282-3.
(25) Reddy, B. M.; Reddy, V. R.; Giridhar, D. Synth. Commun.
2001 31 (23), 3603. doi:10.1081/SCC-100107007.
(26) Laufer, M. C.; Hausmann, H.; Hölderich, W. F. J. Catal. 2003
218 (2), 315. doi:10.1016/S0021-9517(03)00073-3.
(27) Palaniappan, S.; Shekhar, R. C. J. Mol. Catal. A: Chem. 2004
209 (1–2), 117. doi:10.1016/j.molcata.2003.08.006.
(28) Gregg, S. J.; Sing, K. S. W. Adsorption Surface Area and
Porosity, 2nd ed.; Academic Press: New York, 1982.
(29) Khandekar, A. C.; Khadilkar, B. M. Synlett 2002 (01), 0152.
doi:10.1055/s-2002-19332.
(
(
6) Pizzio, L. R. Mater. Lett. 2006 60 (29–30), 3931. doi:10.1016/
j.matlet.2006.07.190.
7) Bennardi, D. O.; Romanelli, G. P.; Autino, J. C.; Pizzio, L. R.
Appl. Catal., A: Gen. 2007 324, 62. doi:10.1016/j.apcata.2007.
0
3.009.
(
(
8) Bennardi, D. O.; Romanelli, G. P.; Autino, J. C.; Pizzio, L. R.
Catal. Commun. 2009 10 (5), 576. doi:10.1016/j.catcom.2008.
1
9) Díez, V. K.; Apesteguía, C. R.; Di Cosimo, J. I. Catal. Today
0.040.
2
010 149 (3–4), 267. doi:10.1016/j.cattod.2009.09.016.
(30) Sharma, G. V. M.; Reddy, J. J.; Lakshmi, P. S.; Krishna, P. R.
Tetrahedron Lett. 2005 46 (36), 6119. doi:10.1016/j.tetlet.
2005.06.166.
(31) Kemp, W. Organic Spectroscopy, 2nd ed.; ELBS/Macmillan:
London, 1987.
(
(
10) Harmer, M. A.; Junk, C.; Rostovtsev, V.; Carcani, L. G.;
Vickery, J.; Schnepp, Z. Green Chem. 2007 9 (1), 30. doi:10.
1
11) Murray, R. D. H.; Mendez, J.; Brown, S. A. The Natural
Coumarins: Occurrence, Chemistry and Biochemistry; Wiley:
New York, 1982.
039/b607428f.
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