Synthesis of substituted coumarins catalyzed by sawdust-SO3H. An efficient and environmentally benign solid acid catalyst under solvent-free conditions

Article abstract of DOI:10.1134/S1070363215090182

The sulfonated sawdust (SD-SO₃H) was easily prepared by treatment of sawdust, a biomass waste material, with chlorosulfonic acid and characterized by elemental analysis, SEM and TGA. The bio-degradable solid acid catalyst has been applied to the Pechmann condensation reaction of phenols with β-ketoesters for the synthesis of coumarin derivatives under solvent-free conditions. This environmentally benign and inexpensive method has such advantages as simplicity in operation, high yields, low catalyst loading and short reaction time. The catalyst can be efficiently recycled with insignificant loss of activity.

Full text of DOI:10.1134/S1070363215090182

ISSN 1070-3632, Russian Journal of General Chemistry, 2015, Vol. 85, No. 9, pp. 2135–2140. © Pleiades Publishing, Ltd., 2015.
Synthesis of Substituted Coumarins Catalyzed
by Sawdust-SO H. An Efficient and Environmentally
Benign Solid Acid Catalyst under Solvent-Free Conditions
3
1
a
b
E. Tahanpesar and L. Sarami
a
Department of Chemistry, College of Science, Ahvaz Branch, Islamic Azad University, Ahvaz, 61349-37333 Iran
e-mail: Etahanpesar@iauahvaz.ac.ir
b
Department of Chemistry, College of Science, Marvdasht Branch, Islamic Azad University, Marvdasht, 73711-13119 Iran
Received May 24, 2015
3
Abstract—The sulfonated sawdust (SD-SO H) was easily prepared by treatment of sawdust, a biomass waste
material, with chlorosulfonic acid and characterized by elemental analysis, SEM and TGA. The bio-degradable
solid acid catalyst has been applied to the Pechmann condensation reaction of phenols with β-ketoesters for the
synthesis of coumarin derivatives under solvent-free conditions. This environmentally benign and inexpensive
method has such advantages as simplicity in operation, high yields, low catalyst loading and short reaction
time. The catalyst can be efficiently recycled with insignificant loss of activity.
3
Keywords: coumarin, sawdust-SO H, Pechmann condensation, solvent free conditions, recyclable catalyst
DOI: 10.1134/S1070363215090182
INTRODUCTION
suitable for certain synthetic applications, some of the
procedures are associated with certain disadvantages
such as high cost, involvement of corrosive reagents
and long reaction time.
Coumarins are important oxygen containing fused
heterocyclic compounds found in nature that have been
used in food and cosmetic industry [1] and possess
biological activities such as antitumor [2],
antimicrobial [3] and anticancer [4]. There are several
methods of their synthesis such as Perkin [5],
Knoevenagel [6, 7], Reformatsky [8], Pechmann [9],
and Wittig [10] reactions that involve acidic as well as
basic catalysts. However, the Pechmann condensation
is one of the simplest and most popular procedures for
synthesis of coumarins due. It involves the reaction of
phenols with β-ketoesters that leads to 4-substituted
coumarins. In a typical procedure the mineral acids
such as sulfuric [11], polyphosphoric [12], and Lewis
The lignocellulose waste material such as wood
sawdust, a waste by-product of the timber industry, is
one of the most abundant materials in the world that
has low or no economic value as it is. It contains
cellulose, hemicelluloses and lignin that have big
number of available reactive functional groups:
hydroxyl, phenolic and carboxylic.
As the development of our earlier studies on
modified sawdust [26, 27] we report here an efficient
and simple procedure for the preparation of substituted
coumarins via the Pechmann condensation using
sawdust sulfonic acid under solvent free conditions
(
InCl [13], ZrCl [14]) were used as catalysts. In the
3 4
Pechmann condensation a number of solid acids have
been used including Alumina sulfuric acid (ASA) [15],
Nafion-H [16], poly(4-vinylpyridinium)hydrogen
sulfate [17], H SO /silica gel [18], Amberlyst-15 [19],
(
Scheme 1). The sulfonated sawdust (SD-SO H) can
3
be easily prepared by treatment of sawdust with
chlorosulfonic acid.
2
4
succinimide-N-sulfonic acid [20], montmorillonite clay
RESULTS AND DISCUSSION
[
[
21], melamine trisulfonic acid [22], zeolite H-BEA
23], modified zirconia [24], and most recently
The product of the sawdust-SO H treatment by
3
In(OTf)3 [25]. Although the above methods are
chlorosulfonic acid was characterized by SEM, TGA
and elemental analysis. The total acid site of SD–SO H
was 4.8 mmol/g as determined by titration (NaOH).
3
1
The text was submitted by the authors in English.
2
135

2
136
TAHANPESAR, SARAMI
3
Scheme 1. Synthesis of coumarins catalyzed by SD-SO H under solvent-free conditions.
SO
3
H
3
SO H
3
SO H
3
SO H
3
SO H
SO
O
3
H
3
SO H
OH
O
Sawdust-SO H
O
O
3
+
Me
OEt
Solvent-free
R
R
Me
7
0−98%
Elemental analysis indicated high sulfur content
6.0 mmol/g). According to the above methods data
most of sulfur containing species on the surface of
(Table 2, entries 2–4), while some solvents demon-
strated no inefficiency (Table 2, entries 5–7). It was
determined that the condensation of α-naphtol 1 with
ethyl acetoacetate 2 proceeded the most efficient way
(
samples were in the form of SO H.
3
under solvent free conditions, catalysis by SD-SO H
3
The catalytic performance of SD-SO H in the
3
(
0.05 g) at 110°C (Table 2, entry 9). Similar conditions
Pechmann condensation of coumarins was tested
initially in the reaction of α-naphtol 1 with ethyl
acetoacetate 2 (Table 1) for optimization of the process
were applied to various phenols with ethyl acetoacetate
and led to good or high yields of the corresponding
coumarins (Table 3, compounds 3a–3j).
conditions. The most efficient amount of SD-SO H
3
that led to 72% yield was 0.05 g.
The plausible mechanism of formation of 7-hyd-
roxy-4-methylcoumarin (3a) consists of activation of
The following reaction was carried out with the
optimum amount of the catalyst in various solvents and
at different temperatures. The reaction proceeded
efficiently under solvent-free conditions (Table 2,
entry 1). The processes carried out in the media of
CHCl , CH CN or CH Cl did not give high yields
Table 2. Effect of solvents and temperature on the synthesis
a
of product 3i
Entry
Solvent
–
T, ºC
90
Time, min
75
Yield, %
3
3
2
2
1
2
3
4
5
6
7
8
9
72
35
10
20
0
CHCl
3
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
70
200
200
200
200
200
200
120
25
Table 1. Influence of SD-SO
the yield of product 3i
3
H catalyst concentration on
a
CH
CH
3
2
CN
Cl
Entry Catalyst, g
T, ºC
Time, min Yield, %
2
THF
MeOH
1
2
3
4
5
6
–
90
90
90
90
90
90
120
120
75
0
0
0.025
0.05
0.075
0.1
40
72
70
60
60
H
2
O
–
0
70
91
92
120
120
120
–
110
1
0
–
130
25
0.15
a
a
Solvent-free reaction of α-naphtol (1 mmol) with ethyl aceto-
Reaction of α-naphtol (1 mmol) with ethyl acetoacetate
acetate (1 mmol).
(1 mmol). The catalyst amount: 0.05 g.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 9 2015

SYNTHESIS OF SUBSTITUTED COUMARINS CATALYZED
2137
Table 3. Coumarins and their synthesis data. Reaction conditions: solvent-free and SD-SO
3
H catalysis at 110ºC
a
Comp. no.
Phenol
Product
O
Time, min Yield, %
mp, ºC
3
a
HO
O
185–187
186–187 [28]
HO
OH
9
98
CH3
O
O
3
b
82–84
83–84 [29]
OH
6
5
70
95
CH3
3
c
CH3
259–264
264 [30]
CH3
6
HO
HO
O
O
O
HO
HO
OH
OH
CH3
O
3
d
257–259
257–258 [31]
1
0
94
OH CH3
O
CH3
3
e
O
165–167
165 [32]
OH
OH
OH
2
1
5
5
91
92
MeO
HO
MeO
HO
CH3
3
f
O
O
O
283–284
280–283 [33]
OH CH3
O
OH
OH
3
3
g
239–240
241–242 [34]
2
2
0
5
90
87
HO
HO
HO
CH3
OH
h
245–247
254–255 [35]
HO
O
O
OH
CH3
O
3
i
154–155
153–155 [36]
OH
2
5
91
O
CH3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 9 2015

2
138
TAHANPESAR, SARAMI
Table 3. (Contd.)
a
Comp. no.
Phenol
Product
H C
Time, min Yield, %
mp, ºC
O
3
j
3
184–187
183–184 [29]
OH
2
5
88
O
a
Yields upon recrystallization.
the carbonyl group of ethyl acetoacetate by the
catalyst can be recycled and used efficiently in three
and more cycles. Upon completing the model reaction
the catalyst was filtered off, washed with dichloro-
methane and reused after drying at 50ºC for 4 h. The
Brønsted acid sites of the catalyst (SD-SO H) leading
3
to the formation of 1. The nucleophilic attack of 1 by
resorcinol gives the intermediate 2 which rapidly
undergoes cyclization via intramolecular condensation
forming 3a via the Pechmann condensation (Scheme 2).
fresh SD-SO H catalyst led to the yield 91% of the
3
product 3i, upon recovery the catalyst gave the yields
of 89, 87, and 87% respectively in three subsequent
cycles.
Comparison of catalytic activity of SD-SO H with
3
several other catalysts in the synthesis of 7-hydroxy-4-
methyl coumarin 3a via the Pechmann condensation
EXPERIMENTAL
(
Table 4) exhibited some technological and econo-
mical advantages of the former system.
All chemicals were commercially available and
used without further purification. The reactions were
monitored by TLC and the yields refer to the isolated
According to our study of SD-SO H in the reaction
3
of α-naphtol with ethyl acetoacetate at 110ºC the
Scheme 2. The plausible mechanism of formation of 7-hydroxy-4-methylcoumarin 3a.
Sawdust
O SO H
3
Me
O
O
O
HO
O
3
a
Me
OEt
H O
2
H
O
O
Me OH
Me
OEt
1
HO
O
O
OH
Me
O
OH
EtOH
OH
OEt
H
HO
OH
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 9 2015

SYNTHESIS OF SUBSTITUTED COUMARINS CATALYZED
2139
Table 4. Comparison of catalytic activity of SD-SO
some other catalysts
3
H with
experimental details are available online as the Sup-
plementary Materials of this paper.
T, Time, Yield,
General procedure for substituted coumarins. A
well stirred mixture of a phenol derivative (1.0 mmol),
Catalyst
References
ºC
min
%
a
ethyl acetoacetate (1.2 mmol) and SD-SO H (0.05 g,
1
SD-SO
3
H
110
9
98 This work
3
0
.24 mmol) was heated at 110°C under solvent-free
conditions. Upon completion of the reaction, as
2
3
4
5
6
7
8
m-ZrP
SCZ
160 240
120 143
94
87
98
95
87
97
95
[37]
[38]
[32]
[39]
[40]
[41]
[42]
indicated by TLC, CHCl was added and the catalyst
3
was filtered off. The filtrate was evaporated and the
residue purified by recrystallization from ethanol to
give the corresponding pure product. Melting points
ASA
100
130
30
20
42
CMK-5-SO
3
H
1
and H NMR spectra of the products were compared
H
6
P
2
W
18
O
62·24H
2
O 130
with and matched well the reference data.
b
Zeolite- E4a
HClO ·SiO
110 180
130 35
CONCLUSIONS
4
2
a
Various substituted coumarins were synthesized
with high yield and purity by condensation of different
phenols with ethyl acetoacetate (the Pechmann
condensation) under solvent free conditions using SD-
Reaction condition: resorcinol (1 mmol), ethyl acetoacetate
1 mmol) and a catalyst (0.05 g) without a solvent.
Toluene as solvent.
(
b
SO H as a heterogeneous, green, highly efficient,
3
recyclable, and inexpensive catalyst.
products. Melting points were measured on an Electro-
thermal apparatus and the elemental analysis was
performed with an Elementar Analysensysteme GmbH
ACKNOWLEDGMENTS
1
VarioEL CHNS mode. The H NMR spectra were
This work was supported by Ahvaz Branch and
Marvdasht Branch, Islamic Azad University.
measured on a Bruker DRX-400Avance spectrometer
using TMS as internal standard. Scanning electron
microphotographs (SEM) were obtained on a LEO
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