Introduction of titania sulfonic acid (TiO2-SO3H) as a new, efficient, and reusable heterogenous solid acid catalyst for the synthesis of biscoumarins

Article abstract of DOI:10.1080/10426507.2013.858254

Titania sulfonic acid (TiO₂-SO₃H) is easily prepared by the reaction of TiO₂ with neat chlorosulfonic acid and characterized using a variety of techniques, including infrared, X-ray diffraction, Brunauer-Emmett-Teller, sca

Full text of DOI:10.1080/10426507.2013.858254

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Phosphorus, Sulfur, and Silicon and the Related
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INTRODUCTION OF TITANIA SULFONIC ACID [TiO -SO H]
2
3
AS A NEW, EFFICIENT AND REUSABLE HETEROGENOUS
SOLID ACID CATALYST FOR THE SYNTHESIS OF
BISCOUMARINS
a
a
a
Farhad Shirini , Masoumeh Abedini & Seddigheh Abroon Kiaroudi
a
Department of Chemistry, College of Science , University of Guilan , Rasht , 41335 , Iran
Accepted author version posted online: 26 Feb 2014.
To cite this article: Farhad Shirini , Masoumeh Abedini & Seddigheh Abroon Kiaroudi (2014): INTRODUCTION OF TITANIA
SULFONIC ACID [TiO -SO H] AS A NEW, EFFICIENT AND REUSABLE HETEROGENOUS SOLID ACID CATALYST FOR THE SYNTHESIS OF
2
3
BISCOUMARINS, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI: 10.1080/10426507.2013.858254
To link to this article: http://dx.doi.org/10.1080/10426507.2013.858254
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ACCEPTED MANUSCRIPT
INTRODUCTION OF TITANIA SULFONIC ACID [TiO -SO H] AS A NEW,
2
3
EFFICIENT AND REUSABLE HETEROGENOUS SOLID ACID CATALYST FOR THE
SYNTHESIS OF BISCOUMARINS
Farhad Shirini*, Masoumeh Abedini, Seddigheh Abroon Kiaroudi
Department of Chemistry, College of Science, University of Guilan, Rasht 41335,
Iran. E-Mail: shirini@guilan.ac.ir; Fax: +98 131 3220066
Abstract: Titania sulfonic acid [TiO -SO H (TSA)] is easily prepared by the reaction of TiO
2
2
3
with neat chlorosulfonic acid and characterized using a variety of techniques including IR, XRD,
BET, SEM, pH analysis and Hammett acidity function. This reagent can be used as an efficient
and reusable solid acid catalyst for the promotion of the synthesis of biscoumarin derivatives in
water. All reactions are performed under completely heterogeneous reaction conditions in
excellent yields during acceptable reaction times.
Ar
OH
O
OH
O
OH
O
TiO -SO H (60 mg)
2
3
2
ArCHO
+
o
H O, 80 C
2
O
OO
Keywords: TiO ; Titania sulfonic acid (TSA); Solid acid, Biscoumarins; Reusable catalyst.
2
1
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Introduction
Biscoumarins are a large group of heterocycles with diverse and interesting biological and
pharmaceutical activities such as antifungal, anti-HIV, anticancer, antithrombotic, anticoagulant,
[
1-3]
[4]
[5]
antimicrobial and antioxidant
activities.
urease inhibitory, cytotoxicity and enzyme inhibitory
In recent years, and because of these important activities, several methods have been reported
[
6-18]
for the synthesis of biscoumarins using of a variety of catalysts and reagents.
However,
many of these methods suffer from disadvantages such as long reaction times (e.g., in the case of
[
4]
[14]
piperidine and SDS
the products were obtained after 3-4 h), unsatisfactory yields (e.g., in
[
9]
the presence of HBF the reaction was completed at 10-12 h in 55-70 % yields ), harsh reaction
4
conditions, expensive reagents, hazardous and toxic solvents or catalysts (e.g., I is a toxic
2
[
6]
[17,18]
catalyst and some of these methodologies were carried out in refluxing toluene
)
and
tedious work-up. Therefore, introduction of efficient and economical catalysts that solves these
drawbacks is desirable.
Very recently, the use of TiO , and its modified derivatives have became an important part of
2
[
19-21]
our ongoing research program.
Herein, and in continuation of these studies, we wish to
report the preparation and characterization of titania sulfonic acid (TSA) and its applicability in
the promotion of the synthesis of biscoumarins. All reactions were performed in water with
acceptable reaction times in good to high yields.
Results and Discussion:
TSA is easily prepared via the addition of ClSO H to a suspension of powdered TiO in dry
3
2
CHCl (as indicated in the experimental section). After preparation of the catalyst its structure is
3
2
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characterized using different types of methods including IR, XRD, BET, SEM, pH analysis and
Hammett acidity function. This information suggested to us that TSA can be used as an efficient
catalyst for the promotion of the reactions which need the use of an acidic catalyst. So we were
interested to investigate the applicability of the reagent in the promotion of the synthesis of
biscoumarins.
In order to optimize the reaction conditions, at first, the prepared catalyst was used for the
promotion of the condensation of 4-chlorobenzaldehyde with 4-hydroxycoumarin and compared
the effect of different solvents and solvent-free conditions and also the effect of the catalyst load
on the reaction yield and time at thermal conditions. The results are shown in Tables 1 and 2. On
the basis of these results it can be concluded that the best result can be obtained under the
conditions showed in Scheme 1. It is important to note that using lower amounts of the catalyst
resulted in lower yields of the products in longer reaction times.
[
Insert Table 1 here]
[
Insert Table 2 here]
To assess the efficiency of TSA in the preparation of biscoumarines derivatives, a wide range
of aromatic, aliphatic and heterocyclic aldehydes were reacted with 4-hydroxycoumarin under
the optimal reaction conditions and the results obtained are tabulated in Table 3.
It was observed that under the selected conditions, aromatic aldehydes containing electron-
withdrawing groups as well as electron-donating groups were easily reacted in short reaction
times with good to excellent isolated yields (Table 3, entries 1-15).
3
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It is important to note that the reaction conditions were mild enough to induce any damage to
the substrates containing acid sensitive functional groups (Table 3, entries 9-11). α,β-Unsaturated
aldehydes were also reacted in high yield using this procedure without by-products (Table 3,
entries 16,17).
[
Insert Table 3 here]
In continuation, we decided to study the catalytic activity of the recycled catalyst for the
synthesis of biscoumarin derivatives. We have found that TSA is a very stable catalyst and can
be recycled by filtration, washing with CH Cl and acetone and drying at 70 °C. For the reaction
2
2
of 4-hydroxycoumarin with 4-nitrorobenzaldehyde, even after six cycles, the catalyst still has
excellent yields of products (Fig. 1). It implied that TSA can be reused without significant
decrease in its activatiy. Further pH analysis of the recovered catalyst showed loading of 0.009
+
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.
[
10,12, 17,18, 25]
A plausible mechanism for this reaction may proceed as depicted in Scheme 2.
To illustrate the efficiency of the present method, Table 4 compares our results using TSA
with the same results reported in the literature.
It is important to note that, some of these methods are performed in toxic solvent or reagents
(Table 4, entry 5, 9, 10) or they need larger amounts of the catalyst for completion (Table 4,
entries 1,4,8). When the reaction is carried out in water (Table 4, entry 7), although the catalyst is
not used, the reaction time is longer than the present method. It is interesting to note that, to
4
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compare the applicability and efficiency of TSA with the other catalysts, we have tabulated the
TOF (Turnover Frequency) of these catalysts in this type of reactions. As it is clear TSA is
superior in terms of TOF to the compared catalysts.
[
Insert Table 4 here]
In conclusion, we have introduced TSA as a highly efficient and reusable catalyst for the
synthesis of biscoumarine derivatives. This method has several advantages such as: ease of
preparation and handling of the catalyst, simplicity and easy work-up, use of green solvent, high
reaction rates and excellent yields. Also, the recovered catalyst could be reused several times
without significant decrease in its activity.
EXPERIMENTAL
General: Chemicals were purchased from Fluka, Merck and Aldrich chemical companies. All
yields refer to the isolated products. Products were characterized by their physical constants and
comparison with authentic samples. The purity determination of the substrate and reaction
monitoring were accompanied by thin layer chromatography (TLC) on silica-gel polygram
SILG-UV 254 plates.
Instrumentation: The FT-IR spectra were run on a VERTEX 70 Bruker company (Germany)
spectrometer. Wide-angle X-ray diffraction (XRD) measurements were performed at room
temperature on a Philips PW 1820 diffractometer using Ni-filtered Co-Kα radiation (λ=0.15418
nm). N physisorption at liquid nitrogen temperature using a SHIBATA APP. SA-1100 surface
2
area analyzer and standard multipoint BET analysis methods were carried out. Samples were
◦
degassed in flowing N for 2h at 250 C before N physisorption measurements were obtained.
2
2
1
13
The H NMR (400 MHz) and C NMR (100 MHz) were run on a Bruker Avance DPX-400 FT-
5
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NMR spectrometer (δ in ppm). Scanning election microphotographs (SEM) were obtained on a
SEM-Philips XL30.
Preparation of titania sulfonic acid (TSA) and determination of its components:
Chlorosulfonic acid (0.3 mL, 13.2 mmol) was added to a suspension of powdered TiO (0.5 g
2
anatase, it has a particle size of -325 mesh), in dry CHCl (15 mL) over a period of 5 min while
3
the mixture was stirred slowly in an ice bath. After, the mixture was stirred for 2 h at room
temperature. Then, CHCl was removed under reduced pressure and the solid powder was
3
washed with methanol (10 mL) and dried at 70 °C. TSA was obtained as a white solid powder
which was stored in a capped bottle (Scheme 3). [Note: At the first step and for optimization of
the amounts of chlorosulfonic acid in the preparation of the more efficient catalyst, three samples
of TSA were prepared using different amounts of ClSO H (0.11 mL, 0.3 mL and 2.2 mL
3
respectively). In order to examine the efficiency of the obtained catalysts, the reaction of 4-
hydroxycoumarin and 4-chlorobenzaldehyde was investigated in the presence of them. All
reactions were run under the same conditions, and similar amounts of the catalysts (60 mg) were
used. As shown in Table 5, satisfactory results were obtained using the catalyst prepared from
the reaction of 0.3 mL (13.2 mmol) ClSO H with 0.5 g TiO .
3
2
[
Insert Table 5 here]
Characterization of the catalyst
IR analysis: The infrared spectra of TiO and TSA are presented in Fig. 2 In the case of TiO ,
2
2
−
1
the peaks at ca. 3427 and 1631 cm corresponded to the -OH stretching vibration of the
[
20]
adsorbed water on TiO2. The spectrum of TSA displays almost the same peaks at 3421 and
6
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−
1
-1
1
630 cm for the adsorbed water. Also bands in 1261, 1093 and 1027 cm are assigned to the
[
22]
asymmetric and symmetric S=O stretching bending vibrations, respectively. This result shows
modification of TiO using chlorosulfonic acid.
2
Powder X-ray diffraction: The powder XRD patterns of TiO and TSA are shown in Fig. 3. It
2
seems that the peak intensities of TiO and TSA are almost same and the peaks remained intact
2
under the conditions used for modification. These results indicate that mesoporosity of the
support remains intact after modification.
Surface area and pore distribution measurements: N adsorption measurements, which have
2
been a powerful tool for mesoporous material characterization, were performed to obtain more
insights into the modified porous materials. The textural properties of TiO were substantially
2
maintained over chlorosulfonic acid functionalization. A slight decrease in surface area was
2
observed for TiO and TSA from 8.9 to7.9 m /g, respectively. This suggests that chlorosulfonic
2
acid may be well confined in the pores of TiO2.
SEM analysis: The SEM micrographs of TiO and TSA showed that with chemical modification
2
the primary structure of TiO was changed via the retardation of the aggregation of particles by
2
loaded ClSO H groups (Fig. 4).
3
7
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pH analysis of catalyst: To an aqueous solution of NaCl (1 M, 25 mL) with a primary pH 5.87,
TSA (500 mg) was added and the resulting mixture was stirred for 2 h after which the pH of
+
[23]
solution decreased to 3.66. This is equal to a loading of 0.011 mmol H /g.
Acidity of the catalyst: The acid strength of TSA was determined by the Hammett indicator
[
24]
method.
It can be calculated by the equation below:
H = pK(I) + log ( [I] / [IH ] )
+
0
aq
s
s
+
Where the pK(I) is the pK value of aqueous solution of indicator, [IH ] and [I] are the molare
aq
a
s
s
concentrations of protonated and un-protonated forms of the indicator in the solvent,
+
respectively. According to Lambert-Beer’s law, the value of [I] / [IH ] can be determined and
s
s
calculated through UV-visible spectrum.
For this purpose, 4-nitroaniline (pK(I) = 0.99) as the basic indicator, and CCl as the solvent
aq
4
were chosen. As can be seen in Fig. 5, the maximal absorbance of the unprotonated form of the
indicator was observed at 331 nm in CCl . When TSA, as a solid acid catalyst, was added to the
4
indicator solution, the absorbance of the unprotonated form of the indicator decreased, which
+
indicated that the indicator was partially in the form of [IH ]. The results obtained show the
acidity strength of TSA (Table 6).
[
Insert Table 6 here]
Synthesis of bis-(4-hydroxycoumarin-3-yl)methanes; General procedure: A mixture of the
aldehyde (1 mmol), 4-hydroxycoumarin (2 mmol) and TSA (60 mg, 0.066 mol%) in H O (3 mL)
2
was stirred at 80 °C for the appropriate time. After completion of the reaction (monitored by
8
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TLC) the mixture was cooled to room temperature and the solvent was evaporated. Then the
solid residue was dissolved in CH Cl (5 mL) and filtered to separate the catalyst. After
2
2
evaporation the residue was recrystallized from EtOH and water (95:5) to afford the pure
product.
ACKNOWLEDGEMENT
We are thankful to the University of Guilan Research Councils for the partial support of this
work.
9
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a
Table 1 The effect of different solvents on the model reaction.
Entry
Solvent
Time (min)
Conversion (%)
1
2
3
4
5
H O
EtOH
Solvent-free
n-Hexane
40
120
120
60
100
80
55
30
30
2
CH CN
60
3
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), 4-hydroxycoumarin (2 mmol), TSA (60
mg, 0.066 mol%), 80 °C.
Table 2 The effect of different amounts of TSA on the reaction of 4-chlorobenzaldehyde and 4-
a
hydroxycoumarin.
Entry
Catalyst (mg)
Time (min)
Conversion (%)
1
2
3
4
0
120
120
80
0
50
70
100
20
40
60
40
a
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), 4-hydroxycoumarin (2 mmol), 80 °C,
water.
1
2
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Table 3 Preparation of biscoumarines using TSA as the catalyst.
a
m. p. (°C)
Reported
Entry
Aldehydes
C H CHO
Time (min)
60
Yield (%)
80
[Ref.]
25]
Found
226-229
[
1
2
3
4
5
6
7
8
9
229-231
6
5
[
26]
4-ClC H CHO
40
98
248-250
220-221
200-202
263-266
232-233
231-233
196-198
248-250
232-234
252-254
217-218
222-225
249-252
215-218
226-228
190-193
182-185
263-265
270-272
250
6
4
[
25]
25]
3-ClC H CHO
35
98
221-223
201-203
264-266
6
4
[
2-ClC H CHO
60
97
6
4
[
7]
4-BrC H CHO
30
98
6
4
[
26]
4-NO C H CHO
10
98
230
229-231
2
6
4
[
7]
3-NO C H CHO
15
98
2
6
4
[
25]
25]
2-NO C H CHO
20
95
198-200
250-252
238-240
258-260
221-223
228-230
254-256
222-224
230-232
2
6
4
[
4-MeOC H CHO
40
98
6
4
[
7]
1
1
1
1
1
1
1
1
1
1
2
0
1
2
3
4
5
6
7
8
9
0
3-MeOC H CHO
55
95
6
4
[
[
[
[
[
[
28]
2-MeOC H CHO
30
95
6
4
14]
25]
23]
14]
12]
2-MeC H CHO
75
90
6
4
4-OHC H CHO
60
80
6
4
2-OHC H CHO
90
80
6
4
4-NMe C H CHO
50
95
2
6
4
Cinnamaldehyde
60
95
[
29]
2-Nitro cinnamaldehyde
PhCH CH CHO
20
95
190-19
[
4]
15
98
190
2
2
[
[
30]
30]
Pyridin-4-carbaldehyde
Pyridin-3-carbaldehyde
60
95
261-263
274-276
120
95
a
Isolated yield.
1
3
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Table 4 Comparison of our results with some of the other methods reported in the literature.
-
1
a
Entry
Catalyst (mol%)
Reaction conditions
Time (h)
Yield
%)
80-96
75-95
90-95
TOF(h )
[Ref.]
(
[
[
14]
29]
1
2
3
SDS (20)
H ꢀ, ꢁ0 C
ꢂ
2.5-3
0.42-0.58
0.25-0.5
1.9
2
RuCl . nH O (5)
H ꢀ, 80 C
ꢂ
40.5
73.1
3
2
2
Silica bonded N-
propylpiperazine sodium n-
propionates (5.2)
H O/EtOH, reflux
2
[
27]
[
9]
4
5
6
Tetrabutylammonium bromide
H ꢀ, 100 C
ꢂ
0.42-0.67
0.5-0.8
82-95
90-96
86-96
12.4
22.1
73.8
2
(
10)
[
18]
[P VPy-BuSO H]Cl-X(AlCl )
Toluene, ꢃ0 C
ꢂ
4
3
3
(
7)
[MIM(CH ) SO H][HSO ] (3)
ꢄolvent-free, 80
ꢂ
C
0.3-0.5
2
4
3
4
[
25]
[
[
31]
12]
7
8
9
On-water
Phosphotungstic acid (15)
H O, 90 C
ꢂ
4-5
0.23-0.42
10-12
0.33-0.53
0.17-2
93-98
90-98
55-70
91-99
80-98
----
18.8
0.55
20.7
2250
2
H ꢀ, 80 C
ꢂ
2
[
9]
HBF (10)
H O, 25 ꢂC
2
4
[
6]
1
1
0
1
I2 (10)
H ꢀ, 100 C
ꢂ
2
[
This work]
TiO -SO H (0.066)
H ꢀ, 80 Cꢂ
2
2
3
a:
Reaction of 4-chlorobenzaldehyde and 4-hydroxycoumarin.
Table 5 Comparison of the effect of different types of TSA on the model reaction.
Time (min)
Entry
Catalyst [ClSO H (mmol)]
Conversion (%)
3
1
2
TSA [4.8]
TSA [13.2]
TSA [96.8]
4
2
2
0
0
0
100
100
3
4
100
0
TiO [0]
20
2
Model reaction conditions: 4-hydroxycoumarin (2 mmol), 4-chlorobenzaldehyde (1 mmol),
catalyst (60 mg); 80 °C, water.
1
4
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Table 6 Calculation of the Hammett acidity function (H ) for TSA.
0
+
[
I] %
[IH ] %
Entry
Catalyst
--
Amax
s
s
H0
--
2
1
.4867
.2688
100
0
1
2
51.02
48.98
1
TSA
Condition for UV–visible spectrum measurement: Solvent: CCl , indicator: 4-nitroaniline (pK
4
−
4
(
I) = 0.99), 1.44×10 mol / L; Catalyst: TSA, 20 mg, 25 °C.
aq
Ar
OH
OH
O
OH
O
TSA (0.066 mol%)
2
ArCHO
+
o
H O, 80 C
2
O
O
O O
SCHEME 1
AH
HA
O
O
Ar
O
Ar
O
O
OH
O
O
-
H O
+
2
OH
+
Ar
H
H
O
O
O
OH
O
Ar
Ar
OH
OH
O
OH
O
O
O
OO
O
OO
HA= TiO -SO H
2
3
SCHEME 2
Neat ClSO H (0.3 mL, 13.2 mmol)
3
Dry CHCl (15 mL)
3
TiO2
TiO -SO H (TSA)
2 3
1)Ice bath
) 2 h, r.t.
(0.5 g)
2
SCHEME 3
1
5
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Fig. 1. Reusability of TSA.
Fig. 2. FT-IR spectra of TiO (A) and TSA (B).
2
1
6
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Fig. 3. XRD patterns of TiO (A) and TSA (B).
2
Fig. 4. SEM images of TiO (a) and TSA (b).
2
1
7
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Fig. 5. Absorption spectra of 4-nitroaniline (indicator) (A) and TSA (catalyst) (B) in CCl4.
1
8
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