# A Fast, Highly Efficient, and Green Protocol for Synthesis of Biscoumarins Catalyzed by Silica Sulfuric Acid Nanoparticles as a Reusable Catalyst

Authors: Bahareh Sadeghi; Tayebe Ziya
Journal: Journal of Chemistry
 (2013)

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## Abstract

Silica sulfuric acid nanoparticles have been prepared and shown to efficiently catalyse the reaction between an aromatic aldehyde or phenylglyoxal and a 4-hydroxycoumarin at reflux in EtOH to afford the biscoumarin derivatives in high yield.


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## Body

## 1. Introduction

A variety of biological activities are associated with coumarins and biscoumarins, for example, anticoagulants and antianthelmintic and antifungal activities [1–3]. Furthermore, these compounds can be complexed with rare earth metals as anti-HIV agents [4]. The synthesis of biscoumarins has been reported in the presence of piperidine [5], molecular iodine [6], tetrabutylammonium bromide [7], [bmim]BF4 [8], sodium dodecyl sulfate [9], SO3H-functionalized ionic liquid [10], and [MIM(CH2)4SO3H][HSO4] [11].In this paper, we report a simple and efficient method for synthesis of biscoumarin derivatives using different aromatic aldehydes and phenylglyoxals and 4-hydroxycoumarin in the presence of silica sulfuric acid nanoparticles under reflux in ethanol. The catalyst is recyclable with reproducible results without any loss of its activity. The morphology of the silica sulfuric acid nanoparticles was observed using a scanning electron microscope (SEM).


## 2. Experimental

### 2.1. General

IR spectra were recorded on a Shimadzu IR-470 spectrometer in KBr discs. The NMR spectra were obtained on a Bruker Avance DRX-500 FT spectrometer (1H NMR at 500 Hz, 13C NMR at 125 Hz) using CDCl3 as solvent with TMS as internal standard. Melting points were determined with an Electrothermal 9100 apparatus. Elemental analyses were performed using a Costech ECS 4010 CHNS-O analyzer at Analytical Laboratory of Science and Researches Unit of Islamic Azad University. The morphology of the catalyst was observed using an SEM model VEGA//TESCAN with an accelerating voltage of 15 kV. The chemicals used in this work were purchased from Sigma Aldrich and Fluka (Buchs, Switzerland) and were used without further purification.


### 2.2. Synthesis of   Silica Sulfuric Acid Nanoparticles

The reagent was prepared by combination of chlorosulfonic acid (23.3 g) drop by drop over 10 min via a syringe to nanosilica gel powder (60 g) in a 100 mL flask at 0°C. The reaction mixture was then stirred, and then after 30 min, the white powder was separated. The dimensions of nanoparticles were observed with SEM (Figure1). The size of particles is between 28 and 32 nm.Figure 1
The SEM images of SiO2-OSO3H NPs.


### 2.3. General Procedure for the Synthesis of Biscoumarin

A mixture of 4-hydroxycoumarin (2 mmol), aromatic aldehyde or arylglyoxal (1 mmol), SiO2-OSO3H NPs (0.003 g), and EtOH (5 mL) was placed in a round bottom flask. The materials were mixed and refluxed for 20 min. The progress of the reaction was followed by TLC (n-hexane:ethylacetate). After completion of the reaction, the mixture was filtered to remove the catalyst. By evaporation of the solvent, the crude product was recrystallized from hot ethanol to obtain the pure compound.


### 2.4. Selected Spectral Data

3,3′-Bis (4-hydroxy coumarin-3yl) (3-nitro-4-chlorophenyl) methane(4m). IR (KBr) νmax: 3450, 3015, 1664, 1603, 1561, 1348, 761 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.3 (s, 1H, CH), 7.27 (d, 2H, J=7.5 Hz, aromatic), 7.34 (d, 2H, J=8.2 Hz, aromatic), 7.48 (d, 1H, J=8.2 Hz, aromatic), 7.55–7.59 (m, 3H, aromatic), 7.79 (s, 1H, aromatic), 7.88 (d, 2H, J=7.7 Hz, aromatic), 12.3 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 36.9, 104.1, 116.8, 118.9, 122.6, 124.6, 131.7, 132.7, 133.3, 143.4, 148.5, 153.2, 165.2, 166.6 ppm. Anal. Calcd. For C25H14ClNO8: C, 61.03; H, 2.83; N, 2.83 Found: C, 61.02; H, 2.87; N, 2.85.3,3′-Bis (4-hydroxy coumarin-3yl) (2,4-dichlorophenyl) methane(4n). IR (KBr) νmax: 3485, 3085, 1664, 1603, 766 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.1 (s, 1H, CH), 7.26 (td, 2H, J=8.5 Hz, J=2 Hz, aromatic), 7.39 (td, 2H, J=6.1 Hz, J=2 Hz, aromatic), 7.41 (d, 2H, J=8Hz, aromatic), 7.43 (s, 1H, aromatic), 7.66 (td, 2H, J=8.5 Hz, J=1.3 Hz, aromatic), 8.05 (d, 2H, J=6.4Hz, aromatic), 11.68 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 31.9, 102.1, 114.2, 119.1, 121.4, 123.7, 130.3, 132.9, 133.3, 135.8, 143.5, 152.1, 165.9, 167.1 ppm. Anal. Calcd. For C25H14Cl2O6: C, 62.38; H, 2.93 Found: C, 62.32; H, 2.79.3,3′-Bis (4-hydroxy coumarin-3yl) (4-nitrophenyl) ethanon (5a). IR (KBr) νmax: 3355, 3015, 1696, 1664, 1547, 1357, 754 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.4 (s, 1H, CH), 7.34 (td, 2H, J=7.4 Hz, J=2 Hz, aromatic), 7.36 (m, 2H, aromatic), 7.58 (dd, 2H, J=7.4 Hz, J=2 Hz, aromatic), 7.78 (m, 2H, aromatic), 7.91 (d, 2H, J=8 Hz, aromatic), 8.29 (d, 2H, J=8 Hz, aromatic), 11.3 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 80.2, 104.1, 115.7, 119.2, 121.7, 124.2, 128.4, 130.2, 132.9, 142.1, 153.7, 158.2, 162.9, 167.2, 198.0 ppm. Anal. Calcd. For C26H15NO9: C, 64.33; H, 3.11; N, 2.88 Found: C, 64.21; H, 3.04; N, 2.85.3,3′-Bis (4-hydroxy coumarin-3yl) (4-bromophenyl) ethanon (5b). IR (KBr) νmax: 3335, 3085, 1696, 1648, 759 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.31 (s, 1H, CH), 7.24 (d, 2H, J=7.5 Hz, aromatic), 7.27 (d, 2H, J=8.3 Hz, aromatic), 7.5 (t, 2H, J=7 Hz, aromatic), 7.58 (d, 2H, J=8.5 Hz, aromatic), 7.71 (d, 2H, J=8.5 Hz, aromatic), 7.84 (d, 2H, J=7.5 Hz, aromatic), 10.41 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 80.0, 102.5, 116.7, 119.0, 121.6, 124.2, 124.7, 130.2, 132.0, 132.4, 153.1, 164.3, 167.2, 165.2, 196.5 ppm. Anal. Calcd. For C26H15BrO7: C, 60.13; H, 2.91 Found: C, 60.08; H, 2.89.3,3′-Bis (4-hydroxy coumarin-3yl) (phenyl) ethanon (5c). IR (KBr) νmax: 3405, 3015, 1692, 1637, 764 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.35 (s, 1H, CH), 7.29 (td, 2H, J=7.4 Hz, J=2 Hz, aromatic), 7.35 (m, 3H, aromatic), 7.47 (d, 2H, J=7.8 Hz, aromatic), 7.57 (m, 2H, aromatic), 7.71 (m, 2H, aromatic), 7.82 (d, 2H, J=8 Hz, aromatic), 10.41 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 80.3, 101.9, 115.5, 118.7, 121.0, 124.3, 129.7, 130.1, 131.8, 133.2, 136.2, 151.3, 161.8, 167.4, 194.2 ppm. Anal. Calcd. For C26H16O7: C, 70.9; H, 3.66 Found: C, 70.7; H, 3.59.


## 2.1. General

IR spectra were recorded on a Shimadzu IR-470 spectrometer in KBr discs. The NMR spectra were obtained on a Bruker Avance DRX-500 FT spectrometer (1H NMR at 500 Hz, 13C NMR at 125 Hz) using CDCl3 as solvent with TMS as internal standard. Melting points were determined with an Electrothermal 9100 apparatus. Elemental analyses were performed using a Costech ECS 4010 CHNS-O analyzer at Analytical Laboratory of Science and Researches Unit of Islamic Azad University. The morphology of the catalyst was observed using an SEM model VEGA//TESCAN with an accelerating voltage of 15 kV. The chemicals used in this work were purchased from Sigma Aldrich and Fluka (Buchs, Switzerland) and were used without further purification.


## 2.2. Synthesis of   Silica Sulfuric Acid Nanoparticles

The reagent was prepared by combination of chlorosulfonic acid (23.3 g) drop by drop over 10 min via a syringe to nanosilica gel powder (60 g) in a 100 mL flask at 0°C. The reaction mixture was then stirred, and then after 30 min, the white powder was separated. The dimensions of nanoparticles were observed with SEM (Figure1). The size of particles is between 28 and 32 nm.Figure 1
The SEM images of SiO2-OSO3H NPs.


## 2.3. General Procedure for the Synthesis of Biscoumarin

A mixture of 4-hydroxycoumarin (2 mmol), aromatic aldehyde or arylglyoxal (1 mmol), SiO2-OSO3H NPs (0.003 g), and EtOH (5 mL) was placed in a round bottom flask. The materials were mixed and refluxed for 20 min. The progress of the reaction was followed by TLC (n-hexane:ethylacetate). After completion of the reaction, the mixture was filtered to remove the catalyst. By evaporation of the solvent, the crude product was recrystallized from hot ethanol to obtain the pure compound.


## 2.4. Selected Spectral Data

3,3′-Bis (4-hydroxy coumarin-3yl) (3-nitro-4-chlorophenyl) methane(4m). IR (KBr) νmax: 3450, 3015, 1664, 1603, 1561, 1348, 761 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.3 (s, 1H, CH), 7.27 (d, 2H, J=7.5 Hz, aromatic), 7.34 (d, 2H, J=8.2 Hz, aromatic), 7.48 (d, 1H, J=8.2 Hz, aromatic), 7.55–7.59 (m, 3H, aromatic), 7.79 (s, 1H, aromatic), 7.88 (d, 2H, J=7.7 Hz, aromatic), 12.3 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 36.9, 104.1, 116.8, 118.9, 122.6, 124.6, 131.7, 132.7, 133.3, 143.4, 148.5, 153.2, 165.2, 166.6 ppm. Anal. Calcd. For C25H14ClNO8: C, 61.03; H, 2.83; N, 2.83 Found: C, 61.02; H, 2.87; N, 2.85.3,3′-Bis (4-hydroxy coumarin-3yl) (2,4-dichlorophenyl) methane(4n). IR (KBr) νmax: 3485, 3085, 1664, 1603, 766 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.1 (s, 1H, CH), 7.26 (td, 2H, J=8.5 Hz, J=2 Hz, aromatic), 7.39 (td, 2H, J=6.1 Hz, J=2 Hz, aromatic), 7.41 (d, 2H, J=8Hz, aromatic), 7.43 (s, 1H, aromatic), 7.66 (td, 2H, J=8.5 Hz, J=1.3 Hz, aromatic), 8.05 (d, 2H, J=6.4Hz, aromatic), 11.68 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 31.9, 102.1, 114.2, 119.1, 121.4, 123.7, 130.3, 132.9, 133.3, 135.8, 143.5, 152.1, 165.9, 167.1 ppm. Anal. Calcd. For C25H14Cl2O6: C, 62.38; H, 2.93 Found: C, 62.32; H, 2.79.3,3′-Bis (4-hydroxy coumarin-3yl) (4-nitrophenyl) ethanon (5a). IR (KBr) νmax: 3355, 3015, 1696, 1664, 1547, 1357, 754 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.4 (s, 1H, CH), 7.34 (td, 2H, J=7.4 Hz, J=2 Hz, aromatic), 7.36 (m, 2H, aromatic), 7.58 (dd, 2H, J=7.4 Hz, J=2 Hz, aromatic), 7.78 (m, 2H, aromatic), 7.91 (d, 2H, J=8 Hz, aromatic), 8.29 (d, 2H, J=8 Hz, aromatic), 11.3 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 80.2, 104.1, 115.7, 119.2, 121.7, 124.2, 128.4, 130.2, 132.9, 142.1, 153.7, 158.2, 162.9, 167.2, 198.0 ppm. Anal. Calcd. For C26H15NO9: C, 64.33; H, 3.11; N, 2.88 Found: C, 64.21; H, 3.04; N, 2.85.3,3′-Bis (4-hydroxy coumarin-3yl) (4-bromophenyl) ethanon (5b). IR (KBr) νmax: 3335, 3085, 1696, 1648, 759 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.31 (s, 1H, CH), 7.24 (d, 2H, J=7.5 Hz, aromatic), 7.27 (d, 2H, J=8.3 Hz, aromatic), 7.5 (t, 2H, J=7 Hz, aromatic), 7.58 (d, 2H, J=8.5 Hz, aromatic), 7.71 (d, 2H, J=8.5 Hz, aromatic), 7.84 (d, 2H, J=7.5 Hz, aromatic), 10.41 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 80.0, 102.5, 116.7, 119.0, 121.6, 124.2, 124.7, 130.2, 132.0, 132.4, 153.1, 164.3, 167.2, 165.2, 196.5 ppm. Anal. Calcd. For C26H15BrO7: C, 60.13; H, 2.91 Found: C, 60.08; H, 2.89.3,3′-Bis (4-hydroxy coumarin-3yl) (phenyl) ethanon (5c). IR (KBr) νmax: 3405, 3015, 1692, 1637, 764 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.35 (s, 1H, CH), 7.29 (td, 2H, J=7.4 Hz, J=2 Hz, aromatic), 7.35 (m, 3H, aromatic), 7.47 (d, 2H, J=7.8 Hz, aromatic), 7.57 (m, 2H, aromatic), 7.71 (m, 2H, aromatic), 7.82 (d, 2H, J=8 Hz, aromatic), 10.41 (broad s, 2H, OH) ppm. 13C NMR (125 MHz, CDCl3): δ 80.3, 101.9, 115.5, 118.7, 121.0, 124.3, 129.7, 130.1, 131.8, 133.2, 136.2, 151.3, 161.8, 167.4, 194.2 ppm. Anal. Calcd. For C26H16O7: C, 70.9; H, 3.66 Found: C, 70.7; H, 3.59.


## 3. Results and Discussion

In continuation of our investigations of the application of solid acids in organic synthesis [12–16], we have investigated the synthesis of biscoumarin derivatives by condensation of  a 4-hydroxycoumarin 1 and an aromatic aldehyde 2 or phenylglyoxals 3 in the presence of 0.003 g SiO2-OSO3H NPs catalyst.The stable silica gel nanoparticles are easily prepared [17] and used for preparation of catalyst (SiO2-OSO3H NPs).To optimize the reaction conditions, the reaction of benzaldehyde and 4-hydroxycoumarin was used as a model reaction. Initially, the catalytic activity of SiO2-OSO3H NPs has been compared with other catalysts, according to the obtained data, and this catalyst afforded good yields; however, it has limitations of long reaction time, harsh reaction conditions, and often expensive catalysts (Table 1, entry 1–6). In order to determine the optimum quantity of SiO2-OSO3H NPs, model reaction was carried out at reflux in ethanol condition (Table 1, entry 7–9). SiO2-OSO3H NPs (0.003 g) gave an excellent yield in 20 min (Table 1, entry 8). The previous reaction was also examined in various solvents. The best results were obtained when EtOH was used as a solvent at reflux (Table 1, entry 8). An interesting feature of this method is that the reagent can be regenerated at the end of the reaction and can be used several times without losing its activity. To recover the catalyst, after completion of the reaction, the mixture was filtered, and catalyst was washed with CHCl3, and then the solid residue dries. This process was repeated for two cycles, and the yield of product 4a did not change significantly (Table 1, entry 12, 13).Table 1
Synthesis of4a under various conditions.
Entry
Catalyst (amount)
Cond./Sol.
Time (min)
Yielda (%)
Reference
1
I2 (10 mol%)
100°C/H2O
25
97
[6]
2
TBABb (4 mol%)
120°C/—
20
85
[7]
3
[bmim]BF4 (4 mmol)
60–70°C/—
120
84
[8]
4
SDSc (0.2 mol, 57.6 mg)
60°C/H2O
140
90
[9]
5
[PSebim][OTf] (0.5 mol%)
70°C/—
120
95
[10]
6
[MIM(CH2)4SO3H][HSO4](3 mol%)
80°C/—
30
92
[11]
7
SiO2-OSO3H NPs (0.001 g)
80°C/EtOH
20
89
—
8
SiO2-OSO3H NPs (0.003 g)
80°C/EtOH
20
93
—
9
SiO2-OSO3H NPs (0.005 g)
80°C/EtOH
20
93
—
10
SiO2-OSO3H NPs (0.003 g)
100°C/H2O
20
87
—
11
SiO2-OSO3H NPs (0.003 g)
40°C/CH2Cl2
20
82
—
12
SiO2-OSO3H NPs (0.003 g), 2nd run
80°C/EtOH
20
89
—
13
SiO2-OSO3H NPs (0.003 g), 3rd run
80°C/EtOH
20
87
—
aIsolated yield, btetrabutylammonium bromide, and csodium dodecyl sulfate.To study the scope of the reaction, a series of aromatic aldehydes or phenylglyoxals and 4-hydroxycoumarin catalysed by SiO2-OSO3H NPs were examined (Scheme 1). The results are shown in Table 2. In all cases, aromatic aldehyde or phenylglyoxals substituted with either electron-donating or electron-withdrawing groups underwent the reaction smoothly and gave products in excellent yields.Table 2
SiO2-OSO3H NPs catalyzed the synthesis of biscoumarin derivatives.
Entry
Ar
Product
Yielda %
m.p./°C
Found
Reported[Ref]
1
C6H5
4a
93
228–230
229–231 [11]
2
4-BrC6H4
4b
86
266–268
265–267 [9]
3
4-FC6H4
4c
90
211–213
213–215 [9]
4
4-MeC6H4
4d
96
268–270
266–269 [11]
5
2-OHC6H4
4e
94
253–255
254–256 [11]
6
4-OHC6H4
4f
93
194–196
193 [5]
7
4-(CH3)2NC6H4
4g
92
221–223
222–224 [9]
8
3-NO2C6H4
4h
95
215–217
214-215 [11]
9
4-NO2C6H4
4i
96
233–235
233–235 [11]
10
3-ClC6H4
4j
91
222–224
221–223 [11]
11
4-ClC6H4
4k
95
262–264
261–263 [11]
12
3-Pyridyl
4l
88
279–281
278 [5]
13
3-NO2-4-ClC6H3
4m
92
249–252
—
14
2,4-ClC6H3
4n
89
198–200
—
15
4-NO2C6H4CO
5a
96
249–251
—
16
4-BrC6H4CO
5b
90
204–207
—
17
C6H5CO
5c
93
209–211
—
aIsolated yield.Scheme 1
Synthesis of biscoumarins by condensation of 4-hydroxycoumarin with an aromatic aldehyde or phenylglyoxals using SiO2-OSO3H NPs as catalyst.The compounds4a–l were characterised by their 1H-NMR and IR spectroscopies and elemental analyses. Spectral data were compared with the literature data [5, 9, 11].Compounds4m, n and 5a–c were new, and their structures were deduced by elemental and spectral analysis. The 1H-NMR spectrum of compound 5a exhibited proton of methine at 6.4 ppm, and OH proton is observed at 11.3 ppm which disappears after addition of some D2O to the CDCl3 solution of 5a. There are observed multiplets between 7.34 and 8.29 ppm which are related to aromatic protons. The 13C-NMR spectrum of compound 5a showed 15 signals in agreement with the proposed structure. The IR spectrum of compound 5a also supported the suggested structure.


## 4. Conclusion

In summary, we have reported an easy and efficient protocol for the synthesis of biscoumarins in the easily accessible SiO2-OSO3H nanoparticles. The method offers marked improvement with its operational simplicity and short reaction time and affords excellent yield. The solid phase acidic catalyst was reusable for a number of times without appreciable loss of activity. The present method does not involve any hazardous organic solvent. Therefore, this procedure could be classified as green chemistry.



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*Source: 179013-2013-08-04.xml*