Silica-bonded S-sulfonic acid as a recyclable catalyst for chemoselective synthesis of 1,1-diacetates

Article abstract of DOI:10.1016/j.tetlet.2009.04.096

A simple and efficient procedure for the preparation of silica-bonded S-sulfonic acid (SBSSA) by reaction of 3-mercaptopropylsilica (MPS) and chlorosulfonic acid in chloroform is described. This solid acid is employed as a recyclable catalyst for the synthesis of 1,1-diacetates from aromatic aldehydes and acetic anhydride under mild and solvent-free conditions at room temperature.

Full text of DOI:10.1016/j.tetlet.2009.04.096

Tetrahedron Letters 50 (2009) 4058–4062
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Silica-bonded S-sulfonic acid as a recyclable catalyst for chemoselective
synthesis of 1,1-diacetates
*
Khodabakhsh Niknam , Dariush Saberi, Maryam Nouri Sefat
Chemistry Department, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 December 2008
Revised 6 April 2009
Accepted 24 April 2009
Available online 3 May 2009
A simple and efficient procedure for the preparation of silica-bonded S-sulfonic acid (SBSSA) by reaction
of 3-mercaptopropylsilica (MPS) and chlorosulfonic acid in chloroform is described. This solid acid is
employed as a recyclable catalyst for the synthesis of 1,1-diacetates from aromatic aldehydes and acetic
anhydride under mild and solvent-free conditions at room temperature.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Silica-bonded S-sulfonic acid
1,1-Diacetates
Aldehydes
Solvent-free
1. Introduction
functional groups by reaction with appropriate nucleophiles.15,16
Numerous methods for the preparation of 1,1-diacetates from
The development of heterogeneous catalysts for organic synthe-
sis has become a major area of research. The potential advantages
of these materials over homogeneous systems (simplified recovery,
reusability and the potential for incorporation in continuous reac-
tors and microreactors) could lead to novel, environmentally be-
nign chemical procedures for academia and industry.1
Application of solid acids in organic transformations is important
because they have many advantages including ease of handling,
decreased reactor and plant corrosion problems and more environ-
mentally safe disposal.2–7
Selective protection and deprotection of carbonyl groups are
essential steps in modern organic chemistry.8 The protection of
aldehydes as acetals, acylals, oxathioacetals or dithioacetals is
common practice for manipulation of other functional groups dur-
ing multi-step syntheses. Protection of aldehydes as acylals is often
preferred due to their ease of preparation and their stability to-
wards basic and neutral conditions.8,9 In addition, the preparation
of 1,1-diacetates from the corresponding aldehydes can be
achieved very easily in the presence of ketones. Moreover, they
also serve as valuable precursors for asymmetric allylic alkyl-
ation10 and natural product synthesis11 as well as for the synthesis
of 1-acetoxydienes and 2,2-dichlorovinylacetates for Diels–Alder
reactions.12,13 Acylals have also been used as cross-linking agents
for cellulose in cotton14 and are useful intermediates in industry.12
Moreover, the acylal functionality can be converted into other
aldehydes and acetic anhydride have been reported.17–39 Although
some of these methods afford good to high yields of the corre-
sponding diacetates, the majority suffer from one or more of the
following disadvantages: reactions under oxidizing conditions,
use of strong acids, high temperatures, long reaction times, mois-
ture sensitivity as well as high cost and high toxicity of the re-
agents. In continuation of our studies on the design and
application of solid acid catalysts in organic transformations,40–43
herein, we describe the preparation of silica-bonded S-sulfonic acid
(SBSSA) and its application as a catalyst for the synthesis of aro-
matic 1,1-diacetates.
We prepared SBSSA by the reaction of 3-mercaptopropylsilica 1
with chlorosulfonic acid as illustrated in Scheme 1.
To study the effect of catalyst loading on the protection of aro-
matic aldehydes as the corresponding 1,1-diacetates the reaction
of 4-methylbenzaldehyde with acetic anhydride was chosen as a
model reaction (Table 1). The results show clearly that SBSSA is
an effective catalyst for this transformation and in the absence of
2 the reaction did not take place, even after 12 h. Although a lower
catalyst loading (1 mg of SBSSA) could be used to accomplish this
protection, 5 mg of SBSSA per 1 mmol of aldehyde was optimum in
terms of reaction time and isolated yield.
The model reaction was also examined in various solvents as
well as under solvent-free conditions in the presence of
5 mg mmolÀ1 of SBSSA (Table 2). The yield of the reaction under
solvent-free conditions was the highest and the reaction time
was the shortest. In protic solvents such as water and ethanol this
protection reaction proceeded in longer reaction times and with
* Corresponding author. Tel.: +98 771 4541494; fax: +98 771 4545188.
E-mail addresses: khniknam@gmail.com, niknam@pgu.ac.ir (K. Niknam).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.04.096

K. Niknam et al. / Tetrahedron Letters 50 (2009) 4058–4062
4059
O
SH
OH
OH
(MeO)3Si
O Si
O
SH
SiO2
SiO2
toluene, reflux, 18 h
OH
1
O
1) ClSO3H/ CHCl3 /4 h
2) wash with MeOH
O Si
S-SO3H
SiO2
O
2
Scheme 1. Preparation of silica-bonded S-sulfonic acid (SBSSA).
Table 1
Benzaldehydes with electron-donating or electron-withdrawing
groups, for example, 4-methylbenzaldehyde 3b or 3-nitrobenzal-
dehyde 3c, were converted into the corresponding acylals 4b and
4c in high yields after very short reaction times. The acid-sensitive
substrate thiophene-2-carbaldehyde 3o gave the expected acylal
4o in 75% yield without any by-product formation (Table 3, entry
o).
We also investigated the reactions of 4-hydroxybenzaldehyde
3h, 3-hydroxybenzaldehyde 3i, 3,4-dihydroxybenzaldehyde 3j, 2-
hydroxy-5-nitrobenzaldehyde 3k and 2-hydroxy-5-methoxyisoph-
thalaldehyde 3l under the above-mentioned conditions and ob-
served that both the carbonyl and phenolic groups were acylated
(Table 3, entries h–l). Several aliphatic and aromatic ketones
including cyclohexanone, acetophenone and 4-chloroacetophe-
none were not reactive under the described experimental condi-
tions, even after 2 h.
Conversion of p-methylbenzaldehyde to the corresponding diacetate with acetic
anhydride in the presence of different amounts of SBSSAa
Entry
Catalyst loading (g)
Time (min)
Yieldb
1
2
3
4
5
6
7
8
9
No catalyst
0.1
0.05
12 h
3
3
3
3
10
25
60
180
0
35
45
65
91
91
90
90
88
0.01
0.005
0.004
0.003
0.002
0.001
a
Reaction conditions: p-methylbenzaldehyde (1 mmol), acetic anhydride
(15 mmol), room temperature, solvent-free.
b
Isolated yield.
Next, we studied the competitive acylation reactions of aro-
matic aldehydes in the presence of ketones using SBSSA. Under
these conditions exclusive acylation of the aldehyde functions
was observed. The chemoselective acylations of benzaldehyde
and 4-chlorobenzaldehyde in the presence of acetophenone and
4-chloroacetophenone are shown in Table 4.
The possibility of recycling the catalyst was examined using the
reaction of p-methylbenzaldehyde and acetic anhydride under the
optimized conditions. Upon completion of acylation, the reaction
mixture was filtered and the remaining solid was washed with
dichloromethane, dried in air and the catalyst reused in the next
reaction. The recycled catalyst was reused twenty times without
any additional treatment. No observation of any appreciable loss
in the catalytic activity of SBSSA was observed (Fig. 1).
Table 2
Conversion of p-methylbenzaldehyde to the corresponding diacetate in different
solvents and under solvent-free conditions in the presence of SBSSA (0.005 g)
Entry
Solventa
Time (min)
Yieldc
1
2
3
4
5
6
EtOH
H2O
CH2Cl2
30
30
3
20
3
10
25
85
80
80
91
n-Hexane
MeCN
Solvent-freeb
3
a
The reaction was carried out in 5 mL of solvent at rt.
The reaction was carried out with 15 mmol of Ac2O at rt.
Isolated yield.
b
c
In conclusion, we have shown that silica-bonded S-sulfonic acid,
which can be prepared from commercially available and cheap
starting materials, catalyzed efficiently the synthesis of aromatic
1,1-diacetates from aryl aldehydes. The catalyst shows high ther-
mal stability and was recovered and reused without any noticeable
loss of activity. The mild reaction conditions and simplicity of the
procedure offer improvements over many existing methods. Stud-
ies on the use of the catalyst 2 for other functional group transfor-
mations are ongoing in our laboratories.
very poor yields, which maybe related to the instability of acetic
anhydride in protic solvents.
Therefore, we employed the optimized conditions (5 mg mmolÀ1
of SBSSA and solvent-free conditions) for the conversion of various
aryl aldehydes into the corresponding acylals (Scheme 2).
The results of the solvent-free preparation of acylals from aro-
matic aldehydes 3 in the presence of SBSSA at room temperature
are shown in Table 3. 1,1-Diacetate 4a was obtained in high yield
in 4 min by the reaction of benzaldehyde with acetic anhydride.
All the products are known compounds (except 4k, 4l and 4m)
and were characterized by comparison of their IR, 1H NMR and 13
C
NMR spectroscopic data and their melting points with reported
values.21–39 Mercaptopropylsilica 1 (MPS) was prepared according
to the procedure reported by Karimi et al.4
SBSSA
Ar-CH(OAc)2
Ar-CHO
+
Ac2O
1.1. Synthesis of silica-bonded S-sulfonic acid 2
Solvent-free, rt
4
3
To a magnetically stirred mixture of 3-mercaptopropylsilica 1
(5 g) in CHCl3 (20 mL), chlorosulfonic acid (1.00 g, 9 mmol) was
Scheme 2. Synthesis of 1,1-diacetate derivatives catalyzed by SBSSA.

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K. Niknam et al. / Tetrahedron Letters 50 (2009) 4058–4062
Table 3
Preparation of various acylals in the presence of SBSSA under solvent-free conditions at room temperaturea
Entry
Ar (3)
Product 4
Time (min)
Yieldb (%)
Mp (°C)
Lit. mp (°C)
CH(OAc)2
a
C6H5–
4
3
84
91
44–45
79–81
4534
CH(OAc)2
b
4-Me–C6H4–
80–8135
Me
O2N
CH(OAc)2
CH(OAc)2
c
3-O2N–C6H4–
4-Cl–C6H4–
2
3
87
85
64–65
81–83
6534
d
8232
Cl
Cl
CH(OAc)2
e
f
2-Cl–C6H4–
4-Br–C6H4–
3
2
89
90
58–60
90–93
5939
CH(OAc)2
92–9522
Br
F
CH(OAc)2
CH(OAc)2
g
4-F–C6H4–
2
2
87
83
51–53
94–96
5132
9533
h
4-HO–C6H4–
AcO
AcO
CH(OAc)2
CH(OAc)2
i
j
3-HO–C6H4–
2
2
82
78
76–77
7633
AcO
AcO
3,4-(HO)2–C6H3–
130–132
128–13022
OAc
CH(OAc)2
k
2-HO,5-O2N–C6H3–
2
2
84
72
121–122
151–152
—
—
NO2
OAc
(AcO)2HC
CH(OAc)2
l
2-HO-3-OHC-5-MeO–C6H2–
OMe
(AcO)2HC
CH(OAc)2
CH(OAc)2
m
n
3-OHC–C6H4–
4-OHC–C6H4–
2-Thienyl–
3
4
4
80
86
75
108–110
172–174
67–68
—
174–17534
66–6721
(AcO)2HC
S
o
CH(OAc)2
a
Reaction conditions: aromatic aldehyde (1 mmol), acetic anhydride (15 mmol), SBSSA (5 mg), room temperature, solvent-free.
Isolated yield.
b

K. Niknam et al. / Tetrahedron Letters 50 (2009) 4058–4062
4061
Table 4
Competitive acylal formation from aldehydes in the presence of ketones using SBSSA under solvent-free conditionsa
Entry
Substrates
Product (selectivity%)b
H
O
O
OAc
OAc
OAc
OAc
1
H
(0%)
(100%)
H
O
O
OAc
OAc
OAc
OAc
2
H
Cl
Cl
Cl
Cl
(0%)
(100%)
a
Reaction conditions: Substrate (1 mmol each), acetic anhydride (15 mmol), catalyst (0.005 g), 5 min at rt.
Conversion.
b
21.77, 84.34, 124.21, 124.79, 126.26, 130.05, 145.98, 153.14,
168.64, 168.74. Anal. Calcd for C13H13NO8: C, 50.17; H, 4.21; N,
4.50. Found: C, 49.87; H, 4.11; N, 4.27.
Compound 4l: IR (KBr): 3480, 3002, 2805, 1750, 1601, 1476,
1437, 1365, 1240, 1200, 1168, 1090, 1040, 970, 942, 880, 759,
723 cmÀ1 1H NMR (500 MHz, CDCl3): d (ppm) 2.07 (s, 12H), 2.32
.
(s, 3H), 3.84 (s, 3H), 7.18 (s, 2H), 7.76 (s, 2H). 13C NMR (125 MHz,
CDCl3): (ppm) 20.96, 21.09, 56.25, 85.22, 115.06, 130.53,
d
139.82, 158.04, 168.66, 170.44. Anal. Calcd for C19H22O11: C,
53.52; H, 5.20. Found: C, 53.20; H, 5.00.
Compound 4m: IR (KBr): 3005, 2820, 1756, 1580, 1430, 1367,
1240, 1200, 1158, 1060, 998, 942, 903, 802, 705 cmÀ1 1H NMR
.
(500 MHz, CDCl3): d (ppm) 2.12 (s, 12H), 7.44 (t, 1H, J = 7.5 Hz),
7.55 (d, 2H, J = 7.5 Hz), 7.65 (s, 1H), 7.68 (s, 2H). 13C NMR
(125 MHz, CDCl3): d (ppm) 21.27, 89.66, 125.44, 128.59, 129.42,
136.49, 169.13. Anal. Calcd for C16H18O8: C, 56.80; H, 5.36. Found:
C, 56.51; H, 5.14.
Figure 1. Recyclability of SBSSA (0.005 g) in the reaction of p-methylbenzaldehyde
(1 mmol) and acetic anhydride (15 mmol) at room temperature. Reaction
time = 4 min.
Acknowledgement
added dropwise at 0 °C over 2 h. After the addition was complete,
the mixture was stirred for another 2 h and then filtered, the solid
washed with methanol (30 mL) and dried at room temperature to
afford silica-bonded S-sulfonic acid as a cream powder (5.22 g).
Elemental analysis showed the S content to be 16.12%. Typically
a loading of 0.35 mmol/g was obtained. When SBSSA was placed
in aqueous NaCl solution, the pH of the solution dropped almost
instantaneously to pH ꢀ1.85, as ion exchange occurred between
the protons and sodium ions (proton exchange capacity:
0.34 mmol/g of SBSSA.
We are thankful to Persian Gulf University Research Council for
partial support of this work.
References and notes
1. Choudhary, D.; Paul, S.; Gupta, R.; Clark, J. H. Green Chem. 2006, 8, 479.
2. Riego, J. M.; Sedin, Z.; Zaldivar, J. M.; Marziano, N. C.; Tortato, C. Tetrahedron
Lett. 1996, 37, 513.
3. Corma, A.; Garcia, H. Chem. Rev. 2002, 102, 3837.
4. Karimi, B.; Khalkhali, M. J. Mol. Catal. A: Chem. 2005, 232, 113.
5. Karimi, B.; Zareyee, D. Tetrahedron Lett. 2005, 46, 4661.
6. Melero, J. A.; Van Grieken, R.; Morales, G. Chem. Rev. 2006, 106, 3790.
7. Karimi, B.; Abedi, S.; Clark, J. H.; Budarin, V. Angew. Chem., Int. Ed. 2006, 45,
4776.
1.2. General procedure for acylation
8. Greene, T. W.; Wuts, P. G. M. Greene’s Protective Groups in Organic Synthesis, 4th
ed.; Wiley: New York, 2007.
9. Kochhar, K. S.; Bal, B. S.; Deshpande, R. P.; Rajadhyaksha, S. N.; Pinnick, H. W. J.
Org. Chem. 1983, 48, 1765.
10. Trost, B. M.; Lee, C. J. Am. Chem. Soc. 2001, 123, 12191.
11. Sandberg, M.; Sydnes, L. K. Org. Lett. 2000, 2, 687.
12. Held, H.; Rengstle, A.; Mayer, A., 5th ed.. In Ullman’s Encyclopedia of Industrial
Chemistry; Gerhartz, W., Ed.; Wiley-VCH: New York, 1985; Vol 1.
13. Freeman, F.; Karcherski, E. M. J. Chem. Eng. Data 1977, 22, 355.
14. Frick, J. G., Jr.; Harper, R. J., Jr. J. Appl. Polym. Sci. 1984, 29, 1433.
15. Van Heerden, F. R.; Huyser, J. J.; Bradley, D.; Williams, G.; Holzapfel, C. W.
Tetrahedron Lett. 1998, 39, 5281.
To a mixture of aldehyde (1 mmol) and acetic anhydride
(15 mmol) was added SBSSA catalyst (5 mg) and the mixture was
stirred at room temperature. When the reaction was complete as
judged by TLC, CH2Cl2 (5 mL) was added and the reaction mixture
was filtered and the remaining solid was washed with CH2Cl2
(3 Â 5 mL) in order to separate the catalyst. The CH2Cl2 layer was
washed with water (2 Â 10 mL) and dried over anhydrous MgSO4.
After removal of the solvent in vacuo, the obtained residue was
recrystallized from ethanol.
16. Sandberg, M.; Sydnes, L. K. Tetrahedron Lett. 1998, 39, 6361.
17. Gregory, M. J. J. Chem. Soc. B 1970, 1201.
18. Carrigan, M. D.; Eash, K. J.; Oswald, M. C.; Mohan, R. S. Tetrahedron Lett. 2001,
42, 8133.
2. Spectral data
19. Firouzabadi, H.; Iranpoor, N.; Nowrouzi, F.; Amani, K. Tetrahedron Lett. 2003, 44,
Compound 4k: IR (KBr): 3010, 2800, 1610, 1565, 1515, 1430,
3951.
1340, 1258, 1235, 1160, 1060, 902, 821, 728 cmÀ1 1H NMR
.
20. Kumar, P.; Hegde, V. R.; Kumar, T. P. Tetrahedron Lett. 1995, 36, 601.
21. Yadav, J. S.; Reddy, B. V. S.; Venugopal, C.; Ramalingam, T. Synlett 2002, 604.
22. Nagy, N. M.; Jakab, M. A.; Konya, J.; Antus, S. Appl. Clay Sci. 2002, 21, 213.
23. Ghosh, R.; Maiti, S.; Chakraborty, A.; Halder, R. J. Mol. Catal. A: Chem. 2004, 215,
49.
(500 MHz, CDCl3): d (ppm) 2.13 (s, 6H), 2.37 (s, 3H), 7.34 (d, 1H,
J = 8.9 Hz), 7.93 (s, 1H), 8.29 (dd, 1H, J1 = 8.9 Hz, J2 = 2.7 Hz), 8.53
(d, 1H, J = 2.7 Hz). 13C NMR (125 MHz, CDCl3): d (ppm) 21.09,

4062
K. Niknam et al. / Tetrahedron Letters 50 (2009) 4058–4062
24. Jin, T. S.; Sun, G.; Li, Y. W.; Li, T. S. Green Chem. 2002, 4, 255.
25. Smith, G.; Reddy, C. S. Tetrahedron 2003, 59, 9571.
26. Aggen, D. H.; Arnold, J. N.; Hayes, P. D.; Smoter, N. J.; Mohan, R. S. Tetrahedron
2004, 60, 3675.
27. Romanelli, G. P.; Thomas, H. J.; Baronetti, G. T.; Autino, J. C. Tetrahedron Lett.
2003, 44, 1301.
28. Hajipour, A. R.; Zarei, A.; Khazdooz, L.; Mirjalilli, F.; Sheikhan, N.; Zahmatkesh,
S. Synthesis 2005, 3644.
29. Ghorbani-Vaghei, R.; Akbari, S. A.; Zolfigol, M. A.; Mirjalili, B. F.; Bamoniri, A.
Mendeleev Commun. 2006, 16, 55.
34. Khan, A. T.; Choudhury, L. H.; Ghosh, S. J. Mol. Catal. A: Chem. 2006, 255, 230.
35. Wang, Q.-Y.; Sheng, S.-R.; Wei, M.-H.; Xie, Z.-L.; Liu, X.-L. Synth. Commun. 2007,
37, 1019.
36. Wang, M.; Song, Z.; Gong, H.; Jiang, H. Synth. Commun. 2008, 38, 961.
37. Saini, A.; Kumar, S.; Sandhu, J. S. Synth. Commun. 2008, 38, 106.
38. Yadav, J. S.; Reddy, B. V. S.; Sreedhar, P.; Kondaji, G.; Nagaiah, K. Catal. Commun.
2008, 9, 590.
39. Jermy, B. R.; Pandurangan, A. Catal. Commun. 2008, 9, 577.
40. Niknam, K.; Zolfigol, M. A.; Khorramabadi-Zad, A.; Zare, R.; Shayegh, M. Catal.
Commun. 2006, 7, 494.
30. Wang, J. M.; Yan, L.; Qian, G.; Yang, K.; Liu, H.; Wang, X. Tetrahedron Lett. 2006,
47, 8309.
41. Niknam, K.; Zolfigol, M. A.; Hossieninejad, Z.; Daneshvar, N. Chin. J. Catal. 2007,
28, 591.
31. Hajipour, A. R.; Zarei, A.; Ruoho, A. E. Tetrahedron Lett. 2007, 48, 2881.
32. Kumar, R.; Tiwari, P.; Maulik, P. R.; Misra, A. K. J. Mol. Catal. A: Chem. 2006, 247, 27.
33. Jeyakumar, K.; Chand, D. K. J. Mol. Catal. A: Chem. 2006, 255, 275.
42. Niknam, K.; Karami, B.; Zolfigol, M. A. Catal. Commun. 2007, 8, 1427.
43. Niknam, K.; Zolfigol, M. A.; Sadabadi, T. J. Iran. Chem. Soc. 2007, 4,
199.