Sulfonated ordered nanoporous carbon (CMK-5-SO3H) as an efficient and highly recyclable catalyst for the silylation of alcohols and phenols with hexamethyldisilazane (HMDS)

Article abstract of DOI:10.1007/s10562-011-0621-3

An environmentally friendly catalytic system for trimethylsilylation of alcohols and phenols with hexamethyldisilazane can be successfully carried out for the first time over sulfonated mesoporous carbon catalyst (CMK-5-SO ₃H) in dichloromethane at ambient temperature and excellent conversions were obtained. Furthermore, the catalyst displays high activity and thermal stability (to 200 °C) and it can be reused repeatedly for at least 25 cycles without any evidence of loss of activity, confirming the stability of covalent bonding of acidic centers.

Full text of DOI:10.1007/s10562-011-0621-3

Catal Lett (2011) 141:1521–1525
DOI 10.1007/s10562-011-0621-3
Sulfonated Ordered Nanoporous Carbon (CMK-5-SO3H)
as an Efficient and Highly Recyclable Catalyst for the Silylation
of Alcohols and Phenols with Hexamethyldisilazane (HMDS)
•
Daryoush Zareyee Mohammad S. Ghandali
•
Mohammad A. Khalilzadeh
Received: 19 January 2011 / Accepted: 8 May 2011 / Published online: 24 May 2011
Ó Springer Science+Business Media, LLC 2011
Abstract An environmentally friendly catalytic system
for trimethylsilylation of alcohols and phenols with hex-
amethyldisilazane can be successfully carried out for the
first time over sulfonated mesoporous carbon catalyst
(CMK-5-SO3H) in dichloromethane at ambient tempera-
ture and excellent conversions were obtained. Furthermore,
the catalyst displays high activity and thermal stability (to
200 °C) and it can be reused repeatedly for at least 25
cycles without any evidence of loss of activity, confirming
the stability of covalent bonding of acidic centers.
disadvantages, since careful extraction and filtration are
required to remove ammonium salts derived from the
reaction of by-produced acids and co-bases during the
silylation reaction.
On the other hand, 1,1,1,3,3,3-hexamethyldisilazane
(HMDS) as an inexpensive, commercially available and
stable reagent, is frequently used for the trimethylsilylation
of hydroxyl groups, giving ammonia as the only byproduct.
Even though the handling of this reagent is easy, its main
drawback is its poor silylating power which needs forceful
conditions and long reaction times in many instances [12].
Therefore, a variety of catalysts have been developed for
activation of this reagent, such as sulfuric acid [1, 2],
(CH3)3SiCl [13], sulfonic acids [14], K-10 montmorilonite
[15, 16], iodine [17], tungstophosphoric acid (H3PW12O40)
[18], LiClO4 [19], Mg(OTf)2 [20], CuSO4Á5H2O [21],
TBBDA, and PBBS [22], [PdCl(g3-C3H5)]2-PPh3 [23],
MgBr2ÁOEt2 [24], InBr3 [25], LaCl3 [26], HReO4 [27],
silica supported perchloric acid [28], trichloroisocyanuric
acid [29], Fe(F3CCO2)3 [30], Zr(OTf)2 [31], Bi(OTf)3 [32],
and TiCl2(OTf)–SiO2 [33]. Although several of these
procedures are useful, some of them suffer from the use of
homogenous and often corrosive catalyst, tedious workup
and long reaction times. Besides, many of these reagents
are expensive and non-recoverable leading to the genera-
tion of large amount of toxic waste particularly when large
scale applications are considered. On these bases, devel-
opments of milder conditions were tried and investigations
on green, simple and highly efficient processes over solid
acid catalysts became the chemists interesting undertaking.
Solid acids are conventional materials that have wide
applications in chemical production, separation, and puri-
fication and the chemical industry is currently searching for
highly active and stable solid acids to improve the envi-
ronmental safety of the production of chemicals [34–40].
Keywords Sulfonated mesoporous carbon Á
CMK-5-SO3H Á Solid acid Á Heterogeneous catalyst Á
Silylation Á HMDS
1 Introduction
Among the routinely employed methodologies for the
protection of hydroxyl groups in organic chemistry, sily-
lation undoubtedly plays a major role, from both analytical
and synthetic point of views [1, 2]. As it is widely known,
silyl ethers are resistant to oxidation, have a good stability
for most non-acidic reagents and are easily deprotected to
provide the free alcohols [3]. Generally, the formation of
silyl ethers carried out by treatment of parent alcohols with
silyl halides or silyl triflates in the presence of stoichiom-
etric amounts of a base [4–6], Li2S [7], and occasion-
ally with a nonionic super base catalyst [8–11]. However,
these base-catalyzed silylation methods have serious
D. Zareyee (&) Á M. S. Ghandali Á M. A. Khalilzadeh
Department of Chemistry, Islamic Azad University,
Qaemshahr Branch, P.O. Box 163, Mazandaran, Iran
e-mail: zareyee@gmail.com
123

1522
D. Zareyee et al.
In other word, the green approach to chemical processes
has stimulated the use of recyclable strong solid acids as
replacement for unrecyclable homogenous acid catalysts.
In this regard, Karimi et al. have demonstrated the appli-
cation of recoverable sulfonic acid functionalized ordered
mesoporous silica (MCM-41-PrSO3H) for efficient silyla-
tion of alcohols and phenols [41].
Table 1 Synthesis of trimethylsilyl ethers using CMK-5-SO3H
(2–3 mol%) in dichloromethane at room temperature
Entry Substrate
Cat.
(mol%)
Time
(min)
Yielda
(%)
1
PhCH2OH
2
2
2
2
2
2
2
3
2
2
2
2
3
2
2
2
30
98
94
99
98
97
80
100
91
90
92
95
100
91
100
93
95
2
3-ClC6H4CH2OH
4-ClC6H4CH2OH
3,5-(Cl)2C6H3CH2OH
4-MeC6H4CH2OH
4-NO2C6H4CH2OH
PhCH2CH2OH
Pyren-1-ylmethanol
Furfuryl alcohol
1-Pentanol
30
3
30
It is notable that, the availability of ordered mesoporous
silica also entails great opportunities for the templating
synthesis of highly ordered mesoporous carbon [42–49] for
reasons of both practical and fundamental interest. Carbon
material is inert and has good conductivity and resistance
to environmental and chemical attack. The carbon surface
has been exclusively used as a support substrate, especially
as electrodes with a wide potential window in electro-
chemistry for catalytic, analytical and biotechnological
applications [46–48]. Moreover, carbonaceous solid acids
can be maintained strong acidity even in water, partici-
pating in many industrially important acid-catalyzed
reactions.
4
35
5
40
6
120
70
7
8
110
100
120
120
150
150
110
120
120
9
10
11
12
13
14
15
16
1-Heptanol
2-Heptanol
2-Adamantanol
Menthol
Cyclohexanol
4-tert-Butyl-
cyclohexanol
17
18
19
20
21
22
PhCH(OH)Ph
PhOH
2
2
2
3
3
2
90
99
93
100
65
80
85
2 Experimental Section
120
180
180
120
120
4-ClC6H4OH
3-NO2C6H4OH
3,5-(Me)2C6H4OH
2.1 General Procedure for the Trimethylsilylation
of Alcohols
2-Hydroxy
benzaldehyde
To a solution of alcohol (1 mmol) and hexamethyldisilaz-
ane (0.7 mmol) in dichloromethane (3 mL) the catalyst
CMK-5-SO3H (23–35 mg, 2–3 mol%) was added. The
mixture was stirred at room temperature for the period of
time indicated in Table 1. Reaction progress was moni-
tored by thin layer and gas chromatography. After com-
pletion of the reaction, the product was isolated by
filtration. Evaporation of the solvent under reduced pres-
sure gave the corresponding silyl ether in good to excellent
yields (Table 1).
23
24
a
1-Adamantanol
(Ph)3COH
3
150
90
(2) 3
24 (h)
(22) 50
Gas chromatography yields
using a Soxhelet apparatus for 36 h and the obtained
SBA-15 was then dried overnight at 100 °C.
2.3 Preparation of CMK-5
2.2 Preparation of SBA-15
Templated synthesis of CMK-5 has been achieved using
known procedure described by Ryoo et al. [49, 51]. Ini-
tially, Al was incorporated into SBA-15 (molar ratio
Si/Al = 20) by well dispersion of calcined SBA-15 into an
aqueous solution of AlCl3, followed by removal of H2O by
rotaevaporator and calcination in air. Impregnation of
furfuryl alcohol (FA) into Al-SBA-15 was achieved by
incipient wetness infiltration at room temperature. The
mixture was then heated up at 80 °C oven for 16 h for
Al-catalyzed polymerization of FA. The obtained com-
posite was recovered by filtration to remove excess and
unpolymerized FA, and washed by EtOH and acetone. The
composite was heated to 850 °C under vacuum at a ramp
of 10 °C/min, and the carbonization was carried out at
the same temperature for 3 h under vacuum. Ordered
The synthesis of SBA-15 has been achieved using known
procedure described by Yu et al. [50] including a mixture
of P123 (0.02 mol), TEOS (1 mol), KCl (1.5 mol), HCl
(6 mol), and H2O (166 mol). Briefly, 12 g of P123 was
dissolved in a mixture of 74.4 g of concentrated HCl and
375.6 g of distilled water at 38 °C, followed by the addi-
tion of 16.5 g of KCl. To the solution, 31.5 g of TEOS was
added with vigorous stirring for 8 min. The mixture was
kept statically at the same temperature for 24 h, and the
mixture was transferred to Teflon lined autoclaves and put
in an oven at 130 °C for another 24 h. The solid was
recovered by filtration, washed by water. The surfactant
was then extracted by refluxing with a solution of EtOH
123

Sulfonated Ordered Nanoporous Carbon (CMK-5-SO3H)
1523
mesoporous carbon (CMK-5) was obtained by removal of
silica template by HF (10% in 1: 1 EtOH–H2O), washed
with copious water and EtOH, and finally dried at 100 °C.
N2
H3PO2, EtOH/H2O, 5 o
SO3H
SO3H
C
2.4 Preparation of 4-Benzenediazoniumsulfonate
4-Benzenediazoniumsulfonate was synthesized by diazoti-
zation of p-sulfonilic acid [52]. In a three-necked ground
flask, 12.99 g (0.075 mol) of p-sulfonilic acid was dis-
persed in 1 M HCl, resulting a 0.1 M suspension. To the
well-stirred suspension in an ice-water bath (3–5 °C), was
dropwise added a 10% excess of 1 M aqueous solution of
NaNO2 (82.5 mL). The solid p-sulfanilic acid was slowly
dissolved during of the addition of NaNO2 and a clear
solution was obtained after all of NaNO2 solution was
added. The mixture was stirred for another 45 min at the
same temperature. The white precipitate formed was fil-
tered off, washed by small amount of cold water, and dried
under reduced pressure.
CMK-5-SO3H
Fig. 1 Schematic representation for the preparation of sulfonated
ordered mesoporous carbon (CMK-5-SO3H)
2.5 Preparation of Sulfonated Ordered Mesoporous
Carbon (CMK-5-SO3H)
In a typical modification, 1.2 g of CMK-5 was added in a
three-necked ground flask containing 12.0 g of 4-benzene-
diazoniumsulfonate in 200 mL of distilled water and
200 mL of ethanol. Subsequently, the mixture was cooled
down to 5 °C and 200 mL of 50 wt% H3PO2 aqueous
solution was added. After stirring for 30 min, another
200 mL of H3PO2 aqueous solution was added. The mix-
ture was stirred at 5 °C for another 30 min. The sulfonic
acid functionalized carbon material (denoted as CMK-5-
SO3H) was recovered by filtration, washed thoroughly with
distilled water and finally acetone, and dried in an oven at
80 °C.
Fig. 2 TG diagram for CMK-5-SO3H
The organic composition of the solid sulfonic acid was
quantitatively determined by potentiometric titration.
Typically a loading of ca. 0.87 0.03 mmol/g was
obtained. It is worthwhile to mention that the weight loss of
CMK-5-SO3H below 100 °C (*7 wt%) can be attributed
to the physically adsorbed water. Further weight loss of
CMK-5-SO3H at higher temperature (about 200 °C)
accounts for loss of the SO3H segment. Accordingly, the
total weight loss reaches 22.4%.
Due to the attributes described above for the use of
sulfonated ordered nanoporous carbon in catalysis and our
current interest in developing environmentally benign
synthetic protocols for different organic transformations
[41, 54–56], we reveal herein for the first time, highly
reusable CMK-5-SO3H catalyzed trimethylsilylation of a
wide variety of alcohols and phenols at ambient tempera-
ture (Scheme 1).
3 Results and Discussion
Covalent attachment of aryl sulfonic acid on ordered
mesoporous carbon with mesoporosity both inside nano-
pipes and between nanopipes can be produced by homog-
enous reduction of 4-benzene-diazoniumsulfonate by
hypophosphorous acid, which has been reported very most
recently by Feng et al. [53], resulted in preparation of
sulfonated ordered mesoporous carbon (CMK-5-SO3H).
This catalyst was prepared in our laboratory following
described procedure (Fig. 1) and was characterized by TGA
(Fig. 2), BET surface area measurement, BJH, and N2
adsorption–desorption analysis (supporting information).
At the outset, efforts were made towards the catalytic
evaluation of CMK-5 towards the synthesis of silyl ethers
using 1 equiv. of benzyl alcohol, 1 equiv. of HMDS and
0.02 g of CMK-5. These were stirred at room temperature
in CH2Cl2. After 2 and 24 h, only 30 and 48% of benzyl-
oxytrimethyl silane were obtained, respectively. It should
123

1524
D. Zareyee et al.
Scheme 1 Trimethylsilylation
of hydroxyl groups with HMDS
using CMK-5-SO3H
SO H
(2-3 mol%)
3
HMDS (0.7 equiv.),
CH2Cl2, rt
R
OH
R
OSiMe3
be noted that, when no catalyst was used, the reaction
yielded only 20% of expected product after 2 h. The same
reaction was then carried out using 23 mg (2 mol%) of
CMK-5-SO3H under similar reaction conditions. Interest-
ingly, a significant improvement was observed and the
yield of silylated product was increased to 99% gas chro-
matography yield after stirring the mixture for only 25 min.
For establishing the best reaction conditions, an optimiza-
tion study was performed using the reaction of benzyl
alcohol in the presence of varying amounts of HMDS and
CMK-5-SO3H. Gratifyingly, 98% of corresponding prod-
uct was obtained in the presence of 0.7 mmol HMDS and
2 mol% of sulfonated catalyst CMK-5-SO3H after only
30 min. After achieving this favorable result, in order to
ascertain the scope and generality of this catalyst, we
screened a range of alcohols and phenols. The experiment
is shown in Scheme 1 and the results are collected in
Table 1.
To demonstrate whether the protection of alcohols cat-
alyzed by CMK-5-SO3H is actually proceeding in a het-
erogeneous pathway, the silylation of benzyl alcohol was
carried out in dichloromethane in which the catalyst was
filtered off at approximately 50% conversion and the
resulting clear solution stirred for additional time in the
absence of the solid. No significant increase in the yield
occurs after removal of the catalyst, thus indicating the
solution does not contain any catalytically active species
that could have leached from the solid to solution and
confirm the covalent stability of acidic centers attached to
mesoporous carbon.
Compared with traditional liquid acid catalysts, the
catalyst CMK-5-SO3H has the attractive property in that it
can be easy recycled. Consequently, after the completion of
the first run silylation of benzyl alcohol under the condi-
tions described in Table 1, which afford the corresponding
benzyloxytrimethyl silane in 98% yield, a new silylation
reaction was then accomplished by removal of solution
using syringe and then addition of fresh reactants to the
reaction mixture. Gratifyingly, CMK-5-SO3H successfully
reused in more than twenty-five successive runs and
exhibited consistent activity to afford an average yield of
97.5% with virtually no significant loss of performance,
which clearly demonstrates the practical recyclability of this
catalyst. This reusability demonstrates the high stability and
turnover of CMK-5-SO3H under the conditions employed.
Noticeably, the recyclability test was stopped after twenty-
five runs, although it can be done continuously.
Compounds that were silylated in this way are benzylic,
primary, hindered and unhindered secondary, and unhin-
dered tertiary alcohols (Table 1). Generally, in the case of
primary alcohols, the reactions were completed within less
than 2 h in CH2Cl2 at room temperature accompanied by a
fast evolution of NH3 gas from the reaction mixture
(Table 1, entries 1–11). This method is also efficient for the
silylation of secondary alcohols (Table 1, entries 12–17).
Meanwhile, primary and secondary aliphatic alcohols were
readily transformed to their corresponding silyl ethers in
high yields (Table 1, entries 10–16). Phenol, 4-chlorophe-
nol, 3-nitrophenol, 3,5-dimethylphenol and 2-hydroxy
benzaldehyde were also silylated in an efficient manner in
excellent yields (Table 1, entries 18–22). Our successful
synthesis of primary and secondary silyl ethers, led us to
embark upon a study of silylation of hindered tertiary
alcohols. 1-Adamantanol was converted to corresponding
silylated product in good yield (Table 1, entry 23). Nev-
ertheless, triphenylmethanol gave related silyl ether in only
22% yield under standard reaction condition after 24 h,
which can be improved to 50% when 3 mol% of CMK-
5-SO3H was used after 24 h (Table 1, entry 24). It should
be noted that, in the case of hindered secondary and tertiary
alcohols no elimination by-products were observed at all.
4 Conclusions
In summary, sulfonated ordered nanoporous carbon (CMK-
5-SO3H), is an efficient, thermally stable (to 200 °C), and
recoverable catalyst for the silylation of alcohols in
dichloromethane at ambient temperature. In view of
excellent catalytic capacity, outstanding stability, the
exceedingly simple workup and uncomplicated recovery,
CMK-5-SO3H was proved the best catalyst for this reac-
tion. Most importantly, this procedure is significant from
the viewpoint of avoiding pollution. As a consequence, this
123

Sulfonated Ordered Nanoporous Carbon (CMK-5-SO3H)
1525
18. Firouzabadi H, Iranpoor N, Amani K, Nowrouzi F (2002) J Chem
Soc Perkin Trans 1:2601
19. Saidi MR, Azizi N (2004) Organometallics 23:1457
20. Firouzabadi H, Iranpoor N, Sobhani S, Ghassamipour S (2004)
J Organomet Chem 689:3197
21. Akhlaghinia B, Tavakoli S (2005) Synthesis 11:1775
22. Ghorbani-Vaghei R, Zolfigol MA, Chegeny M, Veisi H (2006)
Tetrahedron Lett 47:4505
23. Shurakawa E, Hironaka K, Otsuka H, Hayashi T (2006) Chem
Commun 37:3927
24. Mojtahedi MM, Abbasi H, Abaee MS (2006) J Mol Catal A 250:6
25. Yadav JS, Reddy BVS, Basak AK, Baishya G, Vankat Narsaiah
A (2006) Synthesis 22:3881
26. Narsaiah A (2007) J Organomet Chem 692:3614
27. Reis PM, Royo B (2007) Catal Commun 8:1057
28. Shaterian HR, Shahrekipoor F, Ghashang M (2007) J Mol Catal
A 272:142
system represents a substantial improvement over previous
methods, wherein product separation would produces a
large amount of wastes. Additionally, by this method,
primary, bulky secondary, tertiary and phenolic hydroxyl
functional groups were protected in good to excellent
yields. To the best of our knowledge, there has not been
reported silylation of alcohols using sulfonated carbon in
which the catalyst can be recovered and reused over several
reaction cycles without considerable loss of reactivity.
Further studies will be focusing on exploring of this solid
sulfonic acid for other types of functional group transfor-
mations in our laboratories.
29. Khazaei A, Zolfigol MA, Rostami A, Ghorbani-Choghamarani A
(2007) Catal Commun 8:543
5 Supplementary Data
30. Firouzabadi H, Iranpoor N, Jafari AA, Jafari MR (2008)
J Organomet Chem 693:2711
31. Moghadam M, Tangestaninejad S, Mirkhani V, Mohammadpour-
Baltork I, Chahardahcheric S, Tavakoli Z (2008) J Organomet
Chem 693:2041
32. Kadam ST, Kim SS (2009) J Organomet Chem 694:2562
33. Firouzabadi H, Iranpoor N, Farahi S (2009) J Organomet Chem
694:3923
34. Olah GA, Pradeep SI, Prakash GKS (1986) Synthesis 7:513
35. Corma A (1995) Chem Rev 95:559
Experimental procedure and characterization data (TGA,
BET, BJH, and N2 adsorption–desorption isotherm) for
CMK-5 and CMK-5-SO3H, and general procedure for the
trimethylsilylation of alcohols is available.
Acknowledgments The authors acknowledge the Islamic Azad
University of Qaemshahr Research Councils for support of this study.
36. Herron N, Farneth WE (1996) Adv Mater 8:959
37. Harton B (1999) Nature 400:797
38. Anastas PT, Kirchhooff MM (2002) Acc Chem Res 35:686
39. Clark JH, Macquarrie DJ (1998) Chem Commun 8:853
40. Okuhara T (2002) Chem Rev 102:3641
41. Zareyee D, Karimi B (2007) Tetrahedron Lett 48:1277
42. Tamai H, Kakii H, Hirota Y, Kumamoto T, Yasuda H (1996)
Chem Mater 8:454
References
1. Greene TW, Wuts PGM (1991) Protective groups in organic
synthesis, 2nd edn. Wiley, New York
2. Kocienski PJ, Enders R, Noyori R, Trost BM (eds) (1994) In
protective groups. Thieme, Stuttgart
43. Kawashima D, Aihara T, Kobayashi Y, Kyotani T, Tomita A
(2000) Chem Mater 12:3397
3. Langer SH, Connell S, Wender I (1958) J Org Chem 23:50
4. Corey EJ, Venkateswarlu A (1972) J Am Chem Soc 94:6190
5. Chaudhary SK, Hernandez O (1979) Tetrahedron Lett 20:99
6. Lombardo L (1984) Tetrahedron Lett 25:227
7. Olah GA, Gupta BGB, Narang SC, Malhotra R (1979) J Org
Chem 44:4272
8. D’Sa BA, McLeod D, Verkade JG (1997) J Org Chem 62:5057
9. D’Sa BA, Verkade JG (1996) J Am Chem Soc 118:12832
10. Martinez GR, Grieco PA, Williams E, Kanai K, Srinivasan CV
(1982) J Am Chem Soc 104:1436
44. Lee J, Sohn K, Hyeon T (2001) J Am Chem Soc 123:5146
45. Li Z, Jaroniec M (2001) J Am Chem Soc 123:9208
46. Besenhard JO, Friz HP (1983) Angew Chem Int Ed Engl 22:950
47. Rice RJ, Pontikos NM, McCreery RL (1990) J Am Chem Soc
112:4617
48. Tanaka H, Aramata A (1997) J Electroanal Chem 437:29
49. Joo SH, Choi SJ, Oh I, Kwak J, Liu Z, Terasaki O, Ryoo R (2001)
Nature 412:169
50. Yu C, Fan J, Tian B, Zhao D, Stucky GD (2002) Adv Mater
14:1742
51. Kurk M, Jaroniec M, Kim T-W, Ryoo R (2003) Chem Mater
15:2815
11. Aizpurua JM, Palomo C (1985) Tetrahedron Lett 26:475
12. Bruynes CA, Jurriens TK (1982) J Org Chem 47:3966
13. Gauttret P, El-Ghamarti S, Legrand A, Coutrier D, Rigo B (1996)
Synth Commun 26:707
52. Bouchet MJ, Rendon A, Wermuth CG, Goeldner M, Hirth C
(1987) J Med Chem 30:2222
14. Goldschmidt AGT (1979) German Patent 2 758884. Chem Abstr
90:6530c
53. Wang X, Liu R, Waje MM, Chen Z, Yan Y, Bozhilov KN, Feng P
(2007) Chem Mater 19:2395
15. Zhang ZH, Li TS, Yang F, Fu CG (1998) Synth Commun
28:3105
54. Karimi B, Zareyee D (2005) Tetrahedron Lett 46:4661
55. Karimi B, Zareyee D (2008) Org Lett 10:3989
56. Karimi B, Zareyee D (2009) J Mater Chem 19:8665
16. Mojtahedi MM, Saidi MR, Bolourchian M, Heravi MM (2002)
Phosphorus Sulfur Silicon Relat Elem 177:289
17. Karimi B, Golshani B (2000) J Org Chem 65:7228
123