Silica-bonded S-sulfonic acid as a recyclable catalyst for the silylation of hydroxyl groups with hexamethyldisilazane (HMDS)

Article abstract of DOI:10.1139/V09-162

Silica-bonded S-sulfonic acid (SBSSA) was prepared by the reaction of 3-mercaptopropylsilica (MPS) and chlorosulfonic acid in tert-butylmethyl ether, and used as a catalyst for the silylation of hydroxyl groups. A good range of primary, secondary alcohols

Full text of DOI:10.1139/V09-162

164
Silica-bonded S-sulfonic acid as a recyclable
catalyst for the silylation of hydroxyl groups with
hexamethyldisilazane (HMDS)
Khodabakhsh Niknam, Dariush Saberi, Hajar Molaee, and Mohammad Ali Zolfigol
Abstract: Silica-bonded S-sulfonic acid (SBSSA) was prepared by the reaction of 3-mercaptopropylsilica (MPS) and
chlorosulfonic acid in tert-butylmethyl ether, and used as a catalyst for the silylation of hydroxyl groups. A good range of
primary, secondary alcohols and phenolic hydroxyl groups were effectively converted into their corresponding trimethyl-
silyl ethers with hexamethyldisilazane (HMDS) in the presence of catalytic amounts of SBSSA under mild conditions at
room temperature with short reaction times and in good-to-excellent yields. An excellent chemoselective silylation of hy-
droxyl groups in the presence of other functional groups was also observed. The heterogeneous catalyst was recycled for
30 runs upon the reaction of benzyl alcohol with HMDS without lossing its catalytic activity.
Key words: silylation, silica-bonded S-sulfonic acid, hydroxyl groups, alcohols, catalyst.
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Resume : On a prepare de l’acide S-sulfonique lie a de la silice par (ASSLS) par reaction du 3-mercaptopropylsilicium
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(MPS) et de l’acide chlorosulfonique dans le ether de tert-butylmethyle et on l’a utilise comme catalyseur pour la silyla-
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tion de groupes hydroxyles. On a ainsi pu transformer un ensemble representatif de groupes hydroxyles d’alcools primaires
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et secondaires et phenoliques en ethers trimethylsilyles correspondants par reaction avec de l’hexamethyldisilazane
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(HMDS) en presence de quantites catalytiques d’acide S-sulfonique lie a de la silice, dans des conditions douces, a la tem-
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perature ambiante, avec des courts temps de reaction et avec des rendements allant de bons a excellents. On a pu aussi ob-
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server une excellent silylation chimioselective de groupes hydroxyles en presence d’autres groupes fonctionnels. Le
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catalyseur heterogene a pu etre recycle au moins trente fois, sans perte d’activite, pour la reaction de l’alcool benzylique
avec le HMDS.
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Mots-cles : silylation, acide S-sulfonique lie a de la silice, groupes hydroxyles, catalyseur.
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[Traduit par la Redaction]
also requires the use of recyclable catalysts. One way to
overcome the problem of recyclability of the traditional
acid catalysts is to chemically anchor their reactive center
onto an inorganic solid carrier with a large surface area to
create new organic–inorganic hybrid catalyst.5,6 The reactive
centers in these solid-supported catalysts are highly mobile
similar to homogeneous catalysts, and at the same time
have the advantage of recyclability like heterogeneous cata-
lysts. In this view, several types of solid sulfonic-acid-func-
tionalized silica (both amorphous and ordered) have been
synthesized and applied as an alternative to traditional sul-
fonic acid resins and homogeneous acids in catalyzing
chemical transformations.5,7
Herein, we wish to describe the preparation of silica-
bonded S-sulfonic acid (SBSSA) as illustrated in Scheme 1,
and its use as catalyst for the conversion of alcohols into cor-
responding trimethylsilyl ethers. Sulfur content of SBSSA by
conventional elemental analysis was 16.12%. Typically, a
loading at ~0.35 mmol/g is obtained. On the other hand,
when the washed sulfonated product 2 was placed in an
aqueous NaCl solution, the pH of the solution dropped virtu-
ally instantaneously to pH 1.85, as ion exchange occurred
between protons and sodium ions (proton exchange capacity:
0.33 mmol/g of sulfonic acid 2), which is in good agreement
with the result obtained from TGA and titration.
Introduction
In recent years, there has been much attention on the
search for environmentally benign chemical processes or
methodologies, because they are essential for the conserva-
tion of the global ecosystem. The development of heteroge-
neous catalysts for fine chemical synthesis has become a
major area of research, as the potential advantages of these
materials (facile recovery and reusability; the potential for
incorporation in continuous reactors and micro reactors)
over homogeneous systems can lead to novel environmen-
tally benign chemical procedures for academia and indus-
try.1 Application of solid acids in organic transformations is
desirable, owing to their simplicity in handling, decreased
reactor and plant corrosion problems, and more environmen-
tally safe disposal.2–10 Green chemistry not only requires the
use of environmentally benign reagents and solvents, but
Received 13 March 2009. Accepted 9 October 2009. Published
on the NRC Research Press Web site at canjchem.nrc.ca on
29 January 2010.
K. Niknam,1 D. Saberi, and H. Molaee. Chemistry
Department, Faculty of Sciences, Persian Gulf University,
Bushehr 75169, Iran.
M.A. Zolfigol. Faculty of Chemistry, Bu-Ali Sina University,
P.O. Box 4135, Hamedan 6517838683, Iran.
1Corresponding author (e-mail: khniknam@gmail.com).
Protection and deprotection of functional groups are in-
Can. J. Chem. 88: 164–171 (2010)
doi:10.1139/V09-162
Published by NRC Research Press

Niknam et al.
165
Scheme 2. Conversion of different kinds of hydroxyl groups into
Scheme 1. Preparation of silica-bonded S-sulfonic acid.
corresponding silyl ethers
in the presence of SBSSA in CH3CN at room temperature.
The optimal amount of the catalyst was 0.015 g per 1 mmol
of 4-bromobenzyl alcohol and 0.8 mmol of HMDS. Next,
we prepared a range of silylethers under the following reac-
tion conditions: hydroxyl compound (1 mmol), HMDS
(0.8 mmol), SBSSA (0.015 g), and acetonitrile (2 mL)
(Table 1). A wide range of alcohols underwent silylation by
this procedure to provide the corresponding TMS ethers in
good-to-excellent yields. Generally, benzylic alcohols, phe-
nols, and primary and secondary alcohols are faster than ter-
tiary alcohols. Trimethylsilylation of hydroxyl groups
produce corresponding trimethylsilylated compounds under
these conditions, whereas substituted thiophenol, 1-butantiol
(Table 1, entries 8, 25, and 26), aniline derivatives, aliphatic
amines (Table 1, entries 22–24), and N-phenyl acetamide
(Table 1, entry 27) remained intact under the reaction condi-
tions. It is worth mentioning that in the case of p-aminophe-
nol, only the phenolic group reacted under these conditions
and the amino group remains intact (Table 1, entry 19).
We investigated the selective silylation of different binary
mixture of alcohols and also alcohols and phenols in the
presence of amine, amide, and thiols. This method was
shown to be highly selective for primary alcohols, such as
benzyl alcohol and 2-phenylethanol. Primary alcohols were
completely converted to the corresponding silyl ethers, while
tertiary alcohols were converted to the corresponding sily-
lated products with 0% yield (Scheme 3).
Excellent chemoselectivity was also observed for the con-
version of secondary alcohols and phenols in the presence of
tertiary alcohols such as a-terpinene, 1-phenyl-2-methyl-2-
propanol (Scheme 3). We also explored the chemoselectivity
of SBSSA in the silylation method. Alcohols and phenols in
the presence of an amine, amide, and thiols were completely
converted to the corresponding trimethylsilyl ethers as sole
product.
To show the efficiency of the SBSSA in comparison with
previously reported procedures, Table 2 compares some of
our results with LiClO4’/SiO2,21 H-b zeolite,22 HClO4/
SiO2,29 sulfonic-acid-functionalized silica,30 silica sulfuric
acid,31 and alumina sulfuric acid37 with respect to reaction
times and yields of obtained products. It is clear from the
results shown in Table 2, that silylation reactions carried
out with SBSSA require shorter reaction times and lower
catalyst loading.
evitable processes for the synthesis of polyfunctional com-
pounds. Silylation of alcohols and polyols is one of the
most commonly used methods for their protection.11 Trime-
thylsilylation is a classic way to produce volatile derivatives
of alcohols and polyols, as required for their vapor-phase
chromatography/mass spectrometric analysis.12 Another ap-
plication is the conversion of trimethylsilyl ethers into the
corresponding ethers.13 Generally, the formation of trime-
thylsilyl ethers has been carried out by treatment of alcohols
with trimethylsilyl chloride or trimethylsilyl triflate in the
presence of a base,14 Li2S,15 and sometimes a nonionic super
base catalyst.16 However, some of these methods have fre-
quently suffered from drawbacks, such as lack of reactivity
or the difficulty in removal of amine salts derived from the
reaction of by-produced acid and co-bases during the silyla-
tion reaction. 1,1,1,3,3,3-Hexamethyldisilazane (HMDS) is a
stable, commercially available, and inexpensive reagent for
trimethylsilylation of hydrogen-labile substrates,17 giving
ammonia as the only byproduct. On the other hand, silyla-
tion, using this silazan-type reagent, is nearly neutral and
does not need any special precautions. However, the weak
silylating ability of HMDS is a main drawback for its appli-
cation, which needs forceful conditions and long reaction
times in many instances. A variety of catalysts, such as
(CH3)3SiCl,18 silica chloride,19 ZnCl2,20 LiClO4,21 H-b zeo-
lite,22 tungestophosphoric acid,23 poly(N-bromobenzene-1,3-
disulfonamide),24
ultrasound,25
CuSO4Á5H2O
and
Cu(OTf)2,26 Al(HSO4)3,27 KBr,28 silica-supported perchloric
acid,29 sulfonic-acid-functionalized silica,30 silica sulfuric
acid,31 1,3-dibromo-5,5-diethylbarbituric acid,32 tribromoiso-
cyanuric acid and DABCO-Br2,33 Fe(F3CCO2)3,34 tetrabuty-
lammonium bromide,35 tribromomelamine,36 and alumina
sulfuric acid37 have been reported for the silylation of hy-
droxyl groups using HMDS. In addition to the previously re-
ported procedures, the facile and general synthetic
methodology for the silylation of alcohols under essentially
neutral conditions is desirable, so this subject encouraged us
to develop an efficient, convenient, and practical procedure
for the protection of hydroxyl groups under mild and hetero-
geneous conditions.
In all reactions studied, fast evolution of ammonia gas
was observed (HMDS is stronger base than NH3). With this
observation, we have proposed a mechanism in which the
generation of NH3 and catalytic role of SBSSA in a catalytic
cycle is clarified (Scheme 4).29,34
The possibility of recycling the catalyst was examined.
For this purpose, the reaction of benzyl alcohol and HMDS
Results and discussion
The trimethylsilylation of hydroxyl groups is easily car-
ried out at room temperature under mild conditions in the
presence of SBSSA as a catalyst (Scheme 2). First, we
studied the reaction of 4-bromobenzyl alcohol with HMDS
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Can. J. Chem. Vol. 88, 2010
Scheme 3. Chemoselectivity between primary, secondary alcohols,
and phenols in the presence of tertiary alcohols and amides using
SBSSA with HMDS.
Fig. 1. Recyclability of solid silica-bonded S-sulfonic acid as cata-
lyst in the silylation reaction of benzyl alcohol (1 mmol) and
HMDS (1 mmol) at room temperature. Reaction time = 5 min.
Conclusion
In conclusion, a practical, efficient, and convenient
method for the silylation of hydroxyl compounds was de-
scribed. One major advantage of our described method is us-
ing very low molecular ratio of the catalysts in comparison
with the reported procedures in the literature. Therefore, we
think that this method can be a useful addition to the present
methodologies for the silylation of hydroxy groups.
Experimental
General
Chemicals were purchased from Merck, Fluka, and Al-
drich Chemical Companies. IR spectra were run on a Shi-
madzu IR-435 FTIR spectrophotometer. H NMR was run
Scheme 4. Proposed mechanism for the conversion of alcohols into
the corresponding silyl ether by using SBSSA.
1
on JEOL NMR spectrometer (FX 90Q) and Bruker Avance
(DRX 500 MHz). Melting points were recorded on a Melt-
ing Point SMP1 apparatus in open capillary tubes and are
uncorrected. The progress of reaction was followed with
TLC, using silica gel SILG/UV 254 plates. All the products
are known and were characterized by comparison of their
1
spectral (IR, H NMR), TLC, and physical data with those
reported in the literature.22–36 3-Mercaptopropylsilica 1
(MPS) was prepared according to the previously reported
procedure.5a
Catalyst preparation
To a magnetically stirred mixture of 3-mercaptopropylsil-
ica 1 (5 g) in tert-buylmethyl ether (20 mL), chlorosulfonic
acid (1.00 g, 9 mmol) was added dropwise at 0 8C for 2 h.
After addition was complete, the mixture was stirred for 2 h
until HCl gas evolution was stopped. Then, the mixture was
filtered and washed with methanol (30 mL) and dried at
room temperature to obtain silica-bonded functionalized sul-
fonic acid 2 (SBSSA) as cream powder (5.22 g). Sulfur con-
tent of the samples was 16.12% by conventional elemental
analysis. TGA analysis of SBSSA shows a first mass loss
due to the desorption of water below 100 8C (Fig. 2). This
was studied in acetonitrile at room temperature in the pres-
ence of SBSSA. When the reaction was complete, the mix-
ture was filtered and the solid was washed with
dichloromethane, and the recycled catalyst was saved for
the next reaction. The recycled catalyst could be directly
reused 30 times without any treatment. No observation of
appreciable loss in its catalytic activities was noticed
(Fig. 1).
Published by NRC Research Press

Niknam et al.
167
Fig. 2. TGA diagram for a sample of silica-bonded S-sulfonic acid
under nitrogen stream.
(s, 9H), 4.65 (s, 2H), 7.20 (d, 2H, J = 8.4 Hz), 7.46 (d, 2H,
J = 8.6 Hz).
Trimethyl(4-chlorobenzyloxy)silan (Table 1, entry 4)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;36 bp
1
228 8C/760 torr. H NMR (90 MHz, CDCl3, ppm) d: 0.19
(s, 9H), 4.68 (s, 2H), 7.28–7.30 (m, 4H).
Trimethyl(4-nitrobenzyloxy)silan (Table 1, entry 5)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;25 bp >
1
300 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.22
(s, 9H), 4.83 (s, 2H), 7.52 (d, 2H, J = 8.8 Hz), 8.22 (d, 2H, J
= 8.7 Hz). 13C NMR (125 MHz, CDCl3, ppm) d: –0.10,
63.95, 123.95, 127.00, 147.49, 149.16.
is followed by a second mass loss starting at 140 8C, corre-
sponding to the loss of the covalently bound organic group.
From this mass loss, it is calculated that the loading of the
organic group bound to silica surface was 1.78 mmol g–1.
Trimethyl(2-phenylethoxy)silan (Table 1, entry 6)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
1
230 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.11
pH analysis of the SBSSA
(s, 9H), 2.87 (t, 2H, J = 7.3 Hz), 3.81 (t, 2H, J = 7.3 Hz),
To an aqueous suspension of 0.1 g SBSSA, NaOH
(1.8 mL, 0.1 mol/L) was added. This is equal to a loading
of 1.8 mmol SO3H g–1. So, all of the SH functional groups
in 3-mercaptopropylsilica 1 were sulfonated. According to
previous reports,5 the loading of 3-mercaptopropylsilica 1 is
0.33 mmol/g.
7.23–7.33 (m, 5H).
Trimethyl(3-phenylpropyloxy)silan (Table 1, entry 7)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;25 bp
1
245 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.22
(s, 9H), 1.92–1.98 (m, 2H), 2.77 (t, 2H, J = 7.8 Hz), 3.70 (t,
2H, J = 6.4 Hz), 7.26–7.29 (m, 3H), 7.35–7.38 (m, 2H). 13C
NMR (125 MHz, CDCl3, ppm) d: 0.03, 32.60, 34.70, 62.36,
126.17, 128.75, 128.91, 142.58.
General procedure for the silylation of alcohols
To a stirred solution of the compound containing hy-
droxyl groups (1 mmol) and HMDS (0.8 mmol) in CH3CN
(2 mL) was added SBSSA (0.015 g) and stirred at room
temperature. When the reaction was complete by GC (or
TLC, n-hexane/EtOAc, 9:1) analysis, CH2Cl2 was added
(10 mL), and SBSSA was removed by filtration. The solvent
was evaporated and the trimethylsilyl ether was isolated al-
most as a pure crude product. Further purification was car-
ried out by short column chromatography on silica gel
eluting with ethyl acetate/petroleum ether, if necessary.
Trimethyl(2-mercaptoethoxy)silan (Table 1, entry 8)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;38 bp
1
146 8C/760 torr. H NMR (90 MHz, CDCl3, ppm) d: 0.06
(s, 9H), 1.43 (t, 1H, J = 8.1 Hz), 2.44–2.82 (m, 2H), 3.49–
3.82 (m, 2H).
Trimethyl(diphenylmethoxy)silan (Table 1, entry 9)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp >
Trimethyl(benzyloxy)silan (Table 1, entry 1)
Purified on short column of silica gel using petroleum
1
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
300 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.20
1
(s, 9H), 5.88 (s, 1H), 7.32 (t, 2H, J = 7.3 Hz), 7.40 (t, 4H, J
= 7.6 Hz), 7.46 (t, 4H, J = 7.5 Hz). 13C NMR (125 MHz,
CDCl3, ppm) d: 0.65, 77.00, 127.04, 127.53, 128.68, 145.35.
212 8C/760 torr (1 torr = 133.322 Pa). H NMR (500 MHz,
CDCl3, ppm) d: 0.19 (s, 9H), 4.72 (s, 2H), 7.35–7.36 (m,
5H).
Trimethyl(1-phenylethoxy)silan (Table 1, entry 10)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
Trimethyl(4-methoxybenzyloxy)silan (Table 1, entry 2)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
1
1
212 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.15
257–258 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d:
(s, 9H), 1.51 (d, 3H, J = 6.3 Hz), 4.93 (q, 1H, J = 6.3 Hz),
7.28 (t, 1H, J = 6.9 Hz), 7.34–7.40 (m, 4H).
0.18 (s, 9H), 3.81 (s, 3H), 4.66 (s, 2H), 6.91 (d, 2H, J =
8.5 Hz), 7.44 (d, 2H, J = 8.4 Hz). 13C NMR (125 MHz,
CDCl3, ppm) d: 0.30, 55.21, 64.41, 113.75, 128.13, 133.16,
158.90.
Trimethyl(1-phenyl-2-methyl-2-propyloxy)silan (Table 1,
entry 11)
Trimethyl(4-bromobenzyloxy)silan (Table 1, entry 3)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;36 bp
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;36 bp
1
245 8C/760 torr. H NMR (90 MHz, CDCl3, ppm) d: 0.05
1
250 8C/760 torr. H NMR (90 MHz, CDCl3, ppm) d: 0.17
(s, 9H), 1.20 (s, 6H), 2.71 (s, 2H), 7.12–7.38 (m, 5H).
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Can. J. Chem. Vol. 88, 2010
Table 1. Silylation of alcohols, phenols, and naphthols with HMDS in the presence of SBSSA as catalyst at room temperature.
Trimethyl[1-methyl-1-(4-methyl-cyclohex-1-
Trimethylphenoxy silan (Table 1, entry 13)
enyl)ethoxy]silan (Table 1, entry 12)
Purified on short column of silica gel using petroleum
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
ether/ethyl acetate (10:1) as eluent. Colorless liquid;32 bp
211 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.34
1
1
256 8C/760 torr. H NMR (90 MHz, CDCl3, ppm) d: 0.09
(s, 9H), 6.92 (d, 2H, J = 7.8 Hz), 7.02 (t, 1H, J = 7.3 Hz),
7.31 (t, 1H, J = 8.0 Hz).
(s, 9H), 0.94–2.00 (m, 16H), 5.27–5.44 (m, 1H).
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Niknam et al.
Table 1. Concluded.
169
Trimethyl(biphenyl-2-yloxy) silan (Table 1, entry 14)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;39 bp
281 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.05
(s, 9H), 6.92 (dd, 1H, J1 = 8.0 Hz, J2 = 0.7 Hz), 7.06 (dt, 1H
J1 = 7.5 Hz, J2 = 0.8 Hz), 7.21–7.26 (m, 1H), 7.31 (t, 1H,
J = 7.4 Hz), 7.36 (dd, 1H, J1 = 7.5 Hz, J2 = 1.5 Hz), 7.40
(t, 2H, J = 7.5 Hz), 7.54 (d, 2H, J = 8.3 Hz). 13C NMR
(125 MHz, CDCl3, ppm) d: 0.51, 121.03, 122.35, 127.16,
128.26, 128.81, 130.06, 133.78, 139.49, 152.73.
1
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Can. J. Chem. Vol. 88, 2010
Table 2. Comparison of the results of SBSSA (I) with LiClO4/SiO2 (II),21 H-b zeolite (III),22 HClO4/SiO2 (IV),29
sulfonic-acid-functionalized silica (V),30 silica sulfuric acid (VI),31 and alumina sulfuric acid (VII)37 in the synthesis
of trimethylsilyl ether using HMDS.
Trimethyl(4-methylphenoxy) silan (Table 1, entry 15)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
206 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.32
(s, 9H), 2.33 (s, 3H), 6.80 (d, 2H, J = 8.1 Hz), 7.08 (d, 2H,
J = 8.0 Hz).
13C NMR (125 MHz, CDCl3, ppm) d: 0.58, 20.60, 119.13,
122.96, 127.10, 130.03, 137.42, 154.14.
1
Trimethyl(4-aminophenoxy) silan (Table 1, entry 19)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
1
255 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.22
Trimethyl(2-naphtaleneoxy) silan (Table 1, entry 16)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
(s, 9H), 3.34 (s, 2H), 6.51 (d, 2H, J = 8.5 Hz), 6.61 (d, 2H,
J = 8.5 Hz).
1
282 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.41
Trimethyl(4-fluorophenoxy) silan (Table 1, entry 20)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;29 bp
(s, 9H), 7.18 (dd, 1H, J1 = 8.8 Hz, J2 = 2.3 Hz), 7.31 (d, 1H,
J = 2.1 Hz), 7.41 (t, 1H, J = 7.3 Hz), 7.50 (dt, 1H, J1 =
7.6 Hz, J2 = 0.8 Hz), 7.77–7.85 (m, 3H).
1
208 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.25
(s, 9H), 6.75–6.77 (m, 2H), 6.89–6.92 (m, 2H). 13C NMR
(125 MHz, CDCl3, ppm) d: 0.53, 116.10, 121.26, 151.52,
159.08.
Trimethyl(2,4,6-thrimethylphenoxy) silan (Table 1, entry 17)
Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;40 bp
1
241 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.25
Acknowledgement
(s, 9H), 2.17 (s, 6H), 2.23 (s, 3H), 6.78 (s, 2H). 13C NMR
(125 MHz, CDCl3, ppm) d: 1.37, 18.02, 20.94, 128.51,
129.47, 130.70, 150.63.
We are thankful to the Persian Gulf University Research
Council for the partial support of this work.
References
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Purified on short column of silica gel using petroleum
ether/ethyl acetate (10:1) as eluent. Colorless liquid;39 bp
1
243 8C/760 torr. H NMR (500 MHz, CDCl3, ppm) d: 0.26
(s, 9H), 2.32 (s, 3H), 6.62 (dd, 1H, J1 = 8.6 Hz, J2
=
2.8 Hz), 6.72 (d, 1H, J = 2.8 Hz), 7.17 (d, 1H, J = 7.9 Hz).
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