Highly efficient protection of alcohols as trityl ethers under solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H

Article abstract of DOI:10.1016/j.crci.2014.01.003

An efficient method was developed for the protection of alcohols as trityl ethers using triphenylmethanol in the presence of nanoporous MCM-41-SO₃H as a heterogeneous catalyst under solvent-free ball-milling at room temperature. Low catalyst loading, high efficiency, reusability are among the advantages of this new solvent-free and environmentally friendly method. The deprotection of the produced trityl ethers was also efficiently achieved using the same catalyst in wet acetonitrile.

Full text of DOI:10.1016/j.crci.2014.01.003

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C. R. Chimie xxx (2014) xxx–xxx
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Full paper/Memoire
Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable
nanoporous MCM-41-SO3H
*
Zeynab Gholamzadeh, Mohammad Reza Naimi-Jamal , Ali Maleki
Research Laboratory of Green Organic Synthesis & Polymers, Department of Chemistry, Iran University of Science and Technology,
Naarmak, Farjaam street, 16846-13114 Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
An efficient method was developed for the protection of alcohols as trityl ethers using
triphenylmethanol in the presence of nanoporous MCM-41-SO3H as a heterogeneous
catalyst under solvent-free ball-milling at room temperature. Low catalyst loading, high
efficiency, reusability are among the advantages of this new solvent-free and
environmentally friendly method. The deprotection of the produced trityl ethers was
also efficiently achieved using the same catalyst in wet acetonitrile.
Received 10 September 2013
Accepted after revision 7 January 2014
Available online xxx
Keywords:
Alcohols
ß 2014 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Protection
Deprotection
MCM-41-SO3H nanoporous catalyst
Ball-milling
Solvent-free
1. Introduction
conditions, it can be readily removed under mild acidic
conditions. The introduction of this group into the
The protection and deprotection of the alcohol func-
tional group are of high interest, and have been widely
considered because of their basic role in multi-step
syntheses. Whereas protons of alcohols have some acidic
properties and can be separated in the vicinity of strong
bases, hydroxyl functional groups in alcohols can con-
tribute to many unfavorable reactions, even under mild
conditions, resulting in side reactions, thus decreasing the
reaction yield. Therefore, developing mild and efficient
procedures for the protection and deprotection of the
alcohols’ proton is an important aim for synthetic
chemists. One of the conventional methods used to protect
alcohols is their transformation to triphenylmethyl (trityl)
ether. The trityl group (Tr) is one of the most advantageous
protecting groups, because it can be removed easily.
Although the trityl group is stable under neutral or basic
hydroxyl functionality has been carried out using usually
trityl halides and trityl ethers (TrOR), as well as tritylium
salts. According to the literature, there are very limited
examples describing the protection of alcohols as trityl
ethers with triphenylmethanol (TrOH) in the presence of
an acidic catalyst. Some examples are aqueous H2SO4 [1],
B(C6F5)3 [2], ZnCl2 [2], AlCl3 [2] (all in dichloromethane),
and Fe(III) salts in alcoholic solvents [3]. When trityl ethers
(TrOR, R = benzyl-, p-methoxybenzyl- and prenyl-) were
used, protection was carried out in the presence of an
oxidizing agent such as 2,3-dichloro-5,6-dicyano-1,
4-benzoquinone (DDQ) [4] or DDQ/Mn(OAc)3 [5]. Triphe-
nylmethyl chloride and bromide (X = Cl, Br) were usually
used in the presence of an organic base, such as pyridine
[6–8], dimethylaminopyridine (DMAP) [9], 2,4,6-tri-
t-butyl pyridine [10], 2,4,6-collidine,[11] triethylamine
(TEA) [12,13], and 1,8-diazabicyclo[5.4.0]-undec-7-ene
(DBU) [14]. In addition, some tritylating reagents with
ionic character such as TrClO4 [8], TrPF6 [11], TrBF4 [15,16],
and trityl triflate [17,18] were used alone or in the
*
Corresponding author.
E-mail address: naimi@iust.ac.ir (M.R. Naimi-Jamal).
1631-0748/$ – see front matter ß 2014 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2014.01.003
Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003

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In continuation of our previous work on the ability of
the nanoporous MCM-41-SO3H catalyst to promote the
protection of carbonyls as 1,1-diacylals [19], we herein
wish to report the protection reaction of alcohols 1 as trityl
ethers under solvent-free conditions, and their deprotec-
tion at ambient temperature by using MCM-41-SO3H as a
recyclable catalyst (Scheme 1).
2. Results and discussion
In order to find the best conditions for the protection
reaction of alcohols, the reaction of 1.0 mmol of benzyl
alcohol (1a) with 1.0 mmol of triphenylmethanol (2a) by
ball-milling at room temperature was chosen as a model
reaction. The effect of the catalyst type and of loading was
then examined. The catalytic activity of MCM-41 itself and
its modified forms such as boron (B-MCM-41), ferric (Fe-
MCM-41), aluminum (Al-MCM-41), zirconium (Zr-MCM-
41), and MCM-41-SO3H has been studied. The results have
been summarized in Table 1.
Scheme 1. Protection and deprotection reaction of alcohols catalyzed by
MCM-41-SO3H.
presence of substituted pyridines. Some of these methods
require harsh reaction conditions such as azeotropic
removal of water at high reaction temperatures, long
reaction times, use of large quantities of organic solvents
and bases, and tedious work-up procedures. Furthermore,
most of these catalysts are not recoverable, and cannot be
used in further subsequent reactions. To the best of our
knowledge, there are no reports in the literature on
solvent-free protection of alcohols using TrOH, so far.
In recent years, mesoporous materials such as MCMs
have received much attention as potential heterogeneous
catalysts to replace homogeneous catalytic systems, and
have proven to be excellent host materials for developing
organic reactions, because of their high surface area, large
pore volume, uniform porosity, and excellent thermal-,
hydrothermal-, chemical-, and mechanical stability.
It is noteworthy to mention that no reaction occurred in
the absence of a catalyst, even after 24 h (Table 1, entry 1).
As it is seen from the results, MCM-41-SO3H catalyst shows
the highest activity, presumably because of its consider-
able acidic nature. The acidic capacity of MCM-41-SO3H
catalyst was determined as 0.011 mmol [H+] gÀ1 via
titration of 1.0 g of the catalyst with a 0.01 N solution of
NaOH. This will guarantee much milder reaction condi-
tions compared to aqueous H2SO4 which was previously
used [1]. The average pore width (4V/A) of nanoporous
MCM-41-SO3H was measured as 2.62 nm by the BJH
adsorption method.
By using 5 and 10 mg of MCM-41-SO3H catalyst,
moderate yields of 59% and 87% have been obtained after
20 min of ball-milling at room temperature, whereas
increasing the loading to 15 mg has practically converted
Table 1
Protection reaction of benzyl alcohol (1a) with triphenylmethanol (2a) by some modified MCM-41 catalystsa.
catalyst
OH
O
+
H O
2
+
HO
solvent-free, r.t.
3a
1a
2a
Entry
Catalyst
Amount of catalyst (mg)
Time (min)
Yieldb (%)
1
–
–
24 h
60
0
2
MCM-41
B-MCM-41
15
15
15
15
15
5
0
3
90
64%
59%
35%
78%
59%
87%
98%
96%
52%
4
Al-MCM-41
45
120
60
5
Zr-MCM-41
6
Fe-MCM-41
7
MCM-41-SO3H
MCM-41-SO3H
MCM-41-SO3H
MCM-41-SO3H
MCM-41-SO3H
20
8
10
15
20
100
20
9
20
10
11
20
20
a
Reaction conditions: benzyl alcohol (1a) (1.0 mmol), triphenylmethanol (2a) (1.0 mmol), catalyst, solvent-free, ball-milling, room temperature.
b
Isolated yield.
Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003

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3
Table 2
Tritylation of various alcohols using MCM-41-SO3H under optimal conditionsa.
MCM-41-SO3H
ROTr + H2O
ROH + TrOH
Solvent-free, r.t,
ball- milling
Entry
Substrates
Product
Time
Yieldb
(%)
Mp (Obsd)
Mp (Lit.)
(min)
(8C)
(8C)
1
20
98
103–105
102–104 [20]
CH2OH
CH2OTr
1a
3a
2
10
98
117–118
117–117.5 [21]
CH2OH
CH2OTr
Me
1b
Me
3b
3
4
5
15
30
40
96
98
97
101–102
136–138
147–149
Present work
137–138 [22]
Present work
CH2OH
Me
CH2OTr
Me
1c
3c
CH2OH
CH2OTr
Cl
1d
Cl
3d
CH2OH
Cl
CH2OTr
Cl
1e
3e
6
7
60
90
98
96
168–169
150–151
166–167 [21]
Present work
CH2OH
CH2OTr
O2N
1f
O2N
3f
CH2OTr
NO2
CH2OH
NO2
1g
3g
3h
8
9
75
89
61
118–120
153–154
118–119 [23]
154–155 [12]
OTr
OTr
OTr
OH
OH
OH
1h
1i
120
3i
10
11
12
90
60
75
86
94
98
84–85
85 [24]
3j
1j
87–88
87.1–87.8 [25]
Present work
OTr
OH
3k
1k
124–126
OH
OTr
O2N
1l
O2N
3l
Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003

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Table 2 (Continued )
MCM-41-SO3H
ROTr + H2O
ROH + TrOH
Solvent-free, r.t,
ball- milling
Entry
Substrates
Product
Time
Yieldb
(%)
Mp (Obsd)
Mp (Lit.)
(min)
(8C)
(8C)
13
14
105
120
88
55–56
54–55 [1]
OH
OTr
OTr
1m
3m
95
186–188
187–188 [26]
OH
HO
1n
TrO
3nc
15
180
–
–
–
OH
Ph
OTr
Ph
Ph
Ph
Ph
Ph
1o
3o
a
Reaction conditions: alcohol (1.0 mmol), triphenylmethanol (2a) (1.0 mmol), MCM-41-SO3H catalyst (15 mg), solvent-free, ball-milling, room
temperature.
b
Isolated yield.
c
In the presence of two equivalents of TrOH.
all the alcohol into its corresponding ether (Table 1, entries
6–8). Increasing the amount of the catalyst to 100 mg
reduced the yield considerably (Table 1, entry 10).
By employing the optimized reaction conditions,
various aromatic and aliphatic alcohols have been
subjected to trityl protection. Table 2 shows the scope of
the reaction. As it is shown, primary and secondary
aliphatic and benzylic alcohols were converted into their
corresponding trityl ethers very easily, in high yields and
short reaction times.
Comparison between the obtained results showed that
benzyl alcohols including electron-donating groups such
as CH3 (Table 2, entries 2 and 3) required shorter reaction
times compared to benzyl alcohols bearing electron-
withdrawing groups such as Cl and NO2 (Table 2, entries
4–7). Clearly, the presence of electron-donating groups,
especially in ortho and para positions, facilitates the
nucleophilic attack of the alcohols. The secondary alcohols
1h–1j reacted slowly at room temperature to yield the
corresponding trityl ethers, however affording good yields
(Table 2, entries 8–10).
Aliphatic alcohols (Table 2, entries 10–14) need more
time compared to aromatic alcohols. In the case of ethylene
glycol, both hydroxyl groups were protected by using 2
equivalents of triphenylmethanol. By using one equivalent
of TrOH, a mixture of unreacted ethylene glycol along with
mono- and deprotected products was afforded.
The protection reaction seems to be sensible to the steric
situation of the starting alcohol. Comparing entries 1, 9, and
15, one should conclude that with increasing the steric
be protonated at the oxygen atom by the Brønsted acid
MCM-41-SO3H. Intermediate I will then dissociate into
water and trityl carbocation (II). Nucleophilic attack of
alcohol (1) by the trityl cation followed by deprotonation
affords the desired product (3).
It is well understood that trityl carbocation is more
stable than benzylic carbocation and can be formed faster.
To confirm this in the present method, 0.5 mmol of
triphenylmethanol and 0.5 mmol of 4-chlorobenzyl alco-
hol have been poured in two mortars separately, and
MCM-41-SO3H has been added to them. Upon grinding of
triphenylmethanol with the catalyst, the color has been
changed from white to yellow, which suggests the
formation of trityl carbocation. In the mortar containing
4-chlorobenzyl alcohol, no color change was observed and
the alcohol remained unchanged as a white powder. The
formation of the trityl carbocation has been also approved
by UV–Vis spectroscopy (Fig. 1). Thus triphenylmethanol
(A), MCM-41-SO3H catalyst (B), and a grinded mixture of
triphenylmethanol with MCM-41-SO3H catalyst (C) have
been studied using solid-state UV–Visible spectroscopy. As
shown in Fig. 1, a new peak at about 440 nm was observed
in the C sample spectrum, which is related to the yellow
color of Tr+, confirming the formation of the carbocation.
Interestingly, we have observed that MCM-41-SO3H
was also able to catalyze the reverse deprotection reaction
into their parent alcohols. In order to obtain the best
reaction conditions for this purpose, the reaction of benzyl
trityl ether in the presence of MCM-41-SO3H at room
temperature has been chosen as a model one and the effect
of various solvents on it has been examined. As shown in
Table 3, MCM-41-SO3H in wet CH3CN has quantitatively
converted benzyl trityl ether to its parent alcohols. In
water and methanol, the starting material was sparingly
soluble, hence remained practically unreacted. Further
investigations show that the deprotection reaction in wet
CH3CN will be completed at room temperature in 20 min.
Other primary and secondary, and aliphatic or benzylic
trityl ethers were also converted very easily into their
hindrance at the
a-C, the activity of the hydroxyl group
would decrease dramatically. It is noteworthy to mention
that in the case of tertiary alcohol 1o (Table 2, entry 15), no
protection reaction was observed at all. Moreover, in
contrast to some previously reported procedures [3], we
have not observed any elimination or oxidation products.
According to these facts, a possible mechanism for the
catalyzed protection of alcohols by MCM-41-SO3H is
shown in Scheme 2. As shown, triphenylmethanol (2) will
Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003

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Scheme 2. Proposed mechanism for the protection reaction of alcohols
with triphenylmethanol catalyzed by MCM-41-SO3H.
corresponding hydroxyl compounds with
a catalytic
amount of MCM-41-SO3H in wet CH3CN, and in high
yields (Table 4).
Fig. 1. Solid-state UV–Visible spectra of grinded samples of
triphenylmethanol (A), MCM-41-SO3H catalyst (B), and a mixture of
triphenylmethanol with MCM-41-SO3H catalyst (C).
Comparison of the results shows that the substitution
on the benzene ring affects the deprotection reaction time.
Ethers bearing electron-donating groups such as CH3 on
their benzyl moiety (Table 4, entries 2 and 3) reacted in
shorter reaction times compared to those bearing electron-
withdrawing groups such as Cl and NO2 (Table 4, entries 4–
7). Aliphatic trityl ethers were reacted in moderate
reaction times with high yields (Table 4, entries 10–12).
Trityl ethers with sterically hindered groups preceded the
deprotection reaction in longer times (Table 4, entries
8 and 9).
dissociates into the trityl carbocation (4) and the alcohol 1.
Then, in the presence of wet acetonitrile, 4 converts to
triphenylmethanol (2) and the catalyst returns to the
catalytic cycle (Scheme 3).
3. Reusability of MCM-41-SO3H catalyst
Based on the hard-soft acids and bases rule (HSAB), the
acidic proton of MCM-41-SO3H catalyst protonates the trityl
ether oxygen, makes it positive and thereby the inter-
mediate III is formed. In the next step, this intermediate
One of the benefits of heterogeneous catalysts is their
easy separation from
a reaction mixture and their
reusability. The recyclability of the MCM-41-SO3H catalyst
has been investigated in the protection reaction of benzyl
Table 3
Effect of different solvents on the deprotection of benzyl trityl ether in the presence of a catalytic amount of MCM-41-SO3H at room temperaturea.
MCM-41-SO3H
r.t.
OH
O
HO
+
1a
Solvent
2a
3a
Entry
Time (min)
Yieldb (%)
1
2
3
4
5
H2O
120
120
60
-
CH3OH
10
56
79
100
CH2Cl2
CH3NO2
CH3CN (wet)
90
20
a
Reaction conditions: benzyl trityl ether (20 mg), MCM-41-SO3H (20 mg), solvent (2.5 mL), room temperature.
Yields were determined by high-performance liquid chromatography (HPLC).
b
Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003

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Table 4
100
Deprotection of trityl ethers in the presence of MCM-41-SO3H in CH3CN at
room temperaturea.
90
80
70
60
50
40
30
20
10
0
Entry
Substrate
Product
Time (min)
Yieldb (%)
1
3a
3b
3c
3d
3e
3f
1a
1b
1c
1d
1e
1f
20
10
15
20
30
40
45
60
90
40
30
20
100
100
100
100
100
100
100
100
100
100
100
100
2
3
4
5
6
7
3g
3h
3j
1g
1h
1j
8
9
10
11
12
3l
1l
3m
3n
1m
1n
1
2
3
4
Run
a
Reaction conditions: trityl ether (20 mg), MCM-41-SO3H (20 mg),
acetonitrile (2.5 mL), room temperature.
Fig. 2. Recyclability of MCM-41-SO3H catalyst for the protection reaction
of alcohols.
b
Yields were determined by HPLC and/or GC.
4. Conclusion
In summary, we have developed a mild, efficient and
green procedure for the protection of alcohols as trityl
ethers and deprotection of them using the recyclable
MCM-41-SO3H catalyst. Moreover, high reaction yields,
simple work-up, mild conditions, safe and environmen-
tally benign method, short reaction times, and reusability
of the catalyst will make the present method a valuable
methodology for the protection and deprotection reaction
of alcohols. No by-products (e.g., alkenes from elimination,
carbonyls from oxidation, or ethers from homocoupling
reactions) were detected. In addition, this catalyst offers
the opportunity to protect alcohols as trityl ethers in the
presence of a base-sensitive functionality.
Both protection and deprotection reactions proceed with
high yields at room temperature in the presence of MCM-41-
SO3H. It is noteworthy to mention that attempts at
deprotecting the trityl group in similar methods were usually
unsuccessful (for example, the deprotection of the trityl group
by [B(C6F5)3], even at refluxing temperatures [2]).
alcohol 1a with triphenylmethanol 2a. The reactions were
carried out according to the above general procedure for
the synthesis of trityl ethers. After the first run, the catalyst
was washed with EtOAc, dried at room temperature, and
then subjected to a second protection reaction. This
procedure was repeated three more times (Fig. 2). The
average reaction yield for four repeated runs was 95.5%.
As shown in Fig. 2, it is possible that some unreacted
starting materials or even the product be adsorbed on the
surface or in the pores of the catalyst. This part of the
materials can be incorporated in the next run (compare
runs 3 and 4). This can be principally an advantage of the
method, when the catalyst is used industrially in the same
reaction.
5. Experimental
5.1. General
All chemicals and reagents were purchased from Merck,
Aldrich, and Fluka and used without further purification.
Tetraethyl orthosilicate (TEOS) and cetyltrimethylammo-
nium bromide (CTAB) were used as sources of silicon and
structure-directing agent, respectively. Analytical TLC was
carried out using Merck 0.2-mm silica gel 60 F-254 Al-
plates. MCM-41 was synthesized according to procedures
in the literature [27]. MCM-41-SO3H was synthesized
according to the reported procedure and characterized by
FTIR spectroscopy and BJH analysis [28]. B-MCM-41, Fe-
MCM-41 [29a], Zr-MCM-41 [29b], and Al-MCM-41 [30]
catalysts were synthesized via literature reports. Known
products were characterized by comparison of their
melting points and/or spectral data (IR, 1H NMR, and 13C
NMR spectra). FTIR spectra were recorded as KBr pellets on
a Shimadzu FT IR-8400S spectrometer. 1H NMR (500 MHz)
and 13C NMR (125 MHz) spectra were obtained using
Scheme 3. Proposed mechanism for the deprotection reaction of trityl
ethers catalyzed by MCM-41-SO3H.
Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003

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Bruker DRX-500 Avance and Bruker DRX-300 Avance
spectrometers at ambient temperature, respectively.
Melting points were determined using an Electrothermal
9100 apparatus and are uncorrected. High-performance
liquid chromatography (HPLC, Younglin 9120 model) and
gas chromatography (GC, OMEGA WAX 250 model) were
used to determine the completeness of the deprotection
reactions. A ball mill apparatus (Retsch MM2000 model)
having a 20-mL iron cell and two iron balls of diameter
12 mm was used at a frequency of 20 Hz for protection
reactions.
with the two iron balls were fed into the horizontal ball
mill vessel. The mixture was grinded at room temperature
for 10 min up to 2 h, depending on the alcohol used. The
reaction progress was monitored by TLC from time to time.
After completion of the reaction, the product was taken out
from the cell and dissolved in ethanol and filtered. The
solvent was evaporated under reduced pressure and the
solid crude was recrystallized from ethanol, if necessary.
5.5. Typical procedure for the deprotection of trityl ethers
A trityl ether (20 mg) and MCM-41-SO3H catalyst
(20 mg) were added to acetonitrile (2.5 mL) at room
temperature. The mixture was stirred for an appropriate
time, indicated in Table 4. After completion of the reaction,
MCM-41-SO3H catalyst was separated from the mixture
via filtration. Then, acetonitrile was evaporated at reduced
pressure.
5.2. General procedure for the preparation of MCM-41
Diethylamine (2.7 g) was added to deionized water
(42 mL) in a 200-mL beaker, while the mixture was stirred
at room temperature. After 10 min, CTAB (1.47 g) was
added step by step to the above solution under stirring for
30 min, until a clear solution was obtained. Then, TEOS
(2.1 g) was added dropwise to the solution. The pH of the
reaction mixture was adjusted to 8.5 by slow addition of a
1 M hydrochloric acid solution. At this stage, a precipitate
was formed. After 2 h, the solid product was filtered from
the mother liquor and washed with deionized water. The
sample was dried at 45 8C for 12 h. The synthesized MCM-
41 was calcined at 550 8C for 5 h to remove all of the
surfactant [27].
5.6. Spectral data for the selected products
5.6.1. 2-Methylbenzyl trityl ether (3c)
White solid, m.p. 101–102 8C; IR (KBr),
1599, 1445, 1076, 702; 1H NMR (500 MHz, CDCl3):
2.13 (s, 3H), 4.15 (s, 2H), 7.1–7.7 (m, 19H); 13C NMR
(125 MHz CDCl3): (ppm) 18.7, 64.1, 87.0, 125.9, 127.1,
n
(cmÀ1): 3057,
(ppm)
d
d
127.3, 127.6, 127.9, 128.8, 130.0, 136.1, 137.2, 144.2. Anal.
calcd for C27H24O: C, 88.97; H, 6.64; found: C, 89.07; H, 6.77.
5.3. General procedure for preparation of MCM-41-SO3H
5.6.2. 2-Chlorobenzyl trityl ether (3e)
MCM-41was modified using a 100-mL suction flask
White solid, m.p. 147–149 8C; IR (KBr),
1597, 1446, 1369, 1092, 704; 1H NMR (500 MHz, CDCl3):
(ppm) 4.31 (s, 2H) ppm, 7.2–7.9 (m, 19H); 13C NMR
(125 MHz CDCl3): (ppm) 63.2, 87.3, 126.8, 127.2, 128.0,
n
(cmÀ1): 3082,
equipped with
a
constant pressure dropping funnel
d
containing chlorosulfonic acid (ClSO3H) and a gas inlet
tube for conducting HCl gas over an adsorbing solution.
MCM-41 (1 g) suspended in CH2Cl2 (5 mL) was charged to
the flask and ClSO3H (2 mL) was then added dropwise over
a period of 30 min at room temperature. HCl gas evolved
from the reaction vessel immediately. After complete
addition of ClSO3H, the mixture was stirred for 30 min and
the solvent was evaporated under reduced pressure to
obtain a light gray solid (MCM-41-SO3H) [29]. The MCM-
41-SO3H was characterized by BJH analysis and FT–IR
spectroscopy. In the FT–IR spectrum, the broad band in the
region of 3200–3400 cmÀ1 is assigned to the O–H
stretching vibration of hydroxyl groups. The bands at
1286 cmÀ1 and 1321 cmÀ1 are due to the symmetric and
asymmetric stretching vibrations of the S5O bond of the
sulfonic acid group. Moreover, a strong band at 1174 cmÀ1
is assigned to Si–O–Si asymmetric stretching vibrations
and a band at 850 cmÀ1 related to Si–O–Si symmetric
stretching vibrations. The N2 absorption–desorption data
determined the nanostructure of the pores of the MCM-
41-SO3H: 0.0751 cm3/g for BJH adsorption cumulative
volume of pores and BJH adsorption average pore diameter
(4V/A) of 2.62 nm The peak values of pore size distribution
curves were found for pore diameters of 1.7–2.8 nm
d
128.1, 128.2, 128.8, 129.0, 132.2, 137.0, 144.0. Anal. calcd
for C26H21ClO: C, 81.13; H, 5.50; found: C, 80.61; H, 5.52
5.6.3. 2-Nitrobenzyl trityl ether (3g)
White solid, m.p. 150–151 8C; IR (KBr),
3028, 1604, 1520, 1338, 1090, 1067; 1H NMR (500 MHz,
CDCl3):
(ppm) 4.66 (s, 2H), 7.2–8.3 (m, 19H); 13C NMR
(125 MHz CDCl3): (ppm) 63.1, 87.7, 124.6, 127.3, 127.6,
n
(cmÀ1): 3082,
d
d
128.0, 128.5, 128.7, 133.8, 136.0, 143.7, 146.9. Anal. calcd
for C26H21NO3: C, 78.97; H, 5.35; N, 3.54; found: C, 78.97;
H, 5.39; N, 3.68.
5.6.4. (2-(4-Nitrophenyl)ethyl) trityl ether (3l)
White solid, m.p. 124–126 8C; IR (KBr),
3026, 1601, 1518, 1346, 1078, 703; 1H NMR (500 MHz,
DMSO): (ppm) 2.94 (t, 2H), 3.18 (t, 2H), 7.22 (m, 15H),
7.46 (AA’BB’, 2H), 8.12 (AA’BB’, 2H); 13C NMR (125 MHz
CDCl3): (ppm) 37.0, 64.3, 87.2, 123.9, 127.5, 128.3, 129.0,
n
(cmÀ1): 3082,
d
d
130.4, 144.3, 147.0, 148.0 ppm Anal. calcd for C27H23NO3:
C, 79.20; H, 5.66; N, 3.42; found: C, 79.04; H, 5.72; N, 3.58.
Acknowledgements
5.4. Typical procedure for the synthesis of trityl ethers
We are grateful for the financial support from The
Research Council of Iran University of Science and
Technology (IUST), Tehran, Iran. Our special thanks go to
Dr. M. G. Dekamin for providing us with some M-MCM41s.
A mixture of alcohol (1.0 mmol) and triphenylmethanol
(1.0 mmol) and MCM-41-SO3H (15 mg) as a catalyst along
Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003

G Model
CRAS2C-3884; No. of Pages 8
8
Z. Gholamzadeh et al. / C. R. Chimie xxx (2014) xxx–xxx
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Please cite this article in press as: Gholamzadeh Z, et al. Highly efficient protection of alcohols as trityl ethers under
solvent-free conditions, and recovery catalyzed by reusable nanoporous MCM-41-SO3H. C. R. Chimie (2014), http://
dx.doi.org/10.1016/j.crci.2014.01.003