ZSM-5-SO3H as a novel, efficient, and reusable catalyst for the chemoselective synthesis and deprotection of 1,1-diacetates under eco-friendly conditions

Article abstract of DOI:10.1007/s00706-011-0646-8

ZSM-5 has been modified as supported sulfuric acid (ZSM-5-SO₃H) and introduced for the first time as a mild, convenient, reusable, and heterogeneous catalyst. Various types of aldehydes were efficiently converted to their 1,1-diacetates using a catalytic amount of ZSM-5- SO₃H in excellent yields under solvent-free and heterogeneous conditions at room temperature. The deprotection of 1,1-diacetates has also been achieved using this novel catalyst in ethanol. The procedure is operationally simple, environmentally benign, and only a stoichiometric amount of anhydride is used. Springer-Verlag 2011.

Full text of DOI:10.1007/s00706-011-0646-8

Monatsh Chem (2012) 143:643–652
DOI 10.1007/s00706-011-0646-8
ORIGINAL PAPER
ZSM-5-SO3H as a novel, efficient, and reusable catalyst
for the chemoselective synthesis and deprotection of 1,1-diacetates
under eco-friendly conditions
•
Ahmad Reza Massah Roozbeh Javad Kalbasi
•
Anahita Shafiei
Received: 30 March 2010 / Accepted: 1 September 2011 / Published online: 22 October 2011
Ó Springer-Verlag 2011
Abstract ZSM-5 has been modified as supported sulfuric
acid (ZSM-5-SO3H) and introduced for the first time as a
mild, convenient, reusable, and heterogeneous catalyst.
Various types of aldehydes were efficiently converted to
their 1,1-diacetates using a catalytic amount of ZSM-5-
SO3H in excellent yields under solvent-free and heteroge-
neous conditions at room temperature. The deprotection of
1,1-diacetates has also been achieved using this novel
catalyst in ethanol. The procedure is operationally simple,
environmentally benign, and only a stoichiometric amount
of anhydride is used.
a wide range of nucleophiles under neutral and basic con-
ditions [1, 2]. Moreover, they are also used as substrates for
nucleophilic substitution reactions [3–7]. 1,1-Diacetates of
a,b-unsaturated aldehydes are important precursors for
acetoxy dienes [8] and dihalovinyl acetates [9]. Therefore,
methods for their synthesis have received considerable
attention. Usually, they are prepared from aldehydes and
acetic anhydride using sulfuric [10], methanesulfonic [11],
or perchloric acid [12], although the yields in many cases
are poor. Also, several methods have been developed for the
preparation of 1,1-diacetates by employing various Lewis
acids such as Fe(NO3)3.9H2O [13], cupric sulfate [14],
In(OTf)3 [15], P2O5/Al2O3 [16], LiOTf [17], Bi(NO3)3 [18],
Keggin heteropolyacid [19], Al(HSO4)3 [20], titanium-
modified MCM-41 [21], sulfuric acid [3-(3-silicapropyl)
sulfanyl]propyl ester [22], silica-bonded N-propylsulfamic
acid [23], polymer-supported gadolinium triflate [24], dif-
ferent solid acids [25], and Brønsted acidic ionic liquids
under ultrasonic irradiation [26]. However, many of these
existing methodologies suffer from one or more of the
following disadvantages: prolonged reaction times and low
yields [13], high temperatures [19], use of harmful organic
solvents [19, 27, 28], use of moisture-sensitive and costly
catalysts (e.g., triflates) [15, 24], and use of excess Ac2O
[29]. Also, very few reports are applicable to both the
synthesis as well as deprotection of 1,1-diacetates [30–32].
Solvent-free organic synthesis for the preparation of
small molecule libraries is now routinely applied in phar-
maceutical research for the discovery and optimization of
lead compounds [33–37]. On the other hand, solid sup-
ported reagents are unique catalysts that have become
popular recently [38–41]. The high catalytic activity, low
toxicity, moisture and air tolerance, recyclability, and
particularly their low price make the use of solid supported
reagents an attractive alternative to conventional acids.
Keywords 1,1-Diacetate Á Solvent-free Á ZSM-5-SO3H Á
Chemoselectivity Á Aldehydes Á Protection
Introduction
The electrophilic nature of carbonyl groups is a dominant
feature of their extensive chemistry. One of the major
challenging problems during many multi-step syntheses is
how to protect a carbonyl group from nucleophilic attack
until its electrophilic properties can be exploited. Acetyla-
tion is commonly utilized as a protecting method for
carbonyl functions, because 1,1-diacetates are stable against
A. R. Massah (&) Á R. J. Kalbasi (&) Á A. Shafiei
Department of Chemistry, Shahreza Branch,
Islamic Azad University, 86145-311, Shahreza, Isfahan, Iran
e-mail: Massah@iaush.ac.ir
R. J. Kalbasi
e-mail: rKalbasi@iaush.ac.ir
A. R. Massah Á R. J. Kalbasi
Razi Chemistry Research Center, Shahreza Branch,
Islamic Azad University, 86145-311, Shahreza, Isfahan, Iran
123

644
A. R. Massah et al.
Scheme 1
Some of the solid supported acids, e.g., SiO2–OSO3H [29]
and HClO4–SiO2 [42], are utilized as catalysts for the
preparation of 1,1-diacetate derivatives from the corre-
sponding aldehydes. Recently, we have demonstrated the
applicability of SiO2–OSO3H [43], H3PO4/TiO2–ZrO2
[44, 45], H3PO4/ZSM-5 [46], SiO2–OPO3H [47], and
SiO2–Cl [48] as solid supported acids in several organic
transformations.
In continuation of our studies we have found that ZSM-5
reacts with chlorosulfonic acid to give a white powder,
which was shown as ZSM-5-SO3H. It is interesting to note
that the reaction is easy and clean without any work-up
procedure, because HCl gas is evolved from the reaction
vessel immediately [38]. However, we hope that ZSM-5-
SO3H would be a good proton source as well as other
reported solid supported acids or acidic resins, such as
SSA, polystyrene sulfonic acid, and Nafion-H [49]. Herein,
we introduce ZSM-5-SO3H as a reusable catalyst for the
synthesis of 1,1-diacetates from structurally diverse alde-
hydes under mild and solvent-free conditions (Scheme 1).
Results and discussion
Characterization of the catalyst
Initially, a systematic study was carried out for the prep-
aration and characterization of different ZSM-5 supported
SO3H. The infrared spectra of ZSM-5 and the samples with
various amounts of ClSO3H supported on ZSM-5 are pre-
sented in Fig. 1. In the sample Na-ZSM-5 the broad peaks
in the range of 3,200–3,600 cm-1 may be attributed to the
hydroxyl stretching of hydrogen-bonded internal silanol
groups and O–H stretching of water, while the peak at
1,620–1,640 cm-1 corresponds to bending mode of O–H of
water. Beside those, the peaks around 800 and 1,090 cm-1
are attributed to the symmetric and asymmetric stretching
vibrations of the Si–O–Si groups, respectively [50]. The
band at 470 cm-1 is assigned to the bending vibrations of
Si–O–Si or Al–O–Si groups [51]. In the samples with
various amounts of ClSO3H loaded on ZSM-5 some
additional peaks were observed. The asymmetric and
symmetric stretching of the S=O bond at 1,229–1,290 and
1,177 cm-1, respectively, confirms the presence of SO3H
in ClSO3H/ZSM-5 [52, 53]. The other peaks in the range of
750–1,000 cm-1 were attributed to the S–O bond. It should
be mentioned that with increasing the ClSO3H loaded on
Fig. 1 FT-IR spectra of a Na-ZSM-5 and ClSO3H/ZSM-5 catalysts
with b 15 wt% ClSO3H, c 20 wt% ClSO3H, d 28 wt% ClSO3H, and
e 34 wt% ClSO3H
the ZSM-5, the intensity of the peaks related to S=O and
S–O increases.
XRD powder patterns of the calcinated samples of
ZSM-5 and ZSM-5-SO3H with different amounts of loaded
chlorosulfonic acid are presented in Fig. 2. Figure 2a
shows reflections at 2h values of 7–9 and 23–25°, which
agree well with the characteristic peak of MFI structure,
indicating the synthesized composite material ZSM-5
zeolite crystal. The ZSM-5-SO3H samples showed the
same pattern, indicating that the ZSM-5 framework was
well retained after immobilizing. However, the intensity of
the characteristic reflection peaks of ZSM-5-SO3H samples
is found to be reduced to some extent. This may be
attributed to the X-ray shielding caused by absorption of
non-metal material after acid loading over the zeolite
samples. A similar observation has been reported by Breck
[63]. In addition, the composite contains much less ZSM-5
123

ZSM-5-SO3H as a novel, efficient, and reusable catalyst
645
Table 1 Porosity data of ZSM-5 and ZSM-5-SO3H synthesized with
different amounts of chlorosulfonic acid
Sample/%
BET surface area/m2 g-1 VP/cm3 g-1 DP/nm
ZSM-5
375
–
–
ZSM5-SO3H (15) 345
ZSM5-SO3H (20) 286
ZSM5-SO3H (28) 122
ZSM5-SO3H (34) 119
2.07
2.21
2.01
2.29
0.18
0.16
0.068
0.065
Table 1. It is known that ZSM-5 has a high BET surface
area (375 m2 g-1), indicative of its potential application as
a host in inorganic materials. BET surface areas of ZSM-5-
SO3H samples are smaller than ZSM-5. After modification
with ClSO3H, ZSM-5-SO3H samples exhibit a lower BET
surface area in comparison with those of pure ZSM-5
zeolite, which might be due to the presence of SO3H
groups on the pore surface. In addition, the pore volume
decreased with increasing the amount of loaded chloro-
sulfonic acid. This means that the chlorosulfonic acid is
uniformly grafted onto the pore wall surface of ZSM-5-
SO3H zeolite materials.
Fig. 2 XRD powder patterns of the calcinated samples of zeolite
ZSM-5 catalysts containing different amounts of loaded chlorosul-
fonic acid: a 0%, b 15%, c 20%, d 28%, e 34%
Figure 4 shows the SEM images of the ZSM-5 zeolite
and ZSM-5-SO3H (28%). In Fig. 3a, it can be seen clearly
that the ZSM-5 crystal with a size of about 10 lm was
successfully synthesized, and the morphology of synthe-
sized ZSM-5 crystal was spherical-like.
After loading the ClSO3H on ZSM-5, spherical-like
particles remained. So the morphology of the catalyst did
not change, and it can be concluded that the ZSM-5-SO3H
is a stable catalyst with preservation of ZSM-5 crystallinity
(Fig. 4b).
Synthesis and deprotection of 1,1-diacetates
Fig. 3 Nitrogen adsorption-desorption analysis of ZSM-5 zeolite
with various amounts of loaded chlorosulfonic acid: a 15%, b 20%,
c 28%, d 34%
A variety of reaction conditions were performed to opti-
mize the acylation of aldehydes. At first, we tried the
conversion of 4-methoxybenzaldehyde to the correspond-
ing 1,1-diacetate with acetic anhydride in various solvents
and also under solvent-free conditions in the presence of
0.02 g of ZSM-5-SO3H (28%) (Table 2). CH2Cl2 afforded
the minimum amount of side products in high yield, and so
it was selected as solvent of choice (Table 2, entries 1–4).
In comparison, the yield of the product under solvent-free
conditions is higher, and the reaction time is lower. For
optimization of the quantity of acetic anhydride required
for the reaction, we altered the stoichiometry of the reac-
tion. When a 1:1 ratio of 4-methoxybenzaldehyde to acetic
anhydride was tried, the reactions were completed in
4–6 min in good to excellent yields (85–95%) in both
CH2Cl2 and solvent-free conditions, and no further increase
in the yield was observed even after increasing the amount
because of the dilution of the silicious material by ClSO3H;
therefore, this dilution can also account for a decrease in
the peak intensity.
The N2 adsorption–desorption isotherms of ZSM-5-
SO3H (15%) (a), ZSM-5-SO3H (20%) (b), ZSM-5-SO3H
(28%) (c), and ZSM-5-SO3H (34%) (d) samples are shown
in Fig. 3. The isotherms are similar to the type III isotherm
with H1-type hysteresis loops at high relative pressure
according to the IUPAC classification, characteristic of
microporous materials. The specific surface area and the
pore size have been calculated using the Brunauer-Emmett-
Teller (BET) and Barrett-Joyner-Halenda (BJH) methods,
respectively.
The structure data of all these materials (BET surface
area, total pore volume, and pore size) are summarized in
123

646
A. R. Massah et al.
for these reactions, an experiment was conducted in which
the reaction of 4-methoxybenzaldehyde and acetic anhy-
dride was studied in the absence of ZSM-5-SO3H. No
reaction occurred even after 24 h in the absence of the
catalyst (Table 2, entries 10, 11). Obviously, the catalyst
is an essential component of the reaction. Then, a similar
reaction was studied in the presence of various amounts
of catalyst. We observed that the reaction between
4-methoxybenzaldehyde (1 mmol), acetic anhydride
(1 mmol), and ZSM-5-SO3H (0.02 g) was completed after
4 min in solvent-free conditions at room temperature.
Next, the conversion of 4-methoxybenzaldehyde to the
corresponding diacetate was carried out at room tempera-
ture using various ZSM-5 supported sulfuric acids,
including ZSM-5-SO3H (15%), ZSM-5-SO3H (20%), and
ZSM-5-SO3H (34%), resulting in 50, 70, and 70% yields,
respectively. However, the best yield of product (95%)
was obtained when ZSM-5-SO3H (28%) was used as
catalyst.
To demonstrate the versatility and uniqueness of the
present reaction conditions, a variety of aliphatic as well as
aromatic aldehydes were converted into corresponding
1,1-diacetates 1a–1m in high yields (90–98%) at ambient
temperature and under solvent-free conditions. Several
examples illustrating the usefulness of this efficient and
rapid procedure for the preparation of 1,1-diacetates are
summarized in Table 3. Various functional groups were
tolerated under the present conditions, for example, Me, Cl,
OMe, NO2, OH, and Br. It is noteworthy to mention that
aldehydes with electron withdrawing groups like nitroben-
zaldehydes (Table 3, entries 3–5) and acid-sensitive
substrates like butenal (Table 3, entry 14) and 2- furfural-
dehyde (Table 3, entry 12) gave the corresponding
1,1-diacetates in high yields without formation of any side
products. However, when the reaction was extended towards
hydroxybenzaldehydes (Table 3, entry 10) under the present
reaction conditions, it gave a mixture of products. Ketones
proved completely resistant to acylal synthesis with acetic
anhydride: no diacetate formed even under reflux conditions
(Table 3, entries 15, 16). This prompted us to check and
extend the present protocol for chemoselective synthesis of
1,1-diacetate of an aldehyde in the presence of ketone.
Using this catalytic system, the highly selective conversion
of aldehydes was observed (Scheme 2). In addition, the
acylation of 4-methylbenzaldehyde versus 4-nitrobenzal-
dehyde and 3-nitrobenzaldehyde in the presence of one
equivalent of acetic anhydride has been investigated in
solvent and solvent-free conditions. These reactions also
proceeded with high selectivity in the presence of this cat-
alyst and showed the importance of electronic effects upon
these reactions. On the other hand, comparison between
the results obtained in solution and those under solvent-
free conditions show that reactions proceeded faster in
Fig. 4 Scanning electron microscopy (SEM) photographs of a ZSM-
5 and b ZSM-5-SO3H (28%)
Table 2 Conversion of 4-methoxybenzaldehyde to 1,1-diacetate
under different conditions
Entry Solvent
Ac2O/eq ZSM-5-SO3H/g Time/ Yield/
a
min
%
1
Ethyl acetate
1
1
1
1
3
1
3
1
1
3
3
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.01
0.005
–
10
10
10
6
50
70
65
85
88
95
95
82
70
0
2
n-Hexane
CH3CN
3
4
CH2Cl2
5
CH2Cl2
6
6
Solvent-free
Solvent-free
Solvent-free
Solvent-free
CH2Cl2
4
7
4
8
4
9
4
10
11
24 h
24 h
Solvent-free
–
0
Room temperature
a
Yields of isolated products
of acetic anhydride to three or more equivalents (Table 2,
entries 4–7). Hence, we maintained a 1:1 stoichiometry
throughout the reaction. To illustrate the need for catalysts
123

ZSM-5-SO3H as a novel, efficient, and reusable catalyst
647
Table 3 ZSM-5-SO3H catalyzed protection of aldehydes as 1,1-diacetates and deprotection at room temperature
Entry Substrate
Protection
Prod. M.p./°C or b.p./°C (mbar)
Deprotection
Time/min Yield/%b
Solvent-free
CH2Cl2
Found
44–45
Reported
Time/min Yield/%b Time/min Yield/%b
1
2
1
2
95
98
4
2
50
1a
1b
44–45 [29]
60
60
85
88
60
58
89
58–60 [61]
3a
4
96
4
70
1c
91 [16]
30
98
4a
4
4
97
96
4
4
97
80
1d
1e
124
64
124–125 [29]
64–65 [29]
30
30
98
98
5a
6
7
8
9
2
1
4
1
90
97
95
98
4
2
6
5
80
90
85
70
1f
89
90–91 [29]
81 [16]
30
60
40
40
80
90
90
80
1g
1h
1i
80–81
65
64–65 [29]
66–68 [29]
66–67
10
20
30
20
0
–
–
–
–
11
12
1
1
97
98
2
2
40
30
1j
71–73 (20)
73–75 (20) [62] 10
98
80
1k
50
51–52 [16]
40
123

648
A. R. Massah et al.
Table 3 continued
Entry Substrate
Protection
Prod. M.p./°C or b.p./°C (mbar)
Found Reported
Deprotection
Solvent-free
CH2Cl2
Time/min Yield/%b
Time/min Yield/%b Time/min Yield/%b
13
1
95
2
55
1l
Colorless liquid 128–129 (3) [60] 10
98
14
15
1
95
0
2
60
0
1m
93–94 (23)
89–90 (20) [62] 10
98
–
30
30
–
–
–
–
–
16
30
0
30
0
–
–
1
Products were confirmed by H, 13C NMR, and direct comparison with authentic samples
a
1.5 eq of acetic anhdride was used
b
Yields of isolated products
Scheme 2
123

ZSM-5-SO3H as a novel, efficient, and reusable catalyst
649
solvent-free conditions. Therefore, omitting the solvent
makes an easy workup procedure and increases the rate of
reaction.
ZSM-5-SO3H can be used for deprotection as well as
protection of aldehydes. Also, comparison between
ZSM-5-SO3H and SSA, a similar sulfonated catalyst, is
interesting. The novelties of ZSM-5-SO3H over SSA are:
(1) SSA was used only for protection of aldehydes, but
ZSM-5-SO3H can be used for deprotection as well as
protection; (2) SSA was used for protection of aldehydes
up to 3 mmol, but ZSM-5-SO3H can be used for protection
of aldehydes up to 25 mmol; (3) ZSM-5-SO3H is a reus-
able catalyst but there is no report about reusability of SSA
in protection of aldehydes; (4) SSA shows selectivity in the
acylation of aldehydes with different substituents only in
CH2Cl2, whereas we found that ZSM-5-SO3H is a selective
catalyst in solvent-free conditions as well as in CH2Cl2;
(5) ZSM-5-SO3H is a catalyst for acylation of aldehydes
with different carboxylic acid anhydrides (Table 4), while
the SSA method employs only acetic anhydride; and (6)
reaction time and yield are better when ZSM-5-SO3H is
used as catalyst, especially in the case of heterocyclic and
aliphatic aldehydes (Table 5).
In order to generalize the catalytic efficiency of ZSM-
5-SO3H for other acylating agents, we tried the acylation of
4-nitrobenzaldehyde with different carboxylic acid anhy-
drides (Table 4), while most literature methods employ
only acetic anhydride for 1,1-diacetate formation. Acylation
with butyric, isobutyric, pentanoic, and hexanoic anhydride
resulted in good yield of the 1,1-diacylates 2a–2d.
Then, we investigated the use of ZSM-5-SO3H as cat-
alyst in deprotection of acylals to the corresponding
aldehydes by treatment of acylals in ethanol at 50 °C. By
this procedure several aliphatic, aromatic, and a,b-unsatu-
rated 1,1-diacetates have been transformed into the
corresponding aldehydes in high yields (Table 3). It is
worth mentioning that aliphatic 1,1-diacetates provided the
desired aldehydes within 10 min with much better yield
than other reported methods [54, 55]. The interesting
feature to note during the deprotection studies was the
1,1-diacetate of aromatic aldehydes needed longer reaction
times (30–60 min) than those of aliphatic aldehydes
(10 min). This permits the chemoselective deprotection of
1,1-diacetate of an aliphatic aldehyde over an aromatic
aldehyde.
The results clearly show that ZSM-5-SO3H promotes
the reactions more effectively than the other catalysts
and should be considered as one of the best choices
for selecting an economically convenient, user friendly
catalyst.
A comparative study was done for the use of ZSM-5-
SO3H with some of the reported catalysts for the synthesis
of acylals from 4-methylbenzaldehyde, 4-nitrobenzalde-
hyde, and furfural with respect to the amounts of acetic
anhydride, reaction time, and the yield of the products
(Table 5). It is worth mentioning that reactions with the
reported catalysts required a larger amount of acetic
anhydride, catalyst, and longer reaction time. Reaction
with Zeolite-Y as the catalyst was completed after
60–480 min and needed 3 equivalents of acetic anhydride.
The formation of an acylal from furfural resulted in failure
when AlPW12O40 was used as catalyst. Reaction in the
presence of H6P2W18O62 needed 10 eq of acetic anhydride.
In some methods, the preparation of 1,1-diacetates was
performed in solvents such as CH2Cl2. Most of the cata-
lysts were used only for protection of aldehydes, but
Finally, we were interested in studying the reusability of
the catalysts because of economic and environmental
aspects. For this purpose the reaction of 4-methylbenzal-
dehyde with acetic anhydride was chosen as a model
reaction in the presence of ZSM-5-SO3H in both hetero-
geneous and solvent-free conditions. At the end of each
run, the catalyst was recovered from the reaction mixture
by addition of ethyl acetate in the solvent-free and
dichloromethane in heterogeneous reactions, simple filtra-
tion and drying at 100 °C, and then reused. The recycled
ZSM-5-SO3H was used for further runs, and its activity did
not show any significant decrease even after four runs.
Also, the preparative efficiency of the present method
was further established, for example, by scaling up of
benzaldehyde to approximately 25-fold, resulting in the
respective 1,1-diacetate in nearly quantitative yield under
the similar reaction conditions.
In conclusion, ZSM-5-SO3H has been found to be a
novel, highly efficient, low-cost catalyst for 1,1-diacetate
formation from aliphatic and aromatic aldehydes under
solvent-free conditions at room temperature. This method
is selective for the preparation of 1,1-diacetates from
aldehydes in the presence of ketones. 1,1-Diacetates can be
conveniently deprotected by using ZSM-5-SO3H in etha-
nol. Operational simplicity without need of any solvent,
exceptionally fast, low cost, and non-toxic nature of the
catalyst, high yields, excellent chemoselectivity, applica-
bility to large-scale reactions, and reusability of the catalyst
Table 4 Conversion of 4-nitrobenzaldehyde into 1,1-diacylates with
carboxylic acid anhydrides
Entry
Anhydridea
Prod.
Time/min
Yield/%b
1
2
3
4
a
(C3H7CO)2O
(i-C3H7CO)2O
(C4H9CO)2O
(C5H11CO)2O
2a
2b
2c
2d
30
40
25
20
85
83
89
89
2.0 eq of anhydrides were used
Yields of isolated products
b
123

650
A. R. Massah et al.
Table 5 Comparison of the effect of catalysts for 1,1-diacetate synthesis from 4-methylbenzaldehyde, 4-nitrobenbenzaldehyde, and furfural
Substrate
Catalyst
Ac2O/eq
2.5
Time/min
45
Yield/%
87
Ref
P2O5/Al2O3
[16]
SO42-/SnO2
InCl3
2.0
1.0
10
15
97
96
92
92
97
97
89
[32]
60
[59]
H6P2W18O62
SSA
30
[58]
2.0
3.0
1.0
2.5
30
[60]
Zeolite-Y
ZSM-5-SO3H
P2O5/Al2O3
180
1.0
45
[30]
This work
[16]
SO42-/SnO2
InCla3
2.0
1.0
1.0
10
50
99
88
89
88
95
98
97
83
[32]
240
45
[59]
AlPW12O40
H6P2W18O62
SSA
Zeolite-Yb
ZSM-5-SO3H
P2O5/Al2O3
[57]
30
[58]
2.0
3.0
1.5
2.5
15
[60]
420
4.0
45
[30]
This work
[16]
SO42-/SnO2
InCl3
2.0
1.0
1.0
2.0
3.0
1.0
50
30
30
25
60
1.0
99
92
0
[32]
[59]
AlPW12O40
SSA
[57]
65
90
98
[60]
Zeolite-Y
ZSM-5-SO3H
[30]
This work
a
CH2Cl2 used as solvent
b
Reaction was carried out at 70 °C
are the key features of this methodology. Further applica-
tions of this catalyst to other transformations are currently
under investigation.
performed using silica gel 60 (230–400 mesh). All yields
refer to isolated yield.
Catalyst preparation
Experimental
The ZSM-5 zeolite samples with Si/Al ratios of 80 were
synthesized according to a previously published method
[56]. Sodium chloride (2.50 g, 0.04 mol) and 0.59 g of
hydrated aluminum sulfate (0.0009 mol) were dissolved in
10.12 cm3 of distilled water (0.56 mol). Then 1.89 g of
tetrapropylammonium bromide (0.0071 mol), 7.12 cm3 of
distilled water (0.39 mol), and 1.09 g of sulfuric acid
(0.011 mol) were added. The solution was mixed. Sodium
silicate solution (15.0 g, 0.071 mol SiO2) was added, and
the mixture was stirred vigorously for about 1 h. The pH of
All chemicals were purchased from Merck and Fluka
chemical companies. The products were characterized by
comparing the physical data with those of known samples
or by their spectral data. Infrared spectra were recorded on
a Nicolet (impact 400D model) FTIR spectrophotometer.
1H NMR and 13C NMR spectra were recorded on a Bruker
DRX 400 Avance spectrometer in CDCl3 as the solvent and
TMS as internal standard. Column chromatography was
123

ZSM-5-SO3H as a novel, efficient, and reusable catalyst
651
(4-Nitrophenyl)methylene 1,1’-bis(2-methylpropanoate)
(2b, C15H19NO6)
the mixture was 9.15. The mixture was transferred into the
autoclave. The autoclave was kept in an oven at 110 °C for
about 2 h. Then, the temperature was increased to 230 °C
and kept at that level for another 5 h. The solid phase
obtained was filtered, washed with distilled water several
times, dried at 110 °C for about 12 h, and then calcined at
540 °C for about 6 h.
ꢀ
IR (KBr): m = 3,089, 2,968, 1,764, 1,609, 1,528, 1,464,
1,350, 1,176, 980, 855 cm-1; 1H NMR (400 MHz, CDCl3):
d = 1.21 (d, 6H, J = 10.0 Hz), 1.26 (d, 6H, J = 10.0 Hz),
2.62–2.69 (m, 2H), 7.71 (d, 2H, J = 8.8 Hz), 7.76 (s, 1H),
8.29 (d, 2H, J = 8.8 Hz) ppm; 13C NMR (100 MHz,
CDCl3): d = 18.5, 18.7, 33.9, 88.2, 123.9, 127.7, 142.4,
148.6, 174.7 ppm.
A 500 cm3 suction flask was equipped with a constant
pressure dropping funnel containing 23.3 g chlorosulfonic
acid (0.2 mol) and a gas inlet tube for conducting HCl
gas over an adsorbing solution, i.e., H2O. Then 60.0 g of
ZSM-5 was charged into the flask. Chlorosulfonic acid
was added dropwise over a period of 30 min at room
temperature. HCl gas evolved from the reaction vessel
immediately. After the addition was complete, the mixture
was shaken for 30 min. ZSM-5-SO3H was obtained as a
white solid (76 g).
(4-Nitrophenyl)methylene 1,1’-dipentanoate
(2c, C17H23NO6)
ꢀ
IR (KBr): m = 2,979, 1,762, 1,610, 1,529, 1,464, 1,350,
1,155, 981, 853 cm–1; 1H NMR (400 MHz, CDCl3):
d = 0.91 (t, 6H, J = 7.2 Hz), 1.67 (sext, 4H, J = 7.2 Hz),
1.64 (quint, 4H, J = 7.6 Hz), 2.35–2.45 (m, 4H), 7.71 (d,
2H, J = 8.4 Hz), 7.77 (s, 1H), 8.26 (d, 2H, J = 8.8 Hz)
ppm; 13C NMR (100 MHz, CDCl3): d = 13.6, 22.1, 26.6,
33.6, 88.2, 123.8, 127.8, 142.3, 148.6, 171.5 ppm.
General procedure for the synthesis of 1,1-diacetates
(4-Nitrophenyl)methylene 1,1’-dihexanoate
(2d, C19H27NO6)
(1) In CH2Cl2: a mixture of aldehyde (1 mmol), freshly
distilled acetic anhydride (1.0–1.5 mmol), and catalyst
(20 mg) in 3 cm3 dry dichloromethane was stirred at
ambient temperature for appropriate time (as mentioned in
Table 3). After completion of the reaction (GC or TLC) the
mixture was diluted with 10 cm3 dichloromethane and fil-
tered to separate the catalyst. The filtrate was washed with
water (2 9 10 cm3), dried over anhydrous Na2SO4, and
concentrated in vacuum to give pure 1,1-diacetate or chro-
matographed on silica gel [petroleum ether (60–80 °C)—
ethyl acetate] where necessary.
ꢀ
IR (KBr): m = 2,958, 1,764, 1,609, 1,529, 1,464, 1,350,
1,166, 986, 853 cm–1; 1H NMR (400 MHz, CDCl3):
d = 0.89 (t, 6H, J = 7.2 Hz), 1.28–1.38 (m, 8H), 1.67
(quint, 4H, J = 7.2 Hz), 2.38–2.44 (m, 4H), 7.71 (d, 2H,
J = 8.6 Hz), 7.78 (s, 1H), 8.28 (d, 2H, J = 8.8 Hz) ppm;
13C NMR (100 MHz, CDCl3): d = 13.9, 22.2, 24.3, 31.1,
33.9, 86.2, 123.8, 127.8, 142.3, 148.6, 171.5 ppm.
General procedure for the deprotection
of 1,1-diacetates
Acylation with longer chain carboxylic acid anhydrides
was also carried out by this procedure, using 2.0 eq of the
appropriate anhydrides.
A mixture of 1,1-diacetate (2 mmol) and ZSM-5-SO3H
(20 mg) in 5 cm3 ethanol was stirred vigorously at 50 °C
for a specified time as required to complete the reaction
(Table 3). The reaction was monitored by TLC and GC.
After completion of the reaction, the reaction mixture was
diluted with 20 cm3 Et2O and filtered to separate the cat-
alyst. The filtrate was washed with 20 cm3 water and dried
over Na2SO4. The solvent was evaporated under reduced
pressure, and the resultant product was passed through a
short column of silica gel to afford pure aldehyde.
(2) Under solvent-free conditions: to a mixture of
aldehyde (1.0 mmol) and catalyst (20 mg) was added
acetic anhydride (1.0–1.5 mmol) at room temperature, and
the neat reaction mixture was stirred magnetically for an
appropriate time (Table 3). The course of the reaction was
monitored by TLC and GC. After completion of the reac-
tion, the reaction mixture was diluted with 15 cm3 ethyl
acetate, and the products were isolated as described in
procedure (1).
Acknowledgment Support from the Islamic Azad University,
Shahreza Branch (IAUSH) Research Council, is gratefully
acknowledged.
(4-Nitrophenyl)methylene 1,1’-dibutyrate
(2a, C15H19NO6)
ꢀ
IR (KBr): m = 3,089, 2,961, 1,763, 1,609, 1,524, 1,464,
1,349, 1,169, 978, 854 cm-1; 1H NMR (400 MHz, CDCl3):
d = 0.93 (t, 6H, J = 7.2 Hz), 1.67 (sext, 4H, J = 7.2 Hz),
2.33–2.40 (m, 4H), 7.69 (d, 2H, J = 8.8 Hz), 7.76 (s, 1H),
8.23 (d, 2H, J = 8.4 Hz) ppm; 13C NMR (100 MHz,
CDCl3): d = 13.4, 18.1, 35.8, 88.1, 123.8, 127.8, 142.3,
148.5, 171.2 ppm.
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