A new Br?nsted acid MIL-101(Cr) catalyst by tandem post-functionalization; synthesis and its catalytic application

Article abstract of DOI:10.1002/aoc.5717

A new heterogeneous Br?nsted solid acid catalyst was prepared by tandem post-functionalization of MIL-101(Cr) and utilized for acetic acid esterification and alcoholysis of epoxides under solvent-free conditions. First, MIL-101(Cr) was functionalized with pyrazine to achieve MIL-101(Cr)-Pyz. Afterwards, the nucleophilic reaction of MIL-101(Cr)-Pyz with 1,3-propane sultone and next acidification with diluted sulfuric acid gave MIL-101(Cr)-Pyz-RSO₃H Br?nsted solid acid catalyst. Various characterization methods such as Fourier transformation infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), elemental analysis (CHNS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersiveX-ray(EDX) spectroscopy, thermal analysis (TGA/DTA), acid–base titration, and N₂ adsorption/desorption analysis were employed to fully characterize the prepared catalyst. The catalyst showed high activity compared to unmodified MIL-101(Cr) in both catalytic acetic acid esterification and alcoholysis of epoxides. It can also be readily isolated from the reaction mixture and reused three times without major decrease in its activity.

Full text of DOI:10.1002/aoc.5717

Received: 10 December 2019
DOI: 10.1002/aoc.5717
Revised: 12 February 2020
Accepted: 15 February 2020
F U L L P A P E R
A new Brønsted acid MIL-101(Cr) catalyst by tandem post-
functionalization; synthesis and its catalytic application
1
1
2,3
Saeideh-Sadat Mortazavi | Alireza Abbasi
| Majid Masteri-Farahani
1
School of Chemistry, College of Science,
A new heterogeneous Brønsted solid acid catalyst was prepared by tandem
post-functionalization of MIL-101(Cr) and utilized for acetic acid esterification
and alcoholysis of epoxides under solvent-free conditions. First, MIL-
University of Tehran, P.O. Box:
14155-6455, Tehran, Iran
2
Faculty of Chemistry, Kharazmi
University, Tehran, Iran
101(Cr) was functionalized with pyrazine to achieve MIL-101(Cr)-Pyz. After-
3
Research Institute of Green Chemistry,
wards, the nucleophilic reaction of MIL-101(Cr)-Pyz with 1,3-propane sultone
Kharazmi University, Tehran, Iran
and next acidification with diluted sulfuric acid gave MIL-101(Cr)-Pyz-RSO H
3
Correspondence
Brønsted solid acid catalyst. Various characterization methods such as Fourier
transformation infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), ele-
mental analysis (CHNS), X-ray photoelectron spectroscopy (XPS), scanning
electron microscopy (SEM), energy-dispersiveX-ray(EDX) spectroscopy, ther-
Alireza Abbasi, School of Chemistry,
College of Science, University of Tehran,
P.O. Box: 14155-6455, Tehran, Iran.
Email: aabbasi@khayam.ut.ac.ir
Majid Masteri-Farahani, Research
Institute of Green Chemistry, Kharazmi
University, Tehran, Iran.
mal analysis (TGA/DTA), acid–base titration, and N adsorption/desorption
2
analysis were employed to fully characterize the prepared catalyst. The catalyst
showed high activity compared to unmodified MIL-101(Cr) in both catalytic
acetic acid esterification and alcoholysis of epoxides. It can also be readily iso-
lated from the reaction mixture and reused three times without major decrease
in its activity.
Email: mfarahani@khu.ac.ir
Funding information
University of Tehran
K E Y W O R D S
Alcoholysis, esterification, MOF, post-modification, solid acid
1
| INTRODUCTION
and organic linkers, have played as catalyst supports in a
wide range of catalytic reactions due to many advantages
Although Brønsted acids, such as sulfuric, hydrochloric,
and para-toluene sulfonic acid have been generally uti-
lized for manufacturing organic chemicals, these homo-
geneous catalysts suffer from equipment corrosion,
environmental toxicity, and difficult separation from the
arising from their large surface area, porous structure,
[
14–16]
and functionalization ability.
However, there are
few MOFs with Brønsted acid properties due to the nar-
row range of pre-installed sulfonic acid ligands for the
[
17]
preparation of Brønsted acid MOFs.
[1,2]
reaction medium.
Hence, many attempts have been
Post-functionalization of MOFs has opened a new
window to design a broad range of modified MOFs and
different functional groups have been immobilized into
paid for the preparation of heterogeneous Brønsted acid
catalysts via the insertion of sulfonic acid groups onto the
[
3–5]
solid supports e.g. graphene oxide,
mesoporous
their frameworks to produce heterogeneous catalysts for
[6–8]
[9,10]
[11]
[18–26]
silicas.
$132#polymers,
ion exchange resins,
many chemical reactions.
Among different known
and activated carbons with different surface functional
MOFs, MIL-101(Cr)is a suitable candidate for post-
functionalization because of its high surface area, attain-
able cages, high thermal and chemical stabilities, and lots
of coordinatively unsaturated metal sites (CUSs) upon
[12,13]
groups
because of facile work-up and recoverability.
Metal–organic frameworks (MOFs), a kind of novel
porous materials constituted from metal ions/clusters
Appl Organometal Chem. 2020;e5717.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.5717

2
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MORTAZAVI ET AL.
[
27,28]
dehydration process.
It is a chromium (III) tere-
for 24 hr. Before functionalization, the product was acti-
vated at 150 C overnight to generate open metal centers.
ꢀ
phthalate MOF with three-dimensional porous structure
which presents two types of mesoporous cages with
diameters of 2.9 and 3.4Å accessible through microporous
windows of 1.2 and 1.6Å, respectively.
Numerous approaches have been done to produce
MIL-101(Cr)-SO H through post-functionalization
strategy, such as post-synthetic sulfonation of organic
[29]
2.2 | Tandem post-functionalization of
MIL-101(Cr)
3
MIL-101(Cr) (0.5 g) was suspended in 20 ml dry toluene.
After addition of 2.5 mmol pyrazine, the mixture was
refluxed for 16 hr. The mixture was centrifuged and the
solid product washed with 2 × 10 ml of toluene to remove
any unreacted agent. Subsequently, the solid product was
suspended in 20 ml of dry toluene and after addition of
1,3-propane sultone (2.5 mmol, 0.2 ml), the mixture
refluxed for 16 hr. The obtained green solid was collected,
[
30,31]
ligand,
treatment of amino-based MOF with
and encapsulation of heteropoly acids.
[32–34]
[35]
sultone,
Here, we report the preparation of a sulfonic acid
functionalized MIL-101(Cr) by tandem modification on
its CUS using pyrazine which can be coordinated to the
chromium center of MIL-101(Cr) by one N atom, along
with nucleophilic attack to the 1,3-propane sultone
through the other N atom. This newly synthesized cata-
ꢀ
soxhelt washed with ethanol, and dried at 120 C for
lyst, signified as MIL-101(Cr)-Pyz-RSO H, is utilized for
4 hr. The final product was treated by 0.16 M H SO
4
3
2
acetic acid esterification and alcoholysis of epoxides with
high catalytic activity and easy recovery (Scheme 1).
(2.5 mmol concentrated H SO4 in 15 ml ethanol) to
ensure the protonation of all sulfonate groups of MIL-
2
1
1
01(Cr)-Pyz-RSO H. Finally, the functionalized MIL-
3
01(Cr) was collected, washed thoroughly with absolute
ꢀ
2
| EXPERIMENTAL
ethanol, and dried at 60 C for 24 hr. Before using the
catalyst in the catalytic tests, the activation was done for
24 hr at 100 C under vacuum.
ꢀ
Detailes of used materials and instruments are presented
in supporting information.
2
2
.3 | Catalytic test
2
.1 | Synthesis of MIL-101(Cr)
.3.1 | Acetic acid esterification
MIL-101(Cr) was synthesized without employing HF as
reported by Jiang et al.
2
dissolved in 10 ml of distilled water. The mixture was
poured into a Teflon-lined autoclave, heated to 210 C
with a rate of 1.5 C/min and kept for 8 hr at this temper-
[36]
Cr (NO ) ·9H O (0.80 g,
Acetic acid esterification with n-butanol was performed
as follows: a mixture of acetic acid (30 mmol, 1.8 g), n-
butanol (60 mmol, 2.22 g), activated catalyst (0.05 g), and
n-decane (2.56 mmol, 0.5 ml) as an internal standard was
3
3
2
mmol) and Terephthalic acid (0.33 g, 1.99 mmol) were
ꢀ
ꢀ
ꢀ
introduced into the flask, stirred, and heated at 110 C
ature. After cooling to room temperature, the resulting
green solid was filtered, washed with acetone, and
refluxed in dimethyl formamide (DMF) for 24 hr to
exclude any remained terephthalate ligands. Solvent
exchange by ethanol was carried out to expel DMF mole-
cules trapped inside the cavities with soxhlet extraction
and the test was continued at a time range of 1–5 hr. In
order to reach the optimum conditions, various parame-
ters including reaction temperature, catalyst amount,
molar ratio of acetic acid to n-butanol, and reaction time
were varied. The substrates conversion was calculated by
sampling from the reaction mixture at different times
and analysis using a gas chromatograph (Agilent 6890 N)
equipped with a capillary column (HP-5).
2.3.2 | Alcoholysis of epoxides
The alcoholysis of epoxides was performed in a 25 ml
round bottom flask containing epoxide (1 mmol), alcohol
(
5 ml) and catalyst (35 mg) at room temperature. Reac-
tion progress was controlled by sampling from the reac-
tion mixture and analysis with using gas
chromatograph. The used catalyst was isolated from the
SCHEME 1 (a) Acetic acid esterification with n-butanol,
a
(
b) Alcoholysis of epoxides

MORTAZAVI ET AL.
3 of 12
ꢀ
1158 cm−1 owing to asymmetric and symmetric
stretching vibrations of O=S=O. Another band at
mixture, washed with methanol, and dried at 100
under vacuum before reusing in another cycle.
C
039 cm− is related to the S-O stretching vibration.
1
[32,33]
1
X-ray diffraction (XRD) analysis confirmed the crys-
3
3
| RESULTS AND DISCUSSION
.1 | Preparation of the catalyst
tallinity and phase purity of the samples. The observed
pattern of MIL-101(Cr) is the same as simulated XRD
pattern obtained from the CIF file of MIL-101(Cr) single
[
38]
crystal (Figure 1B).
In the XRD pattern of MIL-
The overall steps of chemical functionalization of MIL-
01(Cr) have been illustrated in Scheme 2. To activate
101(Cr)-Pyz-RSO H, all reflections were shifted toward
the lower angles owing to the inclusion of functional
3
1
MIL-101(Cr) and eliminate its coordinated water, the
sample was heated at 150 C overnight to generate the
groups inside the pores of MIL-101(Cr) which extended
ꢀ
[39]
the unit cell parameters.
Nevertheless, the good
open metal centers. Then, pyrazine as a bridge for
attaching propane sultone to solid support, was coordi-
nated to CUS of MIL-101(Cr) by one of its nitrogen
atoms. Afterwards, the nucleophilic attack of the second
nitrogen atom to 1,3-propane sultone resulted in the pro-
duction of sulfonate groups coordinated covalently on
the surface of modified MIL-101(Cr). Finally, subsequent
protonation of the sulfonate groups with diluted sulfuric
acid gave MIL-101(Cr)-PyzRSO3H catalyst.
matching of MIL-101(Cr)-Pyz-RSO H pattern with parent
3
MIL-101(Cr) indicated that the overall structure of MIL-
101(Cr) was maintained during the functionalization
steps, which can be also observed from the octahedral
crystals of the parent and functionalized MIL-101(Cr) by
FE-SEM analysis (Figure 2). On the other hand, the
broadness of diffraction peaks in synthesized compounds
in comparison with the simulated one is related to the
small size of the particles (50–200 nm) as illustrated in
the FE-SEM images.
Chemical modification of MIL-101(Cr) was also
supported by CHNS analysis whose results are summa-
rized in Table 1.
3
.2 | Characterization of the MIL-101(Cr)-
Pyz-RSO H
3
Additional evidence for successful incorporation of
functional groups into the MIL-101(Cr) framework was
obtained from both elemental mapping and EDX analysis
FT-IR spectra of samples were recorded to follow the
modification of MIL-101(Cr) (Figure 1A). As can be seen
in the FT-IR spectrum of MIL-101(Cr)-Pyz, the peaks
of MIL-101(Cr)-Pyz-RSO H. EDX spectrum shows the
3
−
1
appeared in the range of 1067–1070 cm are responsible
presence of –SO H sulfur elements in the MIL-
3
for the coordination of pyrazine molecules to the unsatu-
101(Cr) framework as well as uniform distribution
of N, S, and O elements according to the elemental map-
ping (Figure 3). Furthermore, chemical states of the ele-
ments and composition of the obtained catalyst were
studied by XPS analysis (Figure 4). The N1s signal at
[37]
rated chromium site of MIL-101(Cr).
In the case of
MIL-101(Cr)-Pyz-RSO H, a new band was appeared at
3
2
988 cm− due to the aliphatic C-H stretching vibrations
1
of propyl groups and two bands observed at 1246 and
SCHEME 2 Synthetic steps of MIL-
1
01(Cr)-Pyz-RSO3H

4
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MORTAZAVI ET AL.
FIGURE 1 A) FT-IR spectra
of: (a) MIL-101(Cr), (b) MIL-
101(Cr)-Pyz, (c) MIL-101(Cr)-Pyz-
RSO3H, and (d)reused catalyst. B)
XRD patterns of: (a) simulated
pattern, (b) MIL-101(Cr), (c) MIL-
101(Cr)-Pyz-RSO3H, and (d) reused
catalyst
FIGURE 2 FE-SEM images of: (a) MIL-101(Cr), (b) MIL-101(Cr)-Pyz-RSO3H, and (c) reused catalyst
TABLE 1
Textural parameters and elemental analysis results of the samples
a
b
c
c
S
BET
2
V
T
N content
(mmol/g)
S content
(mmol/g)
Amount of Brønsted
acid sites (mmol/g)
3
d
Sample
(m /g)
(cm /g)
MIL-101(Cr)
2328
1.59
-
-
-
MIL-101(Cr)-Pyz-RSO
3
H
2143
1.4
2.76
0.56
0.64
a
Determined by BET method.
Total pore volume at p/p = 0.990.
0
b
c
Obtained by CHNS analysis.
d
Determined by acid–base titration.
4
01 eV can be ascribed to the nitrogen of the pyrazine.
the pore structure was maintained after functionalization
steps (Figure 5). The BET surface area and total pore vol-
ume of the MIL-101(Cr) were determined to be 2328
The strong S2p peak was clearly seen at 169.7 eV which
is related to the SO H groups.
Nitrogn adsorption–desorption analysis was done to
obtain the surface area, pore volume, and pore structure
of the samples. All of them exhibited type-I isotherms
characteristic of microporous materials and proved that
[40]
3
2
3
m /g and 1.59 cm /g, respectively. These values were
2
3
decreased to 2143 m /g and 1.4 cm /g for MIL-101(Cr)-
Pyz-RSO H, respectively, due to the occupation of cavi-
3
ties by functional groups.

MORTAZAVI ET AL.
5 of 12
FIGURE 3 EDX spectrum and related elemental distribution maps of MIL-101(Cr)-Pyz-RSO3H
FIGURE 4 Full and high
resolution XPS spectra of MIL-
1
01(Cr)-Pyz-RSO3H

6
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MORTAZAVI ET AL.
degradation of organic species which further approves
this statement.
The loading of -SO H groups onto the functionalized
3
MIL-101(Cr) was measured by acid–base titration. In a
typical procedure, the modified sample (50 mg) was
suspended in 10 mL of saturated NaCl aqueous solution.
After stirring at room temperature for 24 hr, the catalyst
was filtered and the acid amount was determined to be
0
0
.64 mmol/g by titration of the clear solution with a
.01 M NaOH solution which is approximately close to
the value obtained by CHNS analysis (Table 1).
3.3 | Catalytic performance
Catalytic properties of the obtained MIL-101(Cr)-Pyz-
FIGURE 5 The N2 adsorption–desorption isotherms of MIL-
RSO H was investigated in both acetic acid esterification
3
1
01(Cr) and MIL-101(Cr)-Pyz-RSO3H
and alcoholysis of epoxides.
Thermal stabilities of the MIL-101(Cr) and MIL-
1
01(Cr)-Pyz-RSO H samples were presented in Figure 6.
3.3.1 | Acetic acid esterification
3
For MIL-101(Cr), a significant mass reduction (52 wt%)
occurs in the range of 50–250 C that may be due to the
loss of water and solvent molecules trapped in the cavi-
ties or physically adsorbed on the external surface
ꢀ
Figure7 shows the effect of different parameters (reaction
time, reactants molar ratio, reaction temperature, and
catalyst amount) on the progress of acetic acid esterifica-
tion with n-butanol.
(Figure 6a). This interpretation was confirmed by the
corresponding endothermic peak in the DTA curve, as
First, the effect of reaction time was examined with
well. Afterwards, the framework is decomposed between
an equal molar ratio of acetic acid to n-butanol over
ꢀ
ꢀ
3
50–600 C due to the decompossition of terephthalic
0.05 g of the MIL-101(Cr)-Pyz-RSO H catalyst at 100 C.
3
acid ligands. This exothermic process can be seen in the
As expected, acetic acid conversion gradually increased
with time up to 4 hr and then, becomes almost constant
(Figure 7a). Accordingly, 4 hr was chosen as the opti-
mum reaction time.
As it has been known, esterification is a relatively
slow reaction promoted in the presence of catalysts to
reach better yields. It is a reversible reaction with water
DTA curve. In the case of MIL-101(Cr)-Pyz-RSO H,
3
ꢀ
approximately 6–8% of mass loss is observed up to 200 C
as most of the coordinated solvent molecules were rep-
laced by functional organic species (Figure 6b). In com-
parison with the parent MIL-101(Cr), the greater mass
ꢀ
loss in the range of 350–600 C is owing to the
FIGURE 6 TGA-DTA profiles of: (a) MIL-101(Cr), (b) MIL-101(Cr)-Pyz-RSO3H

MORTAZAVI ET AL.
7 of 12
FIGURE 7 The effect of various reaction conditions on the acetic acid conversion: (a) time, (b) acetic acid: n-butanol molar ratio,
(
c) temperature, and (d) catalyst amount
as byproduct. Therefore, an excess of n-butanol is
required to shift the equilibrium for improving the effi-
ciency of ester formation. For this reason, the effect of
acetic acid to butanol molar ratio on the conversion of
acetic acid. This effect may be due to the worse disper-
sion and partial covering of acid sites occurred in the
[
45]
excess of catalyst amount.
Results of the Figure 7 sug-
gest that the optimum reaction conditions are acetic acid
to butanol molar ratio of 1:2, 0.05 g of catalyst, tempera-
butyl acetate was investigated over 0.05 g catalyst at
ꢀ
ꢀ
1
00 C in 4 hr. When the molar ratio was increased to
:2, acetic acid conversion reached to 79%. In the higher
ture of 110 C in 4 hr.
1
Additionally, to clarify the effect of -SO H groups
3
ratio, the conversion decreased slightly to 76% due to the
dilution effect of n-butanol(Figure 7b).
introduced in the MIL-101(Cr) on the enhancement of
catalytic activity, the catalytic reaction was conducted in
the presence of unmodified MIL-101(Cr) in the optimum
conditions and acetic acid conversion of 40% was attained
which was only 2% higher than the blank test (38%).
Moreover, the effect of chain length of alcohols in the
acetic acid esterification was compared and the results
were given in Table 2. As displayed, in the case of alco-
hols with longer chains, the acetic acid conversion
decreased because of difficult diffusion of reactants in the
catalyst pores and interaction with catalytic active sites,
which were confirmed by the results of the same reac-
tions in presence of p-toluenesulfonic acid (Table S1 in
the Supporting Information).
[41,42]
Also, it was seen that, with the acetic acid:butanol
ꢀ
ratio of 1:2, changing the temperature from 80 to 110 C
increases the conversion of acetic acid from 29% to 90%.
ꢀ
Further increasing the temperature above 110 C have
not positive effect on the esterification reaction because
[
43,44]
of the low boiling point of the reactants (Figure 7c).
The effect of catalyst amount on the acetic acid con-
ꢀ
version was studied at 110 C with acetic acid to butanol
molar ratio of 1:2 in 4 h (Figure 7d). It can be seen that
when the catalyst amount increases from 0.025 to 0.05 g,
the conversion grows from 69 to 90% because of the exis-
tence of more active sites which results in improving the
acetic acid conversion. However, further increase of the
catalyst amount up to 0.1 g results in lower conversion of
Comparison of the catalytic efficiency of prepared cat-
alyst with different solid supported sulfonic acid catalysts

8
of 12
MORTAZAVI ET AL.
TABLE 2
in the presence of MIL101(Cr)-Pyz-RSO
Esterification of acetic acid with different alcohols
temperature. No conversion was achieved in the presence
of parent MIL-101 or in the absence of any catalyst in the
same reaction conditions.
a
3
H
b
Entry
Alcohol
Conversion %
In order to explore the effect of alcohol type in the
alcoholysis of styrene oxide, various linear and branched
alcohols were utilized. As shown in Table 4, there is a
relation between the alcohol size and styrene oxide con-
version. Methanol with only one carbon atom in the
chain shows the highest conversion (>99%) in 30 min
1
2
3
n-butanol
n-hexanol
n-octanol
90
77
61
a
Reaction conditions: acetic acid (30 mmol), alcohol (60 mmol), cat-
alyst (0.05 g), and n-decane (0.5 ml), 110 C, 4 hr.
Calculated from GC analysis.
ꢀ
b
(
entry 1). It is conspicuous that as the chain length of the
alcohol is increased, the conversion is decreased. In the
case of ethanol, propanol, and butanol, a longer reaction
time (5 hr) is required to reach the conversion of 84, 68,
and 52%, respectively (entry 2–4). Hexanol and octanol
showed conversions of 13% (in 5 hr) and 7% (in 24 hr)
was illustrated in Table 3. Our prepared catalyst shows
higher efficiencies toward butyl acetate production com-
pared to other solid acids at lower catalyst amount (rows
2–4) and reaction time (rows 3–7).
(
2
entry 5 and 6) and branched alcohols i.e., 2-propanol,
-butanol and tert-butanol showed the lowest reactivities
3
.3.2 | Alcoholysis of epoxides
even after 24 hr (entry 7–9). This noticeable difference in
reactivities is due to the steric hindrance of long chain
alcohols and bulky methyl groups of branched alcohols
which hamper to access the catalytic active sites inside
the catalyst pores (and thus the activated epoxide inside
the catalyst pores). Further evidence was provided
by utilization of various sized alcohols in the presence of
p-toluenesulfonic acid as catalyst (Table S2 in the
Supporting Information).
To expand our study, reaction of other epoxides with
methanol was tested in the optimum reaction conditions.
Table 4 shows that the reactivity of styrene oxide is
higher than the other epoxides because of the more sta-
bility of benzylic carbocation formed (entry 1). Also,
1,2-cyclooctene oxide showed the worst performance due
to the high steric hindrance. The activity order of other
epoxides are as follows: 1,2-propylene oxide >1,2-epoxy
hexane >1,2-epoxy octane.
Alcoholysis of epoxides is an important process for phar-
maceuticals and fine chemicals intermediates synthesis.
It is a very slow reaction and needs to be promoted by
Lewis or Brønsted acid catalysts. The application of MOFs
in alcoholysis of epoxides is relatively new and only a few
MOFs based on Fe, Cu, Al, Zr, and Ln metals have been
reported. All of them focused on the Lewis acidic proper-
ties of unsaturated metal centers.
studies show that MIL-101(Cr) has a very negligible cata-
lytic activity despite the presence of Cr which may act
as Lewis acid centers. So, we decided to enhance the cata-
lytic efficiency of MIL-101(Cr) by incorporation of -SO H
groups as Brønsted acidic parts utilizing post-synthetic
modification on the unsaturated chromium site. The pre-
pared catalyst was tested as a Brønsted acid catalyst for
methanolysis of styrene oxide in the mild reaction condi-
tions. Conversion of >99% and selectivity of about 100%
to 2-methoxy-2-phenylethanol were achieved in the pres-
[49–57]
Surprisingly, these
3+
3
It should be noted that, in all cases, 100% selectivity
to A isomer (Scheme 1) displays the regioselectivity of
epoxide alcoholysis which suggests that the nucleophilic
ence of MIL-101(Cr)-Pyz-RSO H only in 30 min at room
3
TABLE 3
3
Comparison of MIL-101(Cr)-Pyz-RSO H with different solid acid catalysts in acetic acid esterification with butanol
Acetic
acid/Butanol
Catalyst
amount
Temperature
( C)
Time
(h)
Conversion
(%)
ꢀ
No. Catalyst
Ref.
This work
[46]
1
2
3
4
5
6
7
MIL-101(Cr)-Pyz-RSO
3
H
1:2
1:2
1.5:1
1:1
1:4
1:4
1:2
2.77 wt%
20 wt%
4.5 wt%
6 wt%
110
130
Reflux
90
4
2
90
84
74
75
70
55
88
SSA
HPW-ampsul-SCMNPs
MIL-125 s
8
[47]
7
[48]
PSSF-mCNTs-GO
PSSF-mCNTs
2 wt%
120
120
117
10
10
9
[43]
2 wt%
[43]
RHANPSO
3
H
1.7 wt%
[44]

MORTAZAVI ET AL.
9 of 12
a
TABLE 4
3
Alcoholysis of epoxides in the presence of MIL-101(Cr)-Pyz-RSO H
b
b
Entry
Epoxide
Alcohol
Time (hr)
Conversion (%)
Selectivity for A/B (%)
1
MeOH
30 (min)
99
100: 0
2
3
4
5
6
7
8
9
EtOH
5
5
84
100: 0
100: 0
100: 0
100: 0
100: 0
100: 0
100: 0
-
n-Propanol
n-Butanol
n-Hexanol
n-Octanol
2-Propanol
2-Butanol
tert-Butanol
MeOH
68
5
52
5
13
24
7
14
24
24
5
24
<1
1
0
24 (5)
96 (64)
100: 0
1
1
1
1
2
3
MeOH
MeOH
MeOH
24 (5)
24 (5)
24
85 (44)
84 (24)
<1
100: 0
100: 0
-
a
Reaction conditions: epoxide (1 mmol), alcohol (5 ml), and catalyst (0.035 g) at room temperature.
Calculated from GC analysis.
b
TABLE 5
3
Comparison of MIL-101(Cr)-Pyz-RSO H with other MOF-based catalysts for methanolysis of styrene oxide
ꢀ
TOF (h−1)
a
Catalyst
Cu-MOF
Fe-BTC
Temperature ( C)
Time (min)
Conversion (%)
Ref.
[52]
RT
40
40
40
40
55
40
RT
120
60
93
99
5.3
10
[49]
Cu
Al
3
(BTC)
2
60
93
9.3
6.7
5.6
0.2
98.5
94
[49]
2
(BDC)
3
60
67
[49]
HKUST-1
Eu-MOF
150
48 h
20
90
[50]
100
99.8
99
[51]
MIL-101(HPW)
[58]
MIL-101(Cr)-Pyz-RSO
3
H
30
This work
a
TOF was calculated by: converted epoxide (mmol)/active sites of catalyst (mmol).reaction time (h)

10 of 12
MORTAZAVI ET AL.
attack occurs on the more substituted carbon atom of the
epoxide.
3.5 | Proposed mechanism of
esterification
Furthermore, comparison of our catalyst with other
MOF-based catalysts has summarized in Table 5. As can
be seen, our catalyst indicates higher efficiency among all
MOF-based catalysts in terms of reaction time and
temperature.
According to the Scheme 3, in the first step, MIL-
101(Cr)-Pyz-RSO H catalyst gives a proton to the acetic
3
acid to produce the intermediate (A). Second, the nucleo-
philic attack of the alcohol to the protonated carbonyl
groups forms the intermediate (B). After proton transfer
to one of the hydroxyl groups, the intermediate (C) is
generated. Then, intermediate (D) is produced with los-
ing a water molecule from (C). Finally, the corresponding
ester is achieved when the O-H bond of hydroxyl group is
cleaved, and the catalyst regenerated.
3.4 | Leaching and reusability test
Filtration test was performed to examine the catalyst sta-
bility. Hence, the catalyst was removed after 10 min of
reaction time and the filtrate was pursued to react for a
further 30 min. No further product was formed after fil-
tration of the catalyst as described in Figure 8 which veri-
fied the heterogeneous nature of the catalyst with
negligible leaching.
3.6 | Proposed mechanism for
methanolysis of styrene oxide
Besides, the catalyst reusability was examined under
reaction conditions. No obvious decrease was observed
for the conversion of styrene oxide during the 3 recycling
methanolysis tests. XRD and FT-IR analyses of the recov-
ered catalyst showed no remarkable change in compari-
son with the fresh catalyst (Figures 1 A and B). Also, FE-
SEM image of the recovered catalyst illustrated that the
According to the high regioselectivity of reaction to pro-
duce primary alcohol, it seems that the alcoholysis of epox-
ides under our Brønsted acid catalyst promotes through an
SN1 mechanism. Scheme 3 shows the probable mechanism
for methanolysis of styrene oxide over MIL-101(Cr)-Pyz-
RSO H. First, the proton of MIL-101(Cr)-Pyz-RSO H cata-
3
3
morphology of MIL-101(Cr)-Pyz-RSO H was almost
unchanged after the catalytic reaction (Figure 2c). These
results prove the good stability and recoverability of MIL-
lyst attaches to the oxygen atom of the epoxide to make the
benzylic carbocation (A). Afterwards, the nucleophilic
attack of alcohol i.e. methanol to the carbocation followed
by protonation of the oxygen atom of the epoxide ring
forms the β-alkoxy alcohol (B).
3
1
01(Cr)-Pyz-RSO H in the epoxide ring opening reaction
3
conditions.
FIGURE 8 Results of the filtration test
and reusability test (inset curve). Reaction
conditions: styrene oxide (1 mmol), methanol
(
5 ml), catalyst (0.035 g), room temperature

MORTAZAVI ET AL.
11 of 12
SCHEME 3 Suggested mechanism for:
(
a) methanolysis of styrene oxide, (b) acetic
acid esterification with nbutanol
[
[
8] P. Zhang, H. Wu, M. Fan, W. Sun, P. Jiang, Y. Dong, Fuel
2
019, 235, 426.
9] K. Dong, J. Zhang, W. Luo, L. Su, Z. Huang, Chem Eng J 2018,
34, 1055.
10] S. Mondal, J. Mondal, A. Bhaumik, ChemCatChem 2015, 7,
570.
11] D. M. Reinoso, G. M. Tonetto, J Environ Chem Eng 2018, 6,
399.
4
| CONCLUSIONS
3
In summary, sulfonic acid functionalized MIL-
01(Cr) was prepared by tandem post- functionalization
[
[
1
3
using pyrazine for attaching sulfonic acid groups to the
chromium sites of the MIL-101(Cr) support. The new
functionalized MIL-101(Cr) acted as a Brønsted solid acid
catalyst in two catalytic reactions i.e. acetic acid esterifi-
cation and alcoholysis of epoxides under solvent-free con-
ditions. The reusability of catalyst was checked for
3
[12] Q. Guan, Y. Li, Y. Chen, Y. Shi, J. Gu, B. Li, R. Miao, Q. Chen,
P. Ning, RSC Adv 2017, 7, 7250.
[
[
[
[
13] Y. Wang, D. Wang, M. Tan, B. Jiang, J. Zheng, N. Tsubaki,
M. Wu, ACS Appl Mater Interfaces 2015, 7, 26767.
14] O. M. Yaghi, M. O'keeffe, N. W. Ockwig, H. K. Chae,
M. Eddaoudi, J. Kim, Nature 2003, 423, 705.
3
times without any variation in crystallinity and mor-
phology. These results showed that tandem post- func-
tionalization is a good way to incorporate acidic groups
into the MOF structure for upgrading the catalytic activ-
ity. Furthermore, it is expected that N-heterocyclic com-
pounds can be potentially used for insertion of various
functional groups within the MOFs for different
applications.
15] S. Kitagawa, R. Kitaura, S. I. Noro, Angew Chem Int Ed 2004,
43, 2334.
16] H. M. Hassan, M. A. Betiha, S. K. Mohamed, E. El-Sharkawy,
E. A. Ahmed, Appl Surf Sci 2017, 412, 394.
[17] J. Jiang, O. M. Yaghi, Chem Rev 2015, 115, 6966.
[
[
18] S. M. Cohen, Chem Rev 2011, 112, 970.
19] Z. Yin, S. Wan, J. Yang, M. Kurmoo, M.-H. Zeng, Coord Chem
Rev 2019, 378, 500.
[20] H. A. Hamzah, T. S. Crickmore, D. Rixson, A. D. Burrows,
Dalton Trans 2018, 47, 14491.
ACKNOWLEDGEMENTS
We are gratefully appreciated for financial support from
the University of Tehran.
[
21] D. Ma, B. Li, Z. Shi, Chin Chem Lett 2018, 29, 827.
[22] G. Xiong, X.-L. Chen, L.-X. You, B.-Y. Ren, F. Ding,
I. Dragutan, V. Dragutan, Y.-G. Sun, J Catal 2018, 361, 116.
[
[
[
23] M. Han, Y. Li, Z. Gu, H. Shi, C. Chen, Q. Wang, H. Wan,
ORCID
G. Guan, Colloids Surf 2018, 553, 593.
24] S. Rostamnia, H. Alamgholiloo, M. Jafari, Appl Organomet
Chem 2018, 32, e4370.
Alireza Abbasi https://orcid.org/0000-0002-0331-0202
REFERENCES
25] M. Bahadori, S. Tangestaninejad, M. Bertmer, M. Moghadam,
V. Mirkhani, I. Mohammadpoor-Baltork, R. Kardanpour,
F. Zadehahmadi, ACS Sustainable Chem Eng 2019, 7, 3962.
26] H. M. Hassan, M. A. Betiha, S. K. Mohamed, E. El-Sharkawy,
E. A. Ahmed, J Mol Liq 2017, 236, 385.
27] J. T. Hupp, K. R. Poeppelmeier, Science 2005, 309, 2008.
28] G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange,
J. Dutour, S. Surblé, I. Margiolaki, Science 2005, 309, 2040.
29] M. S. El-Shall, V. Abdelsayed, S. K. Abd El Rahman,
H. M. Hassan, H. M. El-Kaderi, T. E. Reich, J Mater Chem
[
[
1] K. Nakajima, M. Hara, ACS Catal 2012, 2, 1296.
2] A. Vinu, T. Krithiga, N. Gokulakrishnan, P. Srinivasu,
S. Anandan, K. Ariga, V. Murugesan, V. Balasubramanian,
T. Mori, Microporous Mesoporous Mater 2007, 100, 87.
3] H. Alinezhad, M. Tarahomi, B. Maleki, A. Amiri, Appl
Organomet Chem 2019, 33, e4661.
4] M. Masteri-Farahani, M.-S. Hosseini, N. Forouzeshfar, Renew
Energy 2019, 151, 1092.
5] M.-S. Hosseini, M. Masteri-Farahani, S. Shahsavarifar,
J Taiwan Inst Chem Eng 2019, 102, 34.
[
[
[
[
[
[
[
[
[
2
009, 19, 7625.
30] J. Chen, K. Li, L. Chen, R. Liu, X. Huang, D. Ye, Green Chem
014, 16, 2490.
6] T. T. V. Tran, S. Kongparakul, S. Karnjanakom,
P. Reubroycharoen, G. Guan, N. Chanlek, C. Samart, Fuel
2
2
019, 236, 1156.
[
[
31] M. Saikia, L. Saikia, RSC Adv 2016, 6, 15846.
32] H. Liu, F.-G. Xi, W. Sun, N.-N. Yang, E.-Q. Gao, Inorg Chem
[
7] G. Martínez-Edo, A. Balmori, I. Pontón, A. Marti del Rio,
D. Sánchez-García, Catalysts 2018, 8, 617.
2016, 55, 5753.

12 of 12
MORTAZAVI ET AL.
[
33] R. S. Andriamitantsoa, J. Wang, W. Dong, H. Gao, G. Wang,
RSC Adv 2016, 6, 35135.
[50] L. H. Wee, M. R. Lohe, N. Janssens, S. Kaskel, J. A. Martens,
J Mater Chem 2012, 22, 13742.
[
34] N. Ko, P. G. Choi, J. Hong, M. Yeo, S. Sung,
K. E. Cordova, H. J. Park, J. K. Yang, J. Kim, J Mater Chem A
[51] S. M. Vilela, D. Ananias, J. A. Fernandes, P. Silva,
A. C. Gomes, N. J. Silva, M. O. Rodrigues, J. P. Tomé,
A. A. Valente, P. Ribeiro-Claro, J Mater Chem C 2014, 2, 3311.
[52] D. Jiang, T. Mallat, F. Krumeich, A. Baiker, J Catal 2008,
257, 390.
[53] D. Jiang, A. Urakawa, M. Yulikov, T. Mallat, G. Jeschke,
A. Baiker, Chem A Eur J 2009, 15, 12255.
[54] L. H. Wee, C. Wiktor, S. Turner, W. Vanderlinden,
N. Janssens, S. R. Bajpe, K. Houthoofd, G. Van Tendeloo,
S. De Feyter, C. E. Kirschhock, J Am Chem Soc 2012, 134,
10911.
[55] K. Tanaka, K.-i. Otani, T. Murase, S. Nishihote, Z. Urbanczyk-
Lipkowska, Bull Chem Soc Jpn 2012, 85, 709.
[56] Z. Xue, J. Jiang, M.-G. Ma, M.-F. Li, T. Mu, ACS Sustainable
Chem Eng 2017, 5, 2623.
[57] P. García-García, M. Müller, A. Corma, Chem Sci 2014, 5,
2979.
[58] L. H. Wee, F. Bonino, C. Lamberti, S. Bordiga, J. A. Martens,
Green Chem 2014, 16, 1351.
2
015, 3, 2057.
35] D.-Y. Du, J.-S. Qin, S.-L. Li, Z.-M. Su, Y.-Q. Lan, Chem Soc Rev
014, 43, 4615.
36] D. Jiang, A. D. Burrows, K. J. Edler, CrstEngComm 2011, 13,
916.
[
[
[
[
[
[
2
6
37] K. Nakamoto, Handbook of Vibrational Spectroscopy, John
Wiley & Sons, Inc., New Jersey, 2006.
38] O. Lebedev, F. Millange, C. Serre, G. Van Tendeloo, G. Férey,
Chem Mater 2005, 17, 6525.
39] S. Abednatanzi, A. Abbasi, M. Masteri-Farahani, New J Chem
2
015, 39, 5322.
40] Y. Sun, H. Huang, H. Vardhan, B. Aguila, C. Zhong,
J. A. Perman, A. M. Al-Enizi, A. Nafady, S. Ma, ACS Appl
Mater Interfaces 2018, 10, 27124.
[
[
[
[
[
[
[
41] J.-X. Wang, A.-Q. Wang, Y.-L. Xing, Z.-X. Zhu, X.-L. Wu, Y.-
Q. Wang, L.-X. Yang, RSC Adv 2015, 5, 105908.
42] Y. Zheng, Y. Zheng, S. Yang, Z. Guo, T. Zhang, H. Song,
Q. Shao, Green Chem Lett Rev 2017, 10, 202.
43] G. Bian, P. Jiang, W. Zhang, K. Jiang, L. Hu, Z. Jian, Y. Shen,
P. Zhang, RSC Adv 2015, 5, 90757.
44] F. Adam, K. M. Hello, M. R. B. Aisha, J. Taiwan, Inst Chem
Eng 2011, 42, 843.
45] D. Guliani, K. Kaur, N. Singh, A. Sobti, A. P. Toor, Chem Eng
Commun 2019, 206, 592.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
46] J. Ye, C. Liu, Y. Fu, S. Peng, J. Chang, Energy Fuel 2014, 28,
4
267.
47] M. S. Hosseini, M. Masteri-Farahani, Chem Asian J 2019, 14,
076.
How to cite this article: Mortazavi S-S, Abbasi A,
Masteri-Farahani M. A new Brønsted acid
MIL-101(Cr) catalyst by tandem post-
functionalization; synthesis and its catalytic
application. Appl Organometal Chem. 2020;e5717.
https://doi.org/10.1002/aoc.5717
1
[
48] E. Yılmaz, E. Sert, F. S. Atalay, Cat Com 2017, 100, 48.
[
49] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Chem A Eur J
2
010, 16, 8530.