A mild and efficient method for the synthesis of pyrroles using MIL-53(Al) as a catalyst under solvent-free sonication

Article abstract of DOI:10.1039/c9ra01071h

A highly efficient method for the synthesis of pyrroles using MIL-53(Al) as a catalyst has been developed under solvent-free sonication. This reaction has a broad substrate scope and high yields were obtained within a short reaction time. Remarkably, no additional additives and volatile organic solvent are required for this method and the MIL-53(Al) could be recovered and reused several times without significant drop-off in catalytic activity.

Full text of DOI:10.1039/c9ra01071h

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A mild and efficient method for the synthesis of
pyrroles using MIL-53(Al) as a catalyst under
solvent-free sonication†
Cite this: RSC Adv., 2019, 9, 9093
a
Linh Ho Thuy Nguyen, Tan Le Hoang Doan*ab
ab
Hai Truong Nguyen,
and Phuong Hoang Tran
a
*
A highly efficient method for the synthesis of pyrroles using MIL-53(Al) as a catalyst has been developed
under solvent-free sonication. This reaction has a broad substrate scope and high yields were obtained
within a short reaction time. Remarkably, no additional additives and volatile organic solvent are required
for this method and the MIL-53(Al) could be recovered and reused several times without significant
drop-off in catalytic activity.
Received 10th February 2019
Accepted 11th March 2019
DOI: 10.1039/c9ra01071h
rsc.li/rsc-advances
Hantzsch syntheses. Among these approaches, the Paal–Knorr
reaction is known as an extremely efficient pathway to produce
Introduction
Metal–organic frameworks (MOFs) are a class of crystalline pyrroles from primary amines and 1,4-dicarbonyl compounds
porous materials containing metal clusters (termed secondary under acidic conditions. Over the past decade, several typical
building units, SBUs) connected by a variety of organic acidic catalysts have been widely employed in the Paal–Knorr
1
,2
24–28
bridges. These materials have attracted much interest for reaction including Lewis acids,
metal–organic frame-
29
30
31,32
many potential applications in heterogeneous catalysis due to works, deep eutectic solvents, Brønsted acids.
Despite the
their exceptional properties including crystallinity, active-site potential utility of these catalysts, many of them still suffer from
3
–7
uniformity, and high porosity with permeable channels.
certain drawbacks, including long reaction times, volatile
Especially, aluminum based-MOFs with highly robust struc- organic solvents, low yields, expensive and unrecyclable cata-
tures have recently emerged as promising catalysts in several lysts. Due to the advantages of high activity and easy recovery,
8,9
organic transformations. Among them, the well-known cata- heterogeneous catalysts have been receiving much attention in
lyst is MIL-53(Al), whose porous 3D structure with 1D lozenge- the organic synthesis. Herein, we describe the direct synthesis
shaped channels (Fig. 1) is constructed from a connection of of pyrrole using primary amines and hexa-1,4-dione catalyzed
innite trans-chains of corner-sharing (via OH groups) by MIL-53(Al) under solvent-free sonication. The mild reaction
AlO
dicarboxylate (BDC). Because of the exceptional structural lytic recyclability are the outstanding features of the present
4 2
(OH)
octahedra with ditopic organic linker, 1,4-benzene- conditions, no additional additives, work-up simplicity, cata-
10
1
1,12
properties, the material could play a role as a Brønsted-type
(
work.
13
3+
OH sites) and Lewis-type (Al sites) acid heterogeneous
catalyst. Although there have been a wide number of reported
Experimental
General methods
13
researches used MIL-53(Al) for catalysis in alkylation, cyclo-
14
12
11
addition, Mannich reaction, and cellulose transformation,
the catalytic activity of MIL-53(Al) for organic transformations Powder X-ray diffraction (PXRD) patterns were recorded using
remains an attractive eld.
a D8 Advance diffractometer equipped with a LYNXEYE detector
Pyrroles are important structural motifs present in various (Bragg–Brentano geometry, Cu Ka radiation l ¼ 1.54056 A˚ ).
biologically active molecules and natural products. There Thermal gravimetric analysis (TGA) was performed using a TA
are three commonly used approaches for the synthesis of these Instruments Q-500 thermal gravimetric analyzer under airow
15–23
ꢀ
ꢁ1
essential compounds including Barton–Zard, Paal–Knorr, and with a temperature ramp of 5 C min . Fourier transform
infrared (FT-IR) spectra were measured on a Bruker E400 FT-IR
spectrometer using potassium bromide pellets. Low-pressure
a
Faculty of Chemistry, University of Science, Vietnam National University – Ho Chi
N
2
2
and CO adsorption measurements were carried out on
Minh City, 721337, Vietnam. E-mail: thphuong@hcmus.edu.vn
b
a Quantachrome Autosorb iQ volumetric gas adsorption
Center for Innovative Materials and Architectures, Vietnam National University – Ho
analyzer. A liquid N bath was used for measurements at 77 K.
Chi Minh City, 721337, Vietnam. E-mail: dlhtan@inomar.edu.vn
2
Helium was used as an estimation of dead space. Ultrahigh-
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra01071h
1
purity-grade
N
2
,
and He (99.999% purity) were used
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throughout adsorption experiments. Solution NMR spectra the complete removal of guest molecules in the framework (ESI,
were recorded on a Bruker Advance-500 MHz NMR spectrom- Fig. S2†). The nitrogen adsorption isotherm of MIL-53(Al) at low
eter. Scanning Electron Microscopy (SEM) images were per- pressure and 77 K exhibited a type-I behavior due to the pres-
formed on a JEOL JSM-75FCT. Gas chromatography (GC) ence of micropore within the structure and an internal surface
2
ꢁ1
analyses were performed using Agilent 6890 Series equipped area of 1120 m g based on Brunauer–Emmett–Teller (BET)
with a ame ionization detector (FID) and a DB-5 column method (ESI, Fig. S3†).
(
length ¼ 30 m, inner diameter ¼ 320 mm, lm thickness ¼ 0.25
Subsequently, we employed MIL-53(Al) directly to synthesize
mm). GC-MS analyses were performed on Agilent GC System pyrroles selectively and the desired product was afforded in 96%
7
5
890 Series, equipped with a mass selective detector Agilent yield (Table 1, entry 18). To evaluate the efficiency of catalyst,
973N and a capillary DB-5MS column (length ¼ 30 m, inner the model reaction of acetonylacetone with aniline was carried
diameter ¼ 320 mm, lm thickness ¼ 0.25 mm).
out under solvent-free sonication in the presence of various
catalysts.
As can be seen in Table 1, the corresponding product was
afforded in a good yield of 67–83% in the presence of metal
halides (Table 1, entries 1–6), while low yields were observed
Preparation of MIL-53(Al) catalyst
MIL-53(Al) was hydrothermally synthesized following the re-
33
ported procedure. Al(NO
3 3 2
) $9H O (375 mg, 0.50 mmol) and
when metal oxides were employed (Table 1, entries 7–12). HfCl
and AlCl provided the corresponding product in high yields,
4
1
,4-benzenedicarboxylic acid, H BDC, (83.1 mg, 0.50 mmol)
2
3
were dissolved in 1.5 mL deionized (DI) water in a Teon-lined
steel autoclave. The solution was subsequently heated at 220 C
but these metal halides were not recovered aer the aqueous
work-up. Then, MOFs including MOF-890, MOF-891, MOF-177,
ZIF-8, and HKUST-1 were tested in the model reaction and good
yields of 80–89% were observed (Table 1, entries 13–17). MIL-
ꢀ
for 3 days in an isothermal oven to yield a white precipitate.
Aer cooling the autoclave to room temperature, the white
precipitate was obtained by centrifugation and washed ve
times with DI water. The as-synthesized sample was then
evacuated at room temperature for 24 h. The solid was then
53(Al) displayed the best catalytic activity and high stability
for the Paal–Knorr synthesis (Table 1, entry 18). However, the
reaction could hardly proceed in the absence of a catalyst (Table
ꢀ
heated in air at 330 C for 3 days for removal of the excessive
1
5
, entry 19). According to these results, we reason that MIL-
3(Al) acted as an efficient heterogeneous Lewis acid catalyst
H BDC adsorbed in the pores.
2
in this reaction (as shown in Scheme S1†). Thus, the reaction
conditions were optimized in the presence of MIL-53(Al) cata-
General procedure for Paal–Knorr reaction
MIL-53(Al) (10 mg, 5 mol%), aromatic amine (1.0 mmol), acto- lyst under solvent-free sonication (see Table S1–S4 in the ESI†).
nylacetone (1.2 mmol) was added into a 10 mL pressurized glass
ꢀ
tube. The reaction mixture was sonicated at 80 C for an
a
Table 1 The effect of different catalysts in the Paal–Knorr reaction
appropriate time. The progress of the reaction was monitored
by TLC and GC. Aer completion of the reaction, the catalyst
was ltered from the reaction mixture. The ltrate was diluted
with ethyl acetate (25 mL), washed with H
2
O (5 ꢂ 15 mL), and
dried over Na SO . The solvent was removed under vacuum on
2
4
a rotary evaporator. The pure product was isolated by ash
chromatography (n-hexane, then 10% ethyl acetate in n-hexane). Entry
The purity and identity of the pyrrole were conrmed by GC-MS
Catalyst
CuCl2
Isolated yield (%)
1
13
1
2
3
4
5
6
7
8
9
1
67
76
83
78
83
77
74
70
55
73
14
72
80
82
81
83
89
96
25
spectrometry, H and C NMR spectroscopy.
FeCl
HfCl
FeCl
AlCl
ZnCl
Fe
ZnO
Al
TiO
2
4
Results and discussion
3
3
The MIL-53(Al) was prepared by a hydrothermal reaction of
aluminum chloride and the ditopic linker, 1,4-benzenedi-
carboxylic acid. Aer the reaction nished, the suspension was
cooled to room temperature, and then the white precipitate was
2
2
O
3
2
O
3
0
2
obtained by centrifugation and washed ve times with DI water. 11
MgO
CuO
MOF-890
MOF-891
MOF-177
ZIF-8
HKUST-1
MIL-53(Al)
Non-catalyst
ꢀ
12
13
As-synthesized MIL-53 was heated at 330 C for 3 days and
ꢀ
activated at 120 C for a day to yield the guest-free material.
Aer activation, the purity of MIL-53(Al) framework was deter-
mined by powder X-ray diffraction (PXRD) in which the acti-
1
1
1
4
5
6
vated PXRD pattern for MIL-53(Al) was in good agreement to 17
10
18
that of the simulated MIL-53(Al) (ESI, Fig. S1†). Thermogra-
vimetric analysis (TGA) was utilized to access the activation
procedure. The TGA curve of the activated sample with a single
1
9
a
Reaction condition: aniline (1.0 mmol), acetonylacetone (1.2 mmol) in
ꢀ
the presence of the catalyst (5 mol%) under solvent-free sonication.
step of the linker decomposition above 500 C demonstrated
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a
Table 2 Synthesis of pyrroles catalyzed by MIL-53(Al)
b
Entry
Amine
Time (min)
15
Product
Isolated yield (%)
1
96
86
2
3
4
5
20
30
30
30
85
88
80
6
7
8
15
15
15
96
98
95
9
15
15
98
98
1
0
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Table 2 (Contd.)
b
Entry
Amine
Time (min)
Product
Isolated yield (%)
c
1
1
15
75
1
2
3
20
15
90
98
1
1
1
4
5
15
15
95
98
1
1
6
7
15
20
50
Trace
d
1
8
15
55 (92)
a
b
c
d
The reaction conditions: amines (1 mmol), acetonylacetone (1.2 mmol). Isolated yield. Yield of another isomer was obtained in 15%. Yield in
parenthesis was reported by the reaction with 2.4 equiv. of acetonylacetone.
With the optimized conditions in hand, the scope of was with prolonged the reaction times (20–30 min). Interestingly,
investigated (Table 2). The electronic properties of aromatic the yield of expected product increased to 96% when 4-iodoa-
amines have little inuence on the Paal–Knorr synthesis. niline (Table 2, entry 6) was employed as the substrate. As ex-
Reactions with anilines bearing dihalo groups (Table 2, entries pected, reactions with anilines bearing electron-donating
2–5) could provide the desired products in good yields (>80%) groups in the aromatic ring (Table 2, entries 7–10) could
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effectively deliver the corresponding products in excellent yields revealed that the crystallinity and integrity of this catalyst was
>90%) with 100% conversion of substrates. Interestingly, when maintained aer the fourth cycle (please see Fig. S6 in ESI†).
-nitro-o-phenylenediamine was employed as the substrate and
the yield of major product was obtained in 75% (Table 2, entry
(
4
Conclusion
11). Remarkably, aer the reaction mixtures were exposed to
ultrasound for 15–20 min, anilines bearing electron- In conclusion, we have developed a highly efficient protocol for
withdrawing groups can be converted into the corresponding cyclocondensation between primary amines and acetonylace-
products (Table 2, entry 12–15). The expected products were tone using cheap and easily-prepared MIL-53(Al) under solvent-
afforded in moderate yields with phenylhydrazine (Table 2, free sonication. To the best of our knowledge, this is the rst
entry 16). No product was detected with 2,4-dinitrophenylhy- example of Paal–Knorr synthesis catalyzed by a heterogeneous
drazine (Table 2, entry 17). As expected, the use of 1,2-ethane- MIL-53(Al) under sonication. It is noteworthy that the addi-
diamine as the substrate provided the corresponding bispyrrole tional additives and volatile organic solvents are not required
in 55% yield; attempts to improve the reaction yield by using the for this method. Moreover, MIL-53(Al) employed in catalytic
molar of acetonylacetone to greater than two equiv. were amount and can be recycled at least four times without signif-
successful (Table 2, entry 18). Furthermore, the current protocol icant decrease in its catalytic activity. The detailed mechanistic
was also investigated on a 10 mmol scale reaction between study is in progress within our laboratory.
aniline and acetonylacetone, which provided the corresponding
product in 95% yield. Consequently, the present method can be
potentially applied to the industrial processes.
Conflicts of interest
The recovery and reuse of the developed MIL-53(Al) catalyst There are no conicts to declare.
in the Paal–Knorr synthesis can be achieved by a simple ltra-
tion. A little decrease of the catalytic activity was observed aer
the fourth cycle (Fig. 2). These results demonstrated that the
Notes and references
MIL-53(Al) could be reused at least four times without signi-
cant decline of catalytic activity. PXRD analysis of MIL-53(Al)
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