Magnetite-supported sulfonic acid: A retrievable nanocatalyst for the Ritter reaction and multicomponent reactions

Article abstract of DOI:10.1039/c3gc40457a

Magnetite-sulfonic acid (Nanocat-Fe-OSO₃H), prepared by the wet-impregnation method, serves as a magnetically retrievable sustainable catalyst for the Ritter and multicomponent reactions. The as synthesized catalyst can be used in several reaction cycles without any loss of activity.

Full text of DOI:10.1039/c3gc40457a

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Magnetite-supported sulfonic acid: a retrievable
nanocatalyst for the Ritter reaction and
Cite this: DOI: 10.1039/c3gc40457a
multicomponent reactions†
a
b
c
d
Manoj B. Gawande,‡* Anuj K. Rathi,‡ Isabel D. Nogueira, Rajender S. Varma*
and Paula S. Branco*
a
Received 8th March 2013,
Accepted 7th May 2013
3
Magnetite-sulfonic acid (Nanocat-Fe-OSO H), prepared by the wet-impregnation method, serves as a
DOI: 10.1039/c3gc40457a
magnetically retrievable sustainable catalyst for the Ritter and multicomponent reactions. The as syn-
thesized catalyst can be used in several reaction cycles without any loss of activity.
www.rsc.org/greenchem
Supported-heterogeneous catalysts have garnered much atten- could be separated by an external magnet and reused multiple
1
6
tion in recent years and are actively pursued in the develop- times for the several reaction cycles. Most of them have good
ment of modern organic synthesis and greener reaction selectivity and catalytic activity at par with the conventional
1
–5
protocols.
Homogeneous, flammable, and active protic homogeneous catalysts and are being used for the immobili-
acids have been immobilised on the solid support for deploy- zation of metals, organocatalysts, NHCs, and some other mag-
6
17–24
ment in organic reactions.
netically retrievable nanocatalysts.
The magnetically
Various supports such as silica, carbon, and zirconia separable nanocatalysts are valuable addition to sustainable
among others have been used for the immobilization of homo- methodologies as the demand for benign nanocatalysts and
geneous catalysts/reagents and applied in chemical synthesis their applications in synthesis is on the rise.
7
–11
and sustainable transformations.
In addition, organic poly-
The Ritter reaction is a classical acid-catalyzed reaction
mers have also been extensively investigated as catalyst sup- between a carbocation precursor, such as a substituted olefin
1
2
25
ports. These supports, though advantageous in some cases, or alcohol, and nitriles to generate amides. It has versatile
retain some of the common drawbacks that pertain to the tra- applications for the synthesis of active pharmaceutical inter-
2
6,27
28,29
ditional and cumbersome isolation procedure after completion mediates and heterocycles.
of reactions and most importantly are deficient in the reusabil- trifluoromethane sulfonic anhydride, triflic anhydride, 2,4-
ity aspect. There are few reports on the use of homogeneous nitrobenzenesulfonic acid,
protic acids on the solid supports, such as silica and silica often used for these reactions. In most of these reactions,
In general, sulfuric acid,
3
0
31
3
2
33
FeCl ·6H O
and I /H O are
2 2
3
2
3
4
1
3–15
coated Fe O .
Even so, there is an ample scope in the homogeneous catalysts are frequently involved, which are
2
3
3
5
design of improved supported catalysts from the point of view expensive and not reusable. In recent years there have been
of benign and sustainable protocols. Recently, magnetite-sup- few reports on the Ritter reaction using homogenous reagents
ported catalysts have emerged as the viable alternatives to or catalysts on the immobilized supports such as silica-deco-
existing solid-supported heterogeneous catalysts, as they are rated maghemite nanoparticles, sulfated tungstate and
inert, inexpensive, easy to prepare, and most importantly some other supported catalysts deployed for the Ritter reac-
3
6
37
3
8
tions. So, there is a need to design a more sustainable proto-
col for the Ritter reaction.
A similar protocol has been previously reported using
γ-Fe O supported HClO which requires the use of a volatile
a
36
REQUIMTE, Department of Chemistry, Faculdade de Ciências e Tecnologia,
Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Lisbon, Portugal.
E-mail: m.gawande@fct.unl.pt, paula.branco@fct.unl.pt
2
3
4
b
organic solvent (Et O) and TEOS to decorate the γ-Fe O thus
2
2 3
Jubilant Chemsys Ltd., B-34, Sector-58, Noida-201301, New Delhi, India
c
rendering the protocol expensive. In contrast, the present
research work is simple and inexpensive, in which chlorosulfo-
nic acid is directly added to the magnetite support under neat
conditions.
In continuation of our research endeavors on development of
sustainable protocols and applications of nano-catalysts,
Instituto de Ciência e Engenharia de Materiais e Superfícies, IST, Lisbon, Portugal
d
Sustainable Technology Division, National Risk Management Research Laboratory,
US Environmental Protection Agency, MS 443, 26 West Martin Luther King Drive,
Cincinnati, Ohio 45268, USA. E-mail: Varma.rajender@epa.gov
†
Electronic supplementary information (ESI) available: Experimental section is
depicted in ESI. See DOI: 10.1039/c3gc40457a
Both authors made equal contribution.
16,24,39,40
‡
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Scheme 1 Synthesis of Nanocat-Fe-OSO H.
herein, we report on a highly efficient Nanocat-Fe-OSO H, a mag-
3
netically separable and recyclable catalyst for the Ritter reaction
under solvent-free conditions.
Nanocat-Fe-OSO H was synthesized using an impregnation
3
protocol (Scheme 1) and fully characterized by X-ray diffraction
(XRD), Fourier transform infrared spectra (FT-IR), trans-
mission electron microscopy (TEM), and field-emission gun,
scanning electron microscope electron dispersive spectrometry
Fig. 2 TEM images of (a) magnetite nanoparticles; (b) Nanocat-Fe-OSO
3
H;
(
FEG-SEM-EDS). The loading of SO
pH analysis, and it is found to be 1.76 mmol g of Nanocat-
Fe-OSO H (ESI†).
The infrared spectra of the Nanocat-Fe-OSO
3
H per g was calculated by
−1
(c) SEM-EDS of Nanocat-Fe-OSO H (inset SEM image which is used for EDS scan).
3
3
3
H (see ESI†)
clearly present bands namely at 3367 cm (O–H stretching) at form large clusters were observed; small groups of equiaxial
−
1
−
1
1
614 and between 1200 and 980 cm (SvO and S–O stretch- particles almost entirely detached from each other are
ing), which justify the presence of the sulfonic group on its discernible.
−
1
surface. The band observed at 560 cm confirms the structure
Clustering tendencies could be due to weak forces (hydro-
gen bonding) between the Fe -OSO H molecules (Fig. 2c,
clearly matches with the lite- inset image). This tendency is not surprising, given (MNPs)
rature data from JCPDS 79-0419. Notably, the same peaks were the small size and magnetic characteristics. From EDS ana-
also observed in Nanocat-Fe-OSO
H XRD spectra, with slight lysis, the sulfur peak clearly confirms the presence of a
changes in the nature of peaks; this could be due to the pres- -OSO H group from chlorosulfonic acid (Fig. 2c).
ence of sulfonic acid on the surface of Fe O . The crystallite
The catalytic activity of Nanocat-OSO H was investigated for
H catalyst, determined by the Debye the Ritter reaction. Initial experiments were performed
Scherrer equation, was found to be 18 nm (Fig. 1).
between 1-phenyl ethanol and benzonitrile under solvent-free
transmission electron microscopy (TEM) image of conditions (Table 1, entry 1); the amide 1a was obtained in
of the Fe–O group.
3
O
4
3
3 4
The XRD spectrum of Fe O
3
3
3
4
3
size of a Nanocat-Fe-OSO
3
A
Nanocat-Fe-OSO
3
H exhibited uniform-sized magnetic nano- very good yield. It is important to mention that we chose
particles with almost spherical morphology (Fig. 2a and 2b). solvent-free conditions as the key feature in designing a sus-
NP sizes were in the 15–30 nm range (average NP size: 16 nm) tainable protocol. Further substrate scope investigations were
in relatively good agreement with that observed by XRD. From all conducted under solvent-free conditions using Nanocat-Fe-
analysis of FEG-SEM images using a 25 kV acceleration OSO H (Table 1). It is important to point out that the reactions
3
voltage, uniform-sized magnetic nanoparticles (MNPs) with carried out with the unfunctionalised magnetite (without the
somewhat spherical morphology and a marked tendency to sulfonic acid group appended) provided no desired products
(
1) in the investigated reactions. The scope of the reaction was
further probed under the established optimal reaction con-
ditions. As depicted in Table 1, a wide range of substrate com-
binations were investigated; in all cases, clean and high
yielding reactions were observed. The reaction between a hin-
dered aromatic nitrile and a hindered alcohol also led to the
corresponding amide formation in good yield (entry 2). The
mechanism presumably entails the formation of the carbo-
cation by the acid catalysis of the Nanocat-Fe-OSO H at the
3
alcohol carbocation precursor, which reacts with the nitrile to
form a nitrilium ion. Water hydrolysis and a series of proton
transfer steps then yield the final amide product.
The good activity of the catalyst inspired us to explore its
catalytic activity for the Strecker reaction and the quinoline
synthesis.
3 4 3
Fig. 1 XRD spectra of Fe O and Nanocat-Fe-OSO H MNPs.
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a
Table 1 Ritter reaction catalysed by Nanocat-Fe-OSO
3
H under solvent-free conditions
b
Entry
1
Alcohol
Nitrile
Product (1)
Time (h) yield (%)
(5) 84
2
3
(4) 80
(4) 90
4
5
6
7
(3) 82
(4) 90
(4) 84
(4) 88
8
9
(4) 84
(5) 82
(5) 85
1
0
a
b
Reaction conditions – alcohol (1 mmol), nitrile (1 mmol) and catalyst (100 mg) at 90 °C under solvent-free conditions. Isolated yield.
The Strecker reaction, well-known for the synthesis of
α-aminonitriles, is one of the universal methods potentially hyde, piperidine and TMSCN under solvent-free conditions
expedient for syntheses of amino acids and other bioactive provided the product 2 in 93% yield and for quinoline syn-
The multicomponent reaction between 4-fluorobenzalde-
4
1
ingredients including natural products.
thesis, the condensation reaction between 2-amino benzo-
Quinolines and its derivatives are some of the important phenone and 5,5-dimethyl-1,3-cyclohexandione irradiated in
classes of heterocyclic compounds and are known to possess MW to provide 3 in 92% yield (Scheme 2).
a wide range of biological activities including antimalarial,
After establishing the activity and versatility of the Nanocat-
4
2,43
antibacterial, and some other activities.
Moreover quino- Fe-OSO H catalyst for a variety of reactions, its recyclability was
3
line scaffolds are employed for the preparation of nano- subsequently tested by recycling and reuse of the catalyst in
structures and mesostructures with enhanced electronic and the reaction between 1-phenyl ethanol and benzonitrile under
4
4
photonic functions. There have been many synthetic routes the aforementioned conditions. In each cycle the catalyst was
to the quinoline including the Doebnervon, Miller, Skraup, separated magnetically, washed with ethyl acetate, and finally
Combes and Friedländer. The Friedländer annulation is still dried at 50 °C under vacuum to remove residual solvents.
3
the most facile and simple reaction for the synthesis of Nanocat-Fe-OSO H MNPs could be reused up to five times
quinolines.
without any significant loss of the initial catalytic activity
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Preparation of Fe O -OSO H (Nanocat-Fe-OSO H)
In a two neck round bottom flask, equipped with a constant-
pressure dropping funnel and a gas inlet tube for conducting
HCl gas over an adsorbing solution (i.e. water) was used. Mag-
3 4
netite (Fe O ) (2 g) was stirred in a round bottom flask and
neat chlorosulfonic acid added (0.5 mL) dropwise over a
period of 5 min at room temperature. HCl gas immediately
evolved from the reaction vessel. After addition, the mixture
was shaken for 30 min and solid material was collected as a
brown solid of magnetic sulfonic acid (Nanocat-Fe-OSO H)
3
3
Scheme 2 Nanocat-Fe-OSO H catalyzed protocols.
(
2.35 g).
3
Table 2 Recyclability of Nanocat-Fe-OSO H
Experimental procedure for Ritter reactions
Run
1
2
3
4
5
In a pressure tube, alcohol (1 mmol), nitrile (1 mmol) and
Nanocat-Fe-OSO H (100 mg) were heated at 90 °C under
Yield (%)
84
83
83
81
80
3
solvent-free conditions for respective time (see Table 1 in the
paper). After completion of reactions, monitored by thin layer
chromatography, 5 mL of ethyl acetate was added to the reac-
tion mixture and the catalyst separated magnetically. The
organic solvent was concentrated under reduced pressure and
the crude material subjected to column chromatography with
ethyl acetate and hexane as eluents.
(
Table 2). The structural characteristics of reused nanocatalysts
were checked by FT-IR after 5 runs; notably, no difference in
the peaks was observed (see ESI†).
The salient feature of these protocols is the versatility as the
catalyst can be separated by using an external magnet avoiding
the efforts of filtration and isolation procedures. We believe
that this interesting chemistry can be used for various other
significant reactions, especially to immobilize other protic Preparation of 2-(4-fluorophenyl)-2-(piperidin-1-yl) acetonitrile
super acids and their applications in nanocatalysis and (2)
4
5
organic synthesis.
A mixture of 4-fluorobenzaldehyde (1 mmol), piperidine
1.5 mmol), and Nanocat-Fe-OSO H (50 mg) was stirred at
(
3
room temperature for 1 min. Then TMSCN (1.2 mmol) was
added and the mixture stirred for another 30 min. When TLC
showed completion of the reaction the reaction mixture was
diluted with ethyl acetate (20 mL) and water (20 mL). The
nanocatalyst was separated by use of a magnet. The organic
layer was separated and the aqueous layer was re-extracted
with ethyl acetate (2 × 20 mL). The combined organic layer was
dried over anhydrous sodium sulphate and concentrated
under reduced pressure to give the desired product which was
subsequently purified by column chromatography with ethyl
acetate and hexane as eluents.
Conclusions
3
The present work describes Nanocat-Fe-OSO H as a very pro-
mising nano-catalyst for the Ritter reaction between alcohols
and nitriles under solvent-free conditions. This magnetically
separable catalyst is prepared by a simple procedure using
inexpensive precursors. In addition, the catalyst is reusable for
several cycles without any significant loss in catalytic activity.
3
In addition, the versatility of the Nanocat-Fe-OSO H was tested
for quinoline synthesis and the Strecker reaction. Further
applications of this catalyst are under investigation in our
laboratory.
Synthesis of 3,3-dimethyl-9-phenyl-3,4-dihydroacridin-1(2H)-
one (3)
Experimental
In
1 mmol), 5,5-dimethyl-1,3-cyclohexandione (1 mmol), and
O (5.4 g) and urea (3.6 g) were dissolved in water Nanocat-Fe-OSO H (50 mg) was irradiated in a microwave
200 mL) at 85 to 90 °C for 2 h. The solution turned brown. To (300 W) at 130 °C for 4 h. After completion of the reaction
the resultant reaction mixture cooled to room temperature was monitored by TLC, the reaction mixture was cooled to room
added FeSO ·7H O (2.8 g) and then 0.1 M NaOH until pH 10. temperature, and ethyl acetate (20 mL) was added to sepa-
The molar ratio Fe to Fe in the above system was nearly rate the catalyst by an external magnet. The organic layer was
.00. The obtained hydroxides were treated by ultrasound in washed with water (10 mL) dried over anhydrous sodium sul-
the sealed flask at 30 to 35 °C for 30 min. After ageing for 5 h, phate and concentrated under reduced pressure to get the
a glass tube a mixture of 2-amino benzophenone
3 4
Preparation of Fe O MNPs
(
FeCl ·6H
3
2
3
(
4
2
III
II
2
the obtained black powder (Fe
under vacuum.
3
O
4
) was washed, and dried crude product which was subjected to crystallization with
ethanol.
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2
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