S. M. Agawane, J. M. Nagarkar / Tetrahedron Letters 52 (2011) 5220–5223
5223
Table 5
Recyclability of nano CeO2
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a
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96
Run 1
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Run 2
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Run 3
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11. General procedure for synthesis of nano ceria: CeO2 nanoparticles were prepared
by adding ammonia solution to an aqueous solution of cerium (III) nitrate in
the presence of CTAB. In a typical procedure, added 1 g of Ce(NO3)3 in a
solution of CTAB dissolved in 100 cm3 of water. Mole ratio of Ce/CTAB was kept
at unity. pH of the solution was adjusted between 10–11 by adding 25%
ammonia solution under vigorous stirring for 2–3 h. The resulting mixture was
ultrasonicated for 10 min and then filtered off. The obtained precipitate was
washed with water and subsequently with acetone and dried at 120 °C for
12 h. It was then calcined at 500 °C for 3 h. The prepared CeO2 was
characterized with various techniques, such as X-ray diffractograms (XRD),
Fourier Transform Infra-Red Spectroscopy (FT-IR), Transmission Electron
Microscope (TEM), Field Emission Gun-Scanning Electron Microscopes (FEG-
SEM) coupled with EDAX.
% Yieldb
a
Reaction conditions: phenol (1.2 mmol), 4-nitrochlorobenzene (1 mmol), KOH
(1.2 mmol), 1 mL DMSO, and 2.5 mol % catalyst at 110 °C for 3 h.
b
Isolated yield.
oxide can only catalyze the coupling reaction in which strong elec-
tron withdrawing group is attached to the aryl chloride.
Various substituted phenols, amines, heterocyclic amines, and
thiophenols were also successfully coupled with 4-nitrochloroben-
zene to obtain respective O, N, and S-arylated products (Table 4).
Both the electron donating and electron withdrawing substituents
on the phenol afforded the corresponding O-arylated product with
good to excellent yield. Thiophenol also reacts with 4-nitrochloro-
benzene and gives the product with satisfactory yield.
The reusability of the catalyst was checked for three cycles. The
catalyst was separated by centrifugation, washed twice with
dichloromethane, dried and then used for subsequent run. It was
found that the catalyst activity decreases slightly for the next cycle
(Table 5).
In conclusion, we have prepared nano CeO2 catalyst for Ullmann
type coupling between 4-nitrochlorobenzene and variety of phe-
nols, amines, and thiophenols. The given methodology is an effi-
cient, inexpensive, and environmentally benign heterogeneous
catalyst system for the efficient carbon–heteroatom coupling un-
der ligand-free conditions. This recyclable catalyst offers advanta-
ges like simple work-up and high yields.
Acknowledgment
The authors are thankful to UGC-Green Technology Centre, New
Delhi, India for awarding the fellowship.
12. General procedure for the O-alkylation with 4-nitrochlorobenzene: In a 25 mL
round bottomed flask was taken
a mixture of phenol/amine/thiophenol
(1.2 mmol, 0.112 g), 4-nitrochlorobenzene (1 mmol, 0.157 g), base KOH
(1.2 mmol, 0.08 g) and 1 mL DMSO was added. Further 2.5 mol % catalyst
(4.5 mg) was added to the reaction mixture. The reaction mixture was heated
to 110 °C for appropriate time. Reaction is monitored on TLC. After completion
of the reaction the catalyst was separated by centrifugation and subsequently
washed with dichloromethane. The reaction mixture was diluted with water
and the product was extracted by dichoromethane (3 Â 10 cm3). The organic
layer was dried over anhydrous sodium sulfate and was evaporated under
reduced pressure to give the product. The product was purified by column
chromatography by using pet ether and ethyl acetate solvent system. The
purified product was then confirmed by its spectral analysis after analyzing by
IR, 1H NMR, and mass spectra.
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