Silica supported manganese dioxide: An efficient reagent for oxidation of benzoins

Article abstract of DOI:10.1081/SCC-120012981

A simple and practical method for the oxidative transformation of different benzoins to the corresponding benzils using silica supported manganese dioxide is described.

Full text of DOI:10.1081/SCC-120012981

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SILICA SUPPORTED MANGANESE DIOXIDE: AN EFFICIENT
REAGENT FOR OXIDATION OF BENZOINS
a
a
b
Amit C. Khandekar , Aniruddha M. Paul & Bhushan M. Khadilkar
a
Applied Organic Chemistry Laboratory , University Department of Chemical Technology ,
University of Mumbai , Matunga, Mumbai, 400 019, India
b
Applied Organic Chemistry Laboratory , University Department of Chemical Technology ,
University of Mumbai , Matunga, Mumbai, 400 019, India
Published online: 16 Aug 2006.
To cite this article: Amit C. Khandekar , Aniruddha M. Paul & Bhushan M. Khadilkar (2002) SILICA SUPPORTED MANGANESE
DIOXIDE: AN EFFICIENT REAGENT FOR OXIDATION OF BENZOINS, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:19, 2931-2935, DOI: 10.1081/SCC-120012981
To link to this article: http://dx.doi.org/10.1081/SCC-120012981
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 19, pp. 2931–2935, 2002
SILICA SUPPORTED MANGANESE
DIOXIDE: AN EFFICIENT REAGENT
FOR OXIDATION OF BENZOINS
Amit C. Khandekar, Aniruddha M. Paul,
and Bhushan M. Khadilkar*
Applied Organic Chemistry Laboratory, University
Department of Chemical Technology, University of
Mumbai, Matunga, Mumbai 400 019, India
ABSTRACT
A simple and practical method for the oxidative transforma-
tion of different benzoins to the corresponding benzils using
silica supported manganese dioxide is described.
1,2-Diketones are synthetically important because of their wide
practical applicability. They also find use as photosensitive agents in
[1]
[2]
photocurable coatings, and as precursors for some pharmaceutically
3]
[
important compounds like the antiepileptic phenytoin and the anticonvul-
sant dilantin.
The 1,2-Diketones have been prepared by coupling reactions using
[
4]
pyrophoric lead under sonication conditions, In/DMF, hexabutyltin in
[
the presence of Pd catalyst, coupling of acyltins with acyl halides. They
5]
[
6]
can also be prepared by oxidation of chalcones, alkenes, and a-hydroxy
*
Corresponding author. Fax: 91-22-4145619; E-mail: bhushank@vsnl.com
931
2
DOI: 10.1081/SCC-120012981
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
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2
932
KHANDEKAR, PAUL, AND KHADILKAR
ketones, of which the oxidation of a-hydroxy ketones is the most simple and
an important route to the preparation of a-diketones.
The oxidation of a-hydroxy ketone to a-diketone has been reported by
a variety of reagents namely, nitric acid, Fehling’s solution, pyridinium
[
7]
[
7]
[8]
chlorochromate, ammonium chlorochromate, iodine, CuSO /Pyridine,
4
[
9]
[10]
Fe(NO ) .9H O, and some other supported reagents like clayfen,
3
3
2
[11]
CuSO /Al O ,
[12]
ammonium chlorochromate/Al O .
The use of sup-
offers clearcut advantages like enhanced reactivity,
4
2
3
2
3
[
13]
ported reagent
selectivity, and easy workup for product isolation.
The increasing number of reports on the oxidation of benzoins
prompted us to report the utility of our reagent for the oxidation of a
wide variety of benzoins—symmetrical and unsymmetrical to afford corre-
sponding benzils in high yields. We have reported the use of SiO –
2
[14]
MnO2 (silmang) for oxidation of primary alcohols, deoximation reaction,
and nitrile hydration. We report here the use of silmang as an efficient
reagent for the selective oxidation of different benzoins.
The benzoins were treated with silmang in EDC at reflux (Sch. 1).
After the reaction was complete (TLC) the reagent was removed by filtra-
tion and the product was isolated after the usual workup. The optimum
ratio of substrate to reagent was found to be 1 : 1.5. The benzils obtained are
all known compounds and have been characterized by comparison of their
melting points and spectral data with the authentic samples (Table 1).
In conclusion the oxidation with silica supported manganese dioxide is
a simple, efficient and highly selective method for the transformation of
benzoins to benzils in high yields.
EXPERIMENTAL
The starting compounds were prepared as per the reported pro-
Melting points are uncorrected and were determined in open
[15,16]
cedures.
capillaries on Ostwald Precision Melting Point Apparatus. All yields refer to
isolated pure products. The products were purified by recrystallizing
through appropriate solvents. Infra red spectra were recorded on Jasco
FTIR 410E spectrometer. NMR spectra were recorded on Bruker X-500
using CDCl and TMS as an internal standard.
3
Preparation of Silica-Supported Manganese Dioxide (Silmang)
MnCO (5.75 g, 0.05 mol), NH NO (4.0 g, 0.05 mol) and silica gel (11.5 g,
3
4
3
2
3
2
30–400 mesh, BET surface area ¼ 385.6 m /g, pore volume ¼ 0.65 cm /g)

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SILICA SUPPORTED MANGANESE DIOXIDE
2933
Scheme 1.
Table 1. Oxidation of Benzoins Using SiO –MnO
2
2
ꢁ
ꢁ
M.P. ( C)
(Observed)
M.P. ( C)
(Reported)
Entry
R
1
R
2
% Yield*
[
11]
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
Ph
4-ClPh
4-BrPh
Ph
4-MeOPh
4-MeOPh
4-MePh
94
88
86
9073–74
86
93–94
72–74
84–85
73
92–93
[
16]
4-ClPh
4-BrPh
Ph
73
84–85
[
16]
[
16]
[
16]
Ph
85–86
84–85
[
11]
4-MeOPh
2-ClPh
4-MeOPh
4-MePh
–61 8060 62
90
[
[
[
6]
105–106
131–133
99–100
103–104
102–104
11]
11]
90131–132
92
*Yields refer to isolated pure products.
All products showed satisfactory IR and NMR data.
were accurately weighed and co-ground until homogenous in an agate
mortar. The resulting mixture was taken in a 100 mL round bottom flask
attached with a condenser, in turn connected to a scrubber, kept outside
the oven and irradiated in a modified microwave oven for 5 min to obtain a
black colored supported MnO . After this treatment, the mixture was homo-
2
2
genized to yield a fine black powder (BET surface area ¼ 268.0m /g, pore
3
volume ¼ 0.497 cm /g).
Oxidation of Benzoins (General Procedure)
A mixture of benzoin (5 mmol) and silmang (3.75 g, MnO content,
2
7.5 mmol) in 20mL of dichloroethane was stirred at reflux for 10–14 h. The
progress of the reaction was monitored on TLC (hexane–ethylacetate 9 : 1).
After completion of the reaction, the mixture was filtered hot and the
reagent was washed with hot EDC (3 ꢀ 20mL). The excess solvent was
distilled off under reduced pressure. The resultant yellow solid obtained

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934
KHANDEKAR, PAUL, AND KHADILKAR
was recrystallized through appropriate solvent to afford the pure desired
benzil.
REFERENCES
1
2
3
4
. Trost, B.M.; Fleming, I. Comprehensive Organic Synthesis; Pergamon
Press: Oxford, 1991.
. Matsushita Electric Industrial Co. Ltd; Jpn Kokai Tokkyo Koho 8198,
203; 981. Chem. Abstr 1981, 95, 188163 u.
. Roth, H.J.; Kleeman, A. Pharmaceutical Chemistry Vol. 1: Drug
Synthesis; Ellis Harwood Ltd.: Chichester, West Sussex, England, 1988.
. Baek, H.S.; Lee, S.J.; Yoo, B.W.; Ko, J.J.; Kim, S.H.; Kim, J.H.
Indium-Mediated Reductive Coupling of Acyl Cyanides: A Convenient
Synthesis of 1,2-diketones. Tetrahedron Lett. 2000, 41, 8097.
. Verlhac, J.B.; Chanson, E.; Jousseaume, B.; Quintard, J.P. A Versatile
Access to Unsymmetrical and Symmetrical Diketones via Organo-tin
Reagents. Tetrahedron Lett. 1985, 26, 6075.
5
6
. McKillop, A.; Swann, B.P.; Ford, M.E.; Taylor, E.C. Thallium in
Organic Synthesis. XXXVIII. Oxidation of Chalcones, Deoxy-
benzoins, and Benzoins with Thallium(III) Nitrate (TTN). J. Am.
Chem. Soc. 1973, 95, 3641.
7
8
9
. Mitra, A.K.; De, A.; Karchaudhuri, N. Microwave-assisted Syntheses
of 1,2-Diketones. J. Chem. Res. (S) 1999, 246.
. Corson, B.B.; McAllister, R.W. Oxidation of Benzoins to a-Diketones
with Iodine. J. Am. Chem. Soc. 1929, 51, 2822.
. Zhao, Y.W.; Wang, Y.L. Solvent-Free Oxidation of Benzoins Using
Fe(NO ) ꢂ9H O as the Oxidant. J. Chem. Res.(S) 2001, 70 .
3
3
2
1
1
1
0. Cornelis, A.; Laszlo, P. Clay Supported Copper(II) and Iron(III)
Nitrates: Novel Multi-Purpose Reagents for Organic Synthesis.
Synthesis 1985, 909.
1. Varma, R.S.; Kumar, D.; Dahiya, R. Solid State Oxidation of
Benzoins on Alumina-Supported Copper(II) Sulphate under Micro-
wave Irradiation. J. Chem. Res.(S), 1998, 324.
2. (a) Zhang, G.S.; Shi, Q.Z.; Chen, M.F.; Cai, K. Ammonium Chloro-
chromate Adsorbed on Alumina: A New Reagent for Oxidation of
Alcohols and Benzoins to the Corresponding Carbonyl Compounds.
Synth. Commun. 1997, 27, 953; (b) Zhang, G.S.; Shi, Q.Z.; Chem,
M.F.; Cai, K. Ammonium Chlorochromate Adsorbed on Silica Gel:
A New Reagent for Oxidation of Alcohols and Benzoins to the
Corresponding Carbonyl Compounds. Synth. Commun. 1997, 27,
3691; (c) Heravi, M.M.; Kiakajoori, R.; Hayder, K.T. Ammonium

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SILICA SUPPORTED MANGANESE DIOXIDE
2935
Chlorochromate Adsorbed on Montmorillonite K-10: Selective
Oxidation of Alcohols Under Solvent-Free Conditions. J. Chem.
Res.(S) 1998, 656.
1
1
3. (a) Laszlo, P. Preparative Chemistry Using Supported Reagents;
Academic Press: San Diego, 1987; (b) Clark, J.H. Catalysis of
Organic Reactions by Supported Inorganic Reagents; VCH: NewYork,
1994; (c) McKillop, A.; Young, D.W. Organic Synthesis Using
Supported Reagents-Part I and Part II. Synthesis 1979, 401, 481.
4. Khadilkar, B.M.; Gadre, S.A.; Makwana, V.D.; Madyar, V.R.
An Efficient and Easy Preparation of Manganese Dioxide–Silica
Supported Oxidant. Indian. J. Chem. 1998, 37A, 189.
15. Ide, S.W.; Buck, J.S. Organic Reactions; John Wiley and Sons: New
York, 1948; Vol. IV. pp. 269.
16. Richard, T.A.; Fuson, R.C. A New Synthesis of Mixed Benzoins.
J. Amer. Chem. Soc. 1936, 58, 1295.
Received in the Netherlands September 29, 2001

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