Oxidation of benzoin to benzil using Burgess Reagent

Article abstract of DOI:10.1081/SCC-120003410

Synthetic utility of Burgess Reagent for the mild and efficient oxidation of benzoins to benzils is discussed.

Full text of DOI:10.1081/SCC-120003410

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OXIDATION OF BENZOIN TO BENZIL USING BURGESS
REAGENT
Binoy Jose a , M. V. Vishnu Unni a , Sreedharan Prathapan a & Jean John Vadakkan b
a Department of Applied Chemistry , Cochin University of Science and Technology , Kochi,
682 022, India
b Department of Applied Chemistry , Cochin University of Science and Technology , Kochi,
682 022, India
Published online: 16 Aug 2006.
To cite this article: Binoy Jose , M. V. Vishnu Unni , Sreedharan Prathapan & Jean John Vadakkan (2002) OXIDATION OF
BENZOIN TO BENZIL USING BURGESS REAGENT, Synthetic Communications: An International Journal for Rapid Communication
of Synthetic Organic Chemistry, 32:16, 2495-2498, DOI: 10.1081/SCC-120003410
To link to this article: http://dx.doi.org/10.1081/SCC-120003410
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 16, pp. 2495–2498, 2002
OXIDATION OF BENZOIN TO BENZIL
USING BURGESS REAGENT
Binoy Jose, M. V. Vishnu Unni, Sreedharan Prathapan,
*
and Jean John Vadakkan
Department of Applied Chemistry, Cochin University
of Science and Technology Kochi 682 022, India
ABSTRACT
Synthetic utility of Burgess Reagent for the mild and efficient
oxidation of benzoins to benzils is discussed.
The oxidation of benzoin to benzil has been accomplished by several
reagents such as nitric acid,[1] Fehling’s solution,[1] thallium nitrate,[2]
ammonium nitrate–copper acetate[3] and ammonium chromate–alumina.[4]
Recently, the oxidation of benzoin to benzil on alumina-supported copper
(II) sulphate under microwave irradiation[5] and bismuth (III) nitrate–
copper (II) acetate[6] have been reported. Many of these reagents such as
ammonium chlorochromate are highly toxic and produce wastes that persist
in the environment. In addition, the yields in the case of heteroaromatic
compounds are poor with most of these reagents. We have recently reported
the synthetic utility of Burgess reagent (1) as a mild, efficient, and stereo-
selective reagent for the dehydration of a-aldoximes to nitriles.[7] Burgess
reagent has previously been applied for the dehydration of secondary and
tertiary alcohols to olefins,[8] the chemoselective conversion of amides
*Corresponding author. Fax: 91-484-532495; E-mail: jean@cusat.ac.in
2495
DOI: 10.1081/SCC-120003410
Copyright & 2002 by Marcel Dekker, Inc.
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2496
JOSE ET AL.
Scheme 1.
to nitriles,[9] stereospecific synthesis of dihydrooxazoles from serine and
threonine derivatives,[10] generation of nitrile oxides from nitroalkanes[11]
and in azole synthesis.[12] More recently, PEG-supported Burgess reagent
has been employed for dehydration of aliphatic and aromatic aldoximes[13]
and for cyclodehydration reactions.[14] To our knowledge, no dehydrogena-
tion reaction has been so far reported using Burgess reagent. Here, we
report that Burgess reagent smoothly oxidizes benzoins to the correspond-
ing benzils in good yields (Scheme 1).
Burgess reagent is commercially available, and can be synthesized
easily from chlorosulphonyl isocyanate.[15] Three equivalents of the reagent
are required for smooth oxidation. The work up is simple and products
are obtained in good yields. In contrast to the other methods of oxidation,
the yields are higher and reactions faster in the case of heteroaromatic
compounds. The maximum yield for furil and pyridil was obtained within
two hours and further stirring did not increase the yield. In contrast,
oxidation of benzoin required six hours. The reaction conditions, substrates
and yields are given in the following Table 1.
Table 1.
Starting Benzoin
Reaction Conditions
Product
Isolated Yield
67%
3 equivalents of Burgess
reagent at 25ꢀC in
CH2Cl2 for 6 h
63%
52%
3 equivalents of Burgess
reagent at 25ꢀC in
CH2Cl2 for 6 h
3 equivalents of Burgess
reagent at 25ꢀC in
CH2Cl2 for 6 h

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OXIDATION OF BENZOIN TO BENZIL
2497
Figure 1.
The acidic nature of a-hydrogen in benzoins may be responsible for
the observed dehydrogenation which may be proceeding through the inter-
mediacy of 2. Intramolecular abstraction of a proton followed by
elimination of sulphinite ion from 2 should lead to the formation of the
observed products (Figure 1).
In summary, we have developed a mild and efficient method for
oxidizing benzoins using Burgess reagent. The experimental procedure is
simple. Efforts to understand the mechanism and broaden the scope of
this method are in progress.
Experimental Procedure for Dehydrogenation of Benzoins: The pro-
cedure described below is a general for the dehydrogenation of benzoins.
In a typical experiment, furoin (0.06 g, 0.3 mmol) was dissolved in 1.5 mL of
anhydrous dichloromethane and stirred at 25ꢀC under nitrogen atmosphere.
Burgess reagent was added in five 50 mg portions (1.05 mmol) over 2 h.
Stirring was continued for an additional 15 min. Column chromatography
(silica) of reaction mixture using hexane–dichloromethane (4 : 1) gave furil
(0.038 g, 67%), m.p. 165ꢀC (mixture melting point). The products obtained
in each case were identified by comparing their melting points, TLC and
IR spectra with those of authentic samples.
ACKNOWLEDGMENTS
Financial support from CSIR (grant number: No. 01(1650)/00/EMR-
II), UGC, and Cochin University of Science and Technology is gratefully
acknowledged.
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2498
JOSE ET AL.
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Received in Japan June 7, 2001