Efficient transition-metal-free oxidation of benzylic and secondary alcohols to the carbonyl compounds using an N-bromosuccinimide/NH4Cl system

Article abstract of DOI:10.1080/00397910500522207

The oxidation of a variety of benzylic and secondary alcohols was achieved in excellent yields using an NBS/NH₄Cl system in aqueous acetonitrile (CH₃CN-H₂O; 7/3 v/v) at 80°C under very mild conditions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910500522207

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Efficient Transition‐Metal‐Free Oxidation
of Benzylic and Secondary Alcohols
to the Carbonyl Compounds Using an
N‐Bromosuccinimide/NH Cl System
4
a
a
Suman L. Jain & Bir Sain
a
Chemical and Biotechnology Division, Indian Institute of Petroleum,
Dehradun, India
Version of record first published: 16 Aug 2006.
To cite this article: Suman L. Jain & Bir Sain (2006): Efficient Transition‐Metal‐Free Oxidation of Benzylic
and Secondary Alcohols to the Carbonyl Compounds Using an N‐Bromosuccinimide/NH Cl System, Synthetic
4
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:10,
1459-1462
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Synthetic Communications , 36: 1459–1462, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500522207
Efficient Transition-Metal-Free Oxidation
of Benzylic and Secondary Alcohols
to the Carbonyl Compounds Using
an N-Bromosuccinimide/NH Cl System
4
Suman L. Jain and Bir Sain
Chemical and Biotechnology Division, Indian Institute of Petroleum,
Dehradun, India
Abstract: The oxidation of a variety of benzylic and secondary alcohols was achieved
in excellent yields using an NBS/NH Cl system in aqueous acetonitrile (CH CN-H O;
4
3
2
7/3 v/v) at 808C under very mild conditions.
Keywords: Oxidation, alcohol, NBS, metal free, ketone
Oxidation of alcohols to the corresponding carbonyl compounds is a valuable
transformation in organic synthesis. Many useful reagents and reactions
[
1]
have been developed.
NBS–NH Cl combination as an efficient oxidation reagent (Scheme 1).
In this communication we describe the
4
A variety of benzylic and secondary alcohols were oxidized to their
corresponding carbonyl compounds using N-bromosuccinimide/NH Cl
4
in acetonitrile/water (7:3) at 808C. These results are presented in Table 1.
The presence of ammonium chloride (NH Cl) was essential for this
4
Scheme 1.
Received in India October 11, 2005
Address correspondence to Bir Sain, Chemical and Biotechnology Division, Indian
Institute of Petroleum, Dehradun 248005, India. E-mail: birsain@iip.res.in
1
459

a
Table 1. Oxidation of alcohols to carbonyl compounds using the NBS–NH Cl system
4
Reaction
time (h)
Yield
b
(%)
Entry
Substrate
Product
1
2
6.0
6.0
70
50
3
4
2.0
2.5
92
90
5
6
2.5
3.5
90
75

7
8
9
2.5
3.0
80
80
3.0
2.0
75
85
1
0
1
1
1
2
1.0
1.0
94
92
a
4 3
Reaction conditions: secondary alcohol (1 mmol), N-bromosuccinimide (1 mmol), NH Cl (1.2 mmol), and CH CN-
H O (7/3 v/v; 5 mL) at 808C.
2
b
Isolated yields.

1
462
S. L. Jain and B. Sain
Scheme 2.
reaction; in its absence, the N-bromosuccinimide alone could not oxidize the
cyclohexanol to cyclohexanone. Other ammonium salts such as ammonium
acetate were not effective in oxidizing cyclohexanol to cyclohexanone. The
mechanism of this reaction is not clear at this stage but perhaps involves the
formation of Br-Cl species by the reaction of NBS and NH Cl in the
4
aqueous acetonitrile medium, which then reacts with alcohol 1 to afford hypo-
bromite species, which on the abstraction of hydrogen yield the corresponding
carbonyl compound as shown in Scheme 2.
In summary, we have developed a simple and convenient system for the
oxidation of benzylic and secondary alcohols to carbonyl compounds.
GENERAL EXPERIMENTAL PROCEDURE
N-bromosuccinimide (1 mmol) and NH Cl (1.2mmol) were added to a stirred
4
solution of alcohol (1mmol) in acetonitrile–water (7/3 v/v; 5 mL). The
reaction mixture was heated at 808C. At the end of reaction, the reaction
mixture was extracted with dichloromethane. The combined organic layer
was washed with a saturated solution of NaHCO and dried over MgSO . The
3
4
solvent was evaporated under vacuum, and the residue thus obtained was
purified by column chromatography on silica gel using ethyl acetate/hexane
(1:4) as eluent. Evaporation of the solvent yielded the corresponding carbonyl
compound. The reaction times and yields of the products are given in Table 1.
REFERENCES
1
. (a) Backvall, J. Modern Oxidation Methods; Wiley-VCH: Verlag, 2004;
b) Ley, S. V.; Madin, A. In Comprehensive Organic Synthesis; Trost, B. M. and
Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 7, pp. 305–327.
(