N-methylpyrolidin-2-one hydrotribromide (MPHT) as a new and efficient reagent for the oxidation of sulfides to sulfoxides and sulfones

Article abstract of DOI:10.1080/00397910600764790

The stable and crystalline N-methylpyrolidin-2-one hydrotribromide (MPHT) effects oxidation of various sulfides to sulfoxides and sulfones. Copyright Taylor & Francis Group, LLC.

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N‐Methylpyrolidin‐2‐one Hydrotribromide
(MPHT) as a New and Efficient Reagent for
the Oxidation of Sulfides to Sulfoxides and
Sulfones
Jomy K. Joseph a , Suman L. Jain a & Bir Sain a
a Chemical and Biotechnology Division , Indian Institute of Petroleum ,
Dehradun, India
Published online: 16 Feb 2007.
To cite this article: Jomy K. Joseph , Suman L. Jain & Bir Sain (2006) N‐Methylpyrolidin‐2‐one
Hydrotribromide (MPHT) as a New and Efficient Reagent for the Oxidation of Sulfides to Sulfoxides and
Sulfones, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 36:18, 2743-2747, DOI: 10.1080/00397910600764790
To link to this article: http://dx.doi.org/10.1080/00397910600764790
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Synthetic Communicationsw, 36: 2743–2747, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600764790
N-Methylpyrolidin-2-one Hydrotribromide
(MPHT) as a New and Efficient Reagent for
the Oxidation of Sulfides to Sulfoxides
and Sulfones
Jomy K. Joseph, Suman L. Jain, and Bir Sain
Chemical and Biotechnology Division, Indian Institute of Petroleum,
Dehradun, India
Abstract: The stable and crystalline N-methylpyrolidin-2-one hydrotribromide
(MPHT) effects oxidation of various sulfides to sulfoxides and sulfones.
Keywords: Oxidation, metal free, MPHT, sulfoxide, sulfone
For the oxidation of sulfides to sulfoxides and sulfones,[1] a variety of
reagents/methods have been developed. The use of molecular oxygen and
hydrogen peroxide as terminal oxidants has received great attention both
from economic and environmental points of view.[2] The transition-metal-
catalyzed oxidation of sulfides are selective, but the high cost of the catalyst
makes its utility less attractive. Pyridine hydrobromide perbromide,[3] cetyltri-
methylammonium tribromide,[4] and tetrabutylammonium tribromide[5] are
some of the transition-metal-free catalysts for the oxidation of sulfides.
Although Bekaert et al.[6] have used N-methylpyrolidin-2-one hydrotribro-
mide (MPHT) as green brominating agent, its utility as a selective oxidant
of sulfides was yet to be developed.
The oxidation of a variety of sulfides with MPHT in chloroform/water
(2 : 1) at 658C with the substrate/MPHT ratio 1 : 1.2 under alkaline conditions
Received in India February 14, 2006
Address correspondence to Bir Sain, Chemical and Biotechnology Division, Indian
Institute of Petroleum, Dehradun 248005, India. E-mail: birsain@iip.res.in
2743

2744
J. K. Joseph, S. L. Jain, and B. Sain
Scheme 1.
(pH 8.4) was optimized, and it yielded the corresponding sulfoxides in
excellent yields (Scheme 1).
TYPICAL EXPERIMENTAL PROCEDURE FOR THE
OXIDATION OF SULFIDES TO SULFOXIDES
To a stirred mixture of diphenyl sulfide (372 mg) in alkaline (pH 8.4) CHCl3/
H2O (2 : 1, 5 ml) was added MPHT (960 mg), and the mixture was heated at
658C for 7 h. The progress of the reaction was monitored by TLC (SiO2).
After completion of the reaction, the mixture was extracted with dichloro-
methane three times. The organic layer was separated and dried over
anhydrous Na2SO4. The residue thus obtained was purified by column chrom-
atography on silica gel using ethyl acetate/hexane (1 : 4) as eluent. Evapor-
ation of the solvent yielded diphenyl sulfoxide (151 mg, 75%).
These results are summarized in Table 1. No evidence of sulfone
formation was noted. Among the various sulfides studied, the dialkyl
Table 1. Oxidation of sulfides to sulfoxides with MPHT reagenta
Reaction
time (h)
Yield
(%)b
Entry
1
R1
n-C3H7
n-C4H9
R2
n-C3H7
n-C4H9
i-C3H7
C6H5
2
92
90
87
75
82
85
84
80
70
40
3.5
2.75
7.0
4.5
3.0
3.5
4.5
6.5
12
i-C3H7
C6H5
C6H5CH2
C6H5
C6H5
C6H5
CH3
n-C4H9
C6H5CH2
C6H5
C6H5CH2
C6H4 (OCH3-p)
Dibenzothiophene
aReaction conditions: substrate (2 mmol), MPHT (2.2 mmol), alkaline
CHCl3/H2O (2:1), pH 8.4 at 658C.
bIsolated yields.

Oxidation of Sulfides to Sulfoxides and Sulfones
2745
Table 2. MPHT-mediated oxidation of sulfides to sulfones with aq. hydrogen
peroxidea
Reaction
time (min)
Yield
(%)b
Entry
R1
n-C3H7
n-C4H9
R2
1
2
n-C3H7
n-C4H9
i-C3H7
C6H5
5.0
5.5
3.5
15
98
97
98
96
97
95
96
94
92
50
45
3
i-C3H7
C6H5
4
5
C6H5CH2
C6H5
C6H5
C6H5
CH3
8.0
6.0
7.5
8.0
20
6
7
n-C4H9
C6H5CH2
C6H5
8
C6H5CH2
C6H4 (OCH3-p)
9
10
11
Dibenzothiophene
4,6-Dimethyldibenzothiophene
210
390
aReaction conditions: substrate (2 mmol), MPHT (10 mol%), aq. 30 % H2O2
(5 mmol), acetonitrile (3 ml) at 808C.
bIsolated yields.
sulfides were found to be most reactive, probably because of the electron-
donating nature of the alkyl groups. Similarly, alkyl aryl substituted sulfides
were found to be more reactive as compared to the diaryl sulfides.
Furthermore, the oxidation of sulfides to sulfones with catalytic amount of
N-methylpyrolidin-2-one hydrotribromide (MPHT) and aq. 30% hydrogen
peroxide in refluxing acetonitrile are summarized in Table 2 (Scheme 2 and 3).
GENERAL EXPERIMENTAL PROCEDURE
To a stirred solution of substrate (2 mmol) and MPHT (10 mol%) in aceto-
nitrile (3 ml) was added dropwise 30% hydrogen peroxide (5 mmol), and
the reaction mixture was refluxed for the time as given in Table 2. The
progress of reaction monitored by TLC (SiO2). At the end of the reaction,
Scheme 2.

2746
J. K. Joseph, S. L. Jain, and B. Sain
Scheme 3.
the excess hydrogen peroxide was destroyed by the addition of aq. bisulfite
followed by the filtration through a small Buckner funnel. After filtration,
the reaction mixture was purified by the solvent extraction with dichloro-
methane (three times), and the solvent was evaporated under vacuum. 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 sulfone. The reaction times and yields of the
products are presented in the Table 2.
CONCLUSION
In summary, we have developed new and highly efficient methodologies for
the selective oxidation of sulfides to sulfoxides using a stoichiometric
quantity of N-methylpyrolidin-2-one hydrotribromide (MPHT) as oxidant.
Oxidation of sulfides to sulfones using catalytic amounts of MPHT with
aqueous 30% hydrogen peroxide was described.
ACKNOWLEDGMENTS
We are thankful to the director, IIP, for his kind permission to publish these
results. Jomy K. Joseph and Suman L. Jain are thankful to CSIR, New
Delhi, for the award of research fellowships.

Oxidation of Sulfides to Sulfoxides and Sulfones
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2747
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