Oxidation of alcohols and vic-diols with H2O2 by using catalytic amounts of N-methylpyrrolidin-2-one hydrotribromide

Article abstract of DOI:10.1002/ejoc.200500758

A variety of secondary alcohols, 1,2-diols and primary alcohols were selectively oxidized in excellent yields to their corresponding ketones, 1,2-diketones and aldehydes with aqueous 30 % hydrogen peroxide in refluxing acetonitrile in the presence of catalytic amounts of N-methylpyrrolidin-2-one hydrotribromide (MPHT). Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejoc.200500758

SHORT COMMUNICATION
DOI: 10.1002/ejoc.200500758
Oxidation of Alcohols and vic-Diols with H2O2 by Using Catalytic Amounts of
N-Methylpyrrolidin-2-one Hydrotribromide
Jomy K. Joseph,[a] Suman L. Jain,[a] and Bir Sain*[a]
Keywords: Alcohols/ Aldehydes / Ketones / Oxidation / Synthetic methods
A
variety of secondary alcohols, 1,2-diols and primary
the presence of catalytic amounts of N-methylpyrrolidin-2-
one hydrotribromide (MPHT).
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
alcohols were selectively oxidized in excellent yields to their
corresponding ketones, 1,2-diketones and aldehydes with
aqueous 30% hydrogen peroxide in refluxing acetonitrile in
The oxidation of alcohols to carbonyl compounds is an ability to maintain the desired stoichiometry, find increas-
important synthetic transformation,[1] and in the recent ing applications as substitutes for molecular bromine for a
years emphasis is being given towards the use of environ- variety of organic reactions in the recent years.[12] However,
mentally benign oxidants such as molecular oxygen, hydro- to the best of our knowledge there is no literature report
gen peroxide with a view of developing green methodolo- on organic ammonium tribromide mediated oxidation of
gies.[2] In this context oxidation of alcohols to ketones with alcohols to carbonyl compounds with hydrogen peroxide. A
molecular oxygen by using cobalt-,[3] palladium-,[4] ruthe- recent report by Provot et al. on the use of N-methylpyrroli-
nium-based catalysts[5] and cobalt complexes with 2-methyl- din-2-one hydrotribromide (MPHT)[13] as an efficient and
propanal[6] as the sacrificial aldehyde have been reported in green brominating agent for carbonyl compounds inspired
the literature. However, most of the existing methods are us to explore its potential for the oxidation of alcohols to
associated with one or more drawbacks such as the use of carbonyl compounds. In this letter we wish to report for the
Scheme 1.
expensive and toxic metals like ruthenium and palladium,
oxidation of only activated alcohols such as benzylic and
allylic alcohols, the need for a sacrificial aldehyde, and se-
vere reaction conditions like high pressure.
Solid organic ammonium tribromides (OATB) such as
pyridine hydrobromide perbromide (PyHBr3),[7] tetrameth-
ylammonium tribromide (TMATB),[8] phenyltrimethylam-
monium tribromide (PTATB),[9] cetyltrimethylammonium
tribromide (CetTMATB),[10] and tetrabutylammonium tri-
bromide (TBATB),[11] due to their ease of handling and
[a] Chemical and Biotechnology Division, Indian Institute of Pe-
troleum,
Dehradun 248005, India
E-mail: birsain@iip.res.in
Scheme 2.
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Eur. J. Org. Chem. 2006, 590–594

Oxidation of Alcohols and vic-Diols with H2O2
SHORT COMMUNICATION
first time a new transition-metal-free, simple, convenient (1 mmol), catalytic amounts of MPHT (10 mol-%) and 30
and efficient method for the oxidation of secondary wt.-% aqueous hydrogen peroxide (2 mmol) in acetonitrile
alcohols to ketones, 1,2-diols to 1,2-diketones and primary (Scheme 2).[14] We first carried out the reaction of benzhyd-
alcohols to aldehydes with hydrogen peroxide in the pres- rol (1 mmol) with MPHT (1.2 mmol) in acetonitrile at am-
ence of catalytic amounts of MPHT (Scheme 1).
bient temperature and observed the reaction to be very slow
The protocol developed for the oxidation of various with poor yield of the benzophenone (Table 1, Entry 1).
alcohols and 1,2-diols consist of refluxing substrate Subsequently it was observed that reaction rate increases
Table 1. Oxidation of alcohols and diols by using N-methylpyrrolidin-2-one hydrotribromide (MPHT) as catalyst and hydrogen peroxide
as oxidant.[a]
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J. K. Joseph, S. L. Jain, B. Sain
SHORT COMMUNICATION
Table 1. (Continued)
[a] Reaction conditions: Substrate (1 mmol), MPHT (10 mol-%), aq. hydrogen peroxide (2 mmol, 30 wt.-%), acetonitrile (5 mL) at re-
fluxing temperature. [b] Isolated yields. [c] Experiment carried out using stoichiometric amount of MPHT alone in absence of H2O2 at
room temperature. [d] Experiment carried out using stoichiometric amount of MPHT at refluxing conditions in absence of H2O2. [e] Oxi-
dation carried out with equimolar amounts of MPHT in refluxing acetonitrile in absence of H2O2.
with increasing temperature, and oxidation of benzhydrol to activated alcohols such as borneol and l-menthol. In our
benzophenone could be completed within 2.5 h in refluxing further studies we observed that borneol and l-menthol
acetonitrile (Table 1, Entry 2). In the course of this study it could be easily oxidized to the corresponding ketones in
was found that MPHT alone could not oxidize the non- almost quantitative yields by using catalytic amounts of
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Oxidation of Alcohols and vic-Diols with H2O2
SHORT COMMUNICATION
MPHT and hydrogen peroxide as oxidant in refluxing ace-
In summary, we have developed a new and highly ef-
tonitrile. This protocol was generalized by performing oxi- ficient methodology for the oxidation of various 1,2-diols,
dation of a variety of secondary alcohols to carbonyl com- as well as secondary and primary alcohols to the corre-
pounds, and the results are presented in Table 1 (Entries 3– sponding 1,2-diketones, ketones and aldehydes, respectively,
13). Among the various alcohols studied, benzoins were using catalytic amounts of MPHT and hydrogen peroxide
found to be the most reactive and required shorter reaction as oxidant. The easy synthesis, crystalline nature and cata-
times for their oxidation. Furthermore, aromatic-substi- lytic use of MPHT, the versatility of the developed protocol
tuted alcohols were found to be more reactive as compared towards various substrates, and the capability of the
to the aliphatic/alicyclic alcohols. It was also interesting to method to selectively oxidize primary alcohols to aldehydes
note that while oxidation of benzhydrol with 2 equiv. of hy- make this an attractive and facile method for the oxidation
drogen peroxide, added in one portion, gave a mixture of of alcohols.
benzophenone and unconverted benzhydrol, whereas its
dropwise addition afforded benzophenone in excellent yield
Acknowledgments
within 30 min,. The completion of the reaction was indi-
cated by discoloration of the reaction mixture. A variety of
1,2-diols were smoothly oxidized to their corresponding
1,2-diketones using this protocol. The results obtained are
shown in Table 1 (Entries 14–18). The results clearly indi-
cate that 1,2-diols substituted with electron-donating
groups are more reactive under these reaction conditions.
The selective oxidation of primary alcohols to aldehydes
is also an important and desirable synthetic transformation
as susceptibility of aldehydes for further oxidation to car-
boxylic acids narrows the choice of reagent. We therefore
also studied the oxidation of various primary alcohols using
both catalytic amounts of MPHT along with aqueous 30%
H2O2 and stoichiometric amounts of MPHT without H2O2
as oxidation systems. These results are presented in Table 1
(Entries 19–25). While the benzylic alcohols (Table 1, En-
tries 19–23) yielded the corresponding acids in refluxing
acetonitrile using catalytic amount of MPHT and 30 wt.-%
aqueous hydrogen peroxide as oxidant, the aliphatic pri-
mary alcohols were selectively converted into the corre-
sponding aldehydes under these reaction conditions
(Table 1, Entries 24–25). When oxidation of benzyl alcohols
was carried out with stoichiometric amounts of MPHT
(without using H2O2), the corresponding aldehydes were
obtained selectively (Table 1, Entries 19–23). Among the
various benzyl alcohols studied, the unsubstituted benzyl
We are thankful to the Director, IIP, for his kind permission to
publish these results. J. K. J. and S. L. J. are thankful to CSIR, New
Delhi, for the award of Research Fellowships.
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J. K. Joseph, S. L. Jain, B. Sain
SHORT COMMUNICATION
was added dropwise aq. hydrogen peroxide (2 mmol, 30 wt.-%),
and the reaction mixture was refluxed for the time given in
Table 1. The progress of reaction was monitored by TLC
(SiO2). At the end of reaction, the excess hydrogen peroxide
was deactivated by the addition of aq. bisulfite followed by
filtration through a small Büchner funnel. After filtration, the
reaction mixture was purified by solvent extraction with
dichloromethane (3×), 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
carbonyl compound. The reaction times and yields of the prod-
ucts are presented in Table 1. The products were identified by
comparing their physical and spectroscopic data with those of
authentic compounds reported in the literature. In case of ben-
zylic alcohols the corresponding aldehydes were obtained when
the substrate (1 mmol) was treated with MPHT (1.2 mmol) in
refluxing acetonitrile without using hydrogen peroxide as oxi-
dant.
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Received: October 4, 2005
Published Online: December 5, 2005
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