Greening the Wacker process

Article abstract of DOI:10.1016/j.tetlet.2013.01.082

Wacker oxidation of various terminal olefins with Pd⁰/C- KBrO₃, a nontoxic, environmentally benign, and easy to handle catalyst system, was achieved in high isolated yields. The described protocol offers an alternative to the traditional Wacker system which uses CuCl ₂ as co-catalyst. The catalyst is reusable while maintaining high activity and selectivity.

Full text of DOI:10.1016/j.tetlet.2013.01.082

Tetrahedron Letters 54 (2013) 2293–2295
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Tetrahedron Letters
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Greening the Wacker process
⇑
Mukund G. Kulkarni , Yunnus B. Shaikh, Ajit S. Borhade, Sanjay W. Chavhan, Attrimuni P. Dhondge,
Dnyaneshwar D. Gaikwad, Mayur P. Desai, Deekshaputra R. Birhade, Nagorao R. Dhatrak
Department of Chemistry, University of Pune, Ganeshkhind, Pune 411007, India
a r t i c l e i n f o
a b s t r a c t
Wacker oxidation of various terminal olefins with Pd0/C-KBrO3, a nontoxic, environmentally benign, and
easy to handle catalyst system, was achieved in high isolated yields. The described protocol offers an
alternative to the traditional Wacker system which uses CuCl2 as co-catalyst. The catalyst is reusable
while maintaining high activity and selectivity.
Article history:
Received 3 August 2012
Revised 15 January 2013
Accepted 18 January 2013
Available online 26 January 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Wacker oxidation
Palladium
Potassium bromate
Terminal olefin
Mature industrial chemical processes that are often based on
technologies developed in the first half of the 20th century, like
Wacker oxidation, are no longer acceptable in these environmen-
tally conscious days, as these chemical processes lead to the pro-
duction of enormous quantities of undesired and harmful
substances.1 These have an adverse effect on environment and
have become the biggest challenge the chemistry has to face today.
Conventional Wacker process is a palladium mediated reaction.2 It
is usually conducted with PdCl2 cat./CuCl2 cat./O2 system.3 It leads
to the formation of substantial amounts of ecologically hazardous
chlorinated by-products. Beside this, use of molecular oxygen as
a final oxidant presents a significant safety issue.4 In addition,
use of CuCl2, even in catalytic amount, resulted in the production
of noxious copper waste which is potentially very toxic to aquatic
life, both acutely and chronically, as the environmental impact of
waste is not only determined by its amount but also by its
nature.1b
Therefore, there is a definite need for an environmentally be-
nign system for Wacker oxidation. This can be achieved by using
a recyclable palladium catalyst with an environmentally accept-
able co-oxidant. Several alternatives to this effect have been re-
ported in the literature.5 We have reported a very simple and
inexpensive solution to the problems associated with use of PdCl2
by using Pd0/C–CuCl2 as a heterogeneous recyclable catalyst sys-
tem.6 Elimination of CuCl2 as co-catalyst would render the Wacker
oxidation a completely green process. Potassium bromate (KBrO3)
is an inexpensive, readily available strong oxidizing agent. It has
been used with different catalysts in various organic reactions as
a co-oxidant in stoichiometric quantities.7 Herein we report Wac-
ker oxidation using Pd0/C with KBrO3 as terminal oxidant.
Wacker oxidation of terminal olefin was conducted using 10%
Pd0/C with potassium bromate as co-oxidant in aqueous THF at re-
flux temperature8 and gave corresponding methyl ketone in good
yield without any detectable amounts of side products (Table 1).
Wacker oxidation of different terminal olefins having acid/base
sensitive functional groups was converted smoothly and efficiently
into the corresponding methyl ketones in excellent yields under
established protocol (Table 1).
This finding makes present Wacker oxidation protocol, a practi-
cal, convenient, cheap, and environmentally benign method with
the potential application for large-scale preparation of methyl ke-
tones. Thus, Wacker oxidation smoothly gives the product in sim-
ilar yields.
Various similar other co-oxidants were evaluated for the
Wacker oxidation. Wacker oxidation of 1-octene with NaIO4 gave
corresponding methyl ketone in trace amount only (Table 2, entry
1). Reaction using NaOCl or K2S2O8 gave the product again in very
low yields (Table 2, entries 2 and 3). Wacker oxidation with NaBrO3
leads to 2-octanone in moderate yield (Table 2, entry 5). Decompo-
sition of 1-octene was observed with oxoneÒ (Table 2, entry 6).
This suggested that in Wacker oxidation, as compared to other oxi-
dants KBrO3 serves as the best oxidant with Pd0/C.
In conclusion we have developed a practical, general, and a
green method for Wacker oxidation, which uses an inexpensive
oxidant, can tolerate different functional groups, and provides
product selectively in high yields. This method is of particular
interest for easy recoverability and recyclability of the catalyst
without any decrease in the yield of expected methyl ketones.
⇑
Corresponding author. Tel.: +91 20 25601395x537.
E-mail addresses: mgkulkarni@chem.unipune.ac.in, mgkulkarni@chem.unipune.
ernet.in (M.G. Kulkarni).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.01.082

2294
M. G. Kulkarni et al. / Tetrahedron Letters 54 (2013) 2293–2295
Table 1
Wacker oxidation of terminal olefins with 10% Pd0/C-KBrO3
a
10% Pd0/C, KBrO3
THF/water, reflux
O
O
+
R
R
R
1
2
3
Sr. No.
1
Substrate
Product
Yieldb (%)
84
Sr. No.
12
Substrate
CHO
Product
Yieldb (%)
73
2a
2l
Cl
CHO
2
3
2b
2c
86
73
13
2m
3n
78
76
NO2
O
14c
MeO
O
TsO
OMe
OBn
O
OBn
O
4c
5
3d
2e
2f
76
77
86
15
16
17
2o
2p
2q
69
78
68
BnO
O
MeO
O
OMe
O
O
BnO
BnO
BnO
OMe
O
O
O
O
6
OBn
O
O
O
7
2g
65
18
2r
71
O
OBn
O
O2N
O
8
9
2h
2i
71
68
19
20
2s
2t
79
84
O
NO2
OBz
OBn
OMe
10
11
2j
81
80
21
22
2u
73
—
MeO
MeO
OMe
CHO
d
2k
—
OMe
a
b
c
All reactions were carried out with substrate (1 mmol), 10% Pd0/C (0.05 mmol), KBrO3 (3 mmol), THF/water (4:1, 15 mL), 65 °C.
Isolated yields.
a
-Substituted olefin yielded corresponding aldehyde.9
d
No reaction and all starting material was recovered.
Table 2
Acknowledgments
Screening of oxidant for Wacker oxidation of 1-octene with Pd0/Ca
10% Pd0/C, Oxidant
Authors Y. B. S., A. S. B., A. P. D., S. W. C., D. D. G., M. P. D. and
D. R. B. thank CSIR New Delhi for fellowship.
THF/water, reflux
O
1a
2a
Supplementary data
Entry
Oxidant
Yieldb (%)
1
2
3
4
5
6
NaIO4
6
10
19
84
62
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.
01.082.
NaOCl
K2S2O8
KBrO3
NaBrO3
OxoneÒ
—
c
References and notes
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b
Isolated yields.
Decomposition of 1-octene occurred.
c

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2295
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