Epoxidation of alkenes with hydrogen peroxide catalyzed by iron(III) porphyrins in ionic liquids

Article abstract of DOI:10.1039/b207072n

An efficient procedure is described for catalyst recycling and easy product isolation in alkene epoxidation with hydrogen peroxide catalyzed by water-soluble iron(III) porphyrins in environmentally benign and ambient temperature ionic liquids.

Full text of DOI:10.1039/b207072n

Epoxidation of alkenes with hydrogen peroxide catalyzed by iron(III
)
porphyrins in ionic liquids†
K. A. Srinivas, Anil Kumar and S. M. S Chauhan*
Department of Chemistry, University of Delhi, Delhi 110 007, India.
E-mail: smschauhan@chemistry.du.ac.in
Received (in Cambridge, UK) 18th July 2002, Accepted 3rd September 2002
First published as an Advance Article on the web 24th September 2002
An efficient procedure is described for catalyst recycling and
easy product isolation in alkene epoxidation with hydrogen
peroxide catalyzed by water-soluble iron(III) porphyrins in
environmentally benign and ambient temperature ionic
liquids.
hydrogen peroxide and 1 in 2 gave epoxycyclohexane (7),
2-cyclohexenol (8) and 2-cyclohexenone (9) in 42, 35, 12%,
respectively, but cyclooctene (10) gave only epoxycyclooctane
(11) in 81% yield (Fig. 1).
The organic phase containing product was separated after the
completion of the reaction leaving behind the catalyst im-
mobilized in ionic liquid. The recovered brown oily ionic liquid
containing 1 could be reused for further catalytic reactions
(Table 2). The catalytic activity of catalyst 1 immobilized in
ionic liquid 2 in alkene epoxidation is comparable to the activity
obtained when the same catalyst was supported on other
heterogeneous systems.6,18 Further, the efficiency of catalyst 1
in ionic liquid 2 and in homogeneous solution (water–
acetonitrile, 1+1 v/v) was compared using epoxidation of
styrene and cyclooctene. The epoxide yields were very low in
homogeneous solution (17% in the case of styrene and 21% in
the case of cyclooctene). The mechanism of epoxide formation
is believed to proceed in a similar manner to that of
Metalloporphyrins as model catalysts of cytochrome P450 have
been used to mimic various oxidation reactions such as
hydroxylation of hydrocarbons, epoxidation of olefins and
oxidation of other organic substrates with hydrogen peroxide in
homogeneous organic and aqueous reaction media.1–4 The
intermolecular self-destruction and recovery of the expensive
catalysts are the general problems encountered in homogeneous
reaction media with metalloporphyrins. Therefore, various
heterogeneous methods have been developed to make catalyst
recovery easy and to enhance the catalytic activity.5–7
Ambient room temperature ionic liquids have recently gained
recognition as environmentally benign solvents due to their
unique physical properties such as non-volatility, non-flamma-
bility, and thermal stability.8–11 They have been employed as
solvents for liquid–liquid separations, extractions and for
recycling homogeneous catalysts etc.12–14 Ionic liquids have
also been used as novel reaction media for economically and
environmentally attractive processes in aqueous mono- and
biphasic systems.15,16 Herein, we report the oxidation of
selected olefins with H2O2 catalyzed by anionic water-soluble
porphyrins in ionic liquids under different reaction condi-
tions.
Table 1 Alkene epoxidation with hydrogen peroxide catalyzed by 1
immobilized in 2 under a nitrogen atmospherea‡
Yield (%)b
epoxide
Entry
Substrate
Time/h
Turnoversc
1
2
3
4
3a
3b
6
4
5
5
4
74d
70e
42f
81
1.38 3 103
1.23 3 103
6.4 3 102
1.35 3 103
10
a ‡See footnote. b Yield is based on the substrate and is determined by GC.
c Turnovers calculated from epoxide yield. d Phenylacetaldehyde in 16%
yield was also obtained. e p-Chlorophenylacetaldehyde in 14% yield was
also obtained. f Cyclohexen-2-ol and cyclohexen-2-one were also obtained
in 35 and 12% yield, respectively.
The catalyst tetrakis(2A,6A-dichloro-3A-sulfonatophenyl)por-
phyrinato iron(III) [Cl8TPPS4Fe(III)] (1) was immobilized in
1-butyl-3-methylimidazolium bromide {[Bmim][Br]} (2) due
to its ionic character. The epoxidation of alkenes with hydrogen
peroxide catalyzed by 1 was carried out under biphasic
conditions: a mixture of styrene in dichloromethane and 1 in 2
was stirred with hydrogen peroxide under a nitrogen atmos-
phere for 4 h to give styrene epoxide (4a) and phenyl-
acetaldehyde (5a) in 74% and 16% yield, respectively.
Similarly, the oxidation of p-chlorostyrene (3b) with hydrogen
peroxide and 1 in 2 gave p-chlorostyrene epoxide (4b) and p-
chlorophenylacetaldehyde (5b) in 70% and 14% yield, re-
spectively (Table 1). The oxidation of cyclohexene (6) with
Fig. 1 The epoxidation of alkenes by hydrogen peroxide catalyzed by 1
immobilized in 2.
Table 2 Catalytic activity of the recovered catalyst 1 immobilized in ionic
liquid 2 in the epoxidation of styrene with H2O2
Run
1
2
3
4
5
Yield (%)a
74
73
71
68
62
† Electronic supplementary information (ESI) available: experimental. See
http://www.rsc.org/suppdata/cc/b2/b207072n/
a Based on the substrate and GC analysis.
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CHEM. COMMUN., 2002, 2456–2457
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of different products has been confirmed by 1H NMR, and other
spectroscopic data.
homogeneous medium and proceeded through an iron-oxo
intermediate. Further, the formation of aldehyde may be due to
the rearrangement of an initially formed complex of iron-oxo
intermediate and alkene.19
It is noteworthy that the recycled metalloporphyrin 1 in ionic
liquid 2 showed comparable activity even after 4–5 runs in the
oxidation of styrene with hydrogen peroxide (Table 2).
However, the addition of excess oxidant to the reaction mixture
resulted in the degradation of catalyst.
In summary, the present method of epoxidation by using
ionic liquid as a biphasic system is useful for recycling the
expensive metalloporphyrin catalyst from the reaction mixture.
The activity of the catalyst in ionic liquid is greater than that in
conventional solvents.
1 B. Meunier, Chem. Rev., 1992, 92, 1411.
2 D. Mansuy and P. Battioni, Cytochrome P450 Model Systems in
Metalloporphyrins in Catalytic Oxidations, ed. R. A. Sheldon, Marcel
Dekker, New York, 1994, p. 99.
3 S. M. S. Chauhan and B. B. Sahoo, Bioorg. Med. Chem., 1999, 7,
2629.
4 S. M. S. Chauhan, K. A. Srinivas and B. B. Sahoo, Chem. Pharm. Bull.,
2001, 49, 1375.
5 F. Bedioui, Coord. Chem. Rev., 1995, 144, 39.
6 H. Turk and W. T. Ford, J. Org. Chem., 1991, 56, 1253.
7 C. Gilmartin and J. R. Lindsay Smith, J. Chem. Soc., Perkin Trans. 2,
1995, 243.
8 R. Sheldon, Chem. Commun., 2001, 2399.
9 P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed. Eng., 2000, 39,
3772.
10 T. Welton, Chem. Rev., 1999, 99, 2071.
11 A. E. Visser, R. P. Swatloski, W. M. Reichert, R. Mayton, S. Sheff, A.
Weirzbicki, J. H. Davis and R. D. Roger, Chem. Commun., 2001,
135.
12 M. L. Dietz and J. A. Dzielawa, Chem. Commun., 2001, 2124.
13 L. Gaillon and F. Bedioui, Chem. Commun., 2001, 1458.
14 G. Bar, A. F. Parsons and C. B. Thomas, Chem. Commun., 2001,
1350.
Notes and references
‡
The required ionic liquid [Bmim][Br] was prepared using a literature
method.17 The catalyst Cl8TPPS4Fe(III) is readily soluble in [Bmim][Br]
and its behaviour in [Bmim][Br] is similar to that in conventional
solvents.
A typical procedure for the epoxidation of alkenes using Cl8TPPS4Fe(III
)
immobilized in ionic liquid [Bmim][Br]: The catalyst Cl8TPPS4Fe(III) (1.25
mmol) was dissolved in [Bmim][Br] (2 cm3). To this solution, alkene (125
mmol) in dichloromethane (5 cm3) and hydrogen peroxide (30%, 125
mmol) were added under a nitrogen atmosphere. The two-phase system was
stirred at room temperature for 4–5 h. Progress of the reaction was
monitored by GC. The organic phase was separated, washed with water and
dried with anhydrous Na2SO4. The solvents were removed under reduced
pressure and the residue was chromatographed on silica gel. The formation
15 P. Wasserscheid, C. M. Gordon, C. Hilgars, M. J. Muldoon and I. R.
Dunkin, Chem. Commun., 2001, 1186.
16 J. D. Holbrey and K. R. Seddon, Clean Prod. Processes, 1999, 1,
223.
17 P. Bonhote, A.-P. Dias, N. Papageorgiou, K. Kalyanasundaram and M.
Gratzel, Inorg. Chem., 1996, 35, 1168.
18 S. Campestrini and B. Meunier, Inorg. Chem., 1992, 31, 1999.
19 J. T. Grooves and R. S. Myers, J. Am. Chem. Soc., 1983, 105, 5791.
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