Catalytic Alkene Epoxidation with Hydrogen Peroxide in the Presence of 5,10,15,20-Tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinatomanganese(III) Acetate and Imidazole

Article abstract of DOI:10.1039/a804175j

Different alkene epoxidations were performed with aqueous hydrogen peroxide (35%) in MeCN with low to very high conversions and good to excellent selectivities by 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinato-manganese(III) acetate and i

Full text of DOI:10.1039/a804175j

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772 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 772±773$
Catalytic Alkene Epoxidation with Hydrogen Peroxide
in the Presence of 5,10,15,20-Tetrakis(2,6-dichloro-3-
sulfonatophenyl)porphyrinatomanganese(III) Acetate
and Imidazole$
Daryoush Mohajer* and Hassan Hosseini Monfared
Department of Chemistry, Shiraz University, Shiraz, 71454, Iran
Different alkene epoxidations were performed with aqueous hydrogen peroxide (35%) in MeCN with low to very
high conversions and good to excellent selectivities by 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinato-
manganese(III) acetate and imidazole at room temperature.
Table 1 Epoxidation of alkenes with H2O2 catalysed by
Mn(TDCSPP)(OAc)±imidazolea
The development of new catalytic systems for epoxidation
of alkenes under mild conditions is an important subject
in chemistry and very ecient model systems for alkene
epoxidation, based on cytochrome P-450-dependent mono-
oxygenases, using various manganese porphyrin catalysts
and di€erent oxidants have been reported.1 The water
soluble Mn(TDCSPP)Cl and Fe(TDCSPP)Cl [TDCSPP ˆ
tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrin] complexes
have been used for a variety of oxidations and bond
cleavages,2 and also for kinetic, electrochemical and
dynamic studies.3 However, there are only a few reports
of alkene epoxidation either by unsupported or supported
forms of these catalysts in association with ClO and PhIO
oxidants.4,5 To our knowledge attempts to use hydrogen
peroxide for epoxidation of alkenes by supported
[Mn(TDCSPP)(OAc)] on cationic ion-exchange resins5 and
on montmorillonite K106 have been unsuccessful. Herein we
describe for the ®rst time the ecient homogeneous epoxi-
dation of alkenes by the [Mn(TDCSPP)(OAc)]±imidazole±
H2O2 system in MeCN by maintaining an excess amount of
the oxidant throughout the reaction.
Results of oxygenation of various alkenes are given in
Table 1. Di€erent conversions (21±100%) and greater than
90% selectivities (except for cyclopentene) are observed for
epoxidation of alkenes within 20 to 120 min. In the epoxida-
tion of cycloalkenes, selectivity is decreased on decreasing
the ring size. While cyclooctene was almost quantitatively
oxidised to cyclooctene oxide, selectivities for epoxidation of
cyclohexene and cyclopentene were 90 and 82%, respect-
ively, with the allylic ketones and alcohols as the side
products. Apparently smaller rings are more prone to
oxidation at allylic positions.7 Oxidation of styrene led
to 76% of styrene oxide with 97% selectivity and 2% of
benzaldehyde in 120 min. Epoxidation of cis-stilbene pro-
Conversion Epoxide yield Selectivity Time
(%)c
Substrate
(%)b
(%)b
(min)
Cyclooctene
Cyclohexene
Cyclopentene
Styrene
51
94
50
85
98
90
20
90
100
78
42
82
76
21 (cis)
21 (trans)
15 (trans)
21
82
97
50
50
100
100
100
40
120
120
cis-Stilbene
trans-Stilbene
Hept-1-ene
Indene
15
21
92
120
120
120
92
aReaction conditions: to a solution containing alkene
(1.77 mmol), Mn(TDCSPP)(OAc) (0.00113 mmol) and
imidazole (0.82 mmol) in 3 ml of MeCN, 35% aqueous hydrogen
peroxide (2 ml, 22 mmol) was added dropwise over a period of
5 min, under air at 2822 8C. bGLC conversions and yields are
based on the starting substrates. cSelectivity ˆ [epoxide yield
(%)/conversion (%)] Â 100.
ceeded with 42% conversion within the same period and
resulted in a 1:1 mixture of cis- and trans-stilbene oxides,
whereas oxidation of trans-stilbene produced only trans-
stilbene oxide. The terminal alkene hept-1-ene showed poor
reactivity (21% conversion) and very high selectivity (100%)
for epoxidation.
Table 2 gives the results of epoxidation of cyclohexene
by H2O2 under various conditions. When oxidation
reaction was performed in MeCN with a cyclohexene:
Mn(TDCSPP)(OAc):imidazole:H2O2 ratio of 1566:1:728:20000,
90% conversion with 91% selectivity for epoxidation
was observed in 1 h, whereas oxygenation in dimethyl-
formamide (DMF) as a solvent led almost to the same
conversion (92%) but epoxide selectivity was lower (79%).
When MeCN was replaced by MeOH a much lower con-
Table 2 Epoxidation of cyclohexene under different conditions
Conversion
(%)b
Epoxide yield
(%)b
Selectivity
(%)c
Time
(h)
Conditions
Complete systema
Without Mn(TDCSPP)(OAc)
Without imidazole
MeCN replaced by DMF
MeCN replaced by MeOH
MeCN replaced by H2Od
90
1
5
92
52
27
82
<1
3
73
45
27
91
1
5
2
1
1
1
60
79
87
100
aTo a solution containing cyclohexene (1.77 mmol), Mn(TDCSPP)(OAc) (0.00113 mmol)
and imidazole (0.82 mmol) in 3 ml of MeCN, 35% aqueous hydrogen peroxide (2 ml,
22 mmol) was added dropwise over a period of 5 min, under air at 2822 8C, b,cSee
Table 1. d0.59 mmol of cyclohexene was used.
version (52%) was obtained. The use of the highly polar
*To receive any correspondence.
H2O with very poor solubility for cyclohexene as a reaction
medium gave the lowest conversion. When the oxidation
reaction was performed in MeCN but in the absence of
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

View Article Online
J. CHEM. RESEARCH (S), 1998 773
Received, 3rd June 1998; Accepted, 3rd August 1998
Paper E/8/04175J
imidazole, a dramatic decrease in epoxide yield (3%) and
selectivity (60%) was observed. Both direct coordination of
imidazole to the active manganese center (proximal e€ect)
and its action as a base (distal e€ect) may facilitate the
III
±
± ±
heterolytic cleavage of the O O bond in Mn O OH
species.8 The possibility of involvement of peroxyimidic
acid, as an oxygen donor, was excluded in the oxidation
reactions performed in MeCN, as no MeCONH2 was
observed by the direct treatment of H2O2 and MeCN, under
the catalytic oxidations in the absence of any substrate.9
Exclusion of Mn(TDCSPP)(OAc) catalyst from the oxi-
dation system gave practically no epoxide after 5 h.
References
1 (a) R. A. Sheldon and J. K. Kochi, Metal Catalyzed Oxi-
dation of Organic Compounds, Academic Press, New York, 1981;
(b) F. Montanari, S. Ban® and S. Quici, Pure Appl. Chem., 1989,
61, 1631; (c) D. Mansuy, Pure Appl. Chem., 1990, 62, 741; (d)
T. G. Traylor, Pure Appl. Chem., 1991, 63, 265; (e) B. Meunier,
Chem. Rev., 1992, 92, 1411.
It should be noted that Mn(TDCSPP)(OAc) alone
and particularly in combination with imidazole e€ectively
catalyses the decomposition of hydrogen peroxide.3a,8 Thus,
it was necessary to add a large excess of H2O2, from the
start, in order to achieve good yields in the oxygenation
reaction, in a reasonable time.
In conclusion the water soluble and highly stable
Mn(TDCSPP)(OAc) complex can eciently catalyse the
epoxidation of alkenes with environmentally clean hydrogen
peroxide in the presence of imidazole cocatalyst in MeCN.
Solvents of moderate polarity show good potential as a
medium for this catalytic system.
2 (a) V. Karunaratne and D. Dolphin, J. Chem. Soc., Chem.
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This work was supported through a grant from the
Research Council of Shiraz University.