A Simple and Convenient Method for Epoxidation of Olefins without Metal Catalysts

Article abstract of DOI:10.1002/adsc.200390044

An easy method for epoxidation of olefins using bleach (sodium hypochlorite) and either a stoichiometric or catalytic amount of bromide ion has been developed. Without any transition metal catalyst a variety of non-activated olefins give epoxides in high yields and good selectivity at ambient conditions.

Full text of DOI:10.1002/adsc.200390044

FULL PAPERS
A Simple and Convenient Method for Epoxidation of Olefins
without Metal Catalysts
Markus Klawonn, Santosh Bhor, Gerald Mehltretter, Christian Dˆbler, Christine
Fischer, Matthias Beller*
Institut f¸r Organische Katalyseforschung an der Universit‰t Rostock e.V., Buchbinderstr. 5 6, 18055 Rostock, Germany
Fax: ( ‡ 49)-381-4669324, e-mail: matthias.beller@ifok.uni-rostock.de
Received: September 4, 2002; Accepted: November 14, 2002
Abstract: An easy method for epoxidation of olefins ides in high yields and good selectivity at ambient
usingbleach (sodium hypochlorite) and either a
stoichiometric or catalytic amount of bromide ion
conditions.
has been developed. Without any transition metal Keywords: epoxidation; epoxides; oxidation; sodium
catalyst a variety of non-activated olefins give epox- hypochlorite
0.5 Cl2 + OH–
Introduction
Oxidation reactions of olefins to give epoxides are of
OH–
O
major importance for organic synthesis. Nowadays,
especially asymmetric epoxidation reactions are in the
focus of methodological developments.[1] However, the
OCl–
OH
+ Cl–
Cl
– H2O
synthesis of racemic epoxides is still important on Scheme 1. Chlorohydrin process for propylene oxide.
laboratory as well as industrial scales. A convenient
method for the synthesis of epoxides is the oxidation of
olefins with hydrogen peroxide or alkyl peroxides in the ies described the direct epoxidation of non-activated
presence of transition metal complexes.[2] However, in olefins with hypochlorite without metals beingpres-
general the activity of the catalyst is limited and the ent.[6]
metal catalyst as well as modifyingligands have to be
Some time ago we became interested in the improve-
separated after the reaction. Nevertheless, significant ment of known oxidation reactions of olefins. After
advances have been made in non-asymmetric metal- havingdeveloped a new osmium-catalyzed dihydrox-
[7]
catalyzed epoxidation reactions in the last decade.[3] ylation reaction usingair as terminal oxidant,
we
Especially noteworthy with respect to simplicity and studied selective alcohol oxidation reactions[8] and the
catalyst productivity was the development of redox catalytic dihydroxylation in the presence of sodium
active polyoxometalates (POM×s) in combination with hypochlorite[9] as oxidant. Based on this work, we turned
phase transfer active agents as catalysts in combination our interest to epoxidation reactions applyingsodium
with hydrogen peroxide.
hypochlorite. In this manuscript we describe a novel
More traditionally, epoxides are synthesized by the general method for the epoxidation of olefins using
reaction of olefins with hydrogen peroxide in the sodium hypochlorite in the presence of a catalytic or
presence of acetic or formic acid.[4] This convenient stoichiometric amount of bromide ion.
method involves the in situ formation of the correspond-
ingperacid, which easily undergoes epoxidation reac-
tion. A drawback of this method are potential side- Results and Discussion
reactions of the acid. Hence, the method is only of
limited use for acid-labile olefins or epoxides.
While investigating the oxidation of a-methylstyrene in
An alternative cheap and practical oxidant is bleach the presence of different metal catalysts and sodium
(sodium hypochlorite), which might be used either hypochlorite, we discovered that epoxidation to 2-
directly or is produced in situ from chlorine under basic phenyl-1-epoxypropane proceeds as a side-reaction
conditions. Although in situ generated hypochlorite is independent from the metal catalyst used (Scheme 2).
still used in the two-step commercial process for
After studyingthe available literature we were
propylene epoxide (Scheme 1),[5] comparably few stud- surprised that the direct epoxidation of non-activated
Adv. Synth. Catal. 2003, 345, No. 3
¹ 2003 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim 1615-4150/03/34503-389 392 $ 17.50+.50/0
389

Markus Klawonn et al.
FULL PAPERS
conversion of a-methylstyrene is observed within the
first minute. At the same time 2-phenyl-2-hydroxy-1-
propyl bromide is formed in nearly 90% yield. This
bromohydrin is converted immediately to the desired
epoxide. While nearly 75% of the desired epoxide is
obtained within 5 minutes, a maximum yield of epoxide
(83%) is seen in between 30 and 60 minutes.
OCl–
H2O, t-BuOH
O
+
Cl–
Scheme 2. Epoxidation of a-methylstyrene with hypochlorite.
olefins usingsodium hypochlorite as oxidant has not
Next, we studied the scope and limitations of the
been examined in more detail. Therefore, we decided to procedure. Different types of olefins were tested
take a closer look at this reaction. As shown in Table 1 (Table 2). Aromatic olefins such as styrene, a-methyl-
(entry 1) the reaction proceeds in 15% yield using styrene, b-methylstyrene, p-chlorostyrene, p-methoxy-
simple sodium hypochlorite in a biphasic mixture of styrene, and 1-phenylcyclohexene give the correspond-
water and tert-butyl alcohol at room temperature. We ingepoxide in 70 93% yield (Table 2, entries 1 12). In
thought that the in situ generation of the more active general, the reactionis finished within 1 to2 hours. Much
hypobromide will increase the epoxide yield. Indeed, longer reaction times can lead to slightly lower yields
upon addition of 1.5 equiv. of KBr (with respect to due to subsequent decomposition of the epoxide.
sodium hypochlorite) the reaction proceeds smoothly
In case of aromatic olefins apart from the desired
within 2 h giving the corresponding epoxide in 90% yield epoxidation reaction small amounts of halogenation of
at 25 8C. Longer reaction times lead to slight decom- the aromatic nucleus can be observed. In addition, the
position of the desired product. The solvent system is of 1,2-dibromo or 1,2-chlorobromo derivatives arising
major influence for the outcome of the reaction. Using from halogen addition along the double bond are
tert-butyl alcohol or water alone, the epoxide is obtained detected. The slow increase in product selectivity with
only in 1 4%. Biphasic mixtures of organic solvents and increased reaction time using a-methylstyrene as sub-
water give better results, however the yields with strate (Table 2, entries 3 and 4) arises from the slow
dichloromethane or tetrahydrofuran are still compara- hydrolysis of the byproduct 1,2-dibromo-2-phenylpro-
bly low (ca. 30%). Mixtures of acetonitrile or tert-butyl pane. This subsequent hydrolysis reaction is evident
alcohol and buffered water solution (pH ˆ 10.4) lead to with all substrates formingbenzylic bromides as by-
the best epoxide yield (up to 90%). Variation of the pH products; e.g., all substituted styrenes. All reactions
from 9.5 12.0 and changing the reaction time do not proceed also well in the presence of catalytic amounts of
have a significant influence on the reaction. In general, bromide. However, the addition of 1.5 equiv. of KBr give
most of the reactions are finished after 0.5 h. Slightly slightly improved yields.
lower yields are obtained at pH 11.6 and 12.
Terminal aliphaticolefins, e.g., 1-octene and butyl allyl
Advantageously, the epoxidation reaction with so- ether need longer reaction times for complete conver-
dium hypochlorite also proceeds in the presence of sion (Table 2, entries 13 and 14, 19 and 20). On the other
catalytic amounts of bromide ions. The reduction of the hand internal aliphatic olefins (5-decene, 2,3-dimethyl-
amount of bromide ions from 1.5 equiv. to 0.2 equiv. 2-butene) show a fast conversion of the olefin, but
leads only to a slight decrease of epoxide. Further epoxide formation needs longer times compared to the
reduction of the bromide concentration results in lower aromatic olefins.
epoxide yield (46% at 0.05 equivalents of KBr). Next,
we tested whether a combination of hydrogen peroxide
and bromide ions is also able to effect epoxidation Conclusion
reactions. However, noconversion of a-methylstyrene is
observed under these conditions.
In summary, we have shown that various non-activated
In order to get more information about the mecha- olefins can be converted to epoxides by usingsimply
nism, we studied the concentration-time dependence of sodium hypochlorite and bromide salt. It is surprising
the olefin and reaction products via GC. A > 95% that this type of non-metal-catalyzed epoxidation has
Table 1. Epoxidation of a-methylstyrene usingthe sodium hypochlorite/potassium bromide system.
Entry
Equiv. KBr
Equiv. NaOCl
Time [h]
Co-solvent
Yield[a] [%]
Conv. [%]
Selec. [%]
pH
1
2
3
4
1.1
1.1
1.1
1.1
1
1
1
t-BuOH
t-BuOH
CH3CN
t-BuOH
15
82
90
78
55
100
100
100
28
82
90
78
10.4
10.4
10.4
10.4
1.5
1.5
0.2
21
Conditions: 2 mmol substrate, t-BuOH (10 mL), buffer solution (10 m), 1.1 equiv. NaOCl, Tˆ 258C, 1000 rpm stirring.
[a]
Yields determined by GC.
390
Adv. Synth. Catal. 2003, 345, 389 392

A Method for Epoxidation of Olefins without Metal Catalysts
FULL PAPERS
Table 2. Epoxidation of different olefins usingsodium hypochlorite.
Entry
Substrate
Time [h]
Yield[a] [%]
Conversion [%]
Selectivity [%]
KBr [equiv.]
1
2
1
1
70
80
100
100
70
80
0.2
1.5
3
4
2
2
89
93
100
100
89
93
0.2
1.5
5
6
2
2
84
87
98
100
85
87
0.2
1.5
7
8
20 min
20 min
72
80
100
100
72
80
0.2
1.5
9
10
1
1
81
88
96
100
84
88
0.2
1.5
11
12
1
1
79
81
100
100
79
81
0.2
1.5
13
14
15
16
17
18
24
24
24
5
2
2
69
67
75
70
80
89
94
100
99
100
100
100
73
67
76
0.2
1.5
0.2
1.5
0.2
1.5
70
n.d.[b]
n.d.[b]
19
20
24
24
57
63
73
89
78
71
0.2
1.5
Reaction conditions: 2 mmol substrate, CH3CN (10 mL) aqueous buffer solution pH 10.4 (10 mL, 1.1 equivaOCl; Tˆ 40 C,
1000 rpm stirring.
[a]
Yields determined by GC.
Not determined due to high volatility of the substrate.
[b]
been previously largely overseen. Aromatic olefins General Procedure
furnish the correspondingepoxide with high selectivity
at room temperature to 40 8C in short time ( < 1 2 h).
In a 100-mL Schlenk tube, KBr (357 mg, 3.0 mmol or 47 mg, 0.4
mmol, respectively), buffer (10 mL, prepared by adjustinga 0.5
Aliphatic olefins react somewhat more sluggishly. It is
clear that the method described here is associated with
the production of 1 equivalent of NaCl. Nevertheless,
the procedure can be performed safely without any
additional transition metals at ambient conditions.
Further advantages of the procedure remain in the
simplicity and the low-priced oxidant.
molar solution of KH2PO4 to a pH of 10.4 with a 2 molar NaOH
solution), acetonitrile (10 mL), substrate (2.0 mmol) and
diethylene glycol di-n-butyl ether (100 mL, as internal standard
for GC) were added. The reaction mixture was warmed to
40 8C under 1000 rpm magnetic stirring using a thermostat.
Aqueous NaOCl solution (Fluka commercial sodium hypo-
chlorite, 1.1 mL of a 12.4% solution, d ˆ 1.2 gmL À1, 1.1
equivalents) was added at once and stirringand temperature
were maintained for 15 minutes to 24 hours dependingon the
substrate (see Tables above). Then, Na2SO3 (0.5 g) was added
and the mixture was extracted with 20 mL of ethyl acetate. The
combined organic layers were dried over MgSO4 and analyzed
by GC.
Experimental Section
For isolation of the product, the solvent was removed under
vacuum and the crude epoxide was purified by column
chromatography (hexane/ethyl acetate 10:1) or distillation.
General Information
All reactions were carried out without any special precautions
under an atmosphere of air. Chemicals and solvents were
purchased from Fluka and used as received. 1H and 13C NMR
spectra were obtained on a Bruker ARX 400 spectrometer.
Gas chromatographic analyses were run on a Hewlett-Packard
GC 6890 series, HP 5, 5% phenyl methyl siloxane, capillary (30
m, 250 mm, 0.25 mm).
Acknowledgements
This work was supported by the ™Fonds der Chemischen
Industrie∫, the ∫Bundesministerium f¸r Bildung und Forschung
(BMBF)™, the ∫Deutsche Forschungsgemeinschaft∫, and the
State Mecklenburg-West Pomerania.
Adv. Synth. Catal. 2003, 345, 389 392
391

Markus Klawonn et al.
FULL PAPERS
Am. Chem. Soc. 1998, 120, 7252; i) D. de Vos, T. Bein,
Chem. Commun. 1996, 917; j) R. Neumann, M. Gara, J.
Am. Chem. Soc. 1995, 117, 5066; k) R. Neumann, M.
Gara, J. Am. Chem. Soc. 1994, 116, 5509.
References and Notes
[1] Selected reviews: a) E. Jacobsen, A. Pfaltz (Eds.), Cata-
lytic Asymmetric Synthesis, Springer, Heidelberg, 1999;
b) M. Beller, C. Bolm (Eds.), Transition Metals for
Organic Synthesis, Wiley-VCH, Weinheim, 1998; c) K. A.
Joergensen, Chem. Rev. 1989, 89, 431.
[2] a) R. A. Sheldon, J. K. Kochi, Metal-Catalyzed Oxidations
of Organic Compounds, Academic Press, New York, 1981;
b) G. A. Barf, R. A. Sheldon, J. Mol. Catal. 1995, 102, 23;
c) I. W. C. E. Arends, R. A. Sheldon, Top. Catal. 2002, 19,
133; d) D. Ostovic, T. C. Bruice, Acc. Chem. Res. 1992, 25,
314.
[3] Selected examples: a) K. Sato, M. Aoki, M. Ogawa, T.
Hashimoto, D. Panyella, R. Noyori, Bull. Chem. Soc. Jpn.
1997, 70, 905; b) K. Sato, M. Aoki, M. Ogawa, T.
Hashimoto, R. Noyori, J. Org. Chem. 1996, 61, 8310;
c) D. C. Duncan, R. C. Chambers, E. Hecht, C. L. Hill, J.
Am. Chem. Soc. 1995, 117, 681; d) R. Ben-Daniel, A. M.
Khenkin, R. Neumann, Chem. Eur. J. 2000, 6, 3722; e) D.
Hoegaerts, B. F. Sels, D. E. de Vos, F. Verpoort, P. A.
Jacobs, Cat. Today 2000, 60, 209; f) Y. Ishii, K. Yamawaki,
T. Ura, H. Yamada, T. Yoshida, M. Ogawa, J. Org. Chem.
1988, 53, 3587; g) C. Venturello, R. Daloisio, J. Org. Chem.
1988, 53, 1553; h) M. Bosing, A. Noh, I. Loose, B. Krebs, J.
[4] Recent examples usingperacids for olefin epoxidation
without metal catalyst: a) K. Crawford, V. Rautenstrauch,
A. Uijttewaal, Synlett 2001, 1127; b) U. Wahren, I. Sprung,
K. Schulze, M. Findeisen, G. Buchbauer, Tetrahedron Lett.
1999, 40, 5991; c) D. R. Kelly, J. Nally, Tetrahedron Lett.
1999, 40, 3251.
[5] K. Weissermel, H. J. Arpe, Industrielle Organische Chem-
ie, 5th edn., Wiley-VCH, Weinheim, 1998.
[6] S. Krishnan, D. G.Kuhn, G. A. Hamilton, J. Am. Chem.
Soc. 1977, 99, 8121.
[7] a) C. Dˆbler, G. M. Mehltretter, M. Beller, Angew. Chem.
Int. Ed. 1999, 38, 3026; b) C. Dˆbler, G. M. Mehltretter, U.
Sundermeier, M. Beller, J. Am. Chem. Soc. 2000, 122,
10289; c) C. Dˆbler, G. M. Mehltretter, U. Sundermeier,
M. Beller, J. Organomet. Chem. 2001, 621, 70.
[8] C. Dˆbler, G. M. Mehltretter, U. Sundermeier, M. Beller,
M. Eckert, H.-C. Militzer, Tetrahedron Lett. 2001, 42,
8447.
[9] G. M. Mehltretter, S. Bhor, M. Klawonn, C. Dˆbler, U.
Sundermeier, M. Eckert, H.-C. Militzer, M. Beller,
Synthesis 2003, 295.
392
Adv. Synth. Catal. 2003, 345, 389 392