Epoxldation of terminal alkenes with oxygen and 2-ethyl hexanal, without added catalyst or solvent

Article abstract of DOI:10.1021/op980075b

Two terminal alkenes, 1-decene and methyl 10-undecenoate, were epoxidized with oxygen using 2-ethyl hexanal as coreactant without any added solvent. Under optimal conditions, the yield of methyl 10, 11-epoxyundecanoate was 98.7%. 2-Ethyl hexanal was oxidized mainly to 2-ethyl hexanoic acid and also formed some byproducts. The tested metal complexes retarded the epoxidation reaction slightly and increased the amount of byproducts of 2-ethyl hexanal.

Full text of DOI:10.1021/op980075b

Organic Process Research & Development 1999, 3, 101−103
Epoxidation of Terminal Alkenes with Oxygen and 2-Ethyl Hexanal, without
Added Catalyst or Solvent
Christel Lehtinen* and G o¨ sta Brunow
Laboratory of Organic Chemistry, Department of Chemistry, UniVersity of Helsinki, P.O. Box 55,
FIN-00014 UniVersity of Helsinki, Finland
Abstract:
Scheme 1. Epoxidation of alkenes with oxygen aldehyde as
coreactant
Two terminal alkenes, 1-decene and methyl 10-undecenoate,
were epoxidized with oxygen using 2-ethyl hexanal as coreactant
without any added solvent. Under optimal conditions, the yield
of methyl 10,11-epoxyundecanoate was 98.7%. 2-Ethyl hexanal
was oxidized mainly to 2-ethyl hexanoic acid and also formed
some byproducts. The tested metal complexes retarded the
epoxidation reaction slightly and increased the amount of
byproducts of 2-ethyl hexanal.
Table 1. Epoxidation of 1-decene (experiments 1-8) and
methyl 10-undecenoate (experiments 9-12) with procedure
A
epoxide (%)
solvent aldehyde/
reaction
c
expt T (°C)
(mL)
alkene
at 6 h final time (h)
Introduction
1
2
3
4
5
6
7
8
9
0
1
rt
rt
20
20
20
20
10
3/1a
4.9
16.2
47.9
59.3
63
45.4
19.0
42
7.5
24
22
21
24
24
6
8
6
24
24
The epoxidation of alkenes by molecular oxygen in the
presence of a catalyst and aldehyde has been intensively
studied (Scheme 1).1
a
6/1
6.9
21.6
31.9
41.2
21.6
19.0
38.7
38.7
34.0
18.4
a
40
40
40
40
40
60
60
40
40
6/1
6/1
6/1
-15
b
Several research groups have also
b
reported on epoxidation procedures in the absence of
b
6/1
16-19
catalyst.
In both the presence and the absence of catalyst,
b
4.5/1
4.5/1b
the solvent is thought to be essential for the reaction.
Chlorinated or perfluorinated solvents are recommended
because of their capacity to dissolve molecular oxygen.
However, chlorinated solvents constitute a serious envi-
ronmental problem in large-scale production, and perfluor-
inated solvents do not always allow reactions to be performed
in a homogeneous phase. In view of these drawbacks, we
b
4.5/1
38.7
54.6
32.5
b
1
1
10
6/1
6/1
b
a
Aldehyde, 2-methyl propanal. b Aldehyde, 2-ethyl hexanal. c The aldehyde/
alkene ratio is the final ratio of added substances.
set out to test 2-ethyl hexanal as solvent because the oxidation
product of the aldehyde, 2-ethyl hexanoic acid, is itself in
industrial use. In these preliminary experiments, the reaction
proceeded well without additional solvent. A practical
method for preparative isolation of the product is still under
investigation.
*
To whom correspondence should be addressed. E-mail: Christel.Lehtinen@
Helsinki.fi. Fax: +358-9-191 40366. Phone: +358-9-191 40345.
1) Butterworth, A.; Clark, J.; Walton, P.; Barlow, S. J. Chem. Soc., Chem.
(
Commun. 1996, 1859.
(
(
2) Yamada, T.; Takai, T.; Rhode, O.; Mukaiyama, T. Chem. Lett. 1991, 1.
3) Dell’Anna, M.; Mastrorilli, P.; Nobile, C.; Suranna, G. J. Mol. Catal. A:
Chem. 1995, 103, 17.
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Bregeault, J. C. R. Acad. Sci., Ser. II 1993, 317, 757.
(
(
(
Results and Discussion
We chose to carry out the air epoxidations on two
representative terminal alkenes, 1-decene and methyl 10-
undecenoate, using 2-ethyl hexanal and 2-methyl propanal
as aldehydes. The influence of solvent and metal complexes
was studied as well as the mode of addition of the reactants
at different temperatures. The results are summarized in
Tables 1 and 2.
We found that, under proper conditions, these terminal
alkenes can be epoxidized in good to excellent yields using
air oxidation with 2-ethyl hexanal as aldehyde, without added
solvent or catalyst. Although terminal alkenes react more
sluggishly in epoxidation reactions than do internal ones, this
reaction was clean and could be optimized to yield methyl
(
7) Hamamoto, M.; Nakayama, K.; Nishiyama, Y.; Ishii,Y. J. Org. Chem. 1993,
5
8, 6421.
(
(
8) Mizuno, N.; Hirose, T.; Tateishi, M.; Iwamoto, M. Chem. Lett. 1993, 1839.
9) Punniyamurthy, T.; Bhatia, B.; Iqbal, J. Tetrahedron Lett. 1993, 34, 4657.
10) Kholdeeva, O.; Grigoriev, V.; Maksimov, G.; Fedotov, M.; Golovin, A.;
Zamarev K. J. Mol. Catal. A: Chem. 1996, 114, 123.
11) Bouhlel, E.; Laszlo, P.; Levart, M.; Montaufier, M.; Singh, G. Tetrahedron
Lett. 1993, 34, 1123.
12) Murahashi, S.; Oda, Y.; Naota, T.; Komiya, N. J. Chem. Soc., Chem.
Commun. 1993, 23, 139.
13) Battioni, I.; Bartoli, J.; Leduc, P.; Fontecave, M.; Ansuy, D. J. Chem. Soc.,
Chem. Commun.1987, 10, 791.
(
(
(
(
(
14) Takai, T.; Hata, E.; Yamada, T.; Mukaiyama, M. Bull. Chem. Soc. Jpn.
1
991, 64, 2513.
(
(
15) Wenzel, T. T. Stud. Surf. Sci. Catal. 1991, 66, 545.
16) Kaneda, K.; Haruna, S.; Imanaka, T.; Hamamoto, M.; Nishiyama, Y.; Ishii,
Y. Tetrahedron Lett. 1992, 33, 6827.
17) Sch o¨ ttler, M.; Boland, W. Synlett 1997, 91.
18) Mukaiyama, T.; Yamada, T. Bull. Chem. Soc. Jpn. 1995, 68, 17.
19) Pozzi, G.; Montanari, F.; Rispens, M. Synth. Commun. 1997, 27, 447.
(
(
(
1
0,11-epoxyundecanoate at 98.7%. 2-Ethyl hexanal is less
volatile than the 2-methyl propanal often used in this type
1
0.1021/op980075b CCC: $18.00 © 1999 American Chemical Society and Royal Society of Chemistry
Vol. 3, No. 2, 1999 / Organic Process Research & Development
•
101
Published on Web 01/23/1999

Table 2. Epoxidation of 1-decene with procedure C
experiments 12-15) and methyl 10-undecenoate with
(
a
procedure b (experiments 16-18)
epoxide (%)
aldehyde/
reaction
time (h)
c
expt
alkene
at 4 h
final
1
1
1
1
1
1
1
2
3
4
5
6
7
8
1/1
1/1
2/1
3/1
7/1
13.2/1
8.7/1
38.0
18.8
42.3
28.5
67.5
65.3
39.7
38.0
37.0
71.2
48.6
89.7
98.7
39.7
4
8
8
8
8
11
4
a
Continuous addition of aldehyde, temperature 60 °C. b The aldehyde/alkene
Figure 1. Progress of epoxidation of methyl 10-undecenoate
as a function of time using procedure B. The rate of addition
in experiment 18 is twice that in experiments 16 and 17.
Aldehyde-to-alkene ratios at the end of the reaction were 7/1
ratio is the final ratio of added substances.
(
1
experiment 16), 13.2/1 (experiment 17), and 8.7/1 (experiment
8).
of epoxidations, and it allows higher reaction temperatures
while eliminating the need for added solvent. 2-Ethyl hexanal
also appeared to be slightly more effective in inducing
epoxidations than was 2-methyl propanal (Table 1, experi-
ments 3 and 4).
(
experiments 16 and 17). Further increase in the rate of
addition of aldehyde (22.3 mmol/h) led to a lowering of
epoxide conversions (experiment 18) (Figure 1).
The mode of addition of the reactants, as well as the
proportions of alkene and aldehyde, was important for
obtaining high conversions. In the first set of experiments,
the aldehyde was allowed to react with air from 10 to 15
min before the addition of the alkene. The aldehyde was used
in excess: the initial molar aldehyde-to-alkene ratio was 3/1,
and the rest of the aldehyde was added in portions after 4
and 8 h, bringing the ratio to the final value shown in Table
The oxidation reaction of alkene and aldehyde begins with
autoxidation of the aldehyde to acyl peroxy radicals and
peracids, which then react with the alkenes to form epoxide
20
and acid. Radical reactions are difficult to control, and
byproducts such as 3-heptanol, 3-heptanone, and 3-heptyl
formate were detected in the reaction of 2-ethyl hexanal and
terminal alkenes. The same products were also found along
with heptane in previous work on the autoxidation reaction
1. The results in Table 1 show that the reaction is slower in
21-24
of 2-ethyl hexanal.
the absence of solvent (dichloroethane): in experiments 5
and 6, the conversions to epoxide after 6 h were 41.2% with
solvent and 21.6% without. This effect could be offset,
however, through use of higher temperature in epoxidations
without solvent (60 °C instead of 40 °C, experiment 8). A
reaction temperature of 60 °C was found to be optimal; at
higher temperatures the amount and number of byproducts
from the aldehyde started to increase.
In a second series of experiments (Table 2), we found
that continuous addition of aldehyde gives higher conversions
of alkene to epoxide at a given aldehyde-to-alkene ratio. With
discontinuous addition (experiments 8 and 9) and an alde-
hyde-to-alkene ratio of 4.5/1, the conversion of alkene to
epoxide at 6-h reaction time was 38.7% for both alkenes.
With continuous addition of aldehyde and an aldehyde-to-
alkene ratio 4.2/1, the conversion after 3 h was 47.3%. After
Varying the rate of addition of aldehyde did not signifi-
cantly affect the amount of aldehyde byproducts. In experi-
ments where the final aldehyde-to-alkene ratio was 3/1, the
amount of byproducts was 10-20% after 8 h. Under the
same conditions but with a final aldehyde-to-alkene ratio of
2/1 or 1/1, the amount was still the same. Even in a synthesis
with a final aldehyde-to-alkene ratio of 13.2/1, after 11 h of
reaction, about 16% of the aldehyde had reacted to byprod-
ucts. With added metal complexes, the amount of substances
other than 2-ethyl hexanoic acid was more significant.
Catalytic activity of several metal complexes was tested
in the reaction. The tested metal complexes, Co(NO
Co(OAc) ‚4H O, Ni(OAc) ‚4H O, Fe(OAc) , and Mn(OAc)
O, did not increase the epoxidation rate; in fact, the
3 2 2
) ‚6H O,
2
2
2
2
2
2
‚
2H
2
reaction rate in the presence of metal complex was slightly
lower. The conversion to epoxide after 6 h was between 22
and 26.8%. The progress of epoxide formation during the
reaction is shown in Figure 2.
5
h of reaction and an aldehyde-to-alkene ratio of 6.5/1, the
conversion was already 73.5% (experiment 17).
An increase in the rate of addition of aldehyde increased
the rate of epoxidation. When the amount of alkene was 45
mmol and the rate of aldehyde addition 6.6 mmol/h (experi-
ment 13), the conversion of epoxide was 37% after 8 h, and
when the rate was 11.15 mmol/h (experiment 14), the
conversion increased to 71.2% measured after 8 h.
The addition of metal complexes changed the composition
of the oxidation byproducts of 2-ethyl hexanal. Without metal
complex, the main byproduct was 3-heptyl formate, whereas
with metal complex, the main byproducts were 3-heptanol
and 3-heptanone and no or only traces of 3-heptyl formate.
Addition of acetic acid did not affect either the reaction rate
The best conversion of alkene to epoxide, 98.7%, was
obtained when a 2/1 mixture of aldehyde and methyl 10-
undecenoate (10 mmol) was allowed to react with oxygen
for 1 h, after which aldehyde was added continuously for
about 10 h at a rate of addition 11.15 mmol/h (procedure B)
(
20) Tsuchiya, F.; Ikawa, T. Can. J. Chem. 1969, 47, 3191.
(21) Ladhabhoy, M.; Sharma, M. J. Appl. Chem. 1970, 20, 274.
(
(
22) Glinski, M.; Kijenski, J. React. Kinet. Catal. Lett. 1995, 55, 311
23) Glinski, M.; Kijenski, J. React. Kinet. Catal. Lett. 1995, 55, 319.
(24) Glinski, M.; Kijenski, J. React. Kinet. Catal. Lett. 1995, 55, 305.
102
•
Vol. 3, No. 2, 1999 / Organic Process Research & Development

amount of epoxide present in the reaction mixture. The
oxidation products of 2-ethyl hexanal, 1-decene, and methyl
1
0-undecenoate were identified by GC-mass spectrometry
by comparison with library spectra.
Epoxidation of Alkene with Air with Aldehyde as
Coreactant. Procedure A. The reaction vessel, equipped with
a condenser, was charged with 2-methyl propanal or 2-ethyl
hexanal (30-60 mmol), and 10-20 mL of dichloroethane
if solvent was used. Magnetic stirring (1250 rpm) and air
bubbling through a needle (70 mL/min) to solution were
started, and 1-decene or methyl 10-undecenoate (5-10
mmol) was added to the vessel after 10 min. The alkene-
to-aldehyde ratio was 1/3 in the beginning, with a final ratio
of added alkene and aldehyde of 1/6. The rest of the aldehyde
was added during the reaction in two equal portions at 4
and 8 h. Both reaction temperatures and times varied.
Procedure B. To the reaction vessel equipped with
condenser was added 20 mmol of 2-ethyl hexanal. Stirring
(1250 rpm) and air bubbling (70 mL/min) were commenced.
After 10 min, methyl 10-undecenoate (10 mmol) was added
to the vessel. Continuous addition of aldehyde to the reaction
was begun after 1 h.
Figure 2. Effect of metal complexes in alkene epoxidation,
procedure C.
or the product composition. The amount of byproducts was
greater in the presence of all metal complexes except
Fe(OAc)
was added. In the presence of metal complex, 17-28% of
-ethyl hexanal was converted to products other than 2-ethyl
hexanoic acid in 4 h, and the amount continued to increase
3 2
during the experiment. For example, in the case of Co(NO ) ‚
2
relative to the reactions where no metal complex
2
2
6H O, the amount of byproducts of the aldehyde was about
39% after 8 h of reaction (aldehyde-to-alkene ratio, 2/1).
Conclusions
The epoxidation of terminal alkenes 1-decene and methyl
0-undecenoate with air and 2-ethyl hexanal as solvent and
Procedure C. 1-Decene (45 mmol) was charged to the
reaction vessel; stirring (1250 rpm) and air bubbling (70 mL/
min) were commenced. After 10 min, continuous aldehyde
addition was begun. If metal complex was used, it was added
to the reaction after air bubbling was started. The temperature
in procedures B and C was 60 °C if not otherwise mentioned.
Synthesis of 1,2-Epoxy Decane and Methyl 10,11-
Epoxyundecanoate with Use of m-CPBA as Oxidizing
Agent. A 50-mL two-neck, round-bottomed flask equipped
with a condenser was charged with 1-decene or methyl 10-
undecenoate and 20 mL of dichloroethane. m-Chlorobenzoic
acid (1 g) in dichloroethane (3 mL) was added dropwise (1
h) to the ice-cooled solution of alkene. The reaction mixture
was first maintained for 15 h at room temperature and then
refluxed for 1 h at 45 °C. Ether (10 mL) was added to
generate a clear solution. The solution was washed with 2
1
coreactant proved to be an excellent synthesis route. Con-
tinuous addition of the aldehyde gave the highest epoxidation
rates, and up to a certain point, faster addition of aldehyde
to the reaction mixture speeded up the epoxidation. The
transformation of alkene to epoxide was clean, and no
byproducts of the alkene were detected at low temperatures
(
60 °C). Under optimal conditions, the yield of epoxide was
98.7%. The main product of the oxidation of 2-ethyl hexanal
was 2-ethyl hexanoic acid, but some other products were
also formed. Metal complexes in the synthesis increased the
amount of byproducts and did not advance the epoxidation.
Experimental Section
General. 2-Methyl propanal (Merck) and 2-ethyl hexanal
(
Aldrich) were dried, distilled and kept under inert atmo-
sphere before use. Methyl 10-undecenoate (Pfaltz & Bauer),
-decene (Merck), and dichloroethane (Merck) were kept
over molecular sieves and distilled before use. The metal
complexes, Co(NO ‚6H O (Merck), Co(OAc) ‚4H O (J.T.
Baker), Ni(OAc) ‚4H O (Fluka), Fe(OAc) (Aldrich), and
Mn(OAc) ‚2H O, were used as obtained from the supplier.
× 20 mL of 5% NaHCO
× 20 mL of brine and then dried with MgSO
was removed in a rotary evaporator to yield 1,2-epoxydecane,
3
, 2 × 20 mL of 2% NaOH, and 2
4
. The solvent
1
1
3
[85% (GC 6.3 min), purity 94%; C NMR (200 MHz,
)
3 2
2
2
2
CDCl ) analysis δ 14.1 (C-10), 22.8 (C-9), 26.0 (C-8), 29.3
3
(C-7), 29.5 (C-6), 29.6 (C-5), 31.9 (C-4), 32.6 (C-3), 47.0
(C-1), 52.4] and (C-2) methyl 10,11-epoxyundecanoate [88%
2
2
2
2
2
1
3
In some cases, 1 mL of glacial acetic acid was added. Gas
chromatographic analyses were performed on an HP 6890
instrument: 15-m HP5 column; carrier gas, helium; initial
column temperature, 40 °C; final column temperature 280
(GC 12.4 min), purity 99%; C NMR (200 MHz, CDCl
3
)
analysis δ 26.0 (C-3), 27.1 (C-8), 30.1, 30.2, 33.6 (C-9),
3
35.1 (C-2), 48.0 (C-11), 51.4 (COOCH ), 52.4 (C-10), 174.6
(C-1)].
°
C; progress rate, 9 °C/min. The epoxides were identified
Received for review September 23, 1998.
OP980075B
by comparison with authentic samples. (For preparation, see
below.) Decane was used as standard to calculate the exact
Vol. 3, No. 2, 1999 / Organic Process Research & Development
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