Epoxidation of cycloolefins with H2O2
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
481
The following solvents were used without additional purificaꢀ
tion: dichloromethane, dichloroethane, benzene, chloroform
(reagent grade), and hexane (pure grade). NꢀHexadecylpyridiꢀ
nium chloride (98%, Lancaster or Acros), [CH3(nꢀC8H17)3N]Cl
(Lancaster), and [(C4H9)4N]Сl (reagent grade) were used as
phase transfer catalysts.
MSLꢀ400 instrument (161.978 MHz, scan 10 kHz, pulse duraꢀ
tion 30 µs, pulse delay 15 s; chemical shifts of 31Р were measured
relatively to the external standard (85% H3PO4)).
Procedure of determination of the HPA state under conditions
of twoꢀphase oxidation. The HPA state in the presence of H2O2
and cycloolefin was studied by spectrophotometry at 20 °С. The
absorbance of solutions was determined relatively to equimolar
solutions containing no HPA using a Specord Mꢀ40 UV—VIS
spectrophotometer in 1ꢀmm cells, whose temperature was mainꢀ
tained at a constant level.
Samples for experiments and IR spectroscopic studies were
prepared similarly to described procedures6,13 with some changes:
H3PW12O40•15.4 Н2О (4.0101 g, 1.27 mmol) in water (5 mL)
was stored for 0.5 h in a magnetically stirred solution of 33.4%
Н2О2 (250 mmol). To the solution was added [C5H5NC16H33]Cl
(1.3631 g, 3.81 mmol) or [(C4H9)4N]Сl (1.22 g, 3.81 mmol).
The formed precipitate of Q3{PO4[WO(O2)2]4} (for
[C5H5NC16H33]3{PO4[WO(O2)2]4}, 3.187 g) was filtered off.
To isolate K2[W2O3(O2)4(H2O)2]•2H2O, KCl (4.722 g,
53.72 mmol/1.27 mmoles of HPA) was added to the filtrate
(V = 34 mL), and the mixture was left for 15—20 h at 5 °С. The
precipitated white crystals were separated from the mother liꢀ
quor and washed with minor amounts of water and EtOH. IR
absorption spectra were recorded in the 400—4000 cm–1 region
on a Bomem MBꢀ102 FTIR spectrometer as a suspension in
Nujol.
Kinetic measurements. Reactions were carried out in a shaken
reactor of the "catalytic duck" type14 equipped with a reflux
condenser and a jacket for maintaining a constant temperature.
The temperature of the reaction was maintained at 20—65 °С
using a water thermostat with an accuracy of 0.1 °С.
The frequency of reactor shaking was chosen in such a way
(≥ 600 rpm) that the reaction rate was independent of the shakꢀ
ing frequency.
Procedures for preparation of the reaction mixture. Method A.
At 20 °С, HPA (0.026 mmol), 31.8% Н2О2 (0.056—5.6 mmol),
the corresponding solvent (10 mL), Q+Cl– (0.078 mmol), and
olefin (18 mmol) were simultaneously loaded into a reactor and
rapidly heated (for 1—2 min) to 65 °С using a thermostat. After
this, the reaction was carried out with intense stirring.
Method B. HPA (0.026 mmol) was pretreated with a solution
of 30% Н2О2 (0.056—5.6 mmol) for 0.5 h at 40 °С. The resulting
solution was loaded into a reactor, the corresponding solvent
(10 mL) and Q+Cl– (0.078 mmol) were added, and the solution
was stored for 0.5 h at 20 °С. After olefin (18 mmol) was introꢀ
duced, the reactor was heated to 65 °С, and the reaction was
performed with intense stirring.
Results and Discussion
Epoxidation of cyclic olefins with hydrogen peroxide
occurs at 65 °С in a twoꢀphase water—solvent system in
the presence of molybdenum or tungsten compounds,
mainly by the PW(Mo)xOyz– peroxo complexes formed in
an aqueous HPA—H2O2 medium in combination with a
phase transfer catalyst (Tables 1 and 2). Under these conꢀ
ditions, 1,2ꢀepoxycycloalkanes form in 70—90% yields.
However, we failed to oxidize vinylcyclohexane to the
epoxide using this procedure.
The obtained data show that the reaction rate (estiꢀ
mated from the slope ratio of the initial regions of the
epoxidation product concentration—time curves, see
Fig. 1) in the presence of HPA depends substantially on
the order of introduction of the reactants. The HPA inꢀ
troduced immediately after mixing of all reactants (solꢀ
vent, Н2О2, cyclohexene, and Nꢀhexadecylpyridinium
chloride) exhibits a lower catalytic activity than the HPA
preliminarily stored in a solution of Н2О2. This result
and 31Р NMR data indicate that the variation of the
Table 1. Oxidation of cycloolefins in the HPA—Н2О2—QCl
system at 65 °С with formation of the corresponding
1,2ꢀepoxycycloalkanes (18 mmoles of olefin, [olefin] : [H2O2] =
1 : 2 (mol mol–1), 10 mL of C2H4Cl2, 0.026 mmoles of HPA,
[HPA] : [QCl] = 1 : 3 (mol mol–1))
Cycloolefin
HPA
QCl t/h Ca
Sb
Samples of an organic phase were taken at specified intervals
and analyzed by GLC on a Tsvetꢀ500 chromatograph (flameꢀ
ionization detector, metallic column 3 m×2 mm, 0.4% OVꢀ225
on graphitized thermal carbon black, nitrogen as carrier gas,
30 mL min–1; temperatures 150, 100, and 120 °С of the evapoꢀ
rator, column, and detector, respectively).
Reaction products were identified by GLCꢀMS using
an LKBꢀ2091 instrument (Sweden) (glass capillary column
40 m, Carbowax 20M/Lukopren G 1000 = 1/3; electron imꢀ
pact, 70 eV).
Physicochemical measurements. Samples for 31Р NMR specꢀ
troscopy were prepared using a described procedure.6 30% H2O2
(0.34—34 mmol) was added to H3PW12O40 (0.5 g, 0.17 mmol) in
water (1 mL), and the mixture was stirred for 0.5 h. To
the resulting solution of the complex СНСl3 (3 mL) and
[CH3(nꢀC8H17)3N]+Cl– (0.3 g, 0.53 mmol) were added. The
organic layer was separated and analyzed by 31Р NMR and UV
spectroscopies. 31Р NMR spectra were measured on a Bruker
%
Cyclohexene
Cyclohexene
H3PW12O40
H3PW12O40
4
3
7
7
24
7
6
6
8
6
5
5
85
40
80
6
49
58
10
50
18
16
92
92
90
88
83
85
85
75
75
77
94
85
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclohexene
Cyclooctene
Cyclododecene
Vinylcyclohexane
H3PW12O40
1
4
4
4
4
4
4
4
4
4
H3PW11MoO40
H3PW9Mo3O40
H3PW3Mo9O40
H3PW11VO40
H3PWMo11O40
H3PMo12O40
H3PW12O40
0.15 95
1.0 80
1.0
H3PW12O40
H3PW12O40
—
a Conversion.
b Selectivity.