Epoxidation of Butadiene with Hydrogen Peroxide
1443
3
been made [27] that the active {PO [WO(O ) ] } complex
-
38.7. The IR spectrum (in KBr) agrees with that described
previously [22].
4
2 2 4
is rapidly regenerated with H O under the phase transfer
2
2
catalytic conditions. In this connection, the second aim of our
[(n-C H ) N] {HPO [WO(O ) ] } (TBA-PW2) was
2 2 2
4
9 4
2
4
3
1
work was a direct observation by P NMR of transforma-
tions of the phosphotungstate anions in the process of the
catalytic BD epoxidation.
prepared as previously described [23]. Water solution of
H [PW O ] (0.5 mmol) and H PO (30 mmol) was
3
12 40
3
4
mixed with 30% H O (59 mmol), and the peroxo com-
2
2
We studied epoxidation of BD with aqueous hydrogen
plex anion was precipitated with [(n-C H ) N](NO )
4 9 4 3
peroxide in CH CN solutions using well characterized
3
(10 mmol). The solid was thoroughly washed with water
and dried in air. C H N O PW (1107.7): calcd. C 34.7,
?
tetrabutylammonium (TBA ) and 1-ethyl-3-methylimida-
3
2
73
2
14
2
?
zolium (EMIm ) salts of phosphotungstate anions:
H 6.59, N 2.53, P 2.80, W 33.2; found C 34.4, H 6.50, N
[
[
(n-C H ) N] {PO [WO(O ) ] }, [(n-C H ) N] Na0.6H1.4
4
2.60, P 2.55, W 33.2. IR spectrum (in Nujol): m(O–O)
bands 842, 851 and 883 cm as in [23].
9 4
3
4
2 2 4
4
9 4
5
-
1
PW O ], and [(C H )(CH )C H N] NaH[PW O ].
1
1
39
2
5
3
3
3
5
11 39
The rate of the BD epoxidation has been analyzed in
connection with the composition of active peroxo complex
intermediates. To determine the effect of a cationic moiety
[(n-C H ) N] Na0.6H1.4[PW O ] (TBA-PW11) was
11 39
4
9 4
5
prepared by mixing aqueous solutions of Na [PW O ] (pH
7
11 39
-
4.0, 2.5 mL, 5.8 9 10 mol) and [(n-C H ) N]Br in a
4
4
9 4
?
?
on the catalytic performance, we tested TBA and EMIm
molar ratio 1:10. The solid formed was washed with water till
-
7
salts of [PW O ] anion. The motivation for this study
-
negative reaction on Br ions and dried in air.
C H N Na O PW (3902.9): calcd. C 24.6, H 4.65,
1
1 39
was positive effect of imidazolium salts (ionic liquids) used
as solvents in a number of peroxide reactions [13, 30–35].
8
0
181.4
5
0.6 39
11
N 1.79, Na 0.353, P 0.794, W 51.8; found: C 24.2, H 4.55, N
1
.70, Na 0.320, P 0.674, W 50.8. IR spectrum (in KBr)
7
-
conformed to the structure of heteropolyanion [PW O ]
11 39
2
Experimental
[39]: m = 1079 and 1053 (P–O), 957 (W=O), 891, 817 and
3
1
754 (W–O–W), 597 d(O–P–O), 518 d(W–O–W). P NMR:
2
.1 Materials and Reagents
two broad peaks (-12.3 and -12.8 ppm) in dry CH CN and
3
a narrow peak (-12.5 ppm) in CH CN with water admixture
3
Commercial chemically pure H [PW O ]ÁnH O and
(Fig. S1, b, c).
3
12 40
2
H PO , (n-C H ) NBr of a reagent grade, unstabilized
4
[(C H )(CH )C H N ] NaH[PW O ] (EMIm-PW11)
11 39
3
4
9 4
2
5
3
3
3
2 5
*
34% aqueous H O of special purity (Reachim), CH CN
2
was prepared by mixing aqueous solutions of Na [PW O ]
7 11 39
2
3
-
4
(pH 4.0, 2.5 mL, 5.8 9 10 mol) and EMImBr (0.6 mL,
of high purity (Kriochrom) and 1,3-butadiene (Aldrich)
were used. Na [PW O ] (Na-PW ) was prepared as
-
2.9 9 10 mol). The precipitated solid was washed with
3
7
11 39
11
-
water till negative reaction on Br ions and dried in air.
usual, by mixing H [PW O ] and H PO aqueous solu-
3
3
12 40
4
tions in atomic ratio P/W = 1/11 and adding Na CO to
2
C H N Na O PW (3256.3): calcd. C 11.1, H 1.72, N
30 56 10
3
1
39
11
3
1
pH 4, with subsequent heating at 90 ꢁC for 1 h. P NMR:
a single peak -10.9 ppm [36] (Fig. S1, a).
4.30, Na 0.71, P 0.952, W 62.1; found C 11.1, H 2.10, N 4.30,
Na 0.94, P 0.891, W 57.7. IR (KBr): m = 1078 and 1037 (P–
O), 944 (W=O), 892, 850, 801, 754sh, and 728 (W–O–W),
The [(n-C H ) N](NO ) solution was prepared from the
3
4
9 4
-
1
[
(n-C H ) N]Br solution by adding equimolar amount of
4 9 4
592 d(O–P–O), 508 d(W–O–W) cm .
AgNO in solution and separating the AgBr residue.
3
EMImBr was prepared in the same way as described in
2
2.3 Catalytic Experiments
1
[
37] for BMImCl. H NMR, [ H ] Dimethylsulfoxide, as
6
in [38] d: 9.27 (NCHN), 7.84 (CH NCHCHN), 7.75
Oxidation of BD was carried out in a 28 mL Pyrex reactor
equipped with a magnetic stirrer and Teflon valves for
connecting to a gas burette and for sampling. Catalysts
were dissolved in a mixture of *34% H O (0.1–0.3 mL,
3
(
CH NCHCHN), 4.22 (NCH CH ), 3.88 (NCH ), 1.42
3
2
3
3
(
NCH CH ).
3
2
2
2
2
.2 Synthesis of Phosphotungstates
1–3 mmol of H O ) and CH CN (2 mL) at the reaction
2 2 3
temperature (20–60 ꢁC) for 10 min. The reactor was
purged with BD at ambient pressure, the gas burette was
filled with BD (measurements in the atmosphere of BD) or
argon (measurements at a dosed BD amount of 26 mL,
1 mmol), the system was sealed and the stirrer was on. To
minimize diffusion of BD, the valve between the reactor
and burette was opened only for several seconds just to fix
the BD uptake. The initial rapid gas consumption corre-
sponded to solubility of BD in the reaction mixture
[
(n-C H ) N] {PO [WO(O ) ] } (TBA-PW ) was prepared
4 9 4 3 4 2 2 4 4
via a procedure of Br e´ geault et al. [22]. Water solution of
H [PW O ] (PW ) (6 mmol of W) was mixed with 30%
3
12 40
12
H O (100 mmol), and the peroxo complex anion was
2
2
precipitated with [(n-C H ) N](NO ) (1.6 mmol). The
4
9 4
3
solid was washed thoroughly with water and dried in air.
C H N O PW (1876.4): calcd. C 30.7, H 5.75, N 2.24,
4
8
108
3
24
4
P 1.65, W 39.2; found C 31.4, H 5.90, N 2.24, P 1.64, W
123