PHASE TRANSFER OF THE ORGANIC SUBSTRATE IN THE EPOXIDATION REACTION
887
α, mol %
(curve 1), N,N-dimethylaniline (curve 2), triethyl-
amine (curve 3), pyridine (curve 4), and N-meth-
yldiethanolamine (curve 5), to CPB result in the syn-
ergistic effect in the epoxidation allyl chloride reaction
when their concentration in the mixture is up to 10%.
In the presence of any of the amines alone without
CPB, the systems are almost inactive.
12
14
12
When pyridine (curve 4) and pyridine N-oxide are
used, the experimental data are almost the same. This
implies that pyridine is oxidized with hydrogen perox-
ide to the N-oxide in the two-phase aqueous–organic
system in the presence of oxo–peroxo phosphotung-
state compounds. According to published data [16,
1
0
8
6
4
1
2
3
4
5
17], the presence of a strong and narrow band at 1300–
−1
1
200 cm in the IR spectrum can be reliable evidence
for the in situ formation of N-oxides from the corre-
sponding amines. In the case of pyridine N-oxide,
0
1
0.1
0.9
0.2
0.8
0.3
0.7
0.4
А
−1
such a band was observed at 1276 cm (ether extract).
0.6
CPB
As has been already noted, pyridine N-oxide is
quite well known in the literature as a phase-transfer
carrier for a substrate [8], in particular, allyl chloride
Fig. 1. The dependence of the yield of epichlorohydrin on
[
18]. Thus, we can classify oxides of tertiary amines
the CPB : A (amine) concentration ratio, where A =
primarily as phase-transfer substrate carriers,
(
1) tributylamine, (2) N,N-dimethylaniline, (3) triethyl-
although their role as a ligand in the neutral peroxo
amine, (4) pyridine, and (5) N-methyldiethanolamine.
VAP = 4 mL, VOP = 2 mL, (СNa2WO4 )AP = 0.075 mol/L,
complexes of tungsten WO(O ) L, where L is a tertiary
2 2
amine oxide or pyridine oxide, cannot be entirely
(
СH3PO4 )AP = 0.019 mol/L,(СH2O2 )AP = 4.0 mol/L,
6.13 mol/L, (CCPB C )
.056 mol/L, T = 50°С, ω = 1200 rpm, рН 1, and τ = 1 h.
ruled out according to the obtained experimental data.
(
C
)
=
+
=
C3H5Cl OP
A OP
It can be assumed that when the Venturello com-
plex Q [PW O ], which is active in the epoxidation
0
3
4
24
reaction, and a less active complex WO(O ) L are
2
2
present in the organic phase of the mixture, the reoxi-
dation of the complex Q [PW O ] can proceed
To verify this hypothesis, we used additives of
triphenylphosphine and 8-hydroxyquinoline, which
3
4
24 − х
are poorly oxidized under the reaction conditions and with the involvement of the complex WO(O
cannot interact with the substrate to form a charge- organic phase:
transfer complex but, according to the published data
) L in the
2 2
(
Q [PW O
])OP + WO L
24– х 5 OP
3
4
[
10, 13, 14], are capable of interacting with peroxo
(
13)
L is hydrated and oxidized with
− x
tungstates as a ligand at the metal atom. The influence
of additives was investigated with varying their con-
centration in the mixture with the phase-transfer cat-
→ (Q [PW O ]) + WO5−хL .
3 4 24 OP OP
Then WO
5
hydrogen peroxide to WО(О ) LL', where L' is H O, in
2
2
2
alyst CPB, providing that C
+ C
= const.
CPB
Additive
the aqueous phase:
Whenusingthetriphenylphosphineand8-hydroxy-
quinoline additives in the presence of CPB for the
epoxidation of allyl chloride in systems with the in situ
'
W O 5−хL OP → W O 5−хL L ,
(14)
AP
formation of Q [PW O ], no synergistic effect is
'
W O 5−хL L + Н О
AP 2 2 AP
'
AP
3
4
24
→ WO LL + Н ОAP. (15)
5
2
observed. In contrast, there is some decrease in the
catalytic activity of the systems, possibly, due to the
fact that the complex formed during the interaction
with these ligands is less effective than the Venturello
complex Q [PW O ].
The peroxo complex WO LL’ is dehydrated and
5
migrates to the organic phase:
'
5
W O L L → W O L OP.
(16)
5
Ap
3
4
24
The cycle is closed by the reoxidation reaction of
the complex Q [PW O ] (Eq. (13)).
To verify the influence of amine oxides additives on
the efficiency of the epoxidation reaction,
tertiary amines and pyridine can be used. Under the
3
4
24 − х
The data on the yield of epichlorohydrin and syn-
epoxidation reaction conditions, tertiary amines can ergism coefficients (k ) for the mixtures of CPB and
s
be oxidized with hydrogen peroxide to the corre- tertiary amines (their N-oxides) are presented in
sponding N-oxides [15].
Table 1.
As is seen from the experimental data (Fig. 1),
According to the data of Table 1, a mixture of two
admixtures of tertiary amines, such as tributylamine phase-transfer catalysts, namely, CPB (90 mol %) and
PETROLEUM CHEMISTRY Vol. 58 No. 10 2018