Ethylene and Cyclohexene Oxidation by p-Benzoquinone, Hydrogen Peroxide, and Oxygen in the Solutions of Cationic Pd(II) Complexes in Acetonitrile–Water and Ionic Liquid–Water Binary Solvents

Article abstract of DOI:10.1134/S0023158419010051

Abstract: Optimal conditions are selected for ethylene and cyclohexene oxidation reactions in the acetonitrile (AN)–water system in the presence of Pd(AN)_x(H₂O)_{4 - x}²⁺ complexes. It is shown that hydrogen peroxide oxidizes hydroquinone (QН₂) in acetonitrile solutions and in ionic liquids (BMIM⁺BF₄^-,BMIM⁺PF₆^-, and the rates of ethylene oxidation in the BMIM⁺PF₆^- ionic liquid in the presence of p-benzoquinone (Q) and hydroquinone are the same. It is shown that solid and soluble phthalocyanine iron complexes catalyze oxidation of olefins by oxygen in acidic acetonitrile media by converting p-benzoquinone to the third catalyst of the process. The apparent first-order rate constants of hydroquinone oxidation by oxygen are determined. The use of the IL–Н₂О–Н₂SO₄ system is found to be inappropriate for cyclohexanone synthesis because of the formation of byproducts of cyclohexene conversion.

Full text of DOI:10.1134/S0023158419010051

ISSN 0023-1584, Kinetics and Catalysis, 2019, Vol. 60, No. 1, pp. 52–61. © Pleiades Publishing, Ltd., 2019.
Russian Text © G.E. Efremov, E.A. Bovyrina, A.V. Podtyagina, I.V. Oshanina, O.N. Temkin, 2019, published in Kinetika i Kataliz, 2019, Vol. 60, No. 1, pp. 54–65.
Ethylene and Cyclohexene Oxidation by p-Benzoquinone, Hydrogen
Peroxide, and Oxygen in the Solutions of Cationic Pd(II) Complexes
in Acetonitrile–Water and Ionic Liquid–Water Binary Solvents
G. E. Efremova, E. A. Bovyrinaa, A. V. Podtyaginaa, I. V. Oshaninaa, and O. N. Temkina, *
aMIREA–RussianTechnological University (M.V. Lomonosov Institute of Fine Chemical Technologies), Moscow, 119571 Russia
*e-mail: olegtemkin@mail.ru
Received July 3, 2018; revised August 21, 2018; accepted August 27, 2018
Abstract—Optimal conditions are selected for ethylene and cyclohexene oxidation reactions in the acetoni-
2+
trile (AN)–water system in the presence of
complexes. It is shown that hydrogen peroxide
Pd(AN)x(H2O)4−x
+
−
+
oxidizes hydroquinone (QН ) in acetonitrile solutions and in ionic liquids (
−), and
BMIM BF4 , BMIM PF6
2
+
−
the rates of ethylene oxidation in the
ionic liquid in the presence of p-benzoquinone (Q) and
BMIM PF6
hydroquinone are the same. It is shown that solid and soluble phthalocyanine iron complexes catalyze oxi-
dation of olefins by oxygen in acidic acetonitrile media by converting p-benzoquinone to the third catalyst of
the process. The apparent first-order rate constants of hydroquinone oxidation by oxygen are determined.
The use of the IL–Н2О–Н2SO4 system is found to be inappropriate for cyclohexanone synthesis because of
the formation of byproducts of cyclohexene conversion.
Keywords: ethylene, cyclohexene, oxidation, acetonitrile, ionic liquids, p-benzoquinone, hydrogen peroxide,
oxygen, cationic complexes, palladium
DOI: 10.1134/S0023158419010051
INTRODUCTION
2. The process of formation of active
2+
complexes was studied by NMR
Pd(AN)x(H2O)
4−x
An interest in catalysis of olefin oxidation reactions
by palladium cationic complexes has a number of rea-
sons: the pronounced superelectrophilicity of cationic
metal (Hg, Pt, Pd, Rh, and Au) complexes in various
reactions [1–14], unusual kinetic behavior of palla-
dium cationic complexes [7, 11, 15, 16] in the so-
called Wacker oxidation of olefins [17, 18], and their
high activity in cyclohexene (C6H10) oxidation to
cyclohexanone (C6H10O) in aqueous–organic binary
solvents [7, 11, 19, 20] compared to the processes in
classical catalytic systems in the solution of palladium
chloride complexes [21–23], which makes this process
a promising technology for cyclohexanone synthesis
and electron spectroscopy [24].
3. A bimodal dependence of the initial rate of
cyclohexene oxidation on the molar fraction of water
(
H O) has been determined [20] and phase equilibria
α
2
in the cyclohexene–acetonitrile–water system was
studied [20, 25].
4. Kinetic isotope effects were measured in the
reactions of cyclohexene and ethylene oxidation in the
AN–H2O/D2O system [15] and in the reaction of ethylene
oxidation in the AN–H2O–C2H4/C2D4 system [16].
5. The kinetics of ethylene oxidation by p-benzo-
quinone was studied and the kinetic model was pro-
posed based on the initial rates of the reaction [26].
Earlier, in the Laboratory of Kinetics and Catalysis
of the Chair of Chemistry and Technology of Basic
Organic Synthesis at the Moscow Institute of Fine
Chemical Technology, the following information on
the acetonitrile (АN)–water system with p-benzoqui-
none (Q) oxidant was obtained:
p-Benzoquinone was used for the first time as a
stoichiometric oxidant of olefins to carbonyl com-
pounds in solutions of palladium chloride complexes
by Moiseev and coworkers [18, 27]. p-Benzoquinone
and sulfonaphthoquionone were also used in aqueous
solutions of cationic palladium(II) complexes [28, 29]
Pd(H2O)24+
1. The kinetics of cyclohexene oxidation in the
Pd(OAc)2–HClO4−LiClO4–CH3CN–H2O system
was studied and the kinetic model was proposed [11].
without additional stabilization of
by
ligands. The use of quinones as stoichiometric oxi-
dants in the solutions of cationic complexes in acidic
52

ETHYLENE AND CYCLOHEXENE OXIDATION
53
media indicates the oxidation of palladium hydride form was confirmed by its good solubility in organic
complexes by quinones at the stage of Pd2+ regenera- solvents [54]. H1 NMR spectra of Pd3(CH3COO)6
2+
solutions in CDCl3 confirmed the symmetrical struc-
ture of the molecule with six equivalent acetate groups
and the absence of appreciable amounts of palladium
nitrite complexes [55, 56].
tion or the stabilization of Pd0 and
complexes by
Pd2
0
coordinating quinines (Pd(Q)0,
,
and
Pd(Q)2
Pd2(Q)2+). In the interaction of these complexes with
proton, Pd(II) is regenerated (see, e.g., [30]). The use
of other stoichiometric oxidants in the reaction of ole-
fin oxidation in the solutions of palladium complexes
is known: Н2О2, ROOH [31–33], and O2 [34–37].
Ionic liquids, butylmethylimidazolium tetrafluo-
+
−
roborate
(IL-1) with a concentration of
BMIM BF4
>97% and butylmethylimidazolium hexafluorophos-
BMIM+PF6−
phate (IL-2) with a concentration of
Oxygen as an oxidant for olefins and dienes in solu-
tions of palladium complexes is used directly (e.g.,
>98.5% were produced by Merck, and triethylammo-
[35]), with oxygen-activating catalysts (Co(II) com- nium triflate ТEA+Tf– (IL-3) with a concentration of
plexes with various porphyrins [38]), or in the pres- >99% was synthesized by us. The purity of ionic liquid
was checked by 1Н, 13С, and 19F NMR methods.
ence of a third catalyst: p-benzoquinone [6, 39–41].
The Со(II) [39–41] and Сu(II) [42, 43] complexes
and Fe(II) phthalocyanine [6, 41] are used for the oxi-
dation of hydroquinone (QН2) by oxygen using hydro-
quinone as a component of the initial catalytic system.
Hydroquinone is oxidized by oxygen in chloroform
with catalysis by Со(II) and Mn(II) complexes with
macrocyclic ligands [44]. The oxidation of hydroqui-
none by hydrogen peroxide in acetonitrile catalyzed by
Cu(II), Fe(II), Co(II), and Mn(II) bromide com-
plexes [45].
For further development of this field of olefin oxi-
dation and the choice of binary solvents for carrying
out the process of cyclohexene oxidation, it was neces-
sary to check the possibility of using such oxidants as
Н2О2 and О2 in strongly acidic media in the presence
of palladium cationic complexes in aqueous–organic
solvents and in the presence of catalysts for p-benzo-
quinone regeneration by hydroquinone oxidation with
stoichiometric oxidants (Н2О2 or О2). Moreover, to
solve a number of technological problems of the cyclo-
hexene oxidation process, it was necessary to investi-
gate the possibility of using ionic liquids (IL), which
are used in oxidation processes [46–51], as ionic liq-
uid–water binary solvents in the presence of palla-
dium cationic complexes.
Iron and cobalt phthalocyanine complexes (PcFe,
РсСо, *PcFe and *PcCo, where *Pc is tetra-4-(N-dib-
utylsulfamoyl)phthalocyanine) were synthesized at
NIOPIK State Scientific Center.
Experimental Procedure
Ethylene oxidation by p-benzoquinone and hydro-
gen peroxide, hydroquinone oxidation by oxygen, and
cyclohexene oxidation by oxygen were carried out in a
volumetric setup placed in a thermostatically con-
trolled chamber. Experiments were carried out at 30°C
in a reactor with a magnetic stirrer having a stirring
rate of 1000–1500 rpm. The overall volume of solution
in the reactor was ~10 mL. It was found that the reac-
tion rate in a reactor with a magnetic stirrer does not
depend on the volume of the solution in a range of 5–
15 mL, which indicated the absence of diffusion lim-
itations. The experimental procedure and catalysts
preparation in the acetonitrile system is described in
detail in [11, 26]. The procedure of catalyst prepara-
tion in ionic liquids is described below.
Analysis of Oxidation Products
The reaction products were analyzed by gas–liquid
chromatography (GLC) and chromatography/mass
spectrometry. In the case of the AN–H2O system, the
acid was neutralized with sodium bicarbonate or
potassium carbonate before analysis. In the case of
ionic liquids, after neutralizing the acid, the products
were extracted with diethyl ether or hexane. After
purging from the ionic liquid with nitrogen, acetalde-
hyde was determined by the oxime method.
EXPERIMENTAL
Materials
The following reagents were used in the work: aceto-
nitrile СН3СN (TU 2636-092-44493179-04, reagent
grade, ρ = 0.7828 g/cm3), perchloric acid HClO4 (Acros-
CAS, 70%), ethylene (GOST 25070-87), p-benzoqui-
none (Acros organics, 99%) (before experiments
p-benzoquinone was sublimated) and nonaqueous
lithium perchlorate LiClO4 (TU 6-09-3360-73,
reagent grade).
RESULTS AND DISCUSSION
Ethylene Oxidation in Binary Solvents
Palladium diacetate trimer Pd3(CH3COO)6 was
obtained by palladium black oxidation by concen-
trated nitric acid in glacial acetic acid [52, 53]. The tri-
As noted above, olefins are rather efficiently oxi-
dized by p-benzoquinone in the AN–H2O solutions in
2+
meric crystal structure of the obtained palladium dia- the presence of
palladium com-
Pd(AN)x(H2O)
4−x
cetate and the absence of impurities of the keto–poly- plexes. Thus, for instance, the turnover frequency
KINETICS AND CATALYSIS Vol. 60 No. 1 2019

54
EFREMOV et al.
(TOF) of the catalyst in ethylene oxidation is approx-
imately 130 times higher than in the solution of chlo-
ride complexes [15, 26]. The study of the formation of
active cationic Pd(II) complexes showed [24] that
three catalytic systems (III, IV, and V) may exist that
differing in the distribution of complexes with differ-
ent values of x (1, 2, and 3, respectively) in the initial
Pd(OAc)2–HClO4–LiClO4–AN–H2O solution. Sys-
tem III was prepared after allowing to stay for 20 min
a freshly prepared Pd3(OAc)6–AN solution with
added acid and water. For the preparation of system
IV, a Pd3(OAc)6–AN solution was allowed to stay for
7 days, and then perchloric acid and water were added
to a portion of the solution and after 20 min were
added into the reactor. To prepare system V, system IV
(after adding the acid and water) was allowed to stay
for seven more days. These three systems differ insig-
nificantly in their catalytic activity in ethylene oxida-
R0 × 103, mol L–1 min–1
20
16
12
8
4
0
0.2
0.4
0.6
,
0.8
αH O
molar fraction
2
Fig. 1. Dependence of the initial reaction rate on the molar
fraction of water in catalytic system III.
= 0.87 atm,
Р
С2Н4
–4
[Pd] = 5.0 × 10 mol/L, [Q] = 0.2 mol/L, [HClO ] =
Σ
0
4
0.2 mol/L, [LiClO ] = 0.3 mol/L.
4
tion by p-benzoquinone at
= 0.67 molar fraction
α
H2O
[26]. LiClO4 was used to maintain the ionic strength of
solution.
R0 × 103, mol L–1 min–1
16
The study of the influence of the molar fraction of
water in the AN–H2O system on the initial rate of eth-
ylene oxidation by p-benzoquinone showed the extremal
dependences in an H O range of 0.2–0.3 molar fraction
α
2
12
8
for catalytic systems III (Fig. 1) and IV (Fig. 2). Note
that in the process of cyclohexene oxidation in system
III [11, 20], a bimodal dependence of the initial rate
on H O was obtained. As was shown by I.V. Martynov
α
2
4
in his master’s thesis (Moscow Technological Univer-
sity (Institute of Fine Chemical Technologies) 2016,
unpublished data) and in [24], in system III in a range
of 0.2–0.3 molar fraction of water, the sum of concen-
2+
0
0.2
0.4
0.6
0.8
molar fraction
αH O
,
trations of Pd(AN)3(H2O)2+ and Pd(AN) (H O
)
2
2
2
2
complexes is close to 99% of the overall palladium
concentration. It is likely that the optimal concentra-
tion of the sum of active complexes in the less active
system IV at a point of maximum is achieved with a
lower molar fraction of water due to various processes
occurring in the course of formation of these systems. In
system III, water and acid react with the palladium ace-
tate trimer, and in system IV they react with the acetoni-
trile complex of monomeric palladium acetate [24].
Fig. 2. Dependence of the initial reaction rate on the molar
fraction of water in catalytic system IV.
= 0.87 atm,
Р
С2Н4
–4
[Pd] = 5.0 × 10 mol/L, [Q] = 0.2 mol/L, [HClO ] =
Σ
0
4
0.2 mol/L, [LiClO ] = 0.3 mol/L.
4
5 × 10–4 M Pd, 0.2 M HClO4, 0.2 M p-benzoquinone,
0.3 M LiClO , at
= 0.67 molar fraction, the rate
α
4
H2O
An increase in
above 0.8 molar fraction leads
α
of ethylene oxidation (R0(C2H4), mol L–1 min–1)
increases in the series DMF (0.74 × 10–3) < DMSO
(2.4 × 10–3) < AN (5.5 × 10–3).
H2O
to a significant decrease in the rate of ethylene oxida-
tion by p-benzoquinone and to the instability of the
catalytic system. In the range
= 0.8–0.93 molar
α
H2O
The replacement of perchloric acid used in [11, 15,
16, 24] by H2SO4 with the same molar concentration
leads to a decrease in the initial rate of ethylene oxida-
tion by at most 12%. It was found earlier that, at
[H+] > 0.2 mol/L, the reaction rate remains almost
constant up to [H+] = 0.5 mol/L [26]. Experiments
have also shown that there is a linear dependence of
the initial oxidation rate on [Pd]Σ [26] and that its con-
fraction, palladium is partly reduced to the metal state
during the process. These results point to the import-
ant role of acetonitrile as a ligand, which stabilizes
reduced forms of palladium catalysts (Pd(0) and
Pd(I)) in the solution. The specific role of acetonitrile
can also be judged by comparing the activity of cata-
lytic systems with various components of binary sol-
vents (acetonitrile, dimethylformamide (DMF), and
dimethyl sulfoxide (DMSO)). In a system containing stancy is observed when hydroquinone is added to a
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ETHYLENE AND CYCLOHEXENE OXIDATION
55
Table 1. Effect of [QH2] on the rate of ethylene oxidation
by p-benzoquinone
an increase in [HClO4] to 1 mol/L, the reaction rate
increases to 3.7 × 10–3 mol L–1 min–1.
Thus, the rate of ethylene oxidation by hydrogen
peroxide in the absence of p-benzoquinone is approx-
imately 18 times lower than the rate with its presence
R0(C2H4) × 103,
mol L–1 min–1
[QH2]
[Q]
Run
mol/L
1
2
3
2.0
–
0.06
0.10
5.33
5.34
5.67
(
= 0.93 molar fraction) and increases with an
α
H2O
increase in [Н О ], [HClO ], and
The interac-
.
αH O
2
2
4
2
tion of hydrogen peroxide with acetonitrile is likely to
retard the oxidation process or the acetonitrile com-
plex of Pd(0) is oxidized by hydrogen peroxide more
–4
[Pd] = 5 × 10 mol/L, [HClO ] = 0.2 mol/L, [LiClO ] =
Σ
4
4
0.3 mol/L,
= 0.67 molar fraction.
α
slowly. An increase in α leads to a higher rate of oxi-
H2O
H2O
dation by hydrogen peroxide and a slower rate of oxi-
dation with added p-benzoquinone.
Table 2. Activity of the catalytic systems in ionic liquids in
ethylene oxidation by p-benzoquinone
Then, we checked the possibility of hydrogen per-
oxide to oxidize ethylene in the acetonitrile system in
the presence of hydroquinone. Under these conditions
ethylene proved to be oxidized at a rate R0(C2H4) =
R0(C2H4) × 103,
mol L–1 min–1
αIL
αAN
α
H2O
Ionic liquid
molar fraction
1.0 × 10–3 mol L–1 min–1.
BMIM+BF4−
0.50
0.16
19.4
H O, R0(C2H4) × 103,
[QH2] [Н2О2]
[H2SO4]
[Pd]
α
mo2lar
BMIM+PF6−
ТEA+Tf–
0.34
0.49
0.49
0.17
0.17
3.2
mol L–1 min–1
mol/L
21.6
fraction
–3
[Q] = 0.2 mol/L, [Pd] = 2.5 × 10
mol/L, [H SO ] =
2 4
Σ
0.1
0.3 0.005
1.0
0.67
1.03
0.2 mol/L.
Because hydrogen peroxide almost does not oxi-
dize ethylene in the absence of p-benzoquinone, a
noticeable rate of ethylene oxidation in this experi-
ment points to the ability of hydrogen peroxide to oxi-
dize hydroquinone without additional catalysts.
Ionic liquid–Н2О systems. We also used ionic liq-
uids used in oxidative catalysis, including Wacker oxi-
0.2 M p-benzoquinone solution (Table 1). The rate of
ethylene oxidation remained constant when compar-
ing experiments with 0.1 M p-benzoquinone (7.22 ×
10–3 mol L–1 min–1) and with [Q]/[QH2] = 1 (7.21 ×
10–3 mol L–1 min–1).
Then, we studied the possibility of using hydrogen
peroxide as a stoichiometric oxidant in binary sol-
vents.
+
−
+
dation [47]:
(IL-1),
− (IL-2),
BMIM BF4
BMIM PF
6
and ТEA+Tf– (IL-3). According to our and other [49]
data, IL-1 can be well mixed with water to form homo-
geneous systems up to 76% Н2О. Table 2 shows the
activity of the catalytic system in a ionic liquid in the
reaction of ethylene oxidation by p-benzoquinone
with a catalyst added to the ionic liquid in 1 mL aceto-
nitrile at VΣ = 10 mL.
AN–H2O system with Н2О2. In the “standard” cat-
alytic system with [Pd] = 5 × 10–4 mol/L and
=
α
Σ
H2O
0.67 molar fraction at 30°С, neither hydrogen perox-
ide decomposition at its concentration of 0.3 mol/L
nor ethylene consumption is observed. Only upon the
addition of 0.2 M solution of p-benzoquinone (in
1 mL acetonitrile), the oxidation process begins but
has a low rate (1.8 × 10–3 mol L–1 min–1). To make the
effect of p-benzoquinone addition more pronounced,
the concentration of Pd(II) was increased by a factor
Ionic liquid–Н2О systems with Н2О2. At [Н2О2] =
1.2 mol/L and [H2SO4] = 0.2 mol/L, the process of
ethylene oxidation by hydrogen peroxide in IL-2
begins in the absence of p-benzoquinone. At the tenth
minute, it stops, and only after adding 0.1 M of the
p-benzoquinone solution, ethylene is consumed at a
rate of 1.1 × 10–3 mol L–1 min–1, which is approxi-
mately 3 times lower than without hydrogen peroxide.
An increase in [H2SO4] to 1 mol/L when hydrogen
of five to 2.5 × 10–3 mol/L and
0.93 molar fraction. Then, the rate of ethylene oxida-
tion based on hydrogen peroxide increased from 0 to
2.25 × 10–4 mol L–1 min–1. After adding p-benzoqui-
was increased to
α
H2O
none (0.18 mol/L), the value R0 drastically increased peroxide and p-benzoquinone are used together lead
to an increase in the rate of oxidation to 3.6 × 10–3 mol
L–1 min–1. Under the same conditions in IL-1,
R0(C2H4) is 5.3 × 10-3 mol L–1 min–1.
to 4.2 × 10–3 mol L–1 min–1. An increase in [Н2О2] to
1.07 mol/L at the same values of H O leads to an increase
α
2
in the reaction rate in the presence of p-benzoquinone.
The addition of p-benzoquinone (0.84 × 10–3 mol/L)
The use of hydrogen peroxide with hydroquinone
leads to an increase in the rate by ~2 times, and with additives showed that hydroquinone is rapidly oxi-
KINETICS AND CATALYSIS Vol. 60 No. 1 2019

56
EFREMOV et al.
dized by hydrogen peroxide in IL-2, because the rates
of ethylene oxidation almost coincide (with 0.1 M
hydroquinone (R0(C2H4) = 2.4 × 10–3 mol L–1 min–1
and with 0.1 M p-benzoquinone (R0(C2H4) = 3.0 ×
n(C2H4), mmol
1.2
10–3 mol L–1 min–1) (Fig. 3). An increase in [Pd]Σ in
the ionic liquid leads to a proportional increase in the
rate R0, and a five-fold increase in [H2SO4] in IL-2
containing hydrogen peroxide and hydroquinone
increases approximately five times the rate of ethylene
oxidation. Note that, in the presence of hydrogen per-
oxide in the ionic liquid, the kinetic curves do not have
any pronounced fast and slow segments that are char-
acteristic of reactions with the participation of qui-
nones in acetonitrile systems [11, 15, 26].
0.8
0.4
0
10
20
30
40
t, min
Fig. 3. Dependence of the amount of ethylene absorbed on
time in the presence of p-benzoquinone (h, 0.1 mol/L) or
hydroquinone (e, 0.1 mol/L). [Pd ] = 2.5 × 10 mol/L,
Catalyst preparation for systems containing a ionic
liquid. In the course of studying the oxidation process
in ionic liquids, a question arose of the procedure for
catalyst preparation. Earlier, catalytic systems III and
IV were prepared with acetonitrile. The reactor was
charged with 1 mL of Pd(OAc)2 solution with an acid
in acetonitrile. When working with ionic liquids, the
catalysts were prepared in 1 mL of acetonitrile, in ace-
tic acid (AA), and in a ionic liquid (a weighed sample
of palladium acetate was dissolved in a portion of ace-
tic acid, perchloric or sulfuric acid was added, and the
solution was allowed to stay for 20 min. Alternatively,
0.5 mL of water and 0.6 mL of 92% sulfuric acid were
2+
–3
[H O ] = 1.2 mol/L, [H SO ] = 1 mol/L,
= 0.46 molar
α
2
2
2
4
H2O
fraction, α
= 0.20 molar fraction, α
= 0.34 molar
AN
IL-2
fraction.
quinone oxidation (R0(О2) = (2.4–2.9) × 10–3 mol L–1
min–1). In the case of cobalt catalysts PcCosolid and
*PcCosoluble an order of magnitude lower oxidation rate
(3.9 × 10–4 mol L–1 min–1) was obtained only at a
higher concentration of these catalysts (0.07 mol/L),
although catalysis by porphyrin and salen complexes
of Со(II) is known. It is also known that Cu(OAc)2
catalyzes hydroquinone oxidation by oxygen in
СН3СООН (50°С) [42] and in acetonitrile [43]. The
process in acetonitrile at 25°С occurs very slowly (72 h
with a quinone yield of 50%), and only at a pressure of
BMIM+BF4−,
added to 2 mL
and the solution was
allowed to stay for 20 min. Experiments showed that
the best procedure is the variant with acetonitrile
(Table 3).
Acetaldehyde purging with nitrogen at 40–60°С
from IL-1 with [H2SO4] = 0.3 mol/L, [QH2] =
0.3 mol/L, and [Н2О2] = 4.8 mol/L for 2 h led us to
obtain 70% acetaldehyde based on consumed eth-
ylene and a small amount of CH3COOH with a selec-
tivity of ~8%. Interestingly, in IL-3 without Pd(II) at
= 6–8 atm, the process is fast and selective. Even
PO
2
under these conditions, CuSO4 in acetonitrile does
not catalyze hydroquinone oxidation [43].
Catalysis by copper acetate was tested at
=
α
H2O
= 0.56 molar fraction and [H2SO4] = 1 mol/L,
α
H2O
0.67 molar fraction with perchloric (0.3 mol/L) and
acetic (0.35 mol/L) acids. In both cases, oxygen con-
sumption was not observed for 1 h. Meantime, it is
known that Cu2(OAc)4 ⋅ 2H2О rapidly oxidizes hydro-
quinone in ethanol with the complex formation of a
ethylene is consumed at a low rate (0.3 mmol for
140 min) to form a small amount of ethanol.
Choice of Conditions for Hydroquinone Oxidation
by Oxygen in the AN–H2O System
Solid PcFesolid, PcCosolid and soluble *PcFesoluble
,
Table 3. Comparison of the methods for the preparation of
catalytic systems in IL-1 in ethylene oxidation by hydrogen
peroxide
*PcCosoluble compounds and Cu(OAc) at
= 0.87 atm
PO
2
(30°С) in solutions with H O = 0.67 molar fr2action at the
α
concentrations of reagents 2Pd(OAc)2 (5 × 10–4 mol/L),
HClO4 (0.1 mol/L), and hydroquinone (0.2 mol/L)
were used as catalysts for hydroquinone oxidation.
Hydroquinone is oxidized by oxygen at a noticeable rate
(R0(О2) = (5.0–5.76) × 10–3 mol L–1 min–1) only at high
concentrations of PcFesolid (0.035–0.07 mol/L). When
studying the activity of *PcFesoluble, it was found that
the presence of Pd(OAc)2 in a concentration of 5 ×
Compo-
nent
Catalyst
preparation
procedure
R0(C2H4) × 103,
mol L–1 min–1
αIL-1
α
H2O
molar fraction
Acetonitrile 0.19 (AN) 0.43 0.38
4.42
2.47
1.24
Acetic Acid
Ionic liquid
0.17 (AA) 0.46 0.37
0.66 0.34
–
–3
[Н О ] = 1.2 mol/L, [QH ] = 0.1 mol/L, [Pd] = 2.5 × 10 mol/L,
2
2
2
Σ
10–4 mol/L has almost no effect on the rate of hydro-
[H SO ] = 1 mol/L.
2
4
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ETHYLENE AND CYCLOHEXENE OXIDATION
57
cess. It turned out that only an increase in the Pd(II)
concentration by an order of magnitude and a
decrease in the amount of PcFesolid lead to the oxida-
tion of ethylene with initial rates R0(C2H4) shown in
Fig. 4. At a zero concentration of PcFesolid, the rate of
ethylene oxidation by p-benzoquinone at this composi-
tion of the catalytic system is ~72 × 10–3 mol L–1 min–1.
It also turned out that the rate of oxidation R0(О2) of
formed hydroquinone by oxygen (in a concentration
of 0.1 mol/L) in the presence of PcFesolid decreases
with an increase in the ratio [Fe]/[Pd] > 3. Of possible
explanations for the PcFesolid inhibition of ethylene
oxidation by p-benzoquinone, the most likely is the
adsorption of cationic Pd(II) complexes on the surface
of iron phthalocyanine, which prevents the activation
and oxidation of ethylene by palladium. The reasons
for the inhibition of О2 activation on the active centers
of the PcFesolid surface with an increase in its amount
are not yet clear. Interestingly, the inhibition of eth-
ylene oxidation by the possible interaction of Pd(II)
with iron phthalocyanine also occurs in the case of
soluble *PcFesoluble (Fig. 5a), but in the solution of this
complex, the process of hydroquinone oxidation
occurs predictably faster with increasing concentra-
tion of *PcFesoluble (Fig. 5b).
R0 × 103, mol L–1 min–1
40
30
20
10
0
0.01
0.02
0.03
0.04
[PcFesolid], mol/L
Fig. 4. Dependence of the initial rate of ethylene oxidation
reaction on the concentration of solid iron phthalocya-
–3
nine. [Pd] = 5 × 10
mol/L, [Q] = 0.1 mol/L,
= 0.67 molar fraction, α
Σ
[HClO ] = 0.2 mol/L,
=
AN
α
H2O
4
0.33 molar fraction, V = 10 mL.
Σ
CuI(OAc) with p-benzoquinone [ I (syn-μ -η2η2-
Q)(OAc)2], in which the Cu–Cu distance is very short
(2.73 Å) [57]. In the experiments with perchloric acid
in the presence of Pd(II) cationic complexes, Cu(II)
will also exist in Cu(ClO4)2 and CuSO4 forms, which
are cationic.
Cu2
2
In the system with *PcFesoluble at [Pd]Σ = 5 × 10–3 mol/L,
[Q] = 0.1 mol/L and [H2SO4] = 0.2 mol/L, it was
found that, with an increase in [Fe]/[Pd] from 3 to 7,
the amount of absorbed ethylene is higher than stoi-
chiometric based on p-benzoquinone by a factor of
~1.3. Using GLC analysis, we found that, in addition
to acetaldehyde, a mixture of three isomeric linear
butenes are formed.
The absence of the catalytic effect in the reaction of
hydroquinone oxidation in acetonitrile by oxygen in
this case is probably associated with very high stability
+
constants of acetonitrile complexes of
Cu(I)−Cu(AN)2
+
and
in organic solvents [58] reaching 104–106.
Cu(AN)4
This is reflected in the value of the oxidation potential
of the Cu2+/Cu+ pair in acetonitrile, which is 1.21 V
relative to the standard hydrogen electrode [59] (com-
pared to 0.15 V in water). For the above reasons, Cu(I)
acetonitrile complexes are poorly oxidized by oxygen,
which leads to the absence of catalysis in the reaction
of hydroquinone oxidation.
A similar inhibition by РсFesolid of olefin oxidation
was noted also in the oxidation of cyclohexene by
p-benzoquinone in the presence of PcFesolid purified
by washing with water on filter (Table 4) at a low con-
centration of Pd(II) when hydroquinone almost does
not form at a ratio [Fe]/[Pd] of 70 (run 5), but added
hydroquinone (run 4) is oxidized by oxygen.
Only an increase in the Pd(II) concentration by an
order of magnitude, as in the case of ethylene, led to
the oxidation of cyclohexene to cyclohexanone, the
appearance of hydroquinone, and its oxidation by
oxygen (Table 5). The average productivity with
respect to cyclohexanone during the time of a run in
runs 6 and 8 was 0.23–0.26 mol L–1 min–1.
A kinetic study of hydroquinone oxidation in the
AN–H2O system by oxygen showed that the reaction
is described by the first order in hydroquinone both in
the presence of solid PcFesolid and soluble *PcFesoluble
iron phthalocyanine (Table 6).
When carrying out the process of ethylene oxida-
tion by p-benzoquinone (0.1 mol/L) under standard
conditions with [Pd]Σ = 5 × 10–4 mol/L, we found that
the presence of solid iron phthalocyanine PcFesolid
(0.035 mol/L) completely inhibits the oxidation pro-
Table 4. Effect of [PcFesolid] on the process of cyclohexene
oxidation by oxygen
R0(О2) × 103,
mol L–1 min–1
[C6H10] [QH2]
[PcFesolid
]
[Q]
Run
mol/L
4
5
0.16
0.2
–
–
0.2
0.035
(purified)
3.73
–
A decrease in the rate constant in runs 9 and 10 has
no explanation either. The oxidation of hydroquinone
by oxygen in the presence of PcFesolid (0.035 mol/L)
–4
[Pd] = 5 × 10 mol/L, [HClO ] = 0.1 mol/L,
= 0.32
α
H2O
Σ
4
also occurs in IL-1 (
= 0.57 molar fraction, αAN =
α
molar fraction.
H2O
KINETICS AND CATALYSIS Vol. 60 No. 1 2019

58
EFREMOV et al.
(а)
(b)
R0 × 103, mol L–1 min–1
R0 × 103, mol L–1 min–1
40
2.0
1.6
1.2
0.8
0.4
30
20
10
0
0.01
0.02
0.03
0.04
0
0.01
0.02
0.03
0.04
[*PcFesoluble], mol/L
[*PcFesoluble], mol/L
Fig. 5. Dependence of the initial rate of oxidation of (a) ethylene and (b) hydroquinone on the concentration of soluble iron
–3
phthalocyanine. [Pd] = 5 × 10 mol/L, [Q] = 0.1 mol/L, [HClO ] = 0.2 mol/L,
= 0.67 molar fraction, α = 0.33 molar
α
Σ
4
H2O
AN
fraction, V = 10 mL.
Σ
0.22 molar fraction, αIL-1 = 0.21 molar fraction) at the
rate R0(О2) = 2.3 × 10–3 mol L–1 min–1 and k = 27.7 ×
10–3 s–1.
The process selectivity to cyclohexanone in two
runs is 93%. The transition to the two-phase domain
(II) to solutions with
= 0.26 molar fraction,
α
H2O
α
AN = 0.64 molar fraction, αC6H10 = 0.1 molar fraction
and
= 0.8 molar fraction, αAN = 0.08 molar frac-
α
H2O
Cyclohexene Oxidation in Binary Solvents
tion, αC6H10 = 0.12 molar fraction (shaken reactor) is
Using the results of the study of ethylene and
hydroquinone oxidation in the AN–H2O and ionic
liquid–H2O systems, we chose the conditions for the
reaction of cyclohexene oxidation.
accompanied by a drastic decrease in the selectivity to
cyclohexanone to 45% in the first domain (
0.26, point 1) and 10% in the second domain (
=
α
H2O
=
α
H2O
0.8, point 2). In these systems, high-boiling products
of probable cyclohexene oligomerization in addition
to cyclohexene and cyclohexanone appeared in the
chromatograms [2]. Thus, transition to heterogeneous
systems with high concentrations of cyclohexene leads
to its side transformations in solutions containing an
acid and Pd2+.
AN–H2O system with p-benzoquinone. The study
of phase equilibria in the ternary AN–H2O–С6Н10
system [20, 25] showed (Fig. 6) the presence of
domains of three-phase (I) and two-phase (II) exfoli-
ation and a homogeneous domain (III). This made it
possible to choose the compositions of solutions in the
homogeneous and two-phase domains for carrying
out the reaction of cyclohexene oxidation by p-benzo-
It was shown above (Table 5) that cyclohexene can
be oxidized by oxygen in the AN–H2O system in the
presence of solid iron phthalocyaninate and p-benzo-
quinone:
α
H2O
quinone. In the homogeneous domain at
=
0.3 molar fraction and [C6H10]0 = 0.15–0.16 mol/L in
the Pd(OAc)2 (4 × 10–3 mol/L)–HClO4 (0.2 mol/L)–
Q(0.2 mol/L) system at 30°С, we obtained the follow-
ing results (Table 7).
С6Н10 + ½ О2 = С6Н10О.
Table 5. Cyclohexene oxidation by oxygen in the presence of PcFesolid
[C6H10] [PcFe solid
]
Oxidized
QH2
[C6H10O]
(after a run),
mol/L
R0(О2) × 103,
mol L–1 min–1
C6H10O
yield, %
Absorbed О2
Time
of a run, min
Run
mol/L
mmol
6
7
8
0.16
0.16
0.16
0.01
0.005
0.0025
0.85
1.26
0.66
40
90
40
0.13
0.28
0.12
0.26
0.57
0.23
0.091
0.085
0.104
57
53
65
–3
[Pd] = 5 × 10 mol/L, [Q] = 0.1 mol/L, [HClO ] = 0.2 mol/L,
= 0.32 molar fraction, α = 0.68 molar fraction, V = 10 mL.
AN Σ
α
Σ
4
H2O
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ETHYLENE AND CYCLOHEXENE OXIDATION
59
Table 6. Rate constant of hydroquinone oxidation by oxy-
ponents by extractive distillation. To simplify the tech-
nology of separation of cyclohexanone, it is advisable
to expand the set of organic high-boiling solvents for
aqueous–organic systems.
gen in the presence of PcFe catalysts
[Pd]Σ
PcFe
k × 103, s–1
Run
mol/L
Ionic liquid–Н2О system in cyclohexene oxidation.
Unlike ethylene oxidation, cyclohexene oxidation in
systems with a ionic liquid is not as efficient and selec-
tive. For example, in the case of IL-1, cyclohexene is
converted in the presence of sulfuric acid without pal-
ladium acetate to form high boiling oligomers. At the
same time, cyclohexanone, introduced into a solution
containing palladium cationic complexes, does not
transform within 1 h. In the system with IL-3, cyclo-
hexene is almost not oxidized by p-benzoquinone for
30 min: in the extract (diethyl ether), ~96% of the ini-
tial cyclohexene is found. The oxidation of cyclohex-
ene by oxygen in IL-1 in the presence of hydroqui-
none and PcFesolid for 2 h led to the complete conver-
sion of cyclohexene, but the yields of cyclohexanone
and cyclohexanol, which is the product of cyclohex-
ene hydration were low: 5.5%. It was found by chro-
matography/mass spectrometry that the extract of
diethyl ether contains 2-cyclohexen-1-ol, 2-cyclo-
hexen-1-one, benzene, unsaturated products of cyclo-
hexene oligomerization (dodecane and others), and
the products of oligomer oxidation (hexadecenoic,
octadecenoic and other acids). Apparently, the stron-
ger acidic properties of IL-1 with 0.2 M H2SO4 lead to
the catalysis of nonoxidative reactions: cyclohexene
oligomerization and its hydration. The addition of
PcFesolid is likely to favor the side conversions of cyclo-
hexene. As noted above, the formation of butenes from
ethylene was also detected in the acetonitrile system
when carrying out the reaction in the presence of
9
10
11
12
13
0.005 (solid)
0.015 (solid)
0.005 (soluble)
0.015 (soluble)
0.035 (soluble)
0.005
0.005
0.005
0.005
0.005
9.8
4.8
8.1
12.3
15.3
Table 7. Changes in the concentrations of cyclohexene and
cyclohexanone in the course of experiments
[C6H10]
[C6H10O]
mol/L
Run
14
t, min
0
1
30
60
0
1
45
–
0.153
0.091
0
0
0.043
0.124
0.137
0
0.077
0.154
–
0
15
0.154
0.100
0
–
As a result, for liquid–liquid equilibria in the AN–
H2O–C6H10–C6H10O system, it was found [60] that
the homogeneous system can be separated into com-
PcFesolid
.
The transition to two-phase systems in the case of
IL-1 and IL-2 under conditions of increasing concen-
trations of cyclohexene in the catalytic system leads to
a decrease in the cyclohexanone selectivity to 10–30%
in cyclohexene oxidation by p-benzoquinone.
It follows from the results obtained that the studied
ionic liquid are not suitable media for cyclohexene
oxidation. It is possible that ionic liquids with less pro-
nounced acidic properties [49] will be more suitable as
components of binary solvents for this reaction cata-
lyzed by cationic palladium complexes.
AN
0.9
0.1
III
0.8
Az
0.2
0.3
0.4
0.5
Az
0.7
0.6
0.5
0.4
0.3
0.2
0.1
(1)
II
I
0.6
0.7
0.8
0.9
CH
Az
CONCLUSIONS
(2)
II
A study of ethylene oxidation by p-benzoquinone
in the AN–H2O system in the presence of cationic
palladium complexes showed that the optimal condi-
Az
W
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
tions at 30°C are
0.2 mol/L, [Q] = 0.1–0.2 mol/L at
The selectivity to acetaldehyde is at least 95%. It is shown
that the rate of ethylene oxidation by hydrogen perox-
ide in this system is very low and increases about
= 0.3 molar fraction, [H2SO4] =
α
H2O
Fig. 6. A diagram of phase equilibrium of the ternary sys-
tem water (W)–acetonitrile (АN)–cyclohexene (C H ),
= 0.8–0.9 atm.
P
6
10
C2H4
containing the domains of three-phase (I) and two-phase
(II) (shaded) exfoliation and homogeneous domain (III),
and the arrangement of the chosen points of the composi-
tion (1) and (2) [25]. Az is azeotrope.
KINETICS AND CATALYSIS Vol. 60 No. 1 2019

60
EFREMOV et al.
10 times only when p-benzoquinone is added to the [PcFe]/[Pd] > 3–7 lead to the retardation if ethylene
solution.
It is reasonable to carry out cyclohexene oxidation
by p-benzoquinone under homogeneous conditions at
= 0.3 molar fraction (and at 0.6–0.7 molar frac-
tion), [H2SO4] = 0.2 mol/L, [Q] = 0.1 mol/L, and
[C6H10] < 0.2 mol/L. The selectivity to cyclohexanone
reaches 93%.
and cyclohexene oxidation.
Ionic liquids used by us prove to be inappropriate
media for cyclohexene oxidation in the presence of
sulfuric acid. Thus, in IL-1, cyclohexene is converted
into byproducts of nonoxidative and oxidative types
even at [Pd]Σ = 0.01 mol/L, and in IL-3, the oxidation
process almost does not occur at 25°С.
α
H2O
Comparison of the activity of catalytic systems in
cyclohexene oxidation in binary solvents (with cat-
ionic palladium complexes) with aqueous or aque-
ous–organic catalytic systems based on Pd(II) chlo-
ride complexes with quinone and CuCl2 as oxidants is
very complicated. Comparison of TOF values for dif-
ferent catalytic systems is correct only at the same sub-
strate concentrations and, of course, at the same
orders in a substrate and a catalyst (using [M]Σ; for a
review, see [61]). It is especially difficult to judge the
orders of magnitude of activity values when determin-
ing the TOF from the initial reaction rates in the case
of different kinetic models [11] with different struc-
tures of the apparent rate constants. According to [7],
the transition to cationic Pd(II) complexes in acidic
solutions in a binary AN–H2O solvent accelerates the
oxidation process of cyclohexene by ~50 times com-
pared with all known systems. Unfortunately, we do
not know from that work how this value was obtained.
If we assume the first order in cyclohexene, data pre-
sented in [7] can be used to estimate the apparent rate
constant (k ≈ 0.08 min–1) and calculate the TOF for
[C6H10] = 0.16 mol/L and [Pd]Σ = 5 × 10–3 mol/L. We
ACKNOWLEDGMENTS
This work was supported by the Russian Science
Foundation (project 16-19-10632, I.V. Oshanina and
G.E. Efremov).
The authors thank Professors O.L. Kaliya and
E.A. Luk’yanets for providing us with the samples of
phthalocyanine complexes.
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Translated by Andrey Zeigarnik
KINETICS AND CATALYSIS Vol. 60 No. 1 2019