Glyoxal-promoted homogeneous catalytic oxygenation of cyclohexane with hydrogen peroxide in the presence of V and Co compounds

Article abstract of DOI:10.1007/s11172-005-0253-0

The efficiency of cyclohexane oxidation with hydrogen peroxide catalyzed by vanadyl acetylacetonate at 40°C and atmospheric pressure is enhanced by glyoxal additive. The process selectively produces a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone with a high rate (up to 4400 catalyst turnover number). Cobalt(II) acetylacetonate is much less active but more selective with respect to cyclohexyl hydroperoxide.

Full text of DOI:10.1007/s11172-005-0253-0

3
12
Russian Chemical Bulletin, International Edition, Vol. 54, No. 2, pp. 312—315, February, 2005
Glyoxalꢀpromoted homogeneous catalytic oxygenation of cyclohexane
with hydrogen peroxide in the presence of V and Co compounds
A. P. Pocutsa,aꢀ J. Le Bras, and J. Muzartb
b
aL. V. Pisarzhevsky Institute of Physical Chemistry, the National Academy of Sciences of Ukraine,
Division of Physical Chemistry and Technology of Mineral Fuels,
3
A ul. Nauchnaya, 79053 L´vov, Ukraine.
Fax: (38 0322) 63 5174. Eꢀmail: oleksandr@chem.umn.edu, pocutsa@org.lviv.net
b
UMRꢀCNRS 6519, University of Reims ChampagneꢀArdenne,
B.P. 1039, 51687 Reims Cedex 2, France.*
Fax: (33 0326) 005 3166. Eꢀmail: Jacques.muzart@univꢀreims.fr
The efficiency of cyclohexane oxidation with hydrogen peroxide catalyzed by vanadyl
acetylacetonate at 40 °C and atmospheric pressure is enhanced by glyoxal additive. The process
selectively produces a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone
with a high rate (up to 4400 catalyst turnover number). Cobalt(II) acetylacetonate is much less
active but more selective with respect to cyclohexyl hydroperoxide.
Key words: catalysis, oxidation, cyclohexane, vanadyl acetylacetonate, cobalt(II) acetylꢀ
acetonate, acetic acid, hydrogen peroxide, glyoxal.
The problem of selective and efficient oxidative
heterogeneous10 and homogeneous11 vanadium comꢀ
pounds under mild conditions.
In this work, we report on homogeneous cyclohexane
oxidation in the presence of soluble vanadyl acetylꢀ
functionalization of paraffins with the lowꢀcost and enviꢀ
ronmentally safe oxidative agents, O and H O , is still
2
—3
2
2
drawing attention of researchers.1
The products of
cyclohexane (CyH) oxidation, cyclohexanone (CyO),
cyclohexanol (CyOH), and cyclohexyl hydroperoxide
acetonate VO(acac) and acetic acid.
2
Glyoxal was used as a promoter of CyH oxidation.
This nonꢀvolatile and untoxic aldehyde was chosen to
verify a hypothesis on its possible promoting effect in the
reaction under study by analogy with monoꢀaldehydes.
Thus, one could perform CyH oxidation at 40 °C and
(
CyOOH), are the starting materials for the production of
adipic acid and caprolactam that are the monomers for
4
12
synthetic fibers. Therefore, cyclohexane oxidation is
4
one of the world's largest scale chemical processes. Curꢀ
rently, the industrial oxidation is carried out with air at
atmospheric pressure without activators (pyrazineꢀ2ꢀcarbꢀ
1
1
1
60—180 °C and 0.8—1.5 MPa in the presence of a hoꢀ
oxylic acid) with high selectivity (at least 95% based on
the converted CyH). The reaction temperature was choꢀ
sen in such a way as to prevent the CyH escape at elevated
temperatures and stratification of the reaction mixture
under reduced temperatures.
mogeneous cobalt catalyst. The process operates with
a conversion of 4—6%, a total selectivity to CyO,
CyOH, and CyOOH of 75—80%, and a turnover number
5
—7
of 400—450.
Most of the currently proposed methods for cyclohexꢀ
ane oxidation are not competitive with the industrial
method yet. In some cases, this is due to the need to
operate with very diluted solutions of an alkane under
oxidation in order to achieve the high selectivity and conꢀ
Experimental
Cyclohexane, acetic acid (both Fluka), VO(acac) , and
Co(acac) (both Acros) were used without additional purificaꢀ
2
2
8
version. In other cases, for example, when heterogeꢀ
tion. Aqueous solutions of hydrogen peroxide (35%, Aldrich)
and glyoxal (30%, Fluka) were concentrated by removing of
water on a rotor evaporator to prepare 70% and 45% solutions,
respectively.
Cyclohexane oxidation with hydrogen peroxide (general proꢀ
cedure). To a stirred and thermally controlled (40 °C) solution
containing CyH (28 mmol), a catalyst (8 µmol), and glyoxal
(5 mmol) in AcOH (14 mL) was rapidly added a 70% aqueous
9
neous catalysts are used, the technological scheme beꢀ
comes complicated and therefore extremely expensive.
Recently, an efficient method was developed for alꢀ
kane oxidation with hydrogen peroxide catalyzed by both
*
Unité Mixte de Recherche «Réactions Sélectives et Appliꢀ
cations», CNRS Université de Reims ChampagneꢀArdenne, B.P.
039, 51687 Reims Cedex 2, France.
1
solution of H O2 (14 mmol). Then the reaction mixture was
2
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 307—310, February, 2005.
066ꢀ5285/05/5402ꢀ0312 © 2005 Springer Science+Business Media, Inc.
1

VO(acac) ꢀcatalyzed cyclohexane oxidation with H O Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
313
2
2
2
sampled (1 mL) in specified time intervals and analyzed by GLC
and permanganatometry. The total volume of the reaction mixꢀ
ture was 18 mL in all runs.
Concentrations of the unreacted CyH and the oxidation
products (CyO, CyOH, and CyOOH) were measured by GLC
formation of a mixture of CyO, CyOH, and CyOOH
14
(
1 : 2 : 1 ratio) contradicts the reported data according
to which CyOOH was not formed under similar conꢀ
ditions.
Bubbling air or oxygen through an oxidized mixture
has a slight effect on the yield of the target products
(
chromatograph Hewlett—Packardꢀ5890, series II, flameꢀionꢀ
ization detector, capillary column 30 m × 0.25 mm, immobile
(
Table 1, entries 1 and 2). The CyH conversion somewhat
phase HPꢀInnowax). To determine CyOOH in the presence of
1
3
decreases when the reaction is carried out in an argon
atmosphere (see Table 1, entry 3). When a stoichiometric
amount of H O and a smaller weighed portion of the
CyO and CyOH, an earlier described procedure was used. In
addition to CyO, CyOH, and CyOOH, traces of adipic acid
were identified in the oxidation products. The correctness of
GLC analysis was verified by a chromatomassꢀspectrometry
2
2
–4
catalyst (for example, 1.4•10 eq) are used, the CyH
conversion increases from 3.5 to 5.8%, the relative yield
of CyOOH increases, and the CyO yield markedly deꢀ
creases (see Table 1, entry 4). A similar ratio of the oxidaꢀ
tion products at a conversion of 5.9% is achieved in 3 h in
(
Finnigan Trace MC 2000). Hydrogen peroxide consumption
was determined by titration of a part of each sample (0.5 mL)
with a 0.01 N solution of KMnO4.
Results and Discussion
–5
the presence of only 1.8•10 eq VO(acac) (see Table 1,
2
entry 5). The preliminary treatment of the catalyst with
hydrogen peroxide has no effect on the results of experiꢀ
ments.
In the presence of glyoxal (0.18 eq), the parameters of
process are substantially improved. The turnover number
In preliminary runs, the homogeneousꢀcatalytic oxiꢀ
dation of CyH was performed in the presence of VO(acac)
2
4
(
2.9•10– eq) and a 70% solution of H O (0.5 eq) in
2
2
AcOH for 30 min at 40 °C and atmospheric pressure. The
Table 1. Homogeneousꢀcatalytic oxidation of CyH with hydrogen peroxide in acetic acida
Entry
Conditions
Conversion Consumption Selectivity (%)
[CyO + CyOH + CyOOH]
/mmol L–1
Catalyst
turnover
number
CyH (%)
H O (%)
2 2
Atmosphere H O /mmol
CyO CyOH CyOOH
2
2
VO(acac) (8 µmol)
2
1
2
3
4
5
Air
O2
Argon
Air
Air
14
3.5
3.6
3.1
5.8
5.9
93
97
79
91
60
27
28
24
13
13
50
52
45
45
41
23
20
31
42
46
54
56
47
101
85
120
125
105
455
3040
b
14
14
28
28
c
d
e
VO(acac) (8 µmol) + glyoxal (5 mmol)
2
6
7
8
Air
O2
Air
Air
Argon
Argon
Argon
Air
14
14
28
28
28
28
28
28
4.5
4.9
7.3
7.2
7.1
7.2
6.9
3.3
97
98
92
71
73
72
92
92
35
34
33
16
16
22
34
20
52
39
45
35
38
40
49
41
13
27
22
49
46
38
17
39
71
76
160
170
510
4400
4000
2000
485
b
f
113
122
111
111
108
51
g
9
0 g
c
c
c
1
1
1
1
h
1
2
3
i
f,i
230
Co(acac) (8 µmol)
2
1
1
4
5
Air
O2
14
14
0.5
0.6
19
18
0
0
1
1
99
99
8
9
17
18
b
Co(acac) (8 µmol) + glyoxal (5 mmol)
2
1
1
6
7
Air
O2
14
14
1.0
1.1
43
46
0
0.3
2
1.7
98
98
16
17
35
36
b
a
b
c
d
e
f
Reaction conditions: CyH (28 mmol, 1.6 mol L–1), AcOH (14 mL), atmospheric pressure, 40 °C, 30 min.
–1
Oxygen bubbling rate 20 mL min
Argon bubbling rate 30 mL min–1.
.
–4
1
.4•10 eq. VO(acac)2.
–5
1
.8•10 eq VO(acac)2.
4
0
1
µmol of catalyst.
g
h
i
.5 µmol catalyst for reaction time of 180 min.
.0 µmol of catalyst.
Isobutyral (20 mmol) was used instead of glyoxal.

314
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
Pocutsa et al.
Scheme 1
M = V
3
–1
increases by more than 1.4 times (see Table 1, entries 5
and 9) and the CyH conversion increases by 1.2 times.
A change of glyoxal for isobutyric aldehyde (see
Table 1, entry 13) in the catalytic system under study does
not increase the yield of the target products and alkane
conversion. The role of glyoxal and monoꢀaldehyde in
this oxidative system is unclear. Meanwhile, one can sugꢀ
gest that the mechanisms of oxidation of these reactants
are different and the reactive intermediates are formed in
the presence of glyoxal15 (Scheme 1). The formation of
freeꢀradical species by the reaction between glyoxal and
vanadium(v) has been reported.16
[P]•10 /mol L
60
50
1
2
4
3
2
1
0
3
0
0
0
4
5
Taking into account that cobalt(II) naphtenate is the
main catalyst for the industrial cyclohexane oxidation,5
—7
0
1
0
20
30
40
50
t/min
we studied the effect of Co(acac) on the features of parꢀ
2
affin oxidation in the system under study (see Table 1,
entries 14—17). This catalyst proved to be much less acꢀ
Fig. 1. Kinetics of accumulation of the products of cyclohexane
oxidation (P) in air (1—4) or argon (5) atmosphere in the presꢀ
ence of various catalytic systems: VO(acac)2 + glyoxal (1),
VO(acac) (2), Co(acac) + glyoxal (3), Co(acac) (4, 5) (reacꢀ
tive in CyH oxidation compared to VO(acac) . The coꢀ
2
2
2
2
balt saltꢀcatalyzed CyH oxidation both in the absence and
in the presence of glyoxal afforded CyOOH as the only
product. Noteworthy, in the absence of H O this cataꢀ
tion conditions see Table 1).
2
2
II
III
lytic system has no catalytic effect on CyH oxidation
irrespectively of the nature of the catalyst used.
It was found on the basis of the kinetic data (Fig. 1)
that glyoxal accelerates cyclohexane oxidation and enꢀ
hances the yield of the target products. In addition, the
Co /Co pair is 0.06 V higher than that for H O , and
2 2
due to the difference the generation of the hydroxyl radiꢀ
cals in the catalytic system under study is strongly reꢀ
tarded.
In experiments with more diluted (35%) hydrogen perꢀ
oxide, the reaction rate and the yield of the target prodꢀ
ucts markedly decrease (by 1.5—1.8 times). This gives
evidence of the essential contribution of the free radicals
to the total oxidation rate. In addition, an increase in the
water content in the initial reactive mixture results in the
layer stratification.
process catalyzed by Co(acac) , unlike that catalyzed by
2
the soluble vanadium salt, occurs with a prolonged inducꢀ
tion period, which can be reduced by glyoxal additives
from 15—20 to 5 min.
Since oxygen bubbling does not significantly affect the
yield of the products and the H O decomposition rate,
2
2
one can conclude that the process is controlled mainly by
H O decomposition to hydroxyl radicals induced by
After addition of H O green color of the reactive
2
2
mixture containing VO(acac) in AcOH turned to yellow,
2
2
2
IV
V
metal cations. The redox potential of the pair V /V
being accompanied by fast decay of hydrogen peroxide.
This change is likely due to the mutual transformations of
1
7
(
E° = 1.00 V) is lower than that of H O (E° = 1.77 V).
2 2
IV
V
IV
V
As a result, H O rapidly oxidizes V to V at pH < 7 with
the reduced (V ) and oxidized (V ) catalyst species.
2
2
II
simultaneous formation of highly active hydroxyl radiꢀ
cals, which initiate alkane oxidation. The E° value for the
A change in the poorꢀpink color (Co ) of the initial reacꢀ
tion solution to green color (Co ) after addition of
III

VO(acac) ꢀcatalyzed cyclohexane oxidation with H O Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
315
2
2
2
H O was not observed during oxidation catalyzed by
Co(acac)2.
9. J. M. Thomas, R. Raja, G. Sankar, B. F. Johnson, and
D. W. Lewis, Chem. Eur. J., 2001, 7, 2972.
0. U. R. Pillai and E. SahleꢀDemessie, Chem. Commun., 2002,
2
2
1
1
Hence, VO(acac) in AcOH in the presence of glyoxal
2
2
2
142; U. R. Pillai and E. SahleꢀDemessie, New J. Chem.,
003, 27, 525.
under mild conditions efficiently catalyzes cyclohexane
oxidation with hydrogen peroxide to cyclohexanone,
cyclohexanol, and cyclohexyl hydroperoxide. Addition
of dioxygen to the reaction mixture and the use of the
cobalt catalyst have virtually no effect on the process unꢀ
der study.
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Shul´pin, Appl. Catal. A: Gen., 2001, 217, 111; G. SussꢀFink,
L. Gonzales, and G. B. Shul´pin, Inorg. Chim. Acta, 2004,
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Received November 25, 2003;
in revised form April 13, 2004