Effect of Transition Metal Compounds on the Cyclohexene Oxidation Catalyzed by N-Hydroxyphthalimide

Article abstract of DOI:10.1134/S0023158418060083

Abstract: N-Hydroxyphthalimide (NHPI) is an efficient organic catalyst in the oxidation reactions of organic compounds occurring via a radical mechanism, often used together with redox-active ions or transition metal complexes. In this work the catalytic action of NHPI is studied together with Cu(II), Fe(III), and Mo(VI) compounds in the reaction of aerobic oxidation of cyclohexene in an acetonitrile solution at 60°C. It was found that iron(III) benzoate accelerates the reaction by rapidly generating the active form of the phthalimide-N-oxyl radical (PINO) catalyst, but does not cause decomposition of the hydroperoxide. The oxidation product is 2-cyclohexenyl hydroperoxide formed with a selectivity of 85% at a cyclohexene conversion of 50%. Copper(II) acetate initiates oxidation and is capable of catalyzing the radical decomposition of the hydroperoxide and secondary oxidation of allyl oxygenates. When reaching a cyclohexene conversion close to 80%, the overall selectivity to the main products, 2-cyclohexenyl hydroperoxide and 2-cyclohexen-1-on, was 70%. The addition of iron(III) and molybdenum(VI) compounds led to the intensive generation of hydroperoxide and its activation as an electrophilic reactant capable of cyclohexene epoxidation. As a result of the use of the multifunctional three-component NHPI–Mo(VI)–Fe(III) catalyst, cyclohexene oxidation by molecular oxygen occurred with the formation of epoxycyclohexane. The selectivity to the products of cyclohexene epoxidation was close to 50%, which is a value expected from theory.

Full text of DOI:10.1134/S0023158418060083

ISSN 0023-1584, Kinetics and Catalysis, 2018, Vol. 59, No. 6, pp. 735–743. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © L.I. Kuznetsova, N.I. Kuznetsova, O.A. Yakovina, V.N. Zudin, B.S. Bal’zhinimaev, 2018, published in Kinetika i Kataliz, 2018, Vol. 59, No. 6, pp. 694–703.
Effect of Transition Metal Compounds on the Cyclohexene
Oxidation Catalyzed by N-Hydroxyphthalimide
a,
a
a
a
a
L. I. Kuznetsova *, N. I. Kuznetsova , O. A. Yakovina , V. N. Zudin , and B. S. Bal’zhinimaev
a
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
*
e-mail: livkuzn@catalysis.ru
Received March 23, 2018
Abstract—N-Hydroxyphthalimide (NHPI) is an efficient organic catalyst in the oxidation reactions of
organic compounds occurring via a radical mechanism, often used together with redox-active ions or transi-
tion metal complexes. In this work the catalytic action of NHPI is studied together with Cu(II), Fe(III), and
Mo(VI) compounds in the reaction of aerobic oxidation of cyclohexene in an acetonitrile solution at 60°C. It
was found that iron(III) benzoate accelerates the reaction by rapidly generating the active form of the
phthalimide-N-oxyl radical (PINO) catalyst, but does not cause decomposition of the hydroperoxide. The
oxidation product is 2-cyclohexenyl hydroperoxide formed with a selectivity of 85% at a cyclohexene conver-
sion of 50%. Copper(II) acetate initiates oxidation and is capable of catalyzing the radical decomposition of
the hydroperoxide and secondary oxidation of allyl oxygenates. When reaching a cyclohexene conversion
close to 80%, the overall selectivity to the main products, 2-cyclohexenyl hydroperoxide and 2-cyclohexen-
1
-on, was 70%. The addition of iron(III) and molybdenum(VI) compounds led to the intensive generation of
hydroperoxide and its activation as an electrophilic reactant capable of cyclohexene epoxidation. As a result
of the use of the multifunctional three-component NHPI–Mo(VI)–Fe(III) catalyst, cyclohexene oxidation
by molecular oxygen occurred with the formation of epoxycyclohexane. The selectivity to the products of
cyclohexene epoxidation was close to 50%, which is a value expected from theory.
Keywords: cyclohexene, autoxidation, N-hydroxyphthalimide, transition metal compounds
DOI: 10.1134/S0023158418060083
INTRODUCTION
and cause hydroperoxide decomposition to form
cyclohexenol and cyclohexenone. Currently, it is
known that aerobic liquid-phase cyclohexene oxida-
tion to 2-cyclohexen-1-ol and 2-cyclohexen-1-on
mostly occurs with the participation of soluble com-
plexes or solid catalysts containing redox-active ions
of Cr, Cu, Co, Fe, and Au [8–17]. Nonmetallic solid
catalysts, such as nitrogen-doped carbon nanotubes,
has also been described [18, 19]. In aerobic cyclohex-
ene oxidation, the formation of an epoxide occurs only in
small amounts, whereas common oxidants used for the
synthesis of epoxides are organic peroxides. Reactions of
cyclohexene epoxidation are known in which electro-
philic oxygen species are generated from tert-butyl
hydroperoxide or cyclohexyl hydroperoxide under the
action of homogeneous or supported Mo(VI), V(V),
Ti(IV), Cu(II), and Ni(II) catalysts [20–24].
Of many oxidants used in liquid-phase oxidation,
molecular oxygen, hydrogen peroxide, and hydroper-
oxides are preferred. They have the properties of envi-
ronmentally friendly reagents and are capable of con-
verting hydrocarbons to various oxygenates. Oxygen-
containing products of selective oxidation of cyclic
olefins are valuable reagents used in organic synthesis
[
1]. Allyl oxygenates, cyclohexenone and cyclohexe-
nol, and epoxycyclohexane may be used as initial
reagents in the syntheses of compounds used in agri-
culture, perfumery, and pharmaceutics [2–4].
The formation of allyl oxygenates and epoxide from
cyclohexene occurs at moderate temperatures as a
result of liquid-phase oxidative substitution at the allyl
position and addition to a double bond. These reac-
tions are typical of olefins [1, 5, 6]. At 60°С, in the
absence of any catalyst and activating agents, the reac-
Currently liquid-phase oxidation reactions cata-
tion of cyclohexene oxidation with molecular oxygen lyzed by organic catalysts, especially by N-hydroxyph-
occurs via the autoxidation mechanism. 2-Cyclohexe- thalimide (NHPI), are actively studied. In the works
nyl hydroperoxide is the main product, and the con- by Ishii and coauthors [25, 26], efficient catalytic sys-
centrations of 2-cyclohexen-1-ol, 2-cyclohexene-1- tems for the oxidation of alkanes and alkylaromatic
on and epoxycyclohexane constitute only several per- compounds by molecular oxygen have been proposed.
cent of reacted cyclohexene [7]. A high temperature Further studies have developed toward expanding the
and the presence of catalysts accelerate the reaction range of oxidized substrates and a search for suitable
735

7
36
KUZNETSOVA et al.
solvents and radical initiators [27–35]. It was found
that NHPI in the absence of metal compounds cata-
lyzes the selective conversion of cumene, ethylben-
zene, and cyclohexylbenzene to the corresponding
hydroperoxides [36]. The formation of carbonyl com-
pounds and alcohols occurs when alkylaromatic com-
pounds are oxidized in the presence of NHPI and
transition metal compounds [32, 34, 37] or nonmetal-
EXPERIMENTAL
Materials
N-Hydroxyphthalimide, acetonitrile, copper(II)
acetate monohydrate, molybdenyl acetylacetonate
(
Sigma-Aldrich) and iron(III) benzoate (Reakhim)
were used without additional purification. Cyclohex-
ene (Aldrich) was distilled and then kept in a cold stor-
lic activators [29–31, 35, 38], mostly at an elevated age in a tightly closed bottle.
temperature. Olefin oxidation by oxygen under the
The 3.8%V O /SiO catalyst (I-V) was prepared by
2
5
2
action of the NHPI catalyst were less studied. Interest-
ingly, in a recent work [39], the electrochemically gen-
erated radical form of the NHPI catalyst or its analog
was involved in the selective oxidation of natural ole-
fins to α-β-unsaturated ketones. In the presence of
redox-active compounds of transition metals, NHPI
accelerated cyclohexene autoxidation to form the
products of allylic oxidation [40–42]. Unfortunately,
hydroperoxide was not analyzed in [41, 42] and the
the impregnation of KSK silica gel powder (S
=
sp
2
–1
3
–1
2
60 m g , V
= 0.84 cm g ) with a solution of
pore
ammonium vanadate at 80°С. The sample was dried
and calcined at 650°С in vacuum. The 15%
МоО /SiO catalyst (II-Мо) was prepared by adding
3
2
the same silica gel to a solution of ammonium para-
molybdate at 80°С. The mixture was slowly evapo-
rated while stirring. Then, the sample was dried at
1
00°С and calcined at 500°С in air. The 7.5%
balance of С was not checked. Therefore, the selectiv-
6
МоО /SiO catalyst (III-Мо) was prepared by the
3
2
ity data are unreliable. In [25, 35, 38, 43, 44], the reac-
tivity of cyclohexene in the presence of NHPI without
transition metal compounds were considered in com-
parison with other olefins. Cyclohexene showed a
higher activity than another cyclic olefin α-isopho-
rone [43]. Other authors reported a selectivity of 82%
to 2-cyclohexen-1-on in cyclohexene oxidation at
2 –1
impregnation of Aerosil А-175 powder (S = 175 m g )
by a solution of ammonium paramolybdate with fur-
ther treatment as in the case of the II-Мо catalyst.
sp
Procedure of Catalytic Measurements
1
30°С when g-C N was added [38, 39]. In the oxidation
Cyclohexene oxidation was carried out in a glass
reactor with an internal volume of 28 mL and with
heating by water. The reactor was equipped with two
Teflon valves for gas purging and connection with a
gas burette. The contact of the solution with the gas
phase was maintained by intense stirring with a mag-
netic stirrer. The reactor was charged with a weighed
3
4
of cyclic olefins in the presence of an iron-containing
organic polymer, the portion of products of cyclohexene
allyl oxidation was 97%, whereas cyclooctene was selec-
tively oxidized to epoxide [45]. According to the avail-
able literature data, it is seen that the composition of
products of cyclohexene oxidation by oxygen cata-
lyzed by NHPI can be determined by the nature of
substrate, promoting additives of transition metal
compounds, and reaction conditions.
sample of a salt that was dissolved in 2.0 mL CH CN.
3
Then, NHPI and 0.5 mL of cyclohexene were added.
The reactor was closed, purged with О at atmospheric
2
pressure and room temperature. The burette was filled
with oxygen, and heating and stirring were switched on.
Within 1 min, the pressure in the system was brought to
atmospheric by means of a burette and a stopping flask
with water, and the beginning of reaction was recorded.
The reaction was monitored by changes in the volume
of the gas phase when the pressure in the system was
In this work, we used redox-active organic soluble
salts (copper(II) acetate and iron(III) benzoate) as
well as soluble and supported Mo(VI) catalysts in
combination with an NHPI catalyst in cyclohexene
oxidation by molecular oxygen. To determine the
mechanism of the influence of these compounds on brought to atmospheric. After the reaction, the reactor
the NHPI-catalyzed cyclohexene oxidation, we per- was rapidly cooled to ~15°C and the solution was
formed a cyclohexene oxidation by oxygen with the diluted with 7.5 mL CH CN. The loss of volatile
3
formation of 2-cyclohexenyl hydroperoxide and stud- cyclohexene in these manipulations, evaluated in a
ied the transformation of 2-cyclohexenyl hydroperoxide blank experiment at zero reaction time, was not higher
than 5% and was taken into account when calculating
the balance with respect to cyclohexene.
together with cyclohexene under the action of com-
pounds of these metals in an atmosphere of inert gas and
in the presence molecular oxygen. The choice of a metal
cocatalyst allowed us to control the catalytic properties of
the NHPI-based systems and to find effective ways for
Test reactions with the portions of solution
(
2.5 mL) of 2-cyclohexenyl hydroperoxide prepared
according to the procedure described below, were car-
obtaining the products of cyclohexene selective oxidation ried out in a similar way, but with oxygen replaced by
by molecular oxygen, including epoxide.
argon.
KINETICS AND CATALYSIS
Vol. 59
No. 6
2018

EFFECT OF TRANSITION METAL COMPOUNDS
737
OOH
OH
O
OH
O
O
O
(1)
(2)
(3)
(4)
(5)
(6)
OH
O
O
OH
O
O
OH
O
OH
O
OH
(7)
(8)
(9)
(10)
(11)
(12)
Fig. 1. Products of cyclohexene oxidation by oxygen in the presence of the NHPI catalyst as determined by gas chromatography.
Analysis of Oxidation Products
this temperature for 7 h. The reaction was carried out
at an oxygen partial pressure of 0.5–0.6 atm adding it
2
2
−
The amount of peroxide oxygen O in the solution to the reactor as it was consumed. After that, the reac-
after reaction was determined by iodometric titration. tor was cooled to room temperature and depressur-
Glacial acetic acid (5 mL) mixed with 0.5 g KJ was ized, the solution was discharged from the reactor, and
added to a 1.0-mL solution and allowed to stay for 30 was then used in subsequent experiments. The con-
min in an argon atmosphere at 60°C. Then, 50 mL of tents of peroxides and other oxidation products were
water was added and the mixture was titrated by a 0.04 determined according to the above procedure.
N solution of sodium thiosulfate.
The products of cyclohexene oxidation (Fig. 1)
RESULTS AND DISCUSSION
Cyclohexene Oxidation by Oxygen in the Presence
of NHPI and Soluble Compounds of Transition Metals
were identified by gas chromatography–mass spec-
trometry (GCMS) using an Agilent 7000 triple quadru-
pole GC/MS system (Agilent, USA) with a WAX20M
1
0 m × 0.25 mm × 0.25 μm column. The quantitative
Cyclohexene (1) oxidation in the solution of the
NHPI catalyst was carried out without adding any ini-
tiators for several hours. The reaction had a pro-
nounced induction period (1 h). The main product
was 2-cyclohexenyl hydroperoxide (2) (the selectivity
GC analysis was carried out using an Agilent 7890B
chromatograph (Agilent, USA) with a SOLGEL-WAX
3
0 m × 0.25 mm × 1 μm column. The amount of
products was calculated using calibration curves tak-
ing the solvent as an internal standard. The reaction
solution was analyzed twice: immediately after the
was S = 89% at an olefin conversion of 22%) (Table 1,
2
no. 1). 2-Cyclohexen-1-ol (3) was apparently absent
or formed in trace amounts, because the concentra-
tion of 3 determined by chromatography after treat-
reaction and after the addition of Ph P, which reduced
3
peroxide compounds to alcohols [46]. The amount of
cyclohexene was calculated from chromatogram of the
ment with Ph P coincided with the concentration of
3
solution reduced by Ph P. The content of cyclohexa-
3
peroxide determined by iodometric titration. In addi-
tion to 2, 2-cyclohexen-1-on (4) was also formed in
small amounts. Thus, 2-cyclohexenyl hydroperoxide
was stable under the conditions of NHPI-catalyzed
oxidation, which is typical of other alkyl hydroperox-
ides as well [36, 37]. Reactions (I)–(IV) describe
NHPI-catalyzed formation of 2:
nol was determined as a difference between its amount
after the reduction of solution and the amount of per-
oxide found by iodometric titration. The amount of
epoxycyclohexene did not change as a result of solu-
tion treatment with Ph P.
3
NHPI → PINO,
(I)
Preparation of the Solution
of 2-Cyclohexenyl Hydroperoxide
PINO+ C H → NHPI + C H ,
(II)
6
10
6
9
To prepare solutions of 2-cyclohexenyl hydroper-
oxide, cyclohexene was oxidized by oxygen in a tita-
nium autoclave (Parr Instrument Company, USA)
with a volume of 300 mL. The reactor was charged
with 40 mL CH CN, 10 mL С H , and 0.6 g NHPI.
i
9
i
C H + O → C H OO ,
(III)
6
2
6
9
i
C H OO + NHPI → C H OOH+ PINO. (IV)
6
9
6
9
3
6
10
In the absence of initiators, the generation of the
The reactor was fed with air to a pressure of 2 atm and phthalimide-N-oxyl radical (PINO) (I) in the initial
heated to 60 or 70°С, and the solution was stirred at reaction period was due to organic peroxides [36],
KINETICS AND CATALYSIS Vol. 59 No. 6 2018

7
38
KUZNETSOVA et al.
Table 1. Composition of the main products of cyclohexene oxidation in the presence of NHPI and metal saltsa
n+
Main products, mmol
C balance,
NHPI,
mmol
Conversion
6
M ,
S2–7, %c
93
No.
1
μmol
of 1, %b
2
3
4
5
6 + 7
%f
0
0.23
22
0.91
0
0
0.04
0
0
0
98
Fe(benz)3
2
6
0
<1
0.07
<0.01
0
Not
Not
determined determined
3
4
5
3
6
6
0.09
0.09
0.18
33
27
48
1.14
1.02
1.90
0
0
0
0.09
0.08
0.01
0.02
0.01
0.03
0
0
0
80
88
85
94
97
94
Cu(OAc) · H O
2
2
6
7
8
8.5
8.5
3
0
0.09
0.09
30
66
66
0.71
1.08
1
0.19
0.35
0.92
0.96
0.05
0.05
0.03
0.06
89
71
98
79
0
.2(1.4)d
0
Not determined
Not
Not
determined determined
1
1
.5(1.6)d
9
Traces
3
3
0.09
0.23
0.23
38
79
0
0
0
0.14
1.16
1.18
0.01
0.08
0.01
<0.01
0.02
<0.01
94
66
68
98
73
74
.16(1.4)d
1
0
1e
1.33(1.7)
d
8
0
1
MoO (acac)
2
2
1
2
0.23
8
0.04
0.12
0.02
0.08
0.03
78
98
a
b
c
d
e
f
Conditions: 2.5 mL of 4.65 mmol solution of 1 in CH CN, 60°C, the reaction duration was 4 h, except no. 1 (3 h).
3
Conversion of 1 = 100% × (1
Selectivity S
– 1
)/1
(mol/mol).
initial
initial
final
= 100% × (1 + 2 + 3 + 4 + 5 + 6 + 7)/(1
– 1final) (mol/mol).
2
–7
initial
The amount of peroxide according to iodometric titration.
mmol of Н О added to the solution.
2
2
Relative to the initial solution.
which are usually present in small amounts in hydro-
carbons.
−
+
2
Fe(benz) +1 2O + 2H →
3 2
(VI)
→
2Fe(benz) + H O.
3 2
We studied the effect of soluble Fe(III) and Cu(II)
salts on the catalytic action of the organic catalyst
NHPI in cyclohexene oxidation. As can be seen from
Table 1 (no. 3), the presence of small amounts of
Fe(III) benzoate resulted in the increase of conversion
Copper(II) acetate catalyzed autoxidation with a
prolonged induction period and the formation of the
three main products 2, 3, and 4 (Table 1, no. 6). The
addition of NHPI resulted in a noticeable acceleration
of 1. Note that iron benzoate did not show activity in of the oxidation process; the induction period short-
cyclohexene oxidation in the absence of NHPI (Table 1, ened to several minutes, the conversion of cyclohex-
no. 2). It is important to emphasize that the product of ene increased. The main products were 2 and 4, and
oxidation of 1 was still 2-cyclohexenyl hydroperoxide. alcohol 3 was absent (Table 1, no. 7). In catalysis by
The conversion of 1 and the amount of 2 formed the Cu(II) salt and Cu(II) in combination with NHPI,
increased in the presence of Fe(III) benzoate because epoxycyclohexane (5) was formed in small amounts.
of the faster oxidation and degeneration of the induc- Its formation was also observed in the preceding series
tion period. Interestingly, the amount of products of experiments with NHPI and Fe(III) benzoate. A
low selectivity to epoxide compared with allylic prod-
ucts is characteristic of cyclohexene autoxidation. An
increased selectivity to the epoxide was observed in
remained almost the same when the concentration of
Fe(III) benzoate increased (Table 1, no. 4), but
increased with an increase in the concentration of the
NHPI catalyst (Table 1, no. 5). The selectivity to 2 was
[16, 17] on gold-containing catalysts, which was
attributed by the authors to the properties of gold. It is
also known that a high selectivity to the epoxide in the
aerobic oxidation of olefins is possible as a result of the
intramolecular interaction of the double bond with
hydroperoxide oxygen, which can be seen in the oxi-
dation of cyclooctene in the presence of the CrMCM-
8
5% with cyclohexene conversion of 48%, and the C
6
balance remained at the same level as in the absence of
iron ions. These results show that iron ions do not cat-
alyze side transformations of 1. It is likely that the pro-
moting effect of iron is in the acceleration of the for-
mation of PINO through NHPI oxidation by the
Fe(III) ion [47, 48] with its regeneration by reactions
4
1 catalyst [8]. However, a similar conversion is not
typical of cyclohexenyl hydroperoxide intermediate.
The conversion of 1 and the amount of products did
not decrease with decreasing Cu(OAc) · H O content
(V) and (VI):
2
2
−
+
NHPI + Fe(benz) → PINO+ Fe(benz) + H ,(V) (Table 1, no. 8) up to the trace amount (Table 1, no. 9),
3
3
KINETICS AND CATALYSIS
Vol. 59
No. 6
2018

EFFECT OF TRANSITION METAL COMPOUNDS
739
and the main product was 2. With an increase in the
amount of NHPI, the conversion of 1 increased to
80%, but the amount of the main products only
n, mmol
5
~
slightly changed. As a result, the selectivity to the main
products and the C balance became worse (Table 1,
6
4
3
2
1
no. 10). At the conversion of 1 in the range 66–80%,
the overall selectivity to the main products calculated
on the basis to the substrate consumed was ~70%. The
addition of water, which usually accumulates in the
course of oxygenate formation, had little effect on the
catalytic action (Table 1, no. 11), except for a decrease
in the amount of 5.
1
2
We traced the consumption of substrate 1 and
accumulation of the products 2, 3, and 4 in time.
4
2-Cyclohexene-1-ol (3) was observed during the ini-
3
tial period of the reaction, and then its amount
decreased to zero, probably because of alcohol oxida-
tion to ketone 4 catalyzed by NHPI [28]. The resulting
data shown in Fig. 2 suggest that the selectivity to the
main products decreased from 99 to 66% with time
and with an increase in the conversion of 1 from 15 to
0
1
2
3
4
5
6
7
8
9
t, h
Fig. 2. Kinetics of cyclohexene (1) consumption and accu-
mulation of the products of oxidation of 2-cyclohexenyl
hydroperoxide (2), 2-cyclohexen-1-ol (3) and 2-cyclo-
hexen-1-on (4). Reaction conditions: 1.7 mg (8.5 μmol)
Cu(OAc) · H O, 15 mg (0.092 mmol) NHPI, 4.65 mmol
8
0%. A decrease in the selectivity and the С balance
6
points to the formation of byproducts, which are likely
formed due to secondary oxidation processes. In addition
to the main products, several dioxygenates (6–12),
which are the products of cyclohexene oxidation both
at the allyl position and at the double bond, were iden-
tified by GСMS (Fig. 1). GC analysis of the reaction
solution before and after the reductive treatment by
2
2
3
(
I), 2 mL CH CN, 60°C.
the participation of MoO (acac) , which is known as
2
2
an efficient catalyst for epoxidation [20]. The disad-
vantage of the NHPI–Mo(VI) system was the low
reaction rate, which was likely caused by the presence
of the Mo(VI) compound.
Ph P showed a qualitatively identical composition of
3
oxygenates, but their quantitative distribution changed
after reduction toward alcohols. The detection of dioxy-
genates 8–12 pointed to the fact that, along with 2, dihy-
droperoxides and substituted hydroperoxides were
formed. The latter was confirmed by the fact that for a
rather high conversion of 1, the amount of hydroperoxide
found by titration (given in parentheses in Table 1,
nos. 8–11) was higher than the amount of 2 determined
by GC. At a high conversion of 1, dioxygenates shown in
Fig. 1 could account for more than 20% of the overall
amount of products. However, we did not find any
other compounds from the long list of products of
cyclohexene autoxidation in the presence of metal-
containing catalysts found by Finke et al. [49].
Reactions of Cyclohexene and 2-Cyclohexenyl
Hydroperoxide in an Atmosphere of Inert Gas
In this part of the work, we determined the mech-
anism of participation of the chosen transition metal
compounds in reactions leading to cyclohexene oxida-
tion. With this goal, the transformations of the pri-
mary product of 2-cyclohexenyl hydroperoxide reac-
tion under the influence of metal catalysts were stud-
ied. Test reactions in the argon atmosphere were
carried out with the portions of the solution prepared
by cyclohexene oxidation according to the procedure
described in the experimental section of this work. In
addition to 2, this solution contained unreacted 1,
NHPI, and the products of decomposition of 2 in
small amounts. Experimental conditions for the use of
Unlike redox-active metal compounds, molybde-
num(VI) acetylacetonate had an inhibitory effect on
the rate of cyclohexene oxidation catalyzed by NHPI.
Correspondingly, the conversion of cyclohexene in the
presence of NHPI and dissolved MoO (acac) (Table 1,
2
2
no. 12) was three times lower than in the presence of transition metal compounds, the conversions of 1 and 2,
NHPI only. At the same time, the composition of oxi- and the composition of the main C products, are
6
dation products has changed towards the preferential
given in Table 2.
formation of 3 and 5. In addition to epoxycyclohexane
5
, epoxy derivatives 6 and 7 appeared in noticeable
The mechanism of decomposition of 2 under the
amounts. The autoxidation reactions of isobutane or action of transition metal ions to form unsaturated alco-
alkylbenzenes are known as a method for the synthesis hol and ketone is described by reactions (VII)–(XI).
of hydroperoxides, which can further be used to epox- Since in our experiments the hydroperoxide solution also
idize olefins [50]. It can be assumed that the 2-cyclo- contained olefin 1, the hydroperoxide could be con-
hexenyl hydroperoxide formed in cyclohexene oxida- sumed not only for decomposition, but also for the for-
tion is consumed for the formation of epoxides with mation of epoxide and alcohol by reaction (XII).
KINETICS AND CATALYSIS Vol. 59 No. 6 2018

7
40
KUZNETSOVA et al.
Iron(III) benzoate was inactive in the conversion of 2
n+
(n + 1)+
+ OH− (VII)
C H OOH + M
C H O + M
6
9
6
9
(
Table 2, no. 1). In contrast, copper(II) acetate caused the
(
n + 1)
C H OO + M + H+ (VIII)
n+
rapid decomposition of 2 to alcohol 3 and ketone 4; 5 and
other epoxy derivatives are found only as admixtures
(Table 2, no. 2). In reaction of 2 with V(V)- and Mо(VI)
catalysts, we observed the epoxidation of a double bond
C H OOH + M
6
9
6
9
O
OH
2
C H OO
6
+
+ O2
(IX)
9
[20–22], In addition to epoxycyclohexane (5), 1,2-epoxy-
cyclohexanol-3 (6) and a small amount of 1,2-epoxycyclo-
hexanone-3 (7) were determined (Table 2, nos. 3–6).
Apparently, epoxy alcohol 6 appeared as a result of epoxi-
dation of hydroperoxide 2 or unsaturated alcohol 3 by
reactions (XIII). After the reductive treatment of the ana-
OH
C H O + C H
+ C2H9
(X)
6
9
6
10
C H OO + C H
C H OOH + C H
6
(XI) lyzed solution by Ph P, both epoxidized alcohol and
6
9
6
10
9
6
9
3
hydroperoxide were detected by gas chromatography as 6.
Since ketone 4is weakly susceptible to epoxidation and was
present in the solution in small amounts, the contribution
OH
C H + C H OOH
O +
(XII)
6
10
6
9
of 7 to the sum of epoxy compounds was small.
OOH
OH
OH
OH
OOH
Mo(VI)
+
O +
+
O
O
PPh3
(
XIII)
OH
As can be seen from Table 2, the overall selectivity explained by the participation in the epoxidation of 2
of the consumption of 2 for epoxidation was 63% for and other organic peroxides determined by iodometric
the I-V catalyst supported on SiO and was higher for titration. As a result of reduction of 2 by reaction
2
Mo(VI) catalysts: both homogeneous MoO (acac)
(XII), alcohol 3 was formed. Under the action of het-
2
2
and SiO -supported II-Mo and III-Mo. In the latter erogeneous Mo(VI) oxide catalysts, 2 was almost
2
case, the selectivity was higher than 100%, which is completely consumed for epoxidation, and radical
Table 2. Conversion of cyclohexene (1) and 2-cyclohexenyl hydroperoxide (2) in the presence of metallic catalystsa
Main products, mmol
C6
Catalyst
М , μmol)
S , %b balance,
No.
Time, h
1initial
2final
n+
ep
(
3
4
5
6 + 7
%с
1
2
3
4
5
6
Fe(benz) (18)
4.8
2.0
4.3
2.8
4.0
4.3
3.49
2.72
2.75
2.57
2.14
2.49
1.0
~0
0.05
0.52
0.14
0.08
0.08
0.09
0.01
0.02
0.20
0.01
0.02
0.28
0
0
99
83
80
84
77
86
3
Cu(OAc) · H O (15)
0.10
0.22
0.03
0.14
0.30
0.45
0.12
0.53
0.43
0.38
2
2
20 mg I-V (8)
63
74
91
110
MoO (acac) (17)
0.49 0.2 + 0.01
2
2
30 mg II-Mo (30)
20 mg III-Mo (10)
0.54
0.53
0.21
0.20
a
Conditions: 2.5 mL of the initial solution containing 3.61 mmol (1), 0.14 mmol NHPI, 0.92 mmol (2) (1.0 mmol according to iodo-
metric titration), 0.05 mmol (4), 0.04 mmol (5 + 6 + 7), Ar, 60°С.
b
c
Selectivity S = 100% × Σ(5 + 6 + 7)/(2
– 2
) (mol/mol).
ep
initial
final
Relative to the initial solution.
KINETICS AND CATALYSIS
Vol. 59
No. 6
2018

EFFECT OF TRANSITION METAL COMPOUNDS
741
decomposition was almost absent, which was also
Cyclohexene Epoxidation by 2-Cyclohexenyl
confirmed by the formation of only a small amount of
Hydroperoxide Formed in the Process of Autoxidation
ketone 4. Material balance with respect to С after the
6
For epoxidation, we used either a solution of cyclo-
hexene in acetonitrile or a solution with a similar com-
position already containing a certain amount of
reaction was usually >80%. The balance that is differ-
ent from 100% can be associated with the secondary
conversion of unsaturated products that are easily oxi-
dized at a double bond, as well as the formation of hydroperoxide 2. The latter was used in the experi-
high-boiling resinous products in the decomposition ments described in the previous section, and the
of peroxides. Thus, metal compounds demonstrated preparation procedure for such solutions is given in the
different behavior with respect to 2-cyclohexenyl experimental section of this work. In both cases, the
hydroperoxide: from the inertness of Fe(III) benzoate
and the high activity of radical initiator Cu(II) acetate
to the activation of hydroperoxide oxygen for nonrad-
ical oxidation on V(V) and Mo(VI) oxides. These
results agree with data on the effect of metal com-
pounds on NHPI-catalyzed oxidation of 1. Thus, cop-
per(II) acetate was an active catalyst for the decompo-
sition of 2 to form final products 3 and 4. Iron(III)
benzoate participated in the generation of the active
form of the PINO catalyst, but its oxidative ability
appeared to be insufficient for catalyzing the decom-
position of hydroperoxide 2. Cyclohexene epoxidation
reaction mixture contained NHPI and supported
molybdenum oxide epoxidation catalysts. The kinetics
of the reaction with oxygen is illustrated by the gas
absorption curves (Fig. 3). It was assumed that not
only 2, which is already present in the solution,
reacted with the olefin. Further oxidation of 1 to 2
occurred under the action of the NHPI catalyst. It
turned out that 2 weakly affects the intensity of cyclo-
hexene oxidation by oxygen (Fig. 3, curve 1 for gas
consumption in the absence of 2 and curves 2 and 3 in
the presence of 2), and most of epoxides were formed
by hydroperoxide obtained during cyclohexene oxida- from 2, which was initially present in the solution
tion is of interest. Supported MoO catalysts proved to (Table 3, nos. 2 and 3).
3
be quite efficient in the activation of 2-cyclohexenyl
The initial catalyst system was activated by the
hydroperoxide, but in the experiments described
addition of iron(III) benzoate. With the promoting
above, we failed to combine the reactions of formation
effect of iron by reactions (V), (VI), the rate of cyclo-
and consumption of 2 due to inhibition of the autoxi-
hexene oxidation increased several times (Fig. 3, curve 4),
resulting in the formation of 2-cyclohexenyl hydroper-
oxide (Table 3, no. 4). The resulting 2 was consumed
dation process under the action of the Mo(VI) catalyst
(
Table 1, no. 12) In the next cycle of experiments, we
performed cyclohexene epoxidation under conditions
of the formation of 2-cyclohexenyl hydroperoxide in for epoxidation and converted into alcohol 3 and then
an oxygen atmosphere.
to ketone 4 (reaction sequence (XIV)):
OOH
OH
OH
C6H10
O2
O +
O
(XIV)
O2
[NHPI]
Both cyclohexene and the products of its transfor- and alcohol 3 taking into account the secondary trans-
mation underwent epoxidation, so in addition to formation of part of 3 into epoxides 6 and 7 was lower
epoxycyclohexane 5, dioxygenates 6 and impurity 7 than the amount of epoxides. This discrepancy is due
were formed (Table 3, no. 4). Similar reactions were to the high reactivity of unsaturated oxygenates, which
also observed in the presence of a homogeneous easily undergo various secondary reactions with oxy-
MoO (acac) catalyst (Table 3, no. 5). According to gen. As a consequence, С balance was ~90% taking
2
2
6
the mechanism of epoxide formation (reactions (XII) into account oxidation products (Table 3). Thus, using
and (XIII), (XIV)), the overall amount of epoxides NHPI and small amounts of Fe(III) benzoate com-
should be equal to half of the reacted cyclohexene bined with Mo(VI) catalysts, we carried out in situ
minus the remaining 2. The other half of the reacted epoxidation of cyclohexene by 2-cyclohexenyl
cyclohexene should transform into allylic oxygenates. hydroperoxide formed in the process of autoxidation.
In our experiments, the sum of amounts of ketone 4 Reactions with alkyl hydroperoxides are typical of var-
KINETICS AND CATALYSIS Vol. 59 No. 6 2018

7
42
Vgas, mL
KUZNETSOVA et al.
together. Until recently, we knew only the publication
by Ishii et al. [51], in which the epoxidation of olefins,
including cyclohexene, together with the oxidation of
ethylbenzene, was described. The reaction occurred in
the NHPI–Co(OAc) –Mo(CO) system in the tenfold
excess of ethylbenzene over the olefin. In contrast to this
example of parallel reactions of two substrates with dif-
ferent reactivity, we managed to find conditions when
one olefin participates in two simultaneous reactions of
radical oxygenation at the allyl position and the addition
of electrophilic oxygen to a double bond.
70
60
50
40
30
20
4
2
6
2
CONCLUSIONS
3
1
Thus, we studied the effects of different additives of
transition metal compounds on the NHPI-catalyzed
reaction of cyclohexene oxidation. The iron(III) salt
accelerated the generation of the active PINO radical
and thus accelerated 2-cyclohexenyl hydroperoxide
formation, but did not participate in its decomposi-
tion. The copper(II) salt initiated the reaction of
cyclohexene oxidation, and catalyzed the radical
decomposition of 2-cyclohexenyl hydroperoxide and
secondary oxidation of allyl oxygenates. In the reac-
tion of cyclohexene with oxygen, epoxycyclohexane
was detected in small amounts both in the catalysis by
NHPI, and together with NHPI iron and copper salts.
However, cyclohexene epoxidation occurred under
the action of 2-cyclohexenyl hydroperoxide and
1
0
0
0
50
100
150
200
250
300
t, min
Fig. 3. Kinetics of gas consumption in cyclohexene oxida-
tion by oxygen in the presence of SiO -supported МоО
catalysts II-Mo (20 mg, curves 1 and 2; 40 mg, curve 4)
and III-Mo (40 mg, curve 3) at 60°С. The compositions of
initial mixtures for curves 1–4 corresponds to experiments
nos. 1–4 in Table 3.
2
3
ious olefins and are used for the synthesis of the corre-
sponding epoxides. There are also examples of the Mo(VI) compounds. It was found that the polyfunc-
preparation of alkyl hydroperoxides by the interaction tional three-component NHPI–Mo(VI)–Fe(III) cat-
of oxygen with reactive alkanes or alkylbenzenes. alyst is capable of causing cyclohexene oxidation by
However, it is rarely possible to carry out two reactions molecular oxygen with the formation of epoxides 5
Table 3. Products of oxidation of 1 by oxygen in the presence of NHPI and Мо(VI) catalysts II-Mo (nos. 1, 2, 4), III-Mo
a
(
no. 3), and MoO (acac) (no. 5)
2 2
Composition of the solution after the reaction,
mmol
Initial composition, mmol
C balance,
Time,
h
6
No.
%с
NHPI
M
1
2
1
2
3
4
5
6 + 7
1
0
.23
Mo 0.02
Mo 0.02
4.65
0
4.5
5
3.86
1.68
0.22
0.60
0.13
0.16
0.04 0.22
0.07
0.30
98
88
2b
0
0
.05
3.26 1.10
2.56 1.76
0.29
0.9
3b
4
.13
Mo 0.02
4
4
4
1.25
1.89
2.62
1.25
1.0
0.06 0.50
0.70
0.70
0.49
0.18
0.20
0.24
84
0.18
0.23
Mo 0.04 + Fe 0.006 4.65
Mo 0.02 + Fe 0.006 4.65
0
0
0
0.43
0.33
91
91
5
0.27
0.29
а
b
Conditions: 2.5 mL of С H solution in CH CN, 60°С.
6
10
3
Initial solution no. 2 contained also the impurity, Р = 0.07 mmol (4); initial solution no. 3 contained also the admixture of products,
Р = 0.27 mmol (4) + 0.04 mmol (5) + 0.03 mmol (6 + 7).
c
100% × Σ(1
+ 2
+ 3 + 4 + 5 + 6 + 7)/(1
+ 2initial + Р) (mol/mol).
final
final
initial
KINETICS AND CATALYSIS
Vol. 59
No. 6
2018

EFFECT OF TRANSITION METAL COMPOUNDS
743
and 6 and 2-cyclohexen-1-on (4). Epoxidation 23. Hereijgers, B.P.C., Parton, R.F., and Weckhuysen, B.M.,
Catal. Sci. Technol., 2012, vol. 2, p. 951.
occurred due to the hydroperoxide formed in cyclo-
2
4. Nandi, M., Roy, P., Uyama, H., and Bhaumik, A.,
Dalton Trans., 2011, vol. 40, p. 12510.
hexene oxidation.
2
5. Ishi, Y., Nakajama, K., Takeno, M., Sakaguchi, S.,
Iwahama, T., and Nishiyama, Y., J. Org. Chem., 1995,
vol. 60, p. 3934.
ACKNOWLEDGMENTS
We thank Dr. L.V. Piryutko for providing us with 26. Ishii, Y. and Sakaguchi, S., Catal. Today, 2006, vol. 117,
the vanadium oxide catalyst and Dr. M.V. Shashkov for
p. 105 (and references therein).
carrying out GCMS analyses. This work was carried out 27. Zhou, L., Zang, C., Fang, T., Zhang, B., Wang, Y.,
Yang, X., Zhang, W., and Xu, J., Chin. J. Catal., 2011,
in the framework of state assignment of Boreskov Insti-
vol. 32, p. 118.
tute of Catalysis, Siberian Branch, Russian Academy of
2
2
3
8. Hu, Y., Chen, L., and Li, B., Catal. Commun., 2016,
Sciences (project AAAA-A17-117041710083-5).
vol. 83, p. 82.
9. Zheng, G., Liu, C., Wang, Q., Wang, M., and Yang,
G., Adv. Synth. Catal., 2009, vol. 351, p. 2638.
0. Yang, X., Wang, Y., Zhou, L., Chen, C., Zhang, W.,
and Xu, J., J. Chem. Biotechnol., 2010, p. 564.
REFERENCES
1
2
3
. Weidmann, V. and Maison, W., Synthesis, 2013, vol. 45,
p. 2201.
3
1. Zao, Q., Chen, K., Zhang, W., Yao, J., and Li, H., J.
. Mang, S., Cooper, A.I., Colclough, M.E., Chauhan, N.,
and Holmes, A.B., Macromol., 2000, vol. 33, p. 303.
. Audia, J.E., Boisvert, L., Patten, A.D., Villalobos, A.,
and Danishefsky, S.J., J. Org. Chem., 1989, vol. 54,
p. 3738.
Mol. Catal. A: Chem., 2015, vol. 402, p. 79.
32. Gao, B., Meng, S., and Yang, X., Org. Process Res.
Dev., 2015, vol. 19, p. 1374.
3
3. Bao, L., Li, X., Wu, Z., Yuan, X., and Luo, H., Res.
Chem. Intermed., 2016, vol. 42, p. 5527.
3
4. Latka, P., Kasperczyk, K., Orlinska, B., Drozdek, M.,
Skorupska, B., and Witek, E., Catal. Lett., 2016,
vol. 146, p. 1991.
4
. Polla, M. and Frejd, T., Tetrahedron, 1991, vol. 47,
p. 5883.
5
. Lei, Z., React. Funct. Polym., 2000, vol. 43, p. 139.
. Boghaei, D.M. and Mohebi, S., J. Mol. Catal. A:
Chem., 2002, vol. 179, p. 41.
3
5. Blandez, J.F., Navalón, S., Álvaro, M., and García, H.,
ChemCatChem., 2018, vol. 10, p. 198.
6
3
6. Sheldon, R.A. and Arends, I.W.C.E., J. Mol. Catal. A:
Chem., 2006, vol. 251, p. 200 (and references therein).
7
. Van Sickle, D.E., Mayo, F.R., and Arluck, R.M., J.
Amer. Chem. Soc., 1965, vol. 87, p. 4824.
. Dapurkar, S.E., Kawanami, H., Komura, K.,
Yokoyama, T., and Ikushima, Y., Appl. Catal., A, 2008,
vol. 346, p. 112.
3
3
3
4
7. Orlinska, B. and Romanovska, I., Cent. Eur. J. Chem.,
8
2011, vol. 9, p. 670.
8. Liu, G., Tang, R., and Wang, Z., Catal. Lett., 2014,
vol. 144, p. 717-722.
9. Mallat, T., Meier, D.M., Urakawa, A., and Baiker, A.,
9. Waldvogel, S.R. and Selt, M., Angew. Chem., 2016,
vol. 55, p. 12578.
J. Catal., 2010, vol. 270, p. 26.
10. Yang, C., Li, B., Zang, F., Wang, J., and Ou, E., Catal.
0. Fu, Y., Sun, D., Qin, M., Yuang, R., and Li, Z., RSC
Adv., 2012, vol. 2, p. 3309.
Lett., 2009, vol. 131, p. 440.
11. Silva, F.P., Jacinto, M.J., Landers, R., and Rossi, L.M.,
4
1. Habibi, D., Faraji, A.R., Arshadi, M., Heydari, S., and
Catal. Lett., 2011, vol. 141, p. 432.
Gil, A., Appl. Catal., A, 2013, vol. 466, p. 282.
2. Habibi, D., Faraji, A.R., Arshadi, M., Veisi, H., and
Gil, A., J. Mol. Catal. A: Chem., 2014, vol. 382, p. 41.
3. Wang, C., Wang, G., Mao, J., Jao, Z., and Li, H.,
Catal. Commun., 2010, vol. 11, p. 758.
12. Skobelev, I.Y., Sorokin, A.B., Kovalenko, K.A., Fedin, V.P.,
4
4
4
4
4
and Kholdeeva, O.A., J. Catal., 2013, vol. 298, p. 61.
13. Radman, R., Aouissi, A., and Mekhamed, W., Orient.
J. Chem., 2015, vol. 31, p. 2277.
14. Liu, T., Cheng, H., Lin, W., Zhang, C., Yu, Y., and
4. Melone, L., Franchi, P., Lucarini, M., and Punta, C.,
Adv. Synth. Catal., 2013, vol. 355, p. 3210.
Zhao, F., Catalysts, 2016, vol. 6, p. 24.
1
5. Cai, Z.Y., Zhu, M.Q., Chen, J., Shen, Y.Y., Zhao, J.,
Tang, Y., and Chen, X.Z., Catal. Commun., 2010,
vol. 12, p. 197.
5. Dhakshinamoorthy, A., Alvaro, M., and Garcia, H., J.
Catal., 2012, vol. 289, p. 259.
6. Shul’pin, G.B., J. Mol. Catal. A: Chem., 2002, vol. 189,
p. 39.
16. Dou, J., Tang, Y., Nguyen, L., Tong, X., Thapa, P.S.,
and Tao, F.F., Catal. Lett., 2017, vol. 147, p. 442.
4
7. Krylov, I.B., Paveliev, S.A., Shelimov, B.N., Lokshin, B.V.,
17. Dou, J. and Tao, F.F., Appl. Catal., A, 2017, vol. 529,
Garbuzova, I.A., Tafeenko, V.A., Chernyshev, V.V.,
Budnikov, A.S., Nikishin, G.I., and Terent’ev, Org.
Chem. Front., 2017, vol. 4, p. 1947.
p. 134.
18. Cao, Y., Yu, H., Peng, F., and Wang, H., ASC Catal.,
2
014, vol. 4, p. 1617.
4
4
5
8. Zhang, C., Huang, Z., Lu, J., Luo, N., and Wang, F.,
19. Cao, Y., Yu, H., Wang, H., and Peng, F., Catal. Com-
J. Amer. Chem. Soc., 2018, vol. 140, p. 2032.
mun., 2017, vol. 88, p. 99.
9. Weiner, H., Trovarelli, A., and Finke, R.G., J. Molec.
20. Kotov, St.V. and Balbolov, E., J. Mol. Catal. A: Chem.,
Catal. A: Chem., 2003, vol. 191, p. 217.
2001, vol. 176, p. 41.
0. Sheldon, R.A., J. Mol. Catal., 1980, vol. 7, p. 107.
21. Nandi, M. and Talukhdar, A.K., J. Porous Mater.,
5
1. Iwahama, T., Hatta, G., Sakaguchi, S., and Ishii, Y.,
2016, vol. 23, p. 1143.
Chem. Commun., 2000, p. 163.
2
2. El-Korso, S., Khaldi, I., Bedrane, S., Choukchou-
Braham, A., Thibault-Starzyk, F., and Bachir, R., J.
Mol. Catal. A: Chem., 2014, vol. 394, p. 89.
Translated by Andrey Zeigarnik
KINETICS AND CATALYSIS Vol. 59 No. 6 2018