Kinetics of the liquid-phase oxidation of 2-hydroxycyclohexanone

Article abstract of DOI:10.1134/S0023158413030026

The kinetics of oxygen uptake in the azobisisobutyronitrile-initiated oxidation of 2-hydroxycy-clohexanone (RCH(OH)C(O)R) at 323 K has been investigated (chlorobenzene solvent, [RCH(OH)C(O)R] = 0.15-1.30 mol/L, initiation rate of w _i = 0.016-0.473 mol L^-1 s ^-1). The effective oxidizability parameter k _{p, eff}(2k _t,eff)^-0.5 has been determined by solving the inverse kinetic problem using the entire data array obtained while varying [RCH(OH)C(O)R] and w _i. The rate constants of chain propagation and termination and the equilibrium constant of the addition of the hydroxyperoxyl radical to the ketoalcohol have been derived from the dependence of the oxidizability parameter on the substrate concentration. The rate constant of bimolecular chain initiation has been calculated to be k ₀ = 9.7 × 10^-7 L mol^-1 s^-1. The ratio of the rate constants of quadratic-law peroxyl radical recombination reactions without and with chain termination (k _eff′/k _t,eff′) increases with increasing [RCH(OH)C(O)R], passes through a maximum at a substrate concentration of 0.8 mol/L, and then falls off. It is demonstrated that this effect is due to the variation of the proportions of the hydroperoxyl and organic (1-hydroxy-2-oxocyclohexylperoxyl or 1,2-dihydroxy-1-cyclo- hexylperoxyl) radicals in the reaction medium.

Full text of DOI:10.1134/S0023158413030026

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2013, Vol. 54, No. 3, pp. 270–278. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © A.A. Akimov, S.V. Puchkov, Yu.V. Nepomnyashchikh, A.L. Perkel, 2013, published in Kinetika i Kataliz, 2013, Vol. 54, No. 3, pp. 282–290.
Kinetics of the LiquidꢀPhase Oxidation of 2ꢀHydroxycyclohexanone
A. A. Akimov, S. V. Puchkov, Yu. V. Nepomnyashchikh, and A. L. Perkel’*
Faculty of Chemical Engineering, Kuzbass State Technical University, Kemerovo, 650026 Russia
*eꢀmail: perkel2@rambler.ru
Received January 18, 2012
Abstract—The kinetics of oxygen uptake in the azobisisobutyronitrileꢀinitiated oxidation of 2ꢀhydroxycyꢀ
clohexanone (RCH(OH)C(O)R) at 323
K
has been investigated (chlorobenzene solvent,
[RCH(OH)C(O)R] = 0.15–1.30 mol/L, initiation rate of wi = 0.016–0.473 mol L–1 s–1). The effective oxiꢀ
−0.5
dizability parameter
has been determined by solving the inverse kinetic problem using the
,
k
p, eff (2kt,eff
)
entire data array obtained while varying [RCH(OH)C(O)R] and wi. The rate constants of chain propagation
and termination and the equilibrium constant of the addition of the hydroxyperoxyl radical to the ketoalcohol
have been derived from the dependence of the oxidizability parameter on the substrate concentration. The
rate constant of bimolecular chain initiation has been calculated to be
of the rate constants of quadraticꢀlaw peroxyl radical recombination reactions without and with chain termiꢀ
k0 = 9.7 ×
10–7 L mol–1 s–1. The ratio
nation increases with increasing [RCH(OH)C(O)R], passes through a maximum at a substrate
'
'
keff kt,eff
(
)
concentration of 0.8 mol/L, and then falls off. It is demonstrated that this effect is due to the variation of the
proportions of the hydroperoxyl and organic (1ꢀhydroxyꢀ2ꢀoxocyclohexylperoxyl or 1,2ꢀdihydroxyꢀ1ꢀcycloꢀ
hexylperoxyl) radicals in the reaction medium.
DOI: 10.1134/S0023158413030026
2ꢀHydroxycyclohexanone, which is the main nonꢀ remove organic impurities, the dimer was washed with
peroxide intermediate in the destruction of the carbon peroxideꢀfree diethyl ether. Freshly distilled 2ꢀhydroxꢀ
chain in cyclohexane oxidation [1–4], forms at the ycyclohexanone samples with bp 85
2ꢀhydroperoxycyclohexanone decomposition stage [4– used in the oxidation. The bp value reported in the litꢀ
6]. Although the composition of the 2ꢀhydroxycycloꢀ erature is 83–85 (13 Torr) [10].
Chlorobenzene was purified via a standard proceꢀ
dure [11]. The bp of the purified product was 131.5
(reference value: 132.1 [12]).
°
С (15 Torr) were
°
С
hexanone oxidation products [1–4, 6, 7] and the kinetꢀ
ics and mechanisms of the conversion of peroxide interꢀ
mediates [2, 7, 8] have been the subject of many works,
the oxidizability of 2ꢀhydroxycyclohexanone remains
poorly studied at the quantitative level. The radical
chain oxidation of 2ꢀhydroxycyclohexanone takes
°
С
°
С
The initiator (azobisisobutyronitrile, AIBN) was
recrystallized from ethanol until the substrate oxidation
rate was invariable.
The oxidation rate was measured as oxygen uptake
using a manometric setup. The experiments were conꢀ
ducted in the presence of AIBN at 323 K in the kinetiꢀ
cally controlled regime of the reaction.
place mainly at the CH bond in the ꢀposition to the
α
hydroxyl group. The reactivity of this bond toward the
cumylperoxy radical at 348 K is higher than the reactivꢀ
ity of the ꢀСН bonds of cyclohexanol and cyclohexꢀ
α
anone by a factor of 6.4 and 298, respectively.
The initiation rate was calculated via the following
familiar equation [13]:
Here, we report the kinetics and mechanism of the
liquidꢀphase oxidation of 2ꢀhydroxycyclohexanone. It
is anticipated that these data will be helpful in the estiꢀ
mation of the rate of one of the key steps of the indusꢀ
trial oxidation of cyclohexane into adipic acid and will
contribute to the understanding of the mutual effect of
(1)
wi,AIBN = 2ekd AIBN .
[
]
The AIBN dissociation rate constant was deterꢀ
mined using the following formula [14]:
kd = 0.85 ×1015 exp(−15303 T) s−1.
(2)
the carbonyl and hydroxyl groups in
α
ꢀketoalcohols.
The coefficient of radical escape from the solvent
cage was taken to be 0.6 [15].
Based on data available from the literature [16, 17],
the concentration of oxygen dissolved in chlorobenzene
was estimated at 5.84
EXPERIMENTAL
×
10–3 mol/L.
2ꢀHydroxycyclohexanone (in dimer form) was synꢀ
thesized by 2ꢀchlorocyclohexanone hydrolysis with an
For determining the kinetic parameters of the reacꢀ
aqueous solution of potassium carbonate [9]. To tion, the entire experimental data array was processed
270

KINETICS OF THE LIQUIDꢀPHASE OXIDATION OF 2ꢀHYDROXYCYCLOHEXANONE
271
using the Fletcher–Reeves conjugate gradient method
implemented in the Delphi 6.0 environment.
It would be hypothesized that, in 2ꢀhydroxycycloꢀ
hexanone oxidation, as in the oxidation of other secꢀ
ondary alcohols, chain propagation involves two types
of peroxyl radicals, namely, hydroperoxyl and
α
ꢀ
RESULTS AND DISCUSSION
hydroxyperoxyl ones [18, 19]. Recently, it has been
experimentally demonstrated that there is a dynamic
equilibrium between these radicals and the resulting
ketone and this equilibrium is significant for descripꢀ
tion of the cyclohexanol oxidation kinetics [18].
Owing to the presence of the highly reactive carbonyl
i
As was mentioned above, 2ꢀhydroxycyclohexanone
is among the most readily oxidizable organic comꢀ
pounds. Without an initiator, it oxidizes via a radical
chain mechanism even at 323 K [2, 7, 8]. Its oxidation
products include organic peroxides (mainly 2ꢀhydroxyꢀ
2ꢀhydroperoxycyclohexanone), hydrogen peroxide,
monoperoxyadipic acid, 1,2ꢀcyclohexanedione, adipic
anhydride, adipic acid, and monoꢀ2ꢀoxocyclohexyl
adipate (Fig. 1) [8]. The accumulation curves of these
products (Fig. 1) indicate that, even at 323 K, the cycloꢀ
hexane ring undergoes destruction because of peroxide
decomposition and, possibly, as a result of the converꢀ
sion of peroxide radicals. It is, therefore, necessary to
take into consideration the chain initiation reactions
and to determine the oxidation rates at the lowest posꢀ
sible substrate conversions. In the oxidation of highly
reactive compounds, including cyclohexanol, chain
initiation due to the interaction between the substrate
and dioxygen may be either a bimolecular or a termoꢀ
lecular reaction [18].
group in the ketoalcohol, it is more likely that the
HO2
radical will add to just this group, not to 1,2ꢀcyclohexꢀ
anedione, which forms simultaneously with hydrogen
peroxide (Fig. 1). The much higher substrate concenꢀ
tration (as compared to the product concentrations)
should shift the equilibrium toward the addition prodꢀ
uct (1,2ꢀdihydroxyꢀ1ꢀcyclohexylperoxy radical). It
was also reported that hydroperoxyl and alkylperoxyl
radicals can recombine without causing chain termiꢀ
nation [20].
With the above facts taken into account, the mechaꢀ
nism of the radical chain oxidation of 2ꢀhydroxycycloꢀ
hexanone (RCH(OH)C(O)R) can be represented as
2(CH3) (CN)C•
2(CH3) (CN)COO•,
(I)
k
2O
2
d
(CH3)2(CN)C–N=N–C(CN)(CH3)2
2
2
O
(CH3) (CN)COO• + RCH(OH)C(O)R
RC(OO•)(OH)C(O)R + (CH3) (CN)COOH,
(II)
2
2
2
k
O
2
• RC•(OH)C(O)R
RC(OO•)(OH)C(O)R,
2RC(OO•)(OH)C(O)R,
(III)
(IV)
(V)
0
RCH(OH)C(O)R + O2
2RCH(OH)C(O)R + O2
–HO
2
'
k
0
2O
2RC•(OH)C(O)R
2
2
–H O
2
K
RC(OO•)(OH)C(O)R
RCH(OH)C(O)R + HO2•
RC(O)C(O)R + HO•2 ,
2
K
RC(OH)C(OO•)(OH)R,
(VI)
(VII)
3
k
RC(OO•)(OH)C(O)R + RCH(OH)C(O)R
RC(OOH)(OH)C )R + RC•(OH)C(O)R,
p1
k
HO•2 + RCH(OH)C(O)R
H2O2 + RC•(OH)C(O)R,
(VIII)
p2
RCH(OH)C(OO•)(OH)R + RCH(OH)C(O)R
(IX)
k
RCH(OH)C(OOH)(OH)R + RC•(OH)C(O)R,
p3
RC•(OH)C(O)R + O2
RC(OO•)(OH)C(O)R,
H2O2 + RC(O)C(O)R,
(X)
(XI)
RC(OOH)(OH)C(O)R
RCH(OH)C(O)R + H2O2
RCH(OH)C(OOH)(OH)R,
(XII)
KINETICS AND CATALYSIS Vol. 54
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2013

272
AKIMOV et al.
k
HO•2 + RC(OO•)(OH)C(O)R
(XIII)
(XIV)
(XV)
t1
k
2RC(OO•)(OH)C(O)R
t2
k
2HO•2
t3
molecular
products
'
k
HO•2 + RCH(OH)C(OO•)(OH)R
t4
(XVI)
k
RC(OO•)(OH)C(O)R + RCH(OH)C(OO•)(OH)R
t5
(XVII)
k
2RCH(OH)C(OO•)(OH)R
t6
(XVIII)
'
k
HO•2 + RCH(OO•)(OH)C(O)R
HO•2 + RCH(OH)C(OO•)(OH)R
HO• + RC(O•)(OH)C(O)R + O2,
(XIX)
(XX)
1
'
k
HO• + RCH(OH)C(O•)(OH)R + O2.
2
For this scheme, the rate of the radical chain oxidaꢀ
tion of 2ꢀhydroxycyclohexanone is given by the equaꢀ
tion
k
k
p1[RC(OH)(OO•)C(O)R][RCH(OH)C(O)R]
p3[RCH(OH)C(OO•)(OH)R][RCH(OH)C(O)R]
Eq. (3) can be represented as
=
,
w = (kp1[RC(OH)(OOi )C(O)R] + kp2[HOi2]
+ kp3[RC H( O H )C ( O O i )( O H )R])[RC H( O H )C ( O )R].
w = (kp2[HOi2]
+2kp3[RCH(OH)C(OOi )(OH)])[RCH(OH)C(O)R].
v
v
(3)
(4)
Under
the
assumption
that
the
The concentrations of RCH(OH)C(OO•)(OH)R and
RC(OH)(OO•)C(O)R and RCH(OH)C(OO•)(OH)R
HOi2
radicals are similar in reactivity and are indistinguishꢀ
radicals are related to the equilibrium constant of
able
in
chain
propagation
events,
i.e., reaction (VI) by the expression
K3 = [RCH(OH)C(OOi )(OH)R] [RCH(OH)C(O)R][HOi2].
In view of Eqs. (4) and (5), Eq. (3) appears as
(5)
(6)
w = (kp2 + 2kp3K3[RCH(OH)C(O)R])[HOi2][RCH(OH)C(O)R].
v
The total rate of recombination via reactions (XIII)–(XIX) is expressed as
wt = 2kt1[RC(OH)(OOi )C(O)R][HO2i ] + 2kt2[RC(OH)(OOi )C(O)R]2
+ 2kt3[HOi ]2 + 2kt4[RCH(OH)C(OOi )(OH)R][HOi2]
+ 2kt5[RC(OH)(OOi )C(O)R][RCH(OH)C(OOi )(OH)R]
+ 2kt6[RCH(OH)C(OOi )(OH)R]2.
(7)
Under the assumption that the RC(OH)(OO•)C(O)R
and RCH(OH)C(OO•)(OH)R radicals are indistinꢀ
guishable in the recombination reactions causing
chain termination, i.e.,
wt = 2kt3[HOi2]2
+ 4kt4[RCH(OH)C(OOi )(OH)R][HO2i ]
+ 6kt6[RCH(OH)C(OOi )(OH)R]2.
(8)
(9)
i
2
kt1[RC(OH)(OO•)C(O)R][
]
HO2
i
= 2kt4[RCH(OH)C(OO•)(OH)R][
]
and
t5[RC(OH)(OO•)C(O)R][RCH(OH)C(OO•)(OH)R]
=2
t6[RCH(OH)C(OO•)(OH)R]2,
Eq. (7) can be represented as
Using Eqs. (4) and (5), Eq. (7) can be written as
HO2
2k
wt = 2(kt3 + 2kt4K3[RCH(OH)C(O)R]
+ 3kt6K32[RCH(OH)C(O)R]2)[HOi ]2.
k
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KINETICS OF THE LIQUIDꢀPHASE OXIDATION OF 2ꢀHYDROXYCYCLOHEXANONE
273
Under quasiꢀsteadyꢀstate conditions (wt
=
wi), the cal escape from the solvent cage. With AIBN as the
initiator,
i
concentration of
radicals is given by the equation
HO2
'
(13)
m = 0.5 3 + keff kt,eff
,
)
(
[HOi2] = wi0.5 2(k + 2k K [RCH(OH)C(O)R]
(
t3
t4
3
'
where
and
kt, eff
are the effective rate constants for
keff
(10)
the recombination of peroxyl radicals without and
with chain termination, respectively.
−0.5
+ 3k K 2[RCH(OH)C(O)R]2)
.
)
t6
3
The total rate of peroxyl radical recombination
without chain termination (reactions (XX) and
(XXI)) is
Combining Eqs. (4) and (8) yields
i
w = (kp2 + 2kp3K3[RCH(OH)C(O)R])
v
'
w' = 2(k1[RC(OH)(OO )C(O)R]
(14)
i
ꢀ
× 2(k + 2k K [RCH(OH)C(O)R]
'
(
t3
t4
3
+ k2[RCH(OH)C(OO)(OH)R])[HO2].
(11)
Under
the
assumption
that
the
−0.5
+ 3k K 2[RCH(OH)C(O)R]2)
RC(OH)(OO•)C(O)R and RCH(OH)C(OO•)(OH)R
radicals are indistinguishable in the recombination
reactions without chain termination as well, i.e.,
)
t6
3
× [RCH(OH)C(O)R]wi0.5.
i
•
'
[RC(OH)(OO )C(O)
•
[HO2]
k1
The rate of the radical chain oxidation reaction is
i
'
=
[RCH(OH)C(OO )(OH)R]
[HO2],
k2
related to the oxygen uptake rate ( ) by a familiar
wO
2
Eq. (14) can be rewritten as
equation [13]:
i
i
'
(15)
w' = 4k2[RCH(OH)C(OO )(OH)R][HO2].
(12)
wO = w + mwi − wi,АIBN 2e,
v
2
With Eq. (5) taken into account, Eq. (15) appears as
where m is the coefficient accounting for nonchain
oxygen uptake and/or release in the chain initiation
2
'
'
(16)
w' = 4k2K3[RCH(OH)C(O)R][HO2] .
and termination events and е is the coefficient of radiꢀ Combining Eqs. (16) and (10) yields
'
4k2K3[RCH(OH)C(O)R]
(17)
w' =
wi,
2(kt3 + 2kt4K3[RCH(OH)C(O)R] + 3kt6K32[RCH(OH)C(O)R]2)
whence it follows that
'
'
keff
2k2K3[RCH(OH)C(O)R]
(18)
=
.
kt3 + 2kt4K3[RCH(OH)C(O)R] + 3kt6K32[RCH(OH)C(O)R]2
kt,eff
It follows from Eqs. (13) and (18) that
⎛
⎞
'
2k2K3[RCH(OH)C(O)R]
(19)
(20)
m = 0.5 3 +
.
⎜
⎟
⎟
⎠
kt3 + 2kt4K3[RCH(OH)C(O)R] + 3kt6K32[RCH(OH)C(O)R]2
⎜
⎝
The total rate of initiation via reactions (I), (III), and (IV) is given by
'
2
wi = wi,AIBN + k0[O2][RCH(OH)C(O)R] + k0[O2][RCH(OH)C(O)R] .
It follows from Eqs. (11), (12), (19) and (20) that
wO = (kp2 + 2k K [RCH(OH)C(O)R]) 2(k + 2k K [RCH(OH)C(O)R]
(
p3
3
t3
t4
3
2
+ 3k K 2[RCH(OH)C(O)R]2) −0.5 [RCH(OH)C(O)R]wi0.5 + mwi
(21)
)
t6
3
− wi,АIBN 2e = kp,eff (2kt,eff
)
−0.5[RCH(OH)C(O)R]wi0.5 + mwi − wi,АIBN 2e.
Therefore,
KINETICS AND CATALYSIS Vol. 54
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274
AKIMOV et al.
Concentration, mol/L
–0.5
kр, eff(2kt, eff
)
×
104, L0.5 mol–0.5 s–0.5
; m
Concentration, mol/L
0.06
0.30
0.25
0.20
0.15
0.10
0.05
0
60
50
40
30
20
10
7
1
0.05
0.04
0.03
0.02
0.01
1
6
2
2
5
8
4
3
0
60
120
180
Tme, min
240
300
0
0.5
1.0 1.5
[RCH(OH)C(O)R]
Fig. 1. Accumulation kinetics of the products of noncataꢀ
lytic 2ꢀhydroxycyclohexanone oxidation in chlorobenzene
(1.4 mol/L) at 323 K: (
) 2ꢀoxyꢀ2ꢀhydroperoxycyclohexanone, (
oxide, ( ) monoperoxyadipic acid, ( ) 1,2ꢀcyclohexanediꢀ
one, ( ) adipic anhydride, ( ) adipic acid, and ( ) mono(2ꢀ
oxocyclohexyl) adipate.
1
) peroxides (total concentration),
Fig. 2. Effect of the 2ꢀhydroxycyclohexanone concentraꢀ
tion on the oxidation parameters: (
(2kt,eff
−0.5 and
(2) m (AIBN initiator, 323 K). The points represent experꢀ
(2
3) hydrogen perꢀ
1)
)
kp,eff
4
5
6
7
8
imental data, and the lines represent calculated data.
−0.5
k
p, eff (2kt, eff
)
= (kp2 + 2kp3K3[RCH(OH)C(O)R])(2(kt3 + 2kt4K3[RCH(OH)C(O)R]
+ 3kt6K32[RCH(OH)C(O)R]2)−0.5
(22)
.
From Eqs. (12) and (21), it follows that the four
Based on bimolecular and termolecular chain initiꢀ
ation rate data determined using Eqs. (17) and (20),
for the aboveꢀspecified concentration of dissolved
oxygen in chlorobenzene we calculated the rate conꢀ
stants of chain initiation via the bimolecular reaction
−0.5
'
unknowns
k
,
0
,
, and
m
can be deterꢀ
k
p,eff (2kt,eff
)
k0
mined by varying [RCH(OH)C(O)R] and wi,AIBN
.
−0.5
Since the parameters
and, possibly, m
k
p,eff (2kt,eff
)
,
(
(
k
0 = 9.7 ×
'
10–7 L mol–1 s–1) and termolecular reaction
×
10–10 L2 mol–2 s–1).
in the oxidation of secondary alcohols depend on the
substrate concentration [19, 21, 22], they should be
determined for each particular value of the concentraꢀ
tion [RCH(OH)C(O)R].
= 1.7
k0
It follows from these data that, even under the conꢀ
ditions most favorable for the termolecular reaction
([RCH(OH)C(O)R] = 1.3 mol/L), its contribution to
the total chain initiation rate does not exceed 0.03%.
For solving the problem posed here, we investigated
the effects of the initiation rate (wi,AIBN) and substrate
concentration on the oxygen uptake kinetics in
2ꢀhydroxycyclohexanone oxidation with dioxygen at
323 K in chlorobenzene solution with AIBN as the iniꢀ Fig. 2, the oxidizability parameter
As is clear from the data presented in Table 1 and
−0.5
k
p,eff (2kt,eff )
tiator. In all cases, the initial segments of the oxygen
uptake curves were rectilinear.
depends on the ketoalcohol concentration according
to Eq. (22).
Using the values of the oxidizability parameter
obtained for different substrate concentrations, we
found the constants of Eq. (21) (Table 2) by solving the
inverse kinetic problem. The curve calculated in this
way (Fig. 2, curve 1) is in good agreement with the oxiꢀ
dizability parameter data listed in Table 1.
Table 1 lists the oxygen uptake rates ( ) derived
from experimental data.
wO
2
Simultaneous processing of the entire data array in
terms of type (12) equations enabled us to determine
−0.5
the
and m values (Table 1) and the valꢀ
k
p,eff (2kt,eff )
Since the decrease in the oxidizability parameter
with an increasing substrate concentration is attributed
to the decline of the reactivity of the alcohol and peroxyl
radicals in the chain propagation and termination reacꢀ
tions as a result of solvation effects [21], the values of the
'
ues of the constants k0[O2] and [O2] minimizing the
k0
deviation of the calculated oxygen uptake rates from
the corresponding experimental data (
10–9 s–1 and [O2] = 1.0 10–12 mol–1 s–1).
×
'
k0[O2] = 5.67 ×
k0
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KINETICS OF THE LIQUIDꢀPHASE OXIDATION OF 2ꢀHYDROXYCYCLOHEXANONE
275
Table 1. Effects of the initiation rate and substrate concentration on the kinetics of the AIBNꢀinitiated oxidation of 2ꢀhyꢀ
droxycyclohexanone in chlorobenzene solution at 323 K
106
wi, AIBN
×
108 wi,0
×
108
w ×
107
×
wO
−0.5
v
103,
L0.5 mol–0.5 s–0.5
2
[RCH(OH)C(O)R],
mol/L
Chain
length
×
k
p,eff (2kt,eff )
k
'/kt
m
mol L–1 s–1
1.6
1.9
2.5
3.2
3.6
0.19 0.02 1.01 0.04
0.24 0.04 1.10 0.06
0.29 0.03 1.26 0.05
0.35 0.04 1.43 0.08
0.38 0.05 1.51 0.09
6.3
5.8
5.0
4.5
4.2
0.15
0.25
0.35
0.5
0.08
0.14
0.20
0.28
0.45
0.57
0.74
5.30
6.91 10.8
7.55 12.1
7.82 12.6
11.13 19.3
30.53 58.1
28.80 54.6
22.20 41.4
3.3
6.3
0.41 0.02 1.33 0.03
0.69 0.03 1.84 0.04
0.90 0.06 2.25 0.07
1.12 0.12 2.60 0.13
1.29 0.10 2.91 0.11
4.0
2.9
2.4
2.1
1.8
9.5
2.92
2.42
2.14
1.93
1.70
1.65
12.6
15.8
6.3
9.5
0.56 0.03 2.14 0.05
0.86 0.07 2.62 0.08
1.23 0.11 3.02 0.13
1.48 0.09 3.42 0.10
1.76 0.10 3.69 0.12
3.4
2.8
2.4
2.1
1.9
12.6
16.2
18.9
9.5
12.6
15.8
22.1
25.3
1.33 0.12 3.32 0.13
1.66 0.14 3.82 0.16
2.12 0.18 4.27 0.20
2.77 0.16 5.05 0.17
3.11 0.22 5.40 0.24
3.5
3.0
2.7
2.3
2.1
9.5
12.6
15.8
18.9
22.1
3.20 0.24 4.85 0.26
4.60 0.21 5.56 0.23
5.10 0.32 6.21 0.33
6.23 0.24 6.78 0.25
7.40 0.26 7.32 0.28
5.1
4.4
3.9
3.6
3.3
0.8
9.5
12.6
15.8
19.0
22.1
3.46 0.20 5.39 0.22
4.11 0.22 6.17 0.23
5.83 0.23 6.88 0.25
6.10 0.19 7.52 0.20
7.30 0.25 8.10 0.27
5.7
4.9
4.4
4.0
3.7
1.0
28.4
31.6
36.3
41.0
47.3
7.42 0.24 11.62 0.26
7.86 0.28 12.24 0.30
9.40 0.30 13.09 0.31
10.49 0.33 13.89 0.34
11.65 0.29 14.90 0.31
4.1
3.9
3.6
3.4
3.2
1.3
KINETICS AND CATALYSIS Vol. 54
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276
AKIMOV et al.
Table 2. Calculated rate constants for the AIBNꢀinitiated oxidation of 2ꢀhydroxycyclohexanone in chlorobenzene solution
(1.4 mol/L) at 323 K
kp2
kp1
L mol–1 s–1
=
kp3
2
kt3
2
kt4
L mol–1 s–1
1.84
108
2
kt6
K
3, L/mol
496.6
2170
4.7
1.65
×
109
×
1.87 ×
107
constants obtained here should be considered to be nificance is the cross recombination of more and less
approximate.
reactive ones [23, 30]. Therefore, a likely peroxyl radꢀ
ical recombination event causing no chain terminaꢀ
tion is the interaction between the 1,2ꢀdihydroxyꢀ1ꢀ
i
The values of
m
in the ketoalcohol concentration
range examined are well above 1.5 (Table 1, Fig. 2), the
value that follows from the theory of radical chain oxiꢀ
dation initiated by this type of initiator (AIBN) with
quadraticꢀlaw chain termination [14]. The parameter
as a function of the substrate concentration passes
through an extremum (Table 1, Fig. 2): increases as
cyclohexylperoxyl radical and the
radical (reacꢀ
HO2
tion (XX)). Consequently, the optimum ratio of the
m
formation rates of the 2,2ꢀdihydroxyꢀ1ꢀcyclohexylpꢀ
i
eroxyl and
radicals for reaction (XX) should corꢀ
HO2
m
'
respond to the maximum values of
and m.
keff kt,eff
the concentration is increased from 0.15 to 0.8 mol/L
and then begins to decrease.
i
Indeed, the
radical is dominant at low ketoalcoꢀ
HO2
This phenomenon was observed earlier in the oxidaꢀ
tion of aromatic esters [23, 24], ketones [25, 26], and
carboxylic acids and their methyl esters [20], and it was
explained by the fact that quadraticꢀlaw chain terminaꢀ
tion via the reaction
hol concentrations. As the 2ꢀhydroxycyclohexanone
concentration increases, the relative amount of this
radical decreases and, at substrate concentrations of
>0.8 mol/L, it is insufficient for the maximum
involvement of the 1,2ꢀdihydroxyꢀ1ꢀcyclohexylperꢀ
oxyl radical in the cross recombination.
k
t
2RO2
molecular products + O2,
(XXI)
The cross recombination of the organic peroxyl
radicals
RC(OH)(OO•)C(O)R
and
is accompanied by the recombination of peroxyl radiꢀ
cals without chain termination, which is typical of terꢀ
tiary peroxyl radicals [13, 27, 28]:
HOi2
RCH(OH)C(OO•)(OH)R and
without chain
termination should proceed via the formation of the
intermediate hydrotetroxide ROOOOH. The bond
k'
2RO•2
2RO• + O2.
(XXII)
strengths (
metric dissociation of the O–O bond are DROOO–OH
105.0 2.1 kJ/mol and DRO–OOOH = 87.0
D) for the two possible variants of the asymꢀ
'
=
Using Eq. (13), we found the
ratio
keff kt,eff
(Table 1), which turned out to be much larger than in
the oxidation of not only the above oxygenꢀcontaining
compounds, but also tertꢀbutylperoxy radicals (at
5.8 kJ/mol [31–34]. Therefore, ROOOOH should
decompose mainly at the O–O bond nearest to the
alkyl residue:
'
323 K,
= 8.1 [29]). The finding that
keff kt,eff
RO• + O•OOH.
(XXIII)
'
grows with an increasing substrate concenꢀ
keff kt,eff
ROOOOH
tration can be explained by the decrease in kt,eff
The hydrotrioxyl radical resulting from reaction
(XXIII) decomposes to yield the hydroxyl radical and
the dioxygen molecule [35]:
because of the aboveꢀmentioned decrease in the proꢀ
i
portion of more active
radicals in the reaction
HO2
medium as
a
result of the increasing
HOOO•
HO• + O2.
(XXIV)
[RCH(OH)C(O)R]. However, this explanation is
'
inapplicable to the decrease in
at
keff kt,eff
However, the calculations cited above disregarded
the possible substrate effect on the asymmetric decomꢀ
position of the hydrotetroxide. 2ꢀHydroxycyclohexꢀ
anone is known to exert a considerably stronger effect
on the hydroperoxide decomposition rate than alcohols
or ketones [3, 4], causing hydroperoxide destruction
even at 323 K (Fig. 1). At 433 K, the effective rate conꢀ
stant of tertꢀbutyl hydroperoxide decomposition in the
presence of this ketoalcohol is 50 times larger than in
the presence of cyclohexanol or cyclohexanone. The
causes of the possible effect of 2ꢀhydroxycyclohexꢀ
[RCH(OH)C(O)R] > 0.8 mol/L. The extremum in
'
the dependence of
on the 2ꢀhydroxycycloꢀ
keff kt,eff
hexanone concentration may be due to the variation of
the proportions of two types of peroxyl radicals—
hydroperoxyl and 1,2ꢀdihydroxyꢀ1ꢀcyclohexylperꢀ
oxyl—in the reaction medium. In an earlier study of
the carbon chain length effect on the oxidation kinetꢀ
ics of carboxylic acids and their methyl esters [20], it
was demonstrated that a type (XXII) reaction involving
i
the
radical can take place.
HO2
When the reaction medium contains two types of anone on hydrotetroxide decomposition seem to be
peroxyl radicals differing in reactivity, of greatest sigꢀ fairly complicated. By analogy with hydroperoxide
KINETICS AND CATALYSIS Vol. 54
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2013

KINETICS OF THE LIQUIDꢀPHASE OXIDATION OF 2ꢀHYDROXYCYCLOHEXANONE
277
decomposition via familiar mechanisms [21], the folꢀ mulation of the products to the overall oxidation rate
lowing three intermolecular reaction pathways can be is 46%.
hypothesized:
The initial rate of monoperoxyadipic acid accumuꢀ
lation is 1.25
observed peracid accumulation rate can be ensured by
reactions (XIX) and (XXIX) taking place.
×
10–7 mol L–1 s–1 (Fig. 1). Therefore, the
ROOOOH + RCH(OH)C(O)R
(XXV)
·
·
ROOO + RC(OH)C(O)R,
–H O
2
Reactions like (XIII) can occur not only in the oxiꢀ
ROOOOH + ROH –H O ROOO• + RO•, (XXVI)
dation of
α
ꢀketoalcohols, but also at the early stages of
2
the oxidation of saturated hydrocarbons [20]. In this
ROOOOH + R2=O
i
case, the
radical results from the oxidation of
HO2
R2C(OH)OOOOR
(XXVII)
secondary alcohols as well.
·
·
R2C(OH)O + OOOR.
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Intramolecular interactions with the hydroxyl and
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−0.5
wO = kp,eff (2kt,eff
)
2
(23)
(24)
0.5
× [RCH(OH)C(O)R]w + mwi,0;
i,0
the chain initiation rate, by the equation
wi,0 = k0[O2][RCH(OH)C(O)R]
2
'
+ k0[O2][RCH(OH)C(O)R] .
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=
=
wi,0
0.79
3.8
uct accumulation is
×
10–8 mol L–1 s–1, the gas uptake rate is
wO
2
×
10–7mol L–1 s–1, and the rate of nonchain prodꢀ
= 1.75
×
10–7 mol L–1 s–1.
Therefore, the contribution from the nonchain accuꢀ
mwi,0
KINETICS AND CATALYSIS Vol. 54
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278
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Translated by D. Zvukov
KINETICS AND CATALYSIS Vol. 54
No. 3
2013