Inhibition of the oxidation of styrene epoxide by potassium iodide and bromide in an acidic solution

Article abstract of DOI:10.1134/S096554411002012X

The inhibiting action of potassium iodide and bromide on the oxidation of the binary system of styrene epoxide + p-toluenesulfonic acid and on the hydroperoxide decomposition in the presence of the binary system was revealed. The inhibition mechanism is complex. During the course of the inhibition, the active form of the inhibitor is regenerated, which interacts, according to the kinetic data, with the transient species formed in the binary mixture.

Full text of DOI:10.1134/S096554411002012X

ISSN 0965ꢀ5441, Petroleum Chemistry, 2010, Vol. 50, No. 2, pp. 154–157. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © L.V. Petrov, V. M. Solyanikov, 2010, published in Neftekhimiya, 2010, Vol. 50, No. 2, pp. 164–167.
Inhibition of the Oxidation of Styrene Epoxide by Potassium Iodide
and Bromide in an Acidic Solution
L. V. Petrov and V. M. Solyanikov
Institute of Problems of Chemical Physics, Russian Academy of Sciences
pr. Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia
eꢀmail: plv@isp.ac.ru
Received December 3, 2008
Abstract—The inhibiting action of potassium iodide and bromide on the oxidation of the binary system of
styrene epoxide + pꢀtoluenesulfonic acid and on the hydroperoxide decomposition in the presence of the
binary system was revealed. The inhibition mechanism is complex. During the course of the inhibition, the
active form of the inhibitor is regenerated, which interacts, according to the kinetic data, with the transient
species formed in the binary mixture.
DOI: 10.1134/S096554411002012X
Styrene epoxide (SE) is slowly oxidized via a radiꢀ Otherwise, the experimental procedure did not differ
cal chain mechanism even at a high temperature of from that described in [2–4].
413 K in the presence of dicumyl peroxide, a freeꢀradꢀ
ical initiator [1]. The introduction of small amounts
(<0.1 mol/l) of pꢀtoluenesulfonic (TSA) or sulfuric
RESULTS AND DISCUSSION
acid into acetonitrile or alcohol solutions of styrene
epoxide results in intense oxygen absorption without
any initiator at 343 K. Simultaneously with the oxidaꢀ
tion, a much faster overall acidꢀcatalyzed consumpꢀ
tion of SE occurs [2, 3]. The regularities of hydroperꢀ
oxide decomposition induced by the binary system
(BS) (SE + TSA) in an argon atmosphere were studied
in [4]. The kinetic relationships for the rates of oxygen
uptake (VO2), the buildup of oxidation products, and
hydroperoxide degradation (Vp) as a function of the
TSA and SE concentrations are the same.
Potassium iodide inhibits the TSAꢀcatalyzed oxiꢀ
dation of styrene epoxide. One can see in Fig. 1
(curves
of KI into the oxidized binary system inhibits the oxiꢀ
dation. Curves and in Fig. 1 show the decrease in
1⎯3) that the introduction of various amounts
4
5
the rate of the decomposition of ethylbenzene hydroꢀ
Time, min
0
10
20
30
40
50
60
0.20
120
100
80
In this communication, we report the results of the
investigation of the potassium halide inhibition of the
oxidation of this binary system (SE + TSA) and the
BSꢀinitiated degradation of ethylbenzene and cumene
hydroperoxides in acetonitrile (MeCN) and a mixed
solvent of BUC (90 vol % tertꢀbutanol + 10 vol %
chlorobenzene).
5
0.15
0.10
0.05
0
4
60
1
40
2
3
EXPERIMENTAL
20
The oxidation of the binary system was carried out
in a Rittenberg twoꢀlegged tube for the separate heatꢀ
ing of TSA and SE solutions up to the experimental
temperature. The reactants were mixed by switching
on a shaker. In the experiments with potassium iodide,
KI must be heated in the leg with TSA, rather than
with SE, because of the fast consumption of KI in the
reaction between KI and SE during the heating. The
experiments on the oxidation of isopropanol were carꢀ
ried out in a simple reactor described elsewhere [5].
0
4
8
12
16
20
24
Time, min
Fig. 1. Kinetics of oxygen uptake (1–3) in the oxidation of
the binary system of SE + TSA in the acetonitrile solution
–4
at different [KI], mol/l: (1) 0, (2) 3.5 × 10 , and (3) 11.2 ×
–4
10 ; [SE] = 1.04 and [TSA] = 0.0206 mol/l; 343 K.
0
Kinetics (4, 5) of the EBHP degradation in acetonitrile at
[SE] = 0.73 and [TSA] = 0.045 mol/l, argon, 343 K; [KI],
0
–4
mol/l: (4) 0 and (5) 9 × 10 .
154

INHIBITION OF THE OXIDATION OF STYRENE EPOXIDE
155
peroxide (EBHP) induced by BS in the presence of
KI. The dependence of the rates of BS oxidation (
1)
8
6
4
2
2
and EBHP consumption (
3
) on the KI concentration
.
is given in Fig. 2. Curves
1
and 3 (Fig. 2) are similar in
shape. The efficiency of KI as an inhibitor in both
cases is also almost the same: upon the introduction of
~10–3 mol/l of KI, the rates of BS oxidation and BSꢀ
induced EBHP degradation in an argon atmosphere
decrease almost by a factor of 5–6. Molecular iodine
1
weakly inhibits the oxidation (Fig. 2, curve 2). It is
likely that I– is the active inhibiting agent. Note that
the effective inhibition with potassium iodide is
observed at its concentration well below the working
concentrations of the BS components epoxide and
acid. In the experiments pointed with arrows in Fig. 2,
[KI] is lower than [TSA] by a factor of approximately
20, and lower than [SE]0 by a factor of almost 1000.
Therefore, any assumption that the reactions of the
binary system are inhibited through the direct blockꢀ
ing of one or another component of the system by
potassium iodide, for example, via complexation, is
quite questionable.
3
0
4
8
12 16 20 24 28
[I2]
×
104, [KI] 104, mol/l
×
Fig. 2. The rate of (1, 2) oxygen uptake (
V ) in the binary
O
2
system of SE + TSA and (
Ar atmosphere in the presence of SE and TSA as a function
of the (1, 3) KI and ( ) iodine concentration. [SE] = 1.04,
3) EBHP degradation (V ) in an
p
2
0
[TSA] = 0.021 mol/l, acetonitrile, 343 K.
The experiments in the BUC solvent (tertꢀbutanol
with 10 vol % chlorobenzene) showed that both oxidaꢀ
tion and hydroperoxide degradation (using cumene
hydroperoxide, CHP, as an example) is retarded by
potassium iodide in this medium, but the efficiency
of the inhibition of oxidation in MeCN is almost
an order of magnitude higher (Fig. 2): the
oxidation rate in BUC decreases almost twice at
16
12
1
.
2
8
4
[KI]
≈
4
×
10–3 mol/l, and the oxidation rate in MeCN
decreases twice at [KI]
≈ ×
4
10⎯4 mol/l. The problem
of the low solubility of KI in BUC arises in the study of
the CHP decomposition. Therefore, iodide was introꢀ
duced in the form of the initial acetonitrile solution
3
(see curve 3 in Fig. 3). In the BUC solution, potassium
iodide inhibits the CHP degradation more actively
than the BS oxidation. As was mentioned above, the
efficiency of KI in the inhibition of the BS oxidation
and EBHP degradation is approximately the same in
0
10
20
30
40
50
[KI]
×
104, [KBr]
×
103, mol/l
MeCN. Curve
mide, similar to iodide, inhibits BS oxidation, but the
efficiency of the KBr as an inhibitor is almost an order
2 (Fig. 3) shows that potassium broꢀ
Fig. 3. The oxidation rate (
V ) of the binary system of
O
2
SE + TSA as a function of (
1
) [KI] and (
2
) [KBr] in BUC,
) The effect
V ) in the mixed
p
[TSA] = 0.012, [SE] = 1.04 mol/l, 343 K. (
3
0
of magnitude lower than that of KI (compare curves
1
of KI on the rate of CHP degradation (
solvent 80% BUC + 20% MeCN; [SE] = 1.04 and
and in Fig. 3). The weak inhibition ability of KBr
2
0
along with its low solubility in MeCN and especially in
BUC did not allow us to qualitatively examine the
inhibition of the BS oxidation and the hydroperoxide
degradation with potassium bromide. What is the
mechanism of the oxidation inhibition by iodide?
Does it involve oxygenꢀcontaining particles or is the
activity of the transient species, which have not
reacted with the O2 molecule, suppressed, as in the
case of hydroperoxide degradation in the argon atmoꢀ
sphere? To answer this question, we performed a set of
experiments at [TSA] = 0.041, [SE]0 = 1.04, and
[TSA] = 0.021 mol/l; 343 K.
The interpretation of these data is unambiguous:
the inhibition with iodide is more effective in air, in
which the oxygen concentration is lower, and the conꢀ
centration of the transient species that have not
reacted with oxygen is higher. This means that the
retardation with iodide occurs at the stage preceding
the oxygen reaction with transient species. The results
given below also agree with this conclusion.
[KI] = 4.2
10–4 mol/l in MeCN at 343 K. The rates
×
The retardation of the chain oxidation of secondꢀ
ary alcohol with iodine and iodide is described in [5].
of oxidation in oxygen and air atmospheres in the
presence and absence of KI are collated in the table.
PETROLEUM CHEMISTRY Vol. 50
No. 2
2010

156
PETROV, SOLYANIKOV
initiation with the binary system, the reaction of KI
with a transient species formed in BS may occur if KI
participates in the initiation of IPA oxidation. The
experiments on the oxidation of IPA were carried out
at equal initial rates of oxidation initiated by AIBN
Comparison of the oxidation rates (VO ) of the binary system
2
of SE + TSA in an air and oxygen atmosphere in the presence
and in the absence of KI. [SE] = 1.04, [TSA] = 0.041, and
[KI] = 4.2 × 10–4 mol/l; MeCN; 343 K
and BS, VAOI2BN ≈ VOBS2. It is known that TSA signifiꢀ
106 × VO ,
Run
no.
2
Oxidant gas Presence of KI
Ratio
mol/(l s)
cantly decreases the chain length of IPA oxidation.
Therefore, the equality of the TSA concentration in
the experiments with AIBN and BS is a necessary
experimental condition. The working concentration
1
2
3
4
5
6
7
8
Oxygen
Oxygen
Air
No
Yes
No
Yes
No
Yes
No
Yes
15.45
7.70
9.00
3.53
9.16
3.60
15.00
7.27
V1/
V3/
V5/
V7/
V2 = 2.01
V4 = 2.55
V6 = 2.54
V8 = 2.06
[TSA] =
to the condition VOAI2BN
intersection point of the VOAI2BN
([TSA]) curves (dashed line in Fig. 4). The compariꢀ
9
10–4 mol/l approximately corresponding
×
VBOS2 was found from the
([ТСК]) and VBOS2
Air
=
Air
=
f
=
Air
f
Oxygen
Oxygen
son of the experimental oxidation rates (Fig. 5) clearly
shows that potassium iodide does more efficiently
inhibit the BS (SE + TSA)ꢀinitiated oxidation of IPA.
At equal rates in the control experiments (curves
'), the introduction of KI at a concentration of 1.1
10–4 mol/l results in the inhibition of oxidation in the
experiment initiated with BS (cf. curves and ), with
the ratio of the final rates V2 V2′ being 2.1. When
[KI] = 2.2
10–4 mol/l, the induction period is clearly
) in the oxidation initiated by
AIBN, and the ratio of the final rates V3 V3′ = 2.9 is still
higher.
The mechanism explaining the inhibition by KI in
cyclohexanol, the secondary alcohol oxidized accordꢀ
ing to the radical mechanism, was proposed in [5]. The
chain termination in the oxidation occurs mainly via
the reaction of the hydroxyperoxide radical of the secꢀ
ondary alcohol with KI and I2. The radical reacts with
I2 as a reducing agent and with I– as an oxidant. The
alternation of these reactions provides for the multiple
chain termination of cyclohexanol oxidation per
inhibitor molecule. According to the known data, the
oxidation of the binary system of SE + TSA is not a
chain reaction, although we cannot rule out the particꢀ
ipation of free radicals in this reaction. The inhibition
of BS oxidation is similar to that described in [5] in the
following ways. In both cases, the oxidation is inhibꢀ
ited by both potassium iodide and bromide, with the
latter being the weaker inhibitor. Molecular iodine is
less active then iodide. As in the case of cyclohexanol
[5], the inhibition of BS occurs according to a comꢀ
plex mechanism, not in a reaction with simple stoichiꢀ
ometry. Consider the data of Figs. 1 and 2, in which
1 and
The primary radicals from the initiator AIBN do not
react with the iodine compounds, the inhibitors of
interest. Our binary system of SE + TSA initiates the
radical chain oxidation of secondary alcohol [6]. We
examined the effect of potassium iodide on the oxidaꢀ
1
×
2
2
′
/
×
tion of isopropyl alcohol (IPA) initiated by the binary observed (Fig. 5, curve
3
/
system. The idea of the test was as follows. Under
comparable conditions of running two radical chain
oxidation reactions of IPA, of which one is initiated by
AIBN and the other is initiated by BS, admixed
KI should inhibit the second reaction more efficiently.
The ability of KI to terminate oxidation chains at the
•
stage of the RO2 radical is the same in both cases, but
the roles in the initiation are different. In the case of
2
12
8
1
4
the point marked with an arrow in Fig. 2 (curve
responds to curve (Fig. 1). The oxidation rate at
[KI] = 1.1
10–3 mol/l is almost fivefold lower than
that in its absence, i.e., the inhibitor reacts with four
out of five transient particles, the appearance of which
1) corꢀ
3
×
1.5
1.0
×
103, mol/l
0
0.5
2.0
[TCK]
precedes the oxidation. The ratio
τ
= [KI]/ 0.8
×
V0
(
V
0 = 7.5
×
10–6 mol/l s (Fig. 2)) in this experiment is
Fig. 4. The rate of the radical chain oxidation (
V ) of isoꢀ
O
2
equal to ~180 s, i.e., on the assumption of the simple
inhibition stoichiometry 1 : 1, when an iodide moleꢀ
cule is irreversibly consumed in the reaction of a tranꢀ
propanol initiated by (1) [AIBN] = 0.026 mol/l and (2) the
binary system SE + TSA, [SE] = 0.87 mol/l, as a function
0
of [TSA]; 343 K.
PETROLEUM CHEMISTRY Vol. 50
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2010

INHIBITION OF THE OXIDATION OF STYRENE EPOXIDE
157
sient particle responsible for the propagation of the
oxidation chain, the inhibition in the experiment
(Fig. 1) should cease after 3 min. However, no increase
in the rate was observed during the experiment.
1
3
2
100
80
1'
3
Let us consider Figs. 1 and 2 again: the point
2'
marked with an arrow in curve
3 (Fig. 2) corresponds
60
40
20
to curve (Fig. 1). Proceeding from the same assumpꢀ
5
tions as above in the case of the evaluation of the inhiꢀ
bition period in the BS oxidation, we suggest the simꢀ
ple 1 : 1 stoichiometry for the reactions of a transient
active particle with both ROOH and iodide (ROOH
degradation inhibitor) and find the expected inducꢀ
3'
tion period
binary system to be
Therefore, the inhibitor should be consumed in less
than a minute and the slope of curve (Fig. 1) should
become equal to the slope of curve (Fig. 1). This is
τ
of EBHP degradation induced by the
τ
= (9
×
10–4/0.8 10–5) = 38 s.
× ×
3
0
4
8
12
Time, min
16
20
24
28
5
4
Fig. 5. Kinetics of isopropanol oxidation as a function of
[KI], 343 K: (1–3) initiation by 0.0206 mol/l AIBN in the
presence of [TSA] = 9 × 10 mol/l, and (1'–3') initiation
by the binary system of 0.87 mol/l SE + 9
not the case; consequently, one should assume the
complex character of the inhibition mechanism and
the repeated decay–regeneration of the transient speꢀ
cies on the iodide inhibitor both in the BS oxidation
and ROOH degradation in the presence of BS. To
account for the multiplicity during the ROOH degraꢀ
dation in argon, we should not hypothesize the alterꢀ
nation of the oxidation and reduction stages of radicals
–4
–4
× 10 mol/l
–4
TSA. [KI], mol/l: (1, 1') 0, (2, 2') 1.1 × 10 , (3, 3') 2.2 ×
–4
10
.
mechanism is complex and its specification is still
impossible.
•
•
HO2 or R(OH)OO [7]: the degradation of the secꢀ
ondary and tertiary hydroperoxides EBHP and CHP
occurs in the absence of oxygen and there are no
hydroxyperoxide and hydroperoxide radicals under
these conditions.
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PETROLEUM CHEMISTRY Vol. 50
No. 2
2010