Reaction of chlorine dioxide with phenol

Article abstract of DOI:10.1023/A:1024905223801

The kinetics of phenol oxidation with chlorine dioxide in different solvents (2-methylpropan-1-ol, ethanol, 1,4-dioxane, acetone, acetonitrile, ethyl acetate, dichloromethane, heptane, tetrachloromethane, water) was studied by spectrophotometry. In all solvents indicated, the reaction rate is described by an equation of the second order w = k[PhOH] ? [ClO₂]. The rate constants were measured (at 10-60°C), and the activation parameters of oxidation were determined. The reaction rate constant depends on the solvent nature. The oxidation products are a mixture of p-benzoquinone, 2-chloro-p-benzoquinone, and diphenoquinone.

Full text of DOI:10.1023/A:1024905223801

Russian Chemical Bulletin, International Edition, Vol. 52, No. 5, pp. 1123—1128, May, 2003
1123
Reaction of chlorine dioxide with phenol
ꢀ
I. M. Ganiev, E. S. Suvorkina, and N. N. Kabal´nova
Institute of Organic Chemistry, Ufa Research Center of the Russian Academy of Sciences,
7
1 prosp. Oktyabrya, 450054 Ufa, Russian Federation.
Fax: +7 (347 2) 35 6066. Eꢀmail: chemox@anrb.ru
The kinetics of phenol oxidation with chlorine dioxide in different solvents (2ꢀmethylpropanꢀ
ꢀol, ethanol, 1,4ꢀdioxane, acetone, acetonitrile, ethyl acetate, dichloromethane, heptane,
1
tetrachloromethane, water) was studied by spectrophotometry. In all solvents indicated, the
reaction rate is described by an equation of the second order w = k[PhОН]•[ClO ]. The rate
2
constants were measured (at 10—60 °С), and the activation parameters of oxidation were
determined. The reaction rate constant depends on the solvent nature. The oxidation products
are a mixture of pꢀbenzoquinone, 2ꢀchloroꢀpꢀbenzoquinone, and diphenoquinone.
Key words: oxidation, chlorine dioxide, phenol, rate constants.
The action of oxidants is one of the most popular
methods for the functionalization of compounds belongꢀ
ing to different classes. From this point of view, chlorine
dioxide is of great interest. The most part of works on the
chemistry of chlorine dioxide were carried out in aqueous
solutions at low concentrations of reactants. Data on the
reactions of chlorine dioxide in organic solvents are lackꢀ
ing. At the same time, its use as an oxidant in the synꢀ
thetic organic chemistry is of considerable interest.
Phenol (reagent grade) was purified by double distillation in
argon. All solvents were purified using known procedures.
The reaction kinetics was studied spectrophotometrically by
monitoring the chlorine dioxide consumption (using the change
in the absorption at λ = 400 nm) with a Specord M40 instrument
6
,7
(
Carl Zeiss, Jena, Germany). The contribution of the absorpꢀ
tion of phenol and resulting products at this wavelength to the
8,9
absorbance can be neglected. The temperature of cells with a
solution of phenol and a solvent was maintained at 10—60 °С in
the chamber of the spectrophotometer. Then a necessary amount
of a solution of ClO2 was added to the working cell, and the
change in its absorbance was monitored. The initial concentraꢀ
The oxidation of phenols with chlorine dioxide was
intensely studied1
—4
because the latter is used in some
–
2
tions of phenol and ClO were varied within (0.1—10.0)•10
countries for purification of drinking water (first of all,
from phenols). The products and main kinetic regularities
of oxidation were studied. However, the oxidation of
phenols in nonaqueous solvents was not virtually studied.
In this work, we established the kinetic regularities of
phenol oxidation with chlorine dioxide in different solꢀ
vents (2ꢀmethylpropanꢀ1ꢀol (1), ethanol (2), 1,4ꢀdiꢀ
oxane (3), acetone (4), acetonitrile (5), ethyl acetate (6),
dichloromethane (7), heptane (8), tetrachloroꢀ
methane (9), and water (10)) at 10—60 °С.
2
and (0.5—1.2)•10–3 mol L , respectively.
–1
In order to study the oxygen effect on the kinetic regularities
of the process, oxygen or an inert gas (argon) was bubbled through
the cell containing a solution of phenol, a necessary amount of a
solution of ClO was added, and the consumption kinetics was
2
detected.
Reaction products were analyzed by GLC using a Chromꢀ5
instrument (column 3.5 m × 3 mm, 5% SEꢀ30 on Chromaton)
1
and Н NMR spectroscopy using a Bruker AMꢀ300 instrument
(
300 MHz) with CDCl as a solvent and Me Si as a reference.
3
4
Benzene was used as a label for the quantitative determination
of products.
Experimental
Results and Discussion
Chlorine dioxide was synthesized by the reaction of potasꢀ
sium perchlorate with oxalic acid in the presence of sulfuric
5
acid. The ClO flow was passed through a trap with P O for
2
4
10
Reaction products. It is established that at equimolar
dehydration and then through a column packed with silica gel
amounts of ClO and phenol the reaction products are
2
and cooled to 0 °С, where ClO was adsorbed. To obtain soluꢀ
2
pꢀbenzoquinone (50%), 2ꢀchloroꢀpꢀbenzoquinone (20%),
and diphenoquinone (10%). A similar composition of the
products was found for the oxidation of phenol with chloꢀ
tions of ClO , the column was heated in a thermostat to
2
3
0—35 °С, and ClO was blown out by gaseous argon into a trap
2
filled with a solvent. The concentration of ClO in a solution
2
2
,10
5
rine dioxide in water.
was determined iodometrically using the Bray method and specꢀ
1
trophotometrically. Potassium perchlorate and oxalic acid (both
Reaction kinetics. The reaction kinetics was studied at
reagent grade) were purified by recrystallization from water.
[ClO ] << [PhOH] ([ClO ] and [PhOH] are the initial
2
0
0
2 0
0
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1064—1068, May, 2003.
066ꢀ5285/03/5205ꢀ1123 $25.00 © 2003 Plenum Publishing Corporation
1

1
124
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 5, May, 2003
Ganiev et al.
3
–1
≠
–1
kapp•10 /s
1
2
t•10–3/s
∆H /kJ mol
ln[ClO2]
50
5
1
.5
.0
.5
1
2
4
5
4
1
0
3
–
8
5
6
1
40
–
1.2
–1.1
2
∆
S≠•10–2/J mol–1 K–1
4
3
≠
0
[PhOH]/mol L–1
Fig. 2. Activation enthalpy (∆H ) as a function of the activation
0
.05
0.10
≠
entropy (∆S ) for the oxidation of phenol with chlorine dioxide
Fig. 1. Semilogarithmic anamorphoses of chlorine dioxide conꢀ
in different solvents (Т = 25 °С; number of the point correꢀ
sumption in the reaction with phenol (solvent — acetone,
sponds to the number of the solvent).
–
2
–2
–2
Т = 30 °С): [PhOH] = 3•10 (1), 5•10 (2), 9•10 (3), and
0
–
2
–1
1
3•10 mol L (4) and the apparent rate constant of the reacꢀ
tion (kapp) as a function of the phenol concentration (5).
Ea is accompanied by the increase in the preꢀexponential
factor A (compensation effect)
concentrations of chlorine dioxide and phenol, respecꢀ
tively). In all solvents indicated, the kinetic curves with
the high correlation coefficient (0.980—0.999) are deꢀ
scribed by an equation of the first order (Fig. 1). The
apparent rate constants of the first order kapp = k•[PhOH]n
E = –(2.7±0.5) ꢁ (3.4±0.4)•lnA
(r = 0.99).
a
≠
The linear plot of the activation enthalpy (∆H ) vs.
≠
entropy (∆S ) (Fig. 2) is expressed by the equation
≠
≠
∆
H = (93.7±2.6) ꢁ (0.42±0.02)•∆S
(r = 0.99).
(
k is the secondꢀorder rate constant) were calculated from
the semilogarithmic anamorphoses of the kinetic curves.
The presence of the compensation effect indicates,
most likely, that the reaction mechanism in this series of
solvents remains unchanged.
The plot of kapp vs. [PhOH] is linear (see Fig. 1), which
0
indicates the first order with respect to phenol. In this
case, the kinetic equation of the reaction has the form
Effect of the solvent nature on the reaction rate conꢀ
stant. The isokinetic temperature calculated from the slope
–
d[ClO ]/dt = k[ClO ]•[PhOH].
2 2
≠
≠
of the plot of ∆H vs. ∆S is 150±20 °С, which is much
higher than the reaction temperature (10—60 °С). Thereꢀ
fore, the solvent effect on the kinetic regularities of oxidaꢀ
tion can be analyzed in the studied temperature interval.
Analysis of the data presented in Table 1 shows that the
reaction rate increases in the following series of solvents:
Similar results were obtained by the oxidation of pheꢀ
nol in water.11 The temperature plot of the rate constant
was measured, and the activation parameters were deterꢀ
mined in several solvents (Table 1). It is seen from the
data in Table 1 that the increase in the activation energy
Table 1. Activation parameters of the oxidation of phenol with chlorine dioxide in several solvents (Т = 25 °С)
Solꢀ
vent
k•102
/L mol–1 s–1
lnA
Ea
∆H≠
∆G≠
∆S≠
/J mol–1 K–1
В*
kJ mol–1
1
2
3
4
5
6
7
8
9
0.61±0.03
0.60±0.03
1.12±0.06
1.12±0.06
1.51±0.07
1.72±0.08
28.0±1.4
37.0±1.9
49.0±3.4
24.0±1.6
15±1
15±1
13±1
14±1
13±1
13±1
—
—
—
—
50±4
51±4
45±3
47±3
44±3
42±2
—
—
—
—
48±3
48±3
42±2
44±3
41±2
40±3
—
—
—
—
81±5
81±6
79±5
79±5
78±5
78±6
—
—
—
—
–110±8
–109±7
–124±8
–117±6
–125±8
–128±8
—
236
235
237
224
181
160
23
0
0
156
—
—
—
1
0
*
According to the data in Ref. 12.

Reaction of chlorine dioxide with phenol
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 5, May, 2003
1125
1
< 2 < 3 < 4 < 5 < 6 < 7 < 8 < 9. This implies a tendency
Scheme 1
for decreasing the rate constant of phenol oxidation with
an increase in the polarity of the medium.
We failed to describe the influence of the solvent naꢀ
ture on the reaction rate constant taking into account
only the polarity of the solvent. This can be explained,
most likely, by the contribution of specific solvation. It is
known13 that the affinity of phenol to form hydrogen
bonds with the solvent plays a substantial role in its reacꢀ
tivity. For example, when tetrachloromethane, which does
not form hydrogen bonds, is substituted by 1,4ꢀdioxane,
the rate of the reaction of 2,4,6ꢀtriꢀtertꢀbutylphenꢀ
oxyl with phenol decreases by ∼ 20 times (from 8 to
.38 L mol–1
s ). This is explained by the fact that the
–1
14
0
solvent forming hydrogen bonds shields the О—Н bond
of phenol, thus impeding its attack by phenoxyl. In order
to take into account this contribution in the total influꢀ
ence of the solvent, we chose as a parameter the donor
number В, which is determined from the shift of the abꢀ
sorption band of the OH group in the IR spectrum of
phenol.12
0
In the framework of the equation logk = logk ꢁ βB
k is the reaction rate constant under the conditions
0
(
accepted to be standard), we obtained the linear correlaꢀ
tion (Fig. 3; solvent 10 was excluded from the plot)
As for the reactions of ClO with olefins,2
0—22
the
2
logk = –(0.9±0.1) – (1.7±0.1)•10–2•B (r = 0.98).
formation of an unstable ether intermediate ROClO is
postulated, which rapidly decomposes to form hypochloꢀ
rous acid.
In nonaqueous lowꢀpolarity solvents, phenol does not
virtually dissociate to the proton and phenoxide anion.
Therefore, the transfer of an electron from the phenol
molecule to the ClO molecule can be considered as the
primary act. Then the proton is eliminated to form the
phenoxyl radical and chlorous acid (Scheme 2).
The negative sign of the β parameter indicates that the
1
5
transition state is less polar than the initial state.
Reaction mechanism. As follows from the analysis of
the solvent effect on the rate constant of phenol oxidation
with chlorine dioxide, the kinetic data do not obey reguꢀ
larities characteristic of other media when water is used as
the solvent. This indicates that the mechanism of the
2
reaction in water differs from that in other solvents.
A series of the data9
,11,16—19
in water suggests the disꢀ
sociation of phenol to form the phenoxide anion that
Scheme 2
reacts with ClO (Scheme 1).
2
lnk
0
9
7
8
–
2
4
–
6
4
3
5
1
The phenoxyl radical can either react with another
phenoxyl radical to form diphenoquinone or undergo furꢀ
ther oxidation with chlorine dioxide to form easily deꢀ
composing alkyl chlorite (Scheme 3).
Hypochlorous acid, which appears due to the decomꢀ
position of alkyl chlorite, interacts with organic comꢀ
2
0
100
200
B
Fig. 3. Logarithm of the rate constant of phenol oxidation with
chlorine dioxide (k) as a function of the donor number of the
solvent В (Т = 25 °С; solvent 10 is excluded from the correꢀ
lation).

1
126
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 5, May, 2003
Ganiev et al.
Scheme 3
In the latter case, the Оꢀcentered radical adds to the Cl
atom to form peroxy ether of chloric acid (Scheme 6).
2
5
Scheme 6
5
pounds, which explains the formation of the chloro deꢀ
rivatives by the oxidation of phenol with chlorine dioxide
By analogy to alkyl chlorites, peroxychlorate decomꢀ
poses to quinone and chloric acid (Scheme 7).
(
Scheme 4).
Scheme 4
Scheme 7
It is known that the phenoxyl radicals readily react
with oxygen,23 whose content during kinetic experiments
in solutions is comparable with the concentration of chloꢀ
–
3
–1
rine dioxide ([ClO ] = (0.5—1.2)•10 mol L , [O ] =
1
2
2
–
3
–1 24
.5•10 mol L ). For example, the rate constant of
the reaction of the 2,4,6ꢀtriꢀtertꢀbutylphenoxyl radical
with oxygen is reported to be temperatureꢀindependent
–
1 –1 13
and equal to 2400 L mol
s
.
Therefore, the reaction
of the phenoxyl radical with oxygen should be taken into
account (Scheme 5).
Let us consider how the involvement of molecular
oxygen in the reaction influences the kinetics using the
simplified scheme
Scheme 5
•
PhOH + ClO2
PhO + HClO ,
2
•
PhO + ClO2
OClOPhO,
•
OOPhO•,
PhO + O2
•
•
OOPhO + OOPhO
Termination,
The peroxy radicals formed can either disproportionꢀ
ate or decay in linear termination with chlorine dioxide.
•
•
ClO OOPhO .
2
OOPhO + ClO2

Reaction of chlorine dioxide with phenol
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 5, May, 2003
1127
In this case, the expression for the consumption rate of
chlorine dioxide takes the form
the rate of the reaction of the peroxy radicals with
ClO2 is much higher than that of the reaction with
oxygen.a
Additional data on the role of oxygen in the reaction
were obtained by measuring the rate in the reaction mixꢀ
tures preꢀsaturated with oxygen or purged with an inert
gas. It turned out that the additional bubbling of the reacꢀ
tion mixture with oxygen or an inert gas does not affect
the kinetic regularities of the consumption of chlorine
dioxide. This can be explained by the fact that the reacꢀ
•
–
d[ClO ]/dt = k [PhOH][ClO ] ꢁ k [PhO ][ClO ] ꢁ
2
1
2
2
2
•
ꢁ
k [OOPhO ][ClO ].
3 2
When the quasistationarity condition is applied with reꢀ
•
spect to the PhO radical, we obtain
•
•
d[PhO ]/dt = k [PhOH][ClO ] – k [PhO ][ClO ] –
1
2
2
2
tion of the phenoxyl radicals with ClO occurs much more
2
•
–
k [PhO ][O ] = 0,
rapidly than that with oxygen. Although published data
on rate constants of reactions of phenoxyl radicals with
chlorine dioxide are lacking, we can assume that these
reaction rate constants are close to the rate constants of
the diffusionꢀlimited reactions (note that the rate conꢀ
3
2
•
[
PhO ] = (k [PhOH][ClO ])/(k [ClO ] ꢁ k [O ]).
1 2 2 2 3 2
A similar approach to the determination of the quasiꢀ
•
stationary concentration of OOPhO leads to the trinoꢀ
stants of the reaction of ClO with the phenoxide anions
2
7
9
–1 –1 11
mial equation and a complicated expression for the reacꢀ
tion rate. Therefore, let us consider two ultimate cases:
range within 10 —10 L mol
s ).
Thus, the kinetic regularities of phenol oxidation with
chlorine dioxide were studied in different solvents, the
reaction products were identified, their yields were deterꢀ
mined, and the probable mechanism of the reaction was
proposed.
•
•
OOPhO reacts only with OOPhO (square termination)
•
and OOPhO reacts only with ClO (linear termination).
2
In the first case, where w = 0, from the quasistationarity
5
condition we have
•
•
• 2
d[OOPhO ]/dt = k [PhO ][O ] ꢁ k [OOPhO ] = 0,
3
2
4
References
OOPhO ] = [(k [PhO ][O ])/k ]0.5.
•
•
[
3 2 4
1
2
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4
•
•
•
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