Kinetics of oxidation of phenol with manganese dioxide

Article abstract of DOI:10.1134/S1070363211040141

The kinetics of oxidation of phenol with manganese dioxide at pH 5.5±0.5 were studied. In the temperature range from 393 to 323 K the reaction is of second order, and it occurs in the kinetic mode with an energy of activation of 42.0 kJ/mol. In the temperature range from 333 to 353 K the reaction follows first-order equation and is controlled by external diffusion; the energy of activation is equal to 6.65 kJ/mol. The oxidation products are hydroquinone and 1,4-benzoquinone, the fraction of the latter being less than 10 mol %.

Full text of DOI:10.1134/S1070363211040141

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 4, pp. 704–709. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © D.E. Chirkst, O.V. Cheremisina, M.A. Sulimova, A.A. Kuzhaeva, P.V. Zgonnik, 2011, published in Zhurnal Obshchei Khimii, 2011,
Vol. 81, No. 4, pp. 612–617.
Kinetics of Oxidation of Phenol with Manganese Dioxide
D. E. Chirkst, O. V. Cheremisina, M. A. Sulimova, A. A. Kuzhaeva, and P. V. Zgonnik
St. Petersburg State Mining University, 21 Liniya 2, Vasil’evskii ostrov, St. Petersburg, 199106 Russia
e-mail: ovcheremisina@yandex.ru
Received June 7, 2010
Abstract—The kinetics of oxidation of phenol with manganese dioxide at pH 5.5±0.5 were studied. In the
temperature range from 393 to 323 K the reaction is of second order, and it occurs in the kinetic mode with an
energy of activation of 42.0 kJ/mol. In the temperature range from 333 to 353 K the reaction follows first-order
equation and is controlled by external diffusion; the energy of activation is equal to 6.65 kJ/mol. The oxidation
products are hydroquinone and 1,4-benzoquinone, the fraction of the latter being less than 10 mol %.
DOI: 10.1134/S1070363211040141
log [Mn2+] = const – 2pH.
(2)
Phenol is a component of wastewater in petro-
chemical, by-product-coking, and galvanic processes.
Its concentration in waste water of a by-product coke
plant may reach 1 g/l [1]. Meanwhile, phenol is one of
the most hazardous pollutants. Its maximum allowable
concentration (MAC) in basins for household water
use is set at 0.001 mg/l [2]. In the course of wastewater
treatment phenol is oxidized to hydroquinone or 1,4-
benzoquinone for which MAC is 0.2 mg/l [2].
Purification to such concentration may be achieved by
sorption methods.
Thus manganese(II) transfer to solution sharply
decreases as pH rises, and it becomes harmless at pH >
5.6 [9]. Aqueous manganese dioxide oxidizes phenol
to hydroquinone and 1,4-benzoquinone [11]. The
mechanism of oxidation of benzenediols over MnO2
surface was studied in [9, 10]. The process includes
three steps:
(1) Formation of activated surface complex with
Mn(IV)–Ophenol bonds; the complex is stabilized due to
similarity of the Mn–Mn and O–O distances (277 and
285 pm or 554 and 570 pm for pyrocatechol and
hydroquinone, respectively);
Phenol can be oxidized by biochemical methods,
ultrasonic treatment, and photocatalytic reactions;
however, these procedures are not always effective but
are expensive [3]. Therefore, manganese dioxide was
proposed as oxidant [4–6]. In the pH range from 9 to
10 manganese dioxide acts as catalyst. Manganese(II)
species formed as a result of oxidation of phenol
deposit on the mineral surface as Mn(OH)2 and are
oxidized to MnO2 with dissolved oxygen [7, 8].
However, in acid medium (pH < 4) dissolution of
manganese dioxide and MnO2-containing minerals is
observed, and Mn2+ cations reside in solution [3, 9–
11]. This is undesirable, for manganese(II) compounds
are classed with toxicants (MAC 0.1 mg/l) [2].
Oxidation of benzenediols (hydroquinone [9] and
pyrocatechol [10]) is described by Eq. (1).
(2) Electron transfer;
(3) Decomposition of activated complex with
formation of benzoquinone and manganese(II).
Taking into account the high energy of activation,
58.7±6.6 kJ/mol, the rate-determining step is the
formation of activated surface complex; this reaction at
pH 4 is of pseudofirst order with respect to pyroca-
techol, and the rate constant k id equal to 5× 10–3 s–1
[10].
Studies in the field of phenol oxidation with
manganese dioxide extensively develop, for kinetic
data on the oxidation process are important for the
development of new methods for purification of
phenol-containing wastewater. However, some dis-
crepancies and unresolved problems should be noted.
First of all, the available kinetic data were obtained at
pH 4 [10] and 1.0–2.0 [3], whereas phenolic
C6H4(OH)2 + MnO2 + 2H+ ⇄ C6H4O2 + Mn2+ + 2H2O. (1)
The oxidation products of benzenediols are the cor-
responding benzoquinones. The concentration of Mn2+
in solution is given by Eq. (2).
704

705
KINETICS OF OXIDATION OF PHENOL WITH MANGANESE DIOXIDE
wastewaters are generally neutral. According to the
data of [3], the reaction follows pseudosecond-order
kinetics, and the rate-determining step is external
diffusion with an energy of activation of 11.62 kJ/mol.
Matocha et al. [10] reported that the order of the
reaction is pseudofirst and that the rate-determining
step is surface-chemical reaction. Therefore, in the
present work we examined the kinetics of phenol
oxidation with manganese dioxide in aqueous phase in
the temperature range from 293 to 353 K at pH
5.5±0.5. The given pH value was selected taking into
account that in this case the rate of phenol oxidation
does not depend on the concentration of hydroxonium
ions [10]. Insofar as the pK values for the surface
>MnIV(OH)2 groups are pK1 = 2.3 and pK2 = 3.3, these
groups dissociate almost completely at pH 5–6,
whereas the degree of dissociation of phenolic hydroxy
groups is negligible.
100 ml by adding a 0.1 M solution of sodium
hydroxide. Two 5-ml samples were withdrawn from
the resulting solution. The fist sample was placed into
a volumetric flask and adjusted to a volume of 10 ml
by addition a solution of sodium hydroxide, and the
optical density of the resulting solution at λ 235 nm
was measured against 0.1 M NaOH. The second
sample was diluted to a volume of 10 ml with 0.1 M
hydrochloric acid, and the optical density was
measured at the same wavelength relative to a
neutralized sodium hydroxide solution. The optical
density was linearly related to the phenol concentration
up to 10 mg/l; detection limit 0.5 mg/l. Determination
of phenol was possible in the presence of nitrogen and
sulfur oxides, hydrogen sulfide, aldehydes, ketones,
alcohols, and benzene and its homologs. Amines
exhibiting an analogous red shift interfered with
phenol determination.
The kinetic experiments were performed as follows.
A cell maintained at a constant temperature was
charged with 800 ml of an aqueous solution of phenol
with a concentration of about 1 g/l, 40 g of manganese
dioxide of chemically pure grade was added, and the
mixture was stirred at a speed of 400 rpm. Samples of
the reaction mixture with a volume of 15 ml were
withdrawn at definite time intervals and analyzed for
phenol, hydroquinone, and benzoquinone. All reagents
were of chemically pure grade.
Taking into account that phenol molecule possesses
a nucleophilic center in the para position with respect
to the hydroxy group (due to mesomeric effect),
hydroquinone and 1,4-benzoquinone were presumed as
oxidation products [11]. The concentration of
hydroquinone was determined from the difference
DpH 13 – ΔD. The concentration of 1,4-benzoquinone
was determined by spectrophotometry after oximation
with hydroxylamine hydrochloride [17]. For this
purpose, 0.25 ml of a solution of hydroxylamine
hydrochloride with a concentration of 2 g/l was added
to 2–6 ml of a solution to be analyzed, the mixture was
kept for 5 min, 0.2 ml of 25% aqueous ammonia was
added, and the mixture was diluted with water and
alcohol (for 6-ml samples, only with alcohol) to a
volume of 8 ml. The colored solution was analyzed by
spectrophotometry in a 1-cm cell at λ 436 nm; the
optical density was measured relative to a blank
solution. The concentration of benzoquinone in 200–
250 min increased to 40–50 mg/l, and the sum of the
phenol, hydroquinone, and benzoquinone concentra-
tions was equal to the initial phenol concentration.
Thus the oxidation product of phenol is hydroquinone
with an impurity of 1,4-benzoquinone (<10 mol %).
The low oxidative power of manganese dioxide may
be attributed to relatively high pH value.
The concentration of phenol was determined by
spectrophotometry, by measuring absorbance in the
UV region at λ 235 nm [12–16]. Alkaline solutions
(pH 13) of phenol and its derivatives are characterized
by red shift of the absorption maxima relative to those
observed in neutral solution (pH 7) due to formation of
phenoxide ion. The absorbance in alkaline medium is
proportional to the concentration of both major
component and impurities, whereas the absorbance of
the same solution neutralized to pH 7 originates only
from impurities. The concentration of phenol is then
given by the difference between in the optical densities
at pH 13 and pH 7: ΔD = DpH 13 – DpH 7. Analysis of
the electronic absorption spectra of reference aqueous
solutions of phenol, hydroquinone, pyrocatechol, and
resorcinol with a concentration of 5 mg/l at pH 7
showed that only phenol solution did not absorb at λ
235 nm.
In addition, we determined the concentration of
manganese in solution using a Spectroscan-U X-ray
fluorescent crystal diffraction spectrometer. When the
reaction time was 300 min and longer, the concentra-
tion of manganese in solution did not exceed its
detection limit equal to 4 mg/l. Insofar as stoi-
The concentration of phenol was determined as
follows. A 1-ml sample of a solution containing 1–
0.1 g/l of phenol was transferred into a 100-ml
volumetric flask, and the volume was adjusted to
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 4 2011

706
сm, M
CHIRKST et al.
chiometry of a reaction analogous to reaction (1)
requires the concentration of Mn2+ to exceed 500 mg/l,
we can conclude that manganese(II) is not transferred
to solution at pH > 5.
0.020
0.018
0.016
0.014
0.012
0.010
0.008
0.006
0.004
0.002
0.000
Figure 1 shows the experimental plots of phenol
concentration versus time in the oxidation with
manganese dioxide at pH 5.5±0.5 (V/m = 20 ml/g) at
293, 303, 318, 323, 333, 343, and 353 K. The plots
obtained in the temperature range from 293 to 323 K
were found to be approximated by second-order
kinetic equations. Figure 2 shows the linear plots of
reciprocal phenol concentration versus time. At 333–
353 K, a different mechanism of the reaction is
observed, and the dependences of the phenol
concentration upon time fit first-order kinetic
equations. The plots ln (c0/ct) = f(t) are given in Fig. 3,
and the linear trend equations and rate constants
determined from the slopes are presented in Table 1.
0
100
200
t, min
300
400
Fig. 1. Kinetic curves for the oxidation of phenol (cm) with
manganese dioxide (V/m = 20 ml/g) at (1) 293, (2) 303, (3)
318, (4) 323, (5) 333, (6) 343, (7) 353 K.
The dependences ln k = f(T–1) shown in Fig. 4 are
described by linear equations y = –5052x + 15.988
(R2 = 0.98) in the temperature range from 293 to 323 K
and y = –800.12x – 2.795 (R2 = 0.98) at 333–353 K.
The energies of activation calculated from the slopes
of the linear trends (Ea = Rtanα) are given in Table 1.
1/сt, l/mol
Change of the reaction kinetics in the temperature
range from 323 to 333 K indicates change of the rate-
determining step. On the basis of the reaction order
(n = 2) and energy of activation (42.0 kJ/mol) we
presumed that the rate-determining step at 293–323 K
is the formation of activated complex on the solid
phase surface, as in the oxidation of pyrocatechol over
birnessite surface [10]. The energy of activation
determined in the present work is lower than the value
58.7±6.6 kJ/mol reported in [10]. This may be due to
formation of pyrocatechol activated complex with
more sophisticated structure (coordination of two
functional groups to manganese). The different orders
of the reaction may be rationalized by the fact that
manganese(IV) is reduced to Mn2+ with stable 3d5
electron configuration. Manganese(III) lacks one
electron to fill the 3d sublevel by half and is unstable.
Pyrocatechol molecule donates two electrons to
manganese(IV) atom; therefore, the surface reaction is
of first order. On the other hand, the reduction of Mn4+
to Mn2+ requires two phenol molecules, so that the
rate-determining step is bimolecular, and the order of
the reaction is equal to 2.
t, min
Fig. 2. Linearized kinetic dependences for the oxidation of
phenol with manganese dioxide (V/m = 20 ml/g) at (1) 293,
(2) 303, (3) 318, and (4) 323 K.
t, min
Fig. 3. Linearized kinetic dependences for the oxidation of
phenol with manganese dioxide (V/m = 20 ml/g) at (1) 333,
(2) 343, and (3) 353 K.
The above assumptions were confirmed by analysis
of the kinetic dependence at 318 K and at a V/m ratio
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 4 2011

707
KINETICS OF OXIDATION OF PHENOL WITH MANGANESE DIOXIDE
Table 1. Kinetic parameters for the oxidation of phenol with manganese dioxide at V/m = 20 ml/g
T, K
Reaction order n
Trend equation
Rate constant k, mol l–1 min–1
Ea, kJ/mol
293
303
318
323
333
343
353
2
''
y = 0.314x + 57.48; R2 0.98
y = 0.440x + 68.75; R2 0.95
y = 1.047x + 88.80; R2 0.98
y = 1.556x + 82.91; R2 0.98
y = 0.0055x; R2 0.97
0.314
42.0
0.440
''
''
''
''
1.047
''
1.556
1
''
0.0055а
0.0060а
0.0063а
6.65
y = 0.0060x; R2 0.96
''
''
''
y = 0.0063x; R2 0.97
a min–1.
equal to 50 ml/g. The experimental data are collected
in Table 2, and linearized kinetic dependence in the
coordinates c–1—f(t) is shown in Fig. 5.
major oxidation product is hydroquinone, whereas less
than 10% of phenol is oxidized to 1,4-benzoquinone.
The overall reaction equation with account taken of
preliminary hydrolysis of surface groups and dissocia-
tion of MnIV(OH)2 groups looks as follows.
The linear trend is described by the equation y =
1.050x +58.28 with a reliability factor R2 of 0.99. The
rate constant at V/m = 50 ml/g, k45 = 1.050 l mol–1 min–1,
coincided with the value obtained V/m = 20 ml/g, k45 =
1.047 l mol–1 min–1 (Table 1). The fact that the rate
constant does not depend on the ratio V/m indicates
kinetic control of the process, where the rate-
determining step is surface reaction. By analogy with
the data of [10], the following reaction mechanism
may be proposed.
MnO2 (solid) + 2 C6H5OH (solution) + H2O (liquid)
⇄ MnO (solid) + 2 HOC6H4–OH (solution)
+ 2 H+ (hydrated)
Table 2. Dependence of the concentration of phenol on time
at V/m = 50 ml/g
c, M
Time, min
318 K
343 K
(1) Formation of activated complex via reaction of
manganese(IV) at nucleophilic center of the phenol
molecule in the para position with respect to the
hydroxy group. The >MnIV(OH)2 groups undergo
dissociation, while protons do not participate in the
reaction at pH 5.5±0.5. The rate-determining step is
bimolecular in phenol;
0
2
0.0141
0.0139
0.0136
0.0132
0.0129
0.0127
0.0125
0.0121
0.0100
0.0089
0.0078
0.0063
–
0.0172
0.0159
0.0141
0.0144
0.0143
0.0140
0.0102
0.0086
0.0063
0.0059
0.0042
0.0033
0.0028
–
5
10
15
δ+
δ–
δ+
δ–
>MnIV(2О–) + 2 С6Н5ОН ⇄ [>MnIV(2О–)] ····· (2 С6Н5ОН)
25
35
(2) Electron transfer is a fast step;
60
δ+
δ–
90
[>MnIV(2О–)] ····· (2 С6Н5ОН)
120
180
240
300
330
360
δ+
+
→ >MnII ····· (2О–) ····· (2 С6Н5ОН)
(3) Decomposition of the activated complex with
formation of products. Manganese(II) species are not
transferred to solution, and they reside on the solid
phase surface. According to [7, 8], Mn2+ species are
then oxidized to MnO2 with dissolved oxygen. The
0.0043
–
0.0024
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 4 2011

708
CHIRKST et al.
500
400
300
200
100
0
0
100
200
t, min
300
400
1/T
Fig. 5. Linearized kinetic dependences for the oxidation of
phenol with manganese dioxide (V/m = 50 ml/g) (1) at 318 K
in the coordinates 1/c—f(t) and (2) at 343 K in the
coordinates ln (c0/ct)—f(t).
Fig. 4. Plots of lnk vs. reciprocal temperature in the
temperature ranges (1) 333–353 and (2) 293–323 K.
δ+
+
δ+
surface has no negative charge, and the reaction with
nucleophilic centers in phenol molecules is facilitated.
Therefore, the surface reaction in acid medium is
faster, and the overall rate of the process is limited by
diffusion.
>MnII·····(2О–)·····(2 С6Н5ОН) → >MnII + 2 НО–С6Н5–ОН
The reaction rate rapidly increases as the
temperature rises, and at 333–353 K the process is
controlled by external diffusion. Here, the rate-
determining step is stationary convective diffusion of
phenol molecules in the Nernst layer. This is consistent
with pseudofirst order of the reaction and low energy
of activation, 6.65 kJ/mol. An additional support to the
above assumption was obtained by analysis of the
kinetic dependence at 343 K at a V/m ratio of 50 ml/g.
The experimental data are given in Table 2, and the
kinetic dependence linearized in the coordinates
ln (c0/ct)—f(t) is shown in Fig. 5. The linear trend is
described by the equation y = 0.0035x with a reliability
factor R2 of 0.99. The rate constant at V/m = 50 ml/g is
k70 = 0.0035 min–1, which is lower than at V/m =
20 ml/g, k70 = 0.0060 min–1. The fact that the rate
constant depends on the ratio V/m suggests that the
reaction rate is limited by external diffusion. The
oxidation of pyrocatechol was studied in [10] at lower
temperatures (283–298 K); therefore, the process
occurred in the kinetic mode. The oxidation of phenol
at 293–333 K [3] was found to be controlled by
external diffusion with an energy of activation of 11.62
kJ/mol. However, the kinetic region was not identified.
A probable reason is that the reaction was studied in
[3] at low pH values (1–2) at which manganese di-
Thus the major oxidation product of phenol at pH
5.5±0.5 is hydroquinone; 1,4-benzoquinone is formed
in an amount of less than 10 mol %, and Mn2+ species
are not transferred to solution. In the temperature range
from 293 to 323 K the reaction is characterized by
second order with respect to phenol, the energy of
activation is 42.0 kJ/mol, and the rate-determining step
is surface chemical reaction. The reaction at 333–
353 K follows pseudofirst-order kinetics with an
energy of activation of 6.65 kJ/mol, the rate-
determining step being external diffusion.
REFERENCES
1. Serikov, N.F., Vodnoe khozyaistvo zavodov chernoi
metallurgii (Water Industry in Ferrous Metallurgy),
Moscow: Metallurgiya, 1973.
2. Pit’evaya voda. Gigienicheskie trebovaniya k kachestvu
vody tsentralizovannykh sistem pit’evogo vodosnab-
zheniya. Kontrol’ kachestva (Drinking water. Hygienic
Requirements to Water in Centralized Systems for
Drinking Water Supply), SanPiN 2.1.4.1074-01.
3. Song Yin-xian, Xie Qiao-qin, and Chen Tian-hu, Bull.
Mineral. Petrol. Geochem., 2006, vol. 25, no. 4, p. 324.
oxide possesses
a
higher oxidation potential.
According to the Nernst equation, φ(MnO2, H+/Mn2+,
4. Bernard, S., Chazal, Ph., and Mazet, M., Water Res.,
H2O) = 1.23 – 0.118pH.
1997, vol. 31, no. 5, p. 1216.
At pH < 2, MnIV(OH)2 groups on the solid phase
surface almost do not undergo dissociation, the MnO2
5. Liu Ruixia and Tang Hongxiao, Environ. Chem., 2000,
vol. 19, no. 4, p. 341.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 4 2011

709
KINETICS OF OXIDATION OF PHENOL WITH MANGANESE DIOXIDE
6. Liu Ruixia and Tang Hongxiao, Water Res., 2000,
proizvodstvennykh stochnykh vod (Chemical Analysis of
Industrial Wastewater), Moscow: Khimiya, 1974, p. 271.
13. Sukhanov, P.T. and Korenman, Ya.I., Kontsentrirovanie
i opredelenie fenolov (Concentration and Determination
of Phenols), Voronezh: Voronezh. Gos. Tekhnol. Akad.,
2005.
14. Perez, F., Abstracts of Papers, Pittsburgh Conf. on
Analytical Chemistry and Applied Spectroscopy, New
Orlean, 1998, p. 950.
15. Liu, J. and Lin, Z., Spectrosc. Spectral Anal., 2000,
vol. 20, no. 4, p. 480.
16. Yonqnian, N. and Zhou, X., Spectrosc. Spectral Anal.,
2004, no. 1, p. 118.
vol. 34, no. 16, p. 4029.
7. McBride, M.B., Clays Clay Miner., 1989, vol. 37, no. 4,
p. 341.
8. Ukrainczyk, L. and McBride, M.B., Clays Clay Miner.,
1992, vol. 40, no. 2, p. 157.
9. Hue, N.V., Vega, S., and Silva, J.A., Soil Sci. Soc. Am. J.,
2001, vol. 65, no. 2, p. 153.
10. Matocha, Ch.J., Sparks, D.L., Amonette, J.E., and
Kukkadapu, R.K., Soil Sci. Soc. Am. J., 2001, vol. 65,
no. 1, p. 58.
11. Zhang, L.Z., Chen, Z.L., Ma, J., and Yu, M., Environ.
Sci. (China), 2006, vol. 27, no. 5, p. 945.
17. Belyakov, A.A., Tr. Kom. Anal. Khim., 1963, vol. 13,
p. 405.
12. Lur’e, Yu.Yu. and Rybnikova, A.I., Khimicheskii analiz
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 4 2011