Influence of a reaction medium on the oxidation of aromatic nitrogen-containing compounds by peroxyacids

Article abstract of DOI:10.1134/S0036024411010079

The influence of different solvents on the oxidation reaction rate of pyridine (Py), quinoline (QN), acridine (AN), α-oxyquinoline (OQN) and a-picolinic acid (APA) by peroxydecanoic acid (PDA) was studied. It was found that the oxidation rate grows in the series Py < QN < AN, and the rate of the oxidation reaction of compounds containing a substituent in the α position from a reactive center is significantly lower than for unsubstituted analogues. The effective energies of activation of the oxidation reaction were found. It was shown that in the first stage, the reaction mechanism includes the rapid formation of an intermediate complex nitrogen-containing compound, peroxyacid, which forms products upon decomposing in the second stage. A kinetic equation that describes the studied process is offered. The constants of equilibrium of the intermediate complex formation (K_eq) and its decomposition constant (k₂) in acetone and benzene were calculated. It was shown that the nature of the solvent influences the numerical values of both K_p and k₂. It was established that introduction of acetic acid (which is able to form compounds with Py) into the reaction medium slows the rate of the oxidation process drastically. Correlation equations linking the polarity, polarizability, electrophilicity, and basicity of solvents with the constant of the PDA oxidation reaction rate for Py were found. It was concluded that the basicity and polarity of the solvent have a decisive influence on the oxidation reaction rate, while the polarizability and electrophilicity of the reaction medium do not influence the oxidation reaction rate. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036024411010079

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2011, Vol. 85, No. 1, pp. 45–50. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.S. Dutka, N.V. Matsyuk, Yu.V. Dutka, 2011, published in Zhurnal Fizicheskoi Khimii, 2011, Vol. 85, No. 1, pp. 51–56.
CHEMICAL KINETICS
AND CATALYSIS
Influence of a Reaction Medium on the Oxidation
of Aromatic NitrogenꢀContaining Compounds by Peroxyacids
V. S. Dutka, N. V. Matsyuk, and Yu. V. Dutka
Franko National University of Lviv, Universitetska str. 1, Lviv, 79000 Ukraine
eꢀmail: vdutka@ukr.net
Received January 13, 2010
Abstract—The influence of different solvents on the oxidation reaction rate of pyridine (Py), quinoline
(QN), acridine (AN),
α
ꢀoxyquinoline (OQN) and ꢀpicolinic acid (APA) by peroxydecanoic acid (PDA)
α
was studied. It was found that the oxidation rate grows in the series Py < QN < AN, and the rate of the oxidaꢀ
tion reaction of compounds containing a substituent in the position from a reactive center is significantly
α
lower than for unsubstituted analogues. The effective energies of activation of the oxidation reaction were
found. It was shown that in the first stage, the reaction mechanism includes the rapid formation of an interꢀ
mediate complex nitrogenꢀcontaining compound, peroxyacid, which forms products upon decomposing in
the second stage. A kinetic equation that describes the studied process is offered. The constants of equilibrium
of the intermediate complex formation (Keq) and its decomposition constant (k2) in acetone and benzene
were calculated. It was shown that the nature of the solvent influences the numerical values of both Kp and k2
.
It was established that introduction of acetic acid (which is able to form compounds with Py) into the reaction
medium slows the rate of the oxidation process drastically. Correlation equations linking the polarity, polarꢀ
izability, electrophilicity, and basicity of solvents with the constant of the PDA oxidation reaction rate for Py
were found. It was concluded that the basicity and polarity of the solvent have a decisive influence on the oxiꢀ
dation reaction rate, while the polarizability and electrophilicity of the reaction medium do not influence the
oxidation reaction rate.
Keywords: aromatic nitrogenꢀcontaining compounds, peroxyacids, oxidation.
DOI: 10.1134/S0036024411010079
INTRODUCTION
Peroxyacid was obtained by the reaction of decanoic
acid with hydrogen peroxide in a sulfuric acid medium
[7]. After synthesis, the obtained specimen was recrysꢀ
tallized from hexane several times. The main impurity
in the PDA samples was decanoic acid. Oxidation was
performed in a glass reactor in an argon atmosphere in
a temperature range of 303–328 K. The reactor was
placed in a thermostat, the temperature in which was
maintained with an accuracy of 0.01 K. The initial
solutions of nitrogenꢀcontaining compound and PDA
were thermostated for 20–30 min, then rapidly poured
out, sampled from reaction mixture and analyzed
them for peroxyacid content iodimetrically [8]. Conꢀ
Organic peroxyacids (PAs) are widely used as oxiꢀ
dizers in many reactions. The particulars of the oxidaꢀ
tion of olefines, nitrogenꢀ and sulfurꢀcontaining comꢀ
pounds by PA were considered in [1–4], where it was
proved that these processes are typical electrophilic
reactions. The influence of the solvent in oxidation
processes with the participation of PA remains
poorly studied, but one might expect that the reacꢀ
tion medium would influence both the rate of the
reaction and the product yield. In the present work,
the results from investigating solvents’ influence on
the rate of oxidation of acridine (AN), quinoline (QN),
stants of the oxidation rate (k) were determined at the
α
ꢀoxyquinoline (OQN), pyridine (Py), and
acid (APA) are given.
α
ꢀpicolinic
initial stages of the process, and the error in determinꢀ
ing the values of the rate constant did not exceed 3%.
Infrared spectra were measured on a Specord Mꢀ80
spectrophotometer.
EXPERIMENTAL
All solvents and nitrogenꢀcontaining heterocyclic
compounds were purified by commonly accepted
techniques [5, 6] and distilled in an argon atmosphere.
RESULTS AND DISCUSSION
Acridine,
α
ꢀoxyquinoline, and
α
ꢀpicolinic acid were
It was shown by previous tests that in all cases up to
recrystallized from alcoholic solutions. In all tests, deep degrees of conversion, the first order is observed
peroxydecanoic acid (PDA), the purity of which was for each of the reagents, and the total kinetic order of
no lower than 99.0–99.5%, was used as an oxidizer. the oxidation reaction of nitrogenꢀcontaining comꢀ
45

46
DUTKA et al.
Table 1. Kinetic and activation parameters of the oxidation of nitrogenꢀcontaining compounds by PDA (initial concentraꢀ
tions of PDA and nitrogenꢀcontaining compound were 0.05 mol/l)
Compound
k
×
104, l/(mol s) Eact 5.0, kJ/mol
Solvent–benzene
40.5
Δ
Н#, kJ/mol
–
Δ
S#, J/(mol K)
Δ
G#, kJ/mol
АN
QN
Ру
116
77.6
37.8
41.7
47.2
35.2
153
145
131
171
83.7
88.4
89.6
90.1
44.4
49.9
37.9
42.8
37.4
ОQN
Solvent–acetone
АN
24.6
15.7
13.8
50.1
42.0
44.8
39.4
57.4
53.1
47.4
39.3
42.1
36.7
54.7
50.4
136
165
157
184
121
150
91.3
92.5
92.7
96.1
93.9
98.8
QN
Ру
ОQN
ОQN
АPA
4.16
8.7
1.44
#
#
#
Note: The k value (Δk = 0.03k) was obtained for a temperature of 313 K, while ΔH , ΔS , ΔG was calculated for 323 K. In the case of
OQN (second line), the solvent was ethyl acetate.
pounds by PDA is equal to 2. Judging from the (Table 1, 2). It is noteworthy that the
S# values are
Δ
obtained results, the reaction products have practiꢀ
cally no influence on the process rate. The effective
constants of the oxidation rates of the studied nitroꢀ
genꢀcontaining compounds in acetone and benzene
are presented in Table 1.
negative in all cases, demonstrating the greater order
of the transition state in comparison with the initial
state. The oxidation process of the studied nitrogenꢀ
containing compounds in benzene is characterized by
lower values of
a linear interconnection between the values
H# of the transition state for the oxidation of pyridine
by PDA; i.e., a compensatory effect was observed
Δ
G#than in acetone (Table 1). There is
Δ
S# and
The degree of oxidation of nitrogenꢀcontaining
compounds in benzene is considerably higher than in
acetone. As is well known [1], the epoxidation process
Δ
rate of ethylene compounds by PA is strongly reduced under the conditions of our tests. The linearity of
dependence
Δ
H#
=
f( ) shows the complicated
S#
Δ
in solvents that are able to form intermolecular hydroꢀ
gen bonds with PA (as compared to “inert” solvents).
The peroxyacid molecules of most solvents exist in
cyclic form with an intramolecular hydrogen bond [1],
and the oxidation rate in such solvents is higher. The
reaction rate in both benzene and acetone declines in
the series AN > QN > Py. The oxidation reaction rate
of compounds containing a substituent close to the
reactive centers of OQN and APA is appreciably lower
than for their unsubstituted analogues (Table 1).
nature of the influence of the solvent on the rate and
mechanism of the oxidation process.
Based on the obtained results, we may assume that
at the first stage of the reaction, an intermediate comꢀ
pound forms rapidly and yields reaction products
upon decomposing at the second stage. The reaction
medium will influence both the first and second stage
of the oxidation process. These assumptions have been
confirmed by infrared spectroscopic tests. In Fig. 1, we
present the dependence of the optical density of the
absorption band at 3280 cm–1 on the PDA concentraꢀ
tion in tetrachloromethane solution. It is known from
[9] that the absorption band at 3280 cm–1 corresponds
to the valence vibrations of the OH group associated
with the intramolecular hydrogen bond. A change in
the PDA concentration in the range of 0.01–0.1 mol/l
leads to a proportional increase in the band intensity.
The addition of pyridine to the reaction mixture and
the fast scanning of the band at 3280 cm–1 leads to a
change in the band’s intensity (Fig. 1); in this case, it
splatters. This confirms our assumption as to the forꢀ
mation at the process’s initial stages of the intermediꢀ
Products of the interaction between PDA and
compounds containing a tertiary nitrogen atom are
Nꢀoxide and decanoic acid. The activation energies of
the oxidation process of the studied PDA comꢀ
pounds lie in the range of 37.9–57.4 kJ/mol and are
close to the numerical values given in the literature
[1, 2]. The solvents’ influence on the oxidation rate
of pyridine (Py) is considered in detail in Table 2.
The oxidation process is slowest in dioxane, while
the reaction rate is ~10 times faster in chloroform.
The total energies of activation for the process of
pyridine oxidation by PDA lie in the range of 64.8–
30.6 kJ/mol (Table 2).
The parameters of transition state
Δ
H#
,
Δ
S#, and
Δ
G# were calculated for all oxidation reactions ate compound PyPA. The first stage of the Py oxidaꢀ
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INFLUENCE OF A REACTION MEDIUM
47
Table 2. Kinetic and activation parameters of pyridine (Py) oxidation by peroxydecanoic acid (PDA) in the studied solvents
(the initial concentration of PDA and nitrogenꢀcontaining compound were 0.05 mol/l)
k
×
103 0.03
l/(mol s)
k
,
Eact 5.0,
kJ/mol
Δ
Н#
kJ/mol
,
–
Δ
S#
J/(mol K)
,
Δ
G#
,
kJ/mol
Solvent
Dioxane
1.89
2.38
2.50
2.96
6.76
7.88
8.12
10.8
11.8
19.5
11.5
12.9
68.4
54.9
44.8
47.7
48.1
49.9
50.8
54.0
51.2
52.3
32.8
30.6
65.7
52.2
42.1
45.0
45.4
47.2
48.1
51.3
48.5
49.6
30.1
27.9
86
126
157
146
138
131
128
116
124
116
118
187
93.5
92.8
92.7
92.3
90.0
89.6
90.0
88.8
88.5
87.2
88.6
88.3
Propanolꢀ2
Acetone
Ethyl acetate
Toluene
Benzene
Tetrachloromethane
DMFA
Chlorobenzene
Chloroform
Dichloroethane
Nitrobenzene
#
#
#
Note: The value k was obtained for 323 K; ΔH , ΔS , ΔG were calculated for 323 K.
tion reaction can be characterized by the equilibrium oxidation rate (k'eff) tend to a certain limit with an
constant Кeq
:
increase in the Py concentration. The dependence on
the Py concentration is straightened satisfactorily in
k1
k−1
Ру + PA
РуPA
.
(1)
←⎯→
'
the coordinates
on
, allowing us to deterꢀ
1/ Py
0
1/keff
mine the numerical values of k2 and
ilar regularities are observed for acetone solutions, but
the k2 and eq values differ from the corresponding valꢀ
[
]
The disintegration of the intermediate compound
PyPA is the rateꢀdetermining stage of the process,
which can be described by the “true” rate constant (k2
Keq (Fig. 3). Simꢀ
)
K
of the oxidation reaction:
ues obtained in benzene (Table 3). The values of the
true rate constants of the oxidation reaction in acetone
k2
РуPA
reaction products
.
(2)
(3)
⎯⎯→
The process rate is determined by the equation:
103, mol/l
k Py
[
]
d PDA
[
]
2
cPDA
10.0
×
0
,
PDA
W = −
=
[
]
2.5
5.0
7.5
dt
K + Py
n
0
[
]
where
1
1.2
0.8
0.4
,
K = k + k /k
1
(4)
(
)
n
−1
2
and [Py]0 is an initial pyridine concentration in soluꢀ
tion. Since the pseudomolecular constant is equal to
k Py
=
[
]
2
0
'
,
(5)
keff
K + Py
[
]
n
0
we can obtain the numerical values of k2 and Kn from
this dependence in the coordinates
'
on
.
1/ Py
0
1/keff
[
]
The inverse value of Kn is symbolized as Ke and is the
constant of complex formation for peroxyacid with
pyridine. In this case, the k2 value in expression (4) can
2
be ignored, in comparison with k–1
.
0
5
10
15
20
cРу
25
Tests at a constant concentration of PDA and variꢀ
ous pyridine content were performed to verify proꢀ
posed equations (2)–(5). In Fig. 2, we present the
dependence of the pseudomolecular constants of the
oxidation rate on the Py concentration in benzene
solution. The pseudomonomolecular constants of the
×
103, mol/l
Fig. 1. Dependences of the optical density (
D
) of absorpꢀ
tion band 3280 cm on the concentration of PDA ( ) in
) in tetrachloꢀ
–1
1
tetrachloromethane and pyridine, and (
romethane with 0.05 mol/l of PDA.
2
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48
k eff
DUTKA et al.
1
3
'
×
105, s−
(1/k'eff)
14
×
10− , s
160
120
80
40
0
3
2
1
12
10
8
2
3
1
6
4
2
0.1
0.3
0.5
mol/l
0
10
20
30
40
50
1/
60
cРу, l/mol
cРу,
Fig. 2. Dependences of the pseudomonomolecular conꢀ
stant of the oxidation rate on the pyridine (Py) concentraꢀ
1/ Py
Fig. 3. Dependences
benzene. Temperature, K: (
on
[
]
0. The solvent was
1/ke'ff
tion. The solvent was benzene. Temperature, K: (
) 313; ( ) 323.
1) 303;
(
2
3
1
) 303, (2) 313, ( ) 323.
3
In most works on the influence of reaction media
on oxidation reactions with the participation of PA,
the solvents’ main influence is associated with a
change in the reactivity of the oxidizer. We cannot,
however, rule out the solvation of Py by the solvents, or
the possibility of subsequent changes in the process
rate. We performed tests on the oxidation of Py by
PDA using various contents of acetic acid. As is well
known, acetic acid forms a stable compound with Py
[10]. Py oxidation by PDA will proceed at a moderate
rate. The dependences of the overall constant of the
oxidation reaction rate k on the content of acetic acid
in solutions of tetrachloromethane and chlorobenzene
are given in Fig. 4.
As follows from the obtained data, the addition of a
small amount of acetic acid to the reaction solutions
k2 are slightly lower than the corresponding values
obtained in benzene solution.
The activation energies (Е2) calculated according
to the temperature dependences of true oxidation rate
constant k2 are practically the same as the correspondꢀ
ing parameters obtained for value k (Table 1). As in the
case of benzene and acetone, the calculated values of
Keq increase as the temperature rises (Table 3). As
might be expected, the numerical values for the equiꢀ
librium constants Keq determined in the benzene soluꢀ
tion are slightly higher than the same parameters calꢀ
culated for the acetone systems (Table 3).
The dependences of Keq on temperature in the
coordinates ln(
rily, allowing us to calculate the numerical values for
and of the first stage of the oxidation reaction:
the formation of the intermediate compound PyPA.
The obtained values of and are negative. The
numerical values of for the tests performed in aceꢀ
tone are higher than the corresponding parameters
determined in benzene. The value of the first stage
Keq) on 1/T are straightened satisfactoꢀ
leads to a significant reduction in the
ing the acetic acid content from 0.1 to 0.5 mol/l
changes inappreciably. In the case of tetrachloꢀ
romethane, the value drops from 8.12
10–3 l/(mol s)
k value. Increasꢀ
Δ
Н
Δ
S
k
Δ
Н
Δ
S
k
×
Δ
Н
to 3.02 l/(mol s) when the acetic acid content is
increased from 0 to 0.5 mol/l. A similar change in the
acetic acid content caused the k value for the reaction
mixture in chlorobenzene to fall by 60%.
The obtained results are straightened satisfactorily
in coordinates of k on 1/C, where C is the concentraꢀ
Δ
S
of Py oxidation by PDA in acetone is –119 J/(mol K).
For benzene, this value is considerably higher:
–72 J/(mol K). This testifies to the unequal influence
of the solvents on the studied reaction.
Table 3. Numerical values of the parameters of pyridine oxidation by peroxydecanoic acid in acetone and benzene
, K
T
Е2
kJ/mol
,
–
Δ
H
,
–ΔS,
J/(mol K)
Solvent
Acetone
Benzene
Parameter
kJ/mol
303
313
323
k2
eq, l/mol
k2
104, s–1
eq, l/mol
×
104, s–1
3.80
2.84
5.36
10.4
5.63
2.17
10.3
7.02
11.7
1.09
19.8
5.29
45.7
К
38.84
119
72
×
53.2
К
27.6
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INFLUENCE OF A REACTION MEDIUM
103, l/(mol s)
49
k
×
103, l/(mol s)
k
×
12
10
8
12
10
8
2
1
2
1
6
6
4
4
0
0.1
0.2
0.3
0.4
0.5
, mol/l
0
20
40
60
80
100
C, l/mol
c
1/
Fig. 4. Dependences of the effective constant of the rate of
Py oxidation by PDA (initial concentrations of the compoꢀ
nents were 0.05 mol/l) on the concentration of acetic acid
Fig. 5. Dependences of the effective constant of the rate of
Py oxidation by PDA (initial concentrations of the compoꢀ
nents were 0.05 mol/l) on the inverse concentration of aceꢀ
in solution. Temperature, 323 K. Solvent: (1) tetrachloꢀ
tic acid in solution. Temperature, 323 K. Solvent: (
rachloromethane, ( ) chlorobenzene.
1) tetꢀ
romethane, ( ) chlorobenzene.
2
2
tion of acetic acid in solution (Fig. 5). This confirms
that Py bound with acetic acid in a compound is oxiꢀ
dized by PDA at a moderate rate. Judging from the
obtained results, the salvation of Py by tetrachloꢀ
romethane and chlorobenzene is low. Performing simꢀ
ilar tests in a solution of dioxane or acetone leads to a
reduction in k with a rise in acetic acid concentration
by factors of 1.74 and 1.34, respectively, with the
obtained dependences being nonlinear in coordinates
We used the familiar Palm–Koppel equation to
find correlation dependences combining the main
physicochemical properties of the solvents with the
rate constant of the oxidation reaction [11]. The
numerical values for polarity (
Y
), polarizability (
Р),
electrophilicity ( ), and basicity (
Е
В) were taken from
[11]. The equation obtained from our calculations had
a low value for the multiple correlation coefficient
(R = 0.812), indicating a low correlation dependence
between the constant of the oxidation rate and the
main parameters of the solvents. The constant of the
oxidation rate of Py in DMFA solution exhibits the
of
k from 1/C. This points to the solvation of both Py
and PDA by dioxane and acetone.
Table 4. Experimental and calculated (by correlation equation (6)) constants (
oxydecanoic acid in the studied solvents at 303 K
k
) of the rate of pyridine oxidation by perꢀ
–ln
calculation
k
×
103
l/(mol s)
–lnk
experiment
k
Solvent
Dioxane
– lnk
Δ
0.386
0.644
0.800
0.924
2.04
2.48
2.66
2.86
3.58
5.54
5.46
6.20
7.8597
7.3478
7.1309
6.9868
6.1948
5.9995
5.9294
5.8569
5.6324
5.1958
5.2103
5.0832
7.7491
6.6089
6.9854
6.3875
6.0713
5.9227
5.7364
7.3774
5.4074
5.2111
5.0845
5.2391
0.1105
0.7389
0.1455
0.5993
0.1235
0.0768
0.1930
–1.5205
0.2250
–0.0153
0.1258
–0.1559
Propanolꢀ2
Acetone
Ethyl acetate
Toluene
Benzene
Tetrachloromethane
DMFA
Chlorobenzene
Chloroform
Dichloroethane
Nitrobenzene
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50
DUTKA et al.
greatest deviation from the obtained dependence tion rate, while the role of the solvent polarity is less
(Table 4). Excluding from consideration the results of influential. The electrophilicity and polarizability of
kinetic tests obtained in DMFA led to the correlation the reaction medium do not influence the rate of the
equation
lnk = – 7.7240 + 3.8036Y + 3.1195P + 0.071E
0.0094B, R = 0.975.
coefficient is increased substantially. The
oxidation reaction.
(6)
REFERENCES
–
1. A. I. Prilezhaeva, Prilezhaev Reaction. Electrophilic
Oxidation (Nauka, Moscow, 1974) [in Russian].
The
R
numerical value of the multiple correlation coefficient
(0.975) indicates a good correlation. Alternating the
parameters excluded from consideration yields a
2. G. A. Tolstikov, Hydroperoxide Oxidation Reactions
(Nauka, Moscow, 1976) [in Russian].
3. V. L. Antonovskii, Organic Peroxide Initiators (Khimiya,
Moscow, 1972) [in Russian].
4. V. S. Dutka, Kinet. Katal. 32, 960–963 (1991).
5. A. Weissberger, E. Proskauer, J. Riddick, and E. Toops,
Organic Solvents (Intersci., New York, 1955; Mir, Mosꢀ
cow, 1958).
6. A. J. Gordon and R. A. Ford, The Chemist’s Companion:
A Handbook of Practical Data, Techniques and Referꢀ
ences (Wiley, New York, 1972; Mir, Moscow, 1976).
threeꢀparameter equation. Excluding the
leads to dropping to a value of 0.823, indicating the
influence of polarity on the rate of Py oxidation.
Y
parameter
R
The polarizability of the solvent has practically
Р
no effect on the oxidation process, since excluding this
parameter from consideration does not change the
numerical value of
the parameter also produces no change in the
numerical value of (0.975).
R (0.967). A similar operation with
Е
7. W. E. Parker, C. Riccuti, C. L. Ogg, and D. Swern,
R
J. Am. Chem. Soc. 77, 5459 (1955).
8. V. L. Antonovskii and M. M. Buzlanova, Analytic
Chemistry of Organic Peroxide Compounds (Khimiya,
Moscow, 1978) [in Russian].
9. R. Shriner, R. Fuson, D. Curtin, and T. Morrill, The
Systematic Identification of Organic Compounds (Wiley,
New York, 1980; Mir, Moscow, 1983).
10. A. P. Kreshkov, Analytical Chemistry of NonꢀAqueous
Solutions (Khimiya, Moscow, 1982) [in Russian].
11. V. A. Palm, Principles of the Quantitative Theory of
Organic Reactions (Khimiya, Leningrad, 1977) [in Rusꢀ
sian].
CONCLUSIONS
Based on the obtained results, we may conclude
that the electrophilicity and polarizability of solvents
do not influence the rate of Py oxidation by PDA. Solꢀ
vent basicity greatly influenced the investigated reacꢀ
tion. Excluding this parameter from consideration
leads to a considerable reduction in the multiple corꢀ
relation coefficient
R (to 0.532). The reaction medium
basicity has a decisive influence on the oxidation reacꢀ
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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2011