Kinetics of amine catalysed oxidation of anthrone by oxygen in aprotic solvents

Article abstract of DOI:10.1134/S0036024410030088

Catalytic activity for the series of aliphatic and aromatic amines in liquid-phase oxidation of anthrone with molecular oxygen was studied gas-volumetrically and spectroscopically. It was shown that the studied amines are arranged in the following order of decreasing catalytic activity: NH ₃ > RNH₂ > R¹R²NH > R ¹R²R³N > ArNR². A kinetic scheme for the process is proposed. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0036024410030088

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2010, Vol. 84, No. 3, pp. 391–394. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.A. Serdyuk, M.G. Kasianchuk, I.A. Opeida, 2010, published in Zhurnal Fizicheskoi Khimii, 2010, Vol. 84, No. 3, pp. 456–459.
CHEMICAL KINETICS
AND CATALYSIS
Kinetics of Amine Catalysed Oxidation of Anthrone by Oxygen
in Aprotic Solvents
A. A. Serdyuk, M. G. Kasianchuk, and I. A. Opeida
Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine,
Donetsk, 83114 Ukraine
eꢀmail: ann.serdyuk@rambler.ru
Received February 13, 2009
Abstract—Catalytic activity for the series of aliphatic and aromatic amines in liquidꢀphase oxidation of
anthrone with molecular oxygen was studied gasꢀvolumetrically and spectroscopically. It was shown that the
studied amines are arranged in the following order of decreasing catalytic activity: NH3 > RNH2 > R1R2NH >
R1R2R3N > ArNR2. A kinetic scheme for the process is proposed.
DOI: 10.1134/S0036024410030088
INTRODUCTION
4.5 ppm and the OH group of enol at 10.25 ppm disꢀ
appear during the reaction, and the peaks of the aroꢀ
matic protons of anthraquinone at 7.8 and 8.3 ppm are
left); the presence of peaks of anthrone–triethylamine
Oxidation of organic compounds occurs selectively
and efficiently in the presence of basic catalysts [1].
Anthrone is easily oxidized by an ionic mechanism in
the presence of bases and ammonia.
system at 6.8 ppm (3H, t) and 7.2 ppm (3H, t) indiꢀ
cates the formation of a side product in trace amounts:
bianthrone [2]. Typical kinetic curves are presented in
the figure.
O
O
+O2, NH3
–H2O
Kinetic curves with a high correlation coefficient
(
R2 > 0.98) are described by kinetic equation of the
first order
O
[O2]t = [O2]∞(1 – exp(–kef t)),
(1)
The aim of this work was to investigate the influꢀ
ence of the catalyst structure of amine in the reactions
of liquidꢀphase oxidation of anthrone with molecular
oxygen and the influence of media on this process.
where [O2]t is the volume of oxygen absorbed at
moment, cm3; [O2]∞ is the volume of oxygen that
would be absorbed if the reaction proceeded indefiꢀ
nitely, cm3; keff f is the effective rate constant, s–1; and
t
is time, s.
EXPERIMENTAL
The values of the effective constants, as well as the
The reaction kinetics was controlled volumetrically other kinetic parameters given in Table 1, were
by the absorption of oxygen; the reaction was carried obtained from experimental data using Eq. (1).
out with kinetic control. The initial concentration of
The partial rate constants for amine and anthrone
anthrone in all experiments was equal to 0.05 M;
Т =
were 0.5 and 1, respectively. As can be seen, the greatꢀ
est catalytic effect is exhibited by the primary amines,
while the least effect is exhibited by the tertiary
amines.
307 K. PMR investigations were carried out on a
Bruker Avance II (400 MHz) apparatus.
Anthrone in DMSO is not oxidized with oxygen
without the addition of amine, just as amines do not
oxidize in different solvents without anthrone. The
reaction proceeds rapidly in the presence of ammonia
or aliphatic amines. Kinetic curves appear as saturated
curves; after a certain amount of time, the absorption
of oxygen by the solution comes to an end. The ratio of
the amount of adsorbed oxygen at the end of the reacꢀ
It is entirely logical to assume that the catalytic
effect must depend on the basicity of the catalyst. This
tendency is generally observed; there was, however, no
strict correlation between the rate of anthrone oxidaꢀ
tion and the
рКа of amine (Table 2).
Among the properties of media, the most imporꢀ
tion to initial amount of substrate is stoichiometric tant factors affecting the kinetics and mechanism of
(1 : 1). Anthrone is converted to anthraquinone almost reaction are permittivity ( ), basicity ( ), polarity ( ),
ε
B
μ
completely (as was shown by PMR spectroscopy, the and the ability to form complexes with molecules of
peaks corresponding to the CH2 group of ketone at the substrate. A comparison of the initial reaction rates
391

392
SERDYUK et al.
cO , M
1
2
3
4
5
6
2
0.05
0.04
0.03
0.02
0.01
0
40
80
120
t, min
Kinetic curves of oxygen absorption by anthrone in DMSO in the presence of trimethylamine (molar concentrations are
(1) 0.0160, (2) 0.0080, (
3
) 0.0032, (
4
) 0.0016, (
5
) 0.0008, and (
6
) 0.0002); 307 K, 760 mm Hg.
and the literature data of the properties of the used solꢀ
vents is given in Table 3.
The partial reaction rate constant by oxygen is
equal to 1 in both DMSO and DMF.
The use of amines with aromatic rings near the
amino group (primary, secondary and tertiary
anilines) led to a rapid decline in the anthrone oxidaꢀ
tion rate as compared to the use of aliphatic amines as
catalysts.
It was shown by the examples of N,Nꢀdimethylꢀ
aniline, pꢀmethylaniline and pꢀdibromaniline (c =
0.001 M) that the rate of anthrone oxidation remains
constant and the catalytic effect is less pronounced
than in the case of aliphatic amines. The rate of
anthrone oxidation in DMF in the presence of
N,Nꢀdimethylaniline did not change with the change in
the partial pressure of oxygen (from 450 to 760 mm Hg).
Anthrone exists in equilibrium with its enol form,
the occurrence of which depends on the ability of the
solvent to form a complex with the substrate [6].
As can be seen, the change in the initial rate of oxyꢀ
gen absorption does not correlate with the polarity and
correlates only weakly with permittivity (R2 = 0.73).
The best correlation is with basicity (R2 = 0.99) and
the equilibrium part of the enol (R2 = 0.97).
The PMR spectrum of anthrone in DMSOꢀd6
δ
/ppm is 4.5 (
8.3, there are peaks corresponding to aromatic protons
= 0.11, 0.11, 0.11, 0.1, 10.25 ( = 0.04 Hz, OH).
s, J = 0.02 Hz, CH2); in the range 7.4–
J
s, J
According to the ratio of integral intensities, it was calꢀ
culated that the equilibrium part of the enol form is
76%. No change was observed in 24 h.
RESULTS AND DISCUSSION
According to the results of our PMR investigations,
we may assert that in DMSO and acetonitrile mixtures
with ratios of 1 : 1 and 2 : 1, the tautomeric equilibrium
of anthrone–anthrol is attained slightly more slowly,
and the equilibrium part of the enol form is proporꢀ
tionally less; this correlates with the rate of oxidation.
The obtained kinetic data (rate constant by
anthrone = 1; by oxygen = 1; by amine = 0.5) are in
good agreement with the following brutto scheme of
oxidation:
2А + RN
A2 · NR
A2 · NR, k1
A– + АRN+, k2
AOO–, k3
AO + RN + H2O, k4
,
k–1
,
(2)
(3)
(4)
(5)
,
k–2
,
The influence of the partial pressure of oxygen on
the initial rate of anthrone oxidation in the presence of
amine is shown in Table 4.
A– + O2
AOO– + RN+
,
,
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KINETICS OF AMINE CATALYSED OXIDATION OF ANTHRONE BY OXYGEN
393
Table 1. Kinetic data on the liquidꢀphase oxidation of anꢀ Table 2. Dependence of the rate on the structure of the catꢀ
throne in the presence of amines of different concentrations ( alyst
c)
1
Amine (0.005 М) W0
ꢀbutylamine
×
105, M s⎯
T
,
°
С
pKa [3]
(
kef 0.001)
×
(
W0 0.01)
×
Ns/NO
2
c
, М
102, s–1
105, M/s
t
5.24
4.49
1.80
1.61
0.45
0.38
0.29
34
10.46
10.93
11.01
9.8
t
ꢀbutylamine
1.0
Diethylamine
Triethylamine
Trimethylamine
0.00024
0.0003
0.0006
0.0024
0.0095
0.028
0.055
0.067
0.141
0.132
1.20
1.85
3.31
4.68
5.91
1.0
0.9
1.0
1.0
p
p
ꢀBromaniline
80
3.91
5.12
5.06
ꢀMethylaniline
N,NꢀDimethylaniline
Diethylamine
Note: pK values are given for the aqueous solutions of correspondꢀ
a
ing amine
0.0003
0.0006
0.0018
0.0024
0.0048
0.0095
0.039
0.071
0.078
0.097
0.110
0.105
0.9
1.0
1.1
1.1
1.1
1.1
1.91
2.57
3.39
4.07
4.50
4.95
where A2 ·NR, АRN+ is the complex of anthrone with
amine, and RN is the amine.
O
H
H
Trimethylamine
O
O
0.0002
0.0008
0.0016
0.0032
0.0080
0.0160
0.003
1.0
1.0
1.0
1.0
1.0
0.9
0.26
0.76
0.99
1.47
1.86
2.25
(A)
(AO)
0.010
0.014
0.024
0.036
0.054
H
H
−
O
O−
(A–)
Triethylamine
OO−
0.0001
0.0018
0.0036
0.0072
0.0090
0.0140
0.008
0.027
0.056
0.061
0.074
0.080
1.0
1.0
1.0
1.0
1.0
1.2
0.53
1.27
1.36
1.91
3.25
4.15
H
O
(AOO–)
The rate of oxygen absorption is described by equaꢀ
dcO
2
tion ꢀꢀꢀꢀꢀꢀꢀ
= k3cO c . Under the conditions of the
A–
2
dt
experiment,
then, from cRN
Note: W is the initial rate of oxygen absorption by anthrone soluꢀ
0
c
А ӷ cRN; therefore,
cА ≈ cA
,
0
cA
= cx;
2 ⋅ N
tion;
N
/
N
is the ratio of number of moles of substrate
O2
s
taken and oxygen absorbed at the end of the reaction.
=
cN – cx.
0
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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394
SERDYUK et al.
Table 3. Initial rates of oxygen absorption by anthrone solution (0.05 M) in the presence of triethylamine (0.0072 M) in
different aprotic solvents at 307 K and pO = 760 mm Hg ( is the equilibrium part of enol)
x
2
Solvent
DMSO
ε20 [4]
В
, cm–1 [5]
μ
x
, %
W0
×
105, M/s
49
38
36
35
30
2
362
291
160
67
3.96
3.82
3.92
4.22
–
76
22
~0
10
–
1.9
1.4
0.5
DMF
Acetonitrile
Nitrobenzene
GMFA
<10–2
<10–2
< 10–2
–
Toluene
58
0.36
–
Table 4. Dependence of initial rates of oxygen absorption by anthrone (0.05 M) in aprotic solvents in the presence of triꢀ
ethylamine (0.0072 M) on the partial pressure of oxygen at 307 K
(
W0 0.01)
105, M/s
×
pO , mm Hg
2
DMSO
DMF
150
380
512
580
760
–
0.28
0.60
–
0.88
1.21
1.43
1.93
0.93
1.12
are arranged in the following order of decreasing cataꢀ
If we have
K
=
k1
/k–1 and if cх Ӷ cN ,
0
lytic effect: NH3 > RNH2 > R1R2NH > R1R2R3N >
ArNR2
.
cx = KcA2 cN .
0
0
From Eq. (2),
cA–
dcO
REFERENCES
1/2
=
cx
=
cA (KcN )
,
1. Erkkila Anniinä, Advances in Amine Catalysis: Bronsted
Acids in Iminium and Enamine Activation, Doctoral
Dissertation (Univ. of Technology, Helsinki, 2007).
0
0
2
ꢀꢀꢀꢀꢀꢀꢀ = kefcO cA cN
,
2
0
0
2. R. G. Harvey and Cho Hee, J. Am. Chem. Soc. 98
,
dt
2434 (1974).
where kef
=
k3 K.
3. A. Albert and E. Sergeant, Ionization Constants of Acids
and Bases (Wiley, New York, 1962; Khimiya, Moscow,
1964).
CONCLUSIONS
4. V. A. Pal’m, Principles of Quantitative Theory of Organic
Reactions (Khimiya, Leningrad, 1977) [in Russian].
Amines of different structure and origin are catalytꢀ
ically active in the reactions of anthrone oxidation in
aprotic solvents. Amine behaves as common basic catꢀ
alyst, facilitating the ionization of anthrone. Amines
5. I. A. Koppel and A. I. Paju, Org. Reactiv. 11 (1), 121
(1974).
6. H. Sterck, Monatshafte. Chem. 100, 916 (1969).
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No. 3
2010