Download Computational Study of protonation of ozone

Computational Study of protonation of ozone
© Quyen Quy Ngo, Alexander Yakovlevich Samuilov, Yakov Dmitruevich Samuilov, Fanis
Faritovich Valiullin, Eugenii Ivanovich Grigoriev and Alexander Alexsandrovich Petukhov
Department of Technology of synthetic rubber. Kazan National Research Technological University. Karl
Marx, 68. Kazan, 420015. Tatarstan Republic. Russia.
Тел.: (843) 231-42-14. E-mail: [email protected]
Keywords: ozone, quantum chemistry, B3LYP, protonation, DFT
Abstract
The process of protonation of ozone in the singlet and triplet states was studied by quantum-chemical
method B3LYP / 6-311 ++ G (df, p). It was studied the geometric structure of the products of protonation.
The thermodynamic parameters of protonation reaction of ozone in the singlet and triplet electronic
configuration was described. It was shown that the process of protonation of ozone in all cases is
exothermic and proceeds with a decreasing of free energy and with decrease of entropy.
Introduction
Ozone is widely used in different industries, medicine and life [1, 2].We have conducted
laboratory studies on cleaning of heavy sewage of petrochemical plants, are currently being fired
by recycling. When this was done the technical and economic assessment of energy costs on the
disposal. Was shown the economic feasibility of the use of technological methods of separation
of aromatic hydrocarbons contained in the effluent from the subsequent use of ozonation
technology for final cleaning directed recycled water.
In the course of research of ozonation was experimentally found anomalous change in pH
from 6.7 to 18 by passing the ozone-oxygen mixture through distilled water [3, 4]. In discussing
of the observed phenomena, it was hypothesized that the pH of distilled water is increased not
only due to the formation of negative ions in the interaction of ozone with water, but also due to
ash from the reactor of protonated ozone [4]. The concentration of hydroxide ion is increased,
and the pH of the medium increases.
The existence of protonated ozone previously been proven by computational methods and
confirmed experimentally by several researchers [5, 6]. However, for the calculation were used
outdated methods. This is not allowed reliably reason about thermodynamic stability of
protonated ozone. The purpose of this issue is the thermodynamic estimation of protonation
reaction of ozone.
Experimental part
Quantum chemical calculations were carried out using the program Gaussian09 [5].
Optimization of geometrical parameters of molecular structures was carried out using a threeparameter exchange-correlation functional B3LYP and the basis set 6-311 ++ G (d, p). To
confirm that the structures are minima on the potential energy surface, and to determine the zeropoint energy at the same theoretical level were calculated vibrational frequencies.
Application of the method B3LYP is suitable for studies of most organic reactions [6, 7].
Standard enthalpies of formation and the Gibbs free energy in the gas phase (T = 298.15 K, p = 1
atm) are derived from the zero-point energy, as well as the corresponding-thermal corrections to
the electron energy.
Results and discussions
Early studies [8] have shown that ozone can have singlet and triplet electronic structure.
We have made calculations of the geometric characteristics of the protonated forms of ozone
with singlet and triplet electronic structure. Protonated ozone with singlet electron configuration
has 4 minimum on the potential energy surface. Fig. 1 shows the ball-rod structure of protonated
ozone with singlet electron configuration corresponding to the minima on the potential energy
surface.
Ia
Ib
Ic
Id
Fig. 1. Ball-rod structures of protonated ozone with singlet electron configuration, obtained by
B3LYP / 6-311 ++ G (df, p)
As can be seen from Fig. 1, all forms of protonated ozone singlet electron configuration
are flat. In the first two cases, in the proton is trans- (structure 1a) and cis- (structure 1b) position
with O-O bond of ozone. Oxygen-oxygen bonds in ozone are unequal. Calculated dipole moment
of ozone is 0.69 D; dipole moment of the structure Ia is 11.84D, structure Ib 12.08D, structure Ic
9.89 D, the structure Id 1.39D. The third and fourth minima are structures of protonated ozone in
which the proton is coordinated to the second oxygen atom of ozone (structure Ib) and all three
atoms of oxygen, respectively (structure Id). Table. 1 shows the thermodynamic parameters of
protonation reaction of ozone with singlet electron configuration.
Table. 1. Thermodynamic parameters of ozone protonation reaction with singlet electron
configuration
Structure
ΔGr, kJ/mol
ΔHr,kJ/mol
ΔSr, J/(molK)
Ia
-89.7
-110.2
-68.9
Ib
-95.0
-113.6
-62.5
Ic
-77.4
-98.6
-71.0
Id
-389.0
-419.4
-101.9
As can be seen from Table. 1, all the reactions are exothermic and have large negative
entropy of the reaction. Most favorable, from the thermodynamic point of view, is formation of
structure Id, in which the proton is coordinated by three oxygen atoms. All the above reactions
proceed with a decrease of free energy.
As has been shown previously [8] ozone could have triplet electronic structure, i.e. the
biradical. Protonated ozone with triplet electron configuration also has 4 minimum on the
potential energy surface. Fig. 2 shows the ball-rod structureы of protonated ozone with triplet
electron configuration corresponding to the minima on the potential energy surface.
IIа
IIb
IIc
IId
Fig. 2. Ball-rod structures of protonated ozone with triplet electron configuration, obtained by
B3LYP / 6-311 ++ G (df, p)
As can be seen from Fig. 2, the structure IIa is flat. In structures IIb-d the proton not lie in
plane of oxygen atoms.
Table. 2. The thermodynamic parameters of protonation reaction of ozone with the electron
configuration of triplet
Structure
ΔGr, kJ/mol ΔHr, kJ/mol
ΔSr, J/(molK)
IIa
-169.7
-188.1
-61.8
IIb
-204.3
-71.6
-225.7
IIc
-176.9
-201.7
-83.1
IId
-420.5
-449.6
-97.8
As well as in the previous case, all reactions are exothermic and have large negative
reaction entropy values. Most favorable, from the thermodynamic point of view, is formation of
structures IId, in which the proton is coordinated by three oxygen atoms. All the above reactions
proceed with decreasing free energy.
The calculated dipole moment of structure IIa is 7.45D, structure IIb 5.48D, structure IIc
3.10D, structure IId 1.69D.
Conclusions
1. The thermodynamic parameters of protonation reaction of ozone in the singlet and
triplet electronic configuration described with the quantum-chemical method B3LYP / 6-311 ++
G (df, p).
2. Process of protonation of ozone is exothermic, occurs with decreasing of the free
energy and entropy decrease. The most favorable in the reactions of the proton with singlet and
triplet ozone is formation of an ion in which the proton is coordinated with all three oxygen
atoms.
References
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