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THE KINETIC AND MECHANISM OF THE DECOMPOSITION REACTION OF THE DIACETONE ALCOHOL IN FROZEN SOLUTIONS
Степанов Михаил Борисович Кизилова Арина Сергеевна, Волков Александр Анатольевич Московский государственный технический университет им. Н.Э. Баумана, г. Москва
E-mail: bmstufn5@mail.ru
Abstract. More attention is paid to the study of chemistry in low-temperature processes, the study of their specific features. It is found that the speed range of chemical and biochemical processes at low temperature and freezing of solution may increase.
Keywords: kinetics, analysis, reaction, frozen solution, process speed.
Today, knowledge of the laws of chemical processes at low temperatures becomes a necessary part of human life. Every year the role of low-temperature chemistry - the chemistry section, affecting a wide range of problems in varying degrees, increases. Experts work in the field of polymer chemistry, biochemistry and cryomedicine, food industry, building in the permafrost zone. However, since the low-temperature chemistry is a relatively young science, many processes are not fully explored.
Currently, there are about twenty original works dedicated to the reaction in frozen solutions. Almost all of these works are carried out by two groups of researchers, led by N. Grant and R. E. Pinkok. All authors had studied the kinetics of various processes in frozen solutions showed that the reaction rate of the reactants several chemical and biochemical processes significantly increases when freezing the reaction solution. Some reactions are accelerated by freezing in a few hundred times. In the literature there are two different hypotheses proposed to explain the phenomenon of acceleration:
- Catalytic effect on a hard surface, in particular ice (high mobility of protons, relative orientation suitable ice);
- Liquid inclusions in the solutions in which the solutes are concentrated, and the reaction occurs [4].
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In the late 70-ies of XX century, M.B. Stepanov, the Professor in Bauman Moscow State University (BMSTU), established the first model of the chemical process in frozen solutions, the study, which examined the kinetics and mechanism of the reactions of various types in frozen solutions.
The object of research - practically valuable substances in technical applications
- Diacetone alcohol (4-hydroxy-4-metilpentanon-2, keto alcohols) and catalytic decomposition product - acetone. The aim is to calculate the maximum of low temperature at which this reaction may occur and the constants of reactons' rate.
Tasks:
- To consider methods that can explore the mechanism and kinetics of low-temperature reactions in frozen solutions;
- Consider a model reaction - decomposition of diacetone alcohol;
- Calculate the maximum in frozen water and organic solutions, using the characteristics known for the reaction in the liquid phase.
The decomposition reaction of diacetone alcohol by the action of sodium hydroxide (t = 25°C) was chosen not by chance:
(CH2)^C(.OH)CH2COCH^ + OH' ICH^COCH^
Acetone and diacetone alcohol are used in many manufacturing areas. The first substance used as a simple solvent and cellulose esters, synthetic rubber, resins used to reduce the viscosity of organic systems, the textile industry, in the manufacture of paints and varnishes, inks. Its degradation product - acetone - copes with problems surfaces degreasing, dissolving chlorinated rubber, polyacrylates, vinyl chloride copolymers, epoxy resins, polystyrene, oils, natural resins, various organic substances. That acetone used to dissolve the acetates and cellulose nitrates. In addition to being widely used today acetone in the synthesis of epoxy resins, polyurethanes and polycarbonates, it is also used in industry for drug development, varnishes and even some explosives. As the solvent of cellulose acetate in acetone is present special adhesive composition used for films. Additionally, acetone is used for the storage of acetylene, since the latter has a potential explosion hazard and can not be stored in pure form under pressure. In the food industry as acetone has found its use: it is impossible, without extracting food, vitamins and fat. In the pharmaceutical industry acetone is used as the main raw material for the synthesis of a large number of other compounds, including diacetone alcohol [9].
Thus, the diacetone alcohol and acetone makes our work actual, and its novelty
- the study of the kinetics of the reaction of decomposition of diacetone alcohol in frozen solutions.
Today we know not too many experiments to see the properties of substances and reactions in the negative temperature range.
For example, until the end of the 1970s the low temperature chemiluminescence
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in the matrices of the noble gases in the temperature range of 44-45 K was investigated, and also the interaction of the active surface of the nitrogen in the hydrocarbons of 77 K. These objects are important in practical terms as frozen solutions were not included in the of researchers chemiluminescence. Obviously, the big interest is the chemiluminescent reactions which occur in the liquid and in frozen solutions. For example, the detected low temperature chemical, radiochemical and electrochemical processes involving the formation of electronically excited ions and molecules, shown for the first time the possibility of a chemiluminescence method for studying the kinetics and mechanism of chemical reactions in frozen solutions at the end of the twentieth century. The detected chemiluminescence at the low temperature reactions demonstrated the possibility of using low-temperature chemiluminescence to study the kinetics of phase changes in solutions both during heating and cooling. At the same time has been developed chemiluminescent method for detecting phase transformations of multicomponent frozen systems, justified the using of chemiluminescence to monitor the process of crystallization of sparingly soluble compounds for science-based selection of cryoprotectants and optimization of cryopreservation of biological objects [2].
Currently a huge difference in physical and chemical research acquired spectral methods. The great practical importance is the various spectroscopic analytical techniques, which include molecular spectral analysis.
Big opportunities for the development of molecular spectral analysis have appeared due to the discovery in 1952 by professor E.V. Shpolskii with employees quasiline effect fine structure of the electronic specters of polyatomic molecules. Such spectres are called quasi-line, and the splitting of molecular spectral peaks into narrow quasiline - "Shpolsky effect" [6].
The Shpol'skii's effect means, that the investigated molecules penetrating into the crystal lattice of the appropriately chosen matrix, at a low temperature in a state to which the applicable model "oriented gas". The gaseous molecules can rotate freely and have a large moment of inertia, in most cases, were not even allowed to gas radiospectroscopy with her unattainable for optical methods of resolution. In solutions, where the rotation of the molecules inhibited, the spectrum of polyatomic molecules is more discrete than in its gaseous state. An example of such a relation between the spectra in pairs and in the case of frozen solutions molecule coronene (C24H12 -superbenzol) is shown in fig.1 [8].
The substance is dissolved in a solvent and specially selected and then frozen at the nitrogen boiling temperature (t = -196 °C) or lower. It was possible to obtain the luminescence and absorption spectra, where instead of the usual diffuse bands observed a large number of sharp and narrow lines (fig.2) [1]. Other scientists have shown that these spectres belong to the solute molecules, not crystalline aggregates [7].
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Methods of analysis based on the use of quasi-line spectres, are widely used in oncology, hygiene and sanitation in connection with the issue of prevention of carcinogenic effects, in geochemistry in the study of organic matter of the Earth's crust, accompanied by various geological processes, as a method of monitoring the degree of purity and etc.
Such widespread using has been made possible due to the development of methods of qualitative and quantitative analysis of complex molecules on the quasi -line spectres of luminescence [5].
Fig. 1 The fluorescence specter of coronene T = 300 K: 1-in pairs; 2-in solution
Fig. 2 Part of the fluorescence spectres of 3,4,6,7-dibenzopyrene, T=4,2 K
Let's learn about the practical scope of the investigated reactions in frozen solutions, where the temperature is not below about -30 ° C. Thus, the properties of the material structure may vary depending on the freezing point. Implications for the substances may be different. It is necessary to pre-calculate the maximum freezing temperature of solutions, in which the reaction will proceed under investigation to consider transport, storage and further use of the substances which are produced.
Analysis of the cryochemistry works shows that the literature is a single kinetic theory of chemical reactions in frozen solutions. However, as has been said, the first fundamental study was carried by Stepanov M.B. In his work in a wide temperature range from +25°C to -196°C were investigated solutions of various compositions and methods of electron spin nuclear magnetic resonance. One experiment (oxidation hydrazobenzene by iminoxyl radical in the frozen dioxane) was performed with the
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next steps. The reaction solution in the ampoule was frozen in liquid nitrogen for 30 seconds and then placed in the cavity of the ESR spectrometer where the desired temperature was maintained within ± 2 ° C. The phase state of each sample was investigated by ESR at a temperature ranging from the freezing point of the solution to -196°C. It can be judged based on the plurality of the obtained results that in frozen solutions are not homogeneous. They consist of a solid solvent and the microphase in which the solutes are concentrated. Thus, the kinetic model was proposed chemical processes in frozen solutions, which allows to calculate the speed of frozen solutions in processes using the characteristics known for reactions in the liquid phase [4].
We analyze the derived formulas for calculating the maximum freezing temperature of the decomposition reaction of diacetone alcohol in a solvent:
E - activation energy of the reaction (87 kJ/mol), the R - gas constant (8.314 J/ mol*K), T0 - solvent freezing temperature (K). In this case, we made the calculation for the widely used solvents such as water (T0 = 0 K) and benzene (T0= = 278.7 K)
[3].
We made calculations using the software tool Mathcad 15 (tab.1).
Table 1
Results of calculating the freezing temperature in solvents
Water, K Benzene, K
T := MV >
( 2 6\ 3 3 273 87.6-106 87.6-103 87.6-103--+---= 266.3 8.314 2 2-8.314 ^ 4-8.314 ) T := MV \ ( .2 6^ 3 3 278.7 87.62-10 87.6-10 87.6-10 --+---= 271 . 7 8314 4-8.3142 J 2-8314
It was interesting to calculate the rate constant k of the same reaction in a frozen solution at a temperature T (Table 2):
where A - cryoscopic constant solvent (A (water)=1.86 K, A (benzene)=5.1 K), k0 - pre-exponential factor for the reaction of the solvent in the liquid phase. The value of the pre-exponential factor we chose with the help of the experimental data by professor Stepanov's work for this type of reaction: k0 (water)=7*104 l/mol*sec, k0 (benzene)=1.4*104 l/mol*sec.
Table 2
Results of calculating the reaction rate in solvents
Water, l/mol*sec
Benzene, l/mol*sec
ft
k := 7-10exp
vv
-5000 ' 8.314-266.3,
273-266:! 2.636 x 104
((
k := 1.4-1 0 exp
-5000
VV 8.314-271.7,
f 278.7 - 271.71 3
I = 2.101 x 103
V
5.1
The following conclusions:
- The optimal freezing temperature of the reaction will be characteristic temperature for making it in inorganic solvents;
- Reaction rate in water of about 12.5 times higher than in benzene;
- Acetone is much effective to synthesize in inorganic solvents (for example,
H2O).
Thus, the first analysis of the decomposition reaction of the diacetone alcohol in frozen solutions was made. The maximum freezing temperature in organic and inorganic solvents, which was calculated, in our opinion, will be important to synthesize the acetone and to store. Also the results may be useful for companies such as "Synthesis of acetone" (Nizhny Novgorod), "Himabsolyut" (Moscow), whose main activity is the production of basic inorganic and organic chemicals and the transportation of it in Russia.
The prospects of work - to confirm the values obtained experimentally using spectroscopy in BMSTU, to explore other widely used in the technical application reactions, to calculate the maximum freezing temperature in different solvents and constants of rates of the reactions.
Literature:
1. Bolotnikova T.N. Spectroscopy simple aromatic hydrocarbons in the frozen crystalline solutions. Kand. diss. M., 1959. 176 p.
2. Lotnikow S.W. Low temperature chemiluminescent reactions in frozen solutions: abstract dis. Dr. chem. sciences. Ufa, 1993. 37 p.
3. Melvin Hughes E.A. Equilibrium and kinetics of reactions in solutions. Trans. from English. ed. Dr. chem. science I.P. Beletskaya. M:. "Chemistry", 1975. 472 p.
4. Stepanov M.B. Kinetics and mechanism of certain chemical reactions in frozen solutions. The thesis for the degree of Candidate of Chemical Sciences. M:. MSU. Lomonosov Moscow State University, 1973. 133 p.
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5. Teplitskaya T.A. Quasiline luminescence spectra as a method for studying complex natural organic compounds. M Univ. Of Moscow University Press, 1971. 105 p.
6. Teplitskaya T.A., Alekseeva T.A., M. Waldman. Atlas quasilinear luminescence spectres. Moscow University, 1978. 51 p.
7. Shpolskii E.V., Klimova L.A., Nersesova G.N., Glyadkovsky V.I. Concentration dependence of fluorescence and absorption spectra // Optics and Spectroscopy, 1968.
8. Shpolskii E.V. Problem of the origin and structure of the quasilinear spectra of organic compounds at low temperatures // Physics-Uspekhi, 1962, p. 57-59.
9. Key features of acetone and its scope. - Access: http://freezante.ru/blog/ speczhidkosti/speczhidkosti_45.html (reference date: 04/03/2016)
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