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Received: January 15, 2012 / Accepted: February 07, 2012 / Published: April 25, 2012.
Abstract: The gas-phase monooxidation of ethylene by hydrogen peroxide on a biomimetic heterogeneous catalyst, perfluorinated iron (III) tetraphenylporphyrin, deposited on alumina (per-FTPhPFe3+OH/Al2O3) was studied under comparatively mild conditions. The biomimetic oxidation of ethylene with hydrogen peroxide was shown to be coherently synchronized with the decomposition of H2O2. Depending on reaction medium conditions, one of two desired products was formed, either ethanol or acetaldehyde. The probable mechanism of ethylene transformation was studied. A kinetic model that fits the experimental data is studied on the basis of the most probable mechanism of ethylene oxidation by hydrogen peroxide over a biomimetic catalyst (per-FTPhPFe3+OH/Al2O3). Effective rate constants for the catalase and monooxygenase reactions and their effective activation energies are found.
Key words: Catalase, biomimetic, oxidation, ethylene, kinetic model, hydrogen peroxide, mechanism, activation energy. concentration of a solution of hydrogen peroxide in water, 30%; molar ratio C2H4:H2O2 = 1:1.7), an acetaldehyde yield of 34.6 wt% (ethanol 4.6 wt%). The selectivity of the process under the conditions of maximum ethyl alcohol yield and minimum acetaldehyde yield was virtually 100 wt%, recalculated for monooxygenase products. Selectivity in obtaining maximum acetaldehyde yield was somewhat lower (87 wt%) due to the production of CO2 as a by-product.
If the Michaelis-Menten equation is used, we thus make a number of assumptions; of course, these assumptions influence the kinetic model’s degree of adequacy: (1) an average value is taken in estimating the reaction rates for each temperature, and it cannot be understood from this average value whether the reaction rates in each experiment deviate from one another (the temperature is constant); (2) only one full reaction is described in the case of conjugation.
These disadvantages can be largely avoided if we employ the method of stationary concentrations, which is widely used in chemical kinetics [1]. In this method, we must propose one or a number of hypothetical mechanisms, of which only one fits the experimental data.
Using the average value of keff determined for each temperature, the Arrhenius equation was used to determine Eeff = 59.0 kJ/mol (Table 1). This value also agrees with the activation energy values for enzymatic reactions.
Note that the method of stationary concentrations has certain disadvantages: (1) the difference between the rates of accumulation and consumption of a highly active intermediate substance is equal to zero; (2) the coherent synchronous character of the primary and secondary reactions is not taken into account.
In this relation, the obtained kinetic information is incomplete: on the one hand, there is no kinetic estimate of the coherence between synchronous reactions (catalase and monooxygenase); on the other hand, the production of molecular oxygen is completely ignored (Fig. 3).
It follows from the proposed probabilistic mechanism (Fig. 3) of biomimetic ethylene oxidation by hydrogen peroxide that the monooxygenase reaction(the oxidation of ethylene into ethyl alcohol) takes place in conjugation with the catalase reaction (the decomposition of hydrogen peroxide).
It is known [1] that a necessary condition for achieving chemical conjugation in this system is its quantitative characteristic, determined by the equation
This ratio demonstrates that the rate constant of the catalase reaction exceeds the constant rate of the monooxygenase reaction by a factor of approximately 2 × 102, verifying the known data on the rates of these reactions [1].
By comparing the kinetic parameters obtained using the three different methods, we conclude that in kinetic descriptions of complex chemical reactions (including coherent synchronized reactions) the determinant equation yields a more complete description than other methods. Thus, for example, the method of stationary concentrations uses certain assumptions, while the determinant equation is free from them, which is the main advantage of this equation. Moreover, the determinant equation allows us to reveal interaction (coherence) between the synchronous chemical reactions and to quantitatively estimate this interaction.
synchronized catalase and monooxygenase reactions adequately describes the experimental data. The synchronous reactions (catalase and monooxygenase) consistently interact (i.e., are coherent) with each other, as is demonstrated by the determinant values (D = 0.1-0.4). As a result, chemical interference is observed in the studied catalytic system [1]: the primary reaction amplifies the secondary reaction; and the latter, in turn, slows down the primary reaction; and vice versa.
References
[1] T.M. Nagiev, Coherent Synchronized Oxidation Reactions by Hydrogen Peroxide, Elsevier, Amsterdam, 2007.
[2] L.M. Gasanova, C.A. Mustafaeva, I.T. Nagieva, in: Proceedings of the 14th International Congress on Catalysis, Jul. 13-18, 2008.
[3] U.V. Nasirova, L.M. Gasanova, I.T. Nagieva, in: Catalysis or a Sustainable World, Proceedings of the EuropaCat IX, Salamanca, Spain, Aug. 30-Sept. 4, 2009, p. 313.
[4] U.V. Nasirova, L.M. Gasanova, I.T. Nagieva, in: Proceedings of the 16th European Symposium on Organic Chemistry ESOC 2009, Prague, Czech Republic, Jul. 12-16, 2009, p. 2.055.
[5] T.M. Nagiev, Interaction of Synchronous Reactions in Chemistry and Biology, Elm, Baku, 2001. (in Russian).
Abstract: The gas-phase monooxidation of ethylene by hydrogen peroxide on a biomimetic heterogeneous catalyst, perfluorinated iron (III) tetraphenylporphyrin, deposited on alumina (per-FTPhPFe3+OH/Al2O3) was studied under comparatively mild conditions. The biomimetic oxidation of ethylene with hydrogen peroxide was shown to be coherently synchronized with the decomposition of H2O2. Depending on reaction medium conditions, one of two desired products was formed, either ethanol or acetaldehyde. The probable mechanism of ethylene transformation was studied. A kinetic model that fits the experimental data is studied on the basis of the most probable mechanism of ethylene oxidation by hydrogen peroxide over a biomimetic catalyst (per-FTPhPFe3+OH/Al2O3). Effective rate constants for the catalase and monooxygenase reactions and their effective activation energies are found.
Key words: Catalase, biomimetic, oxidation, ethylene, kinetic model, hydrogen peroxide, mechanism, activation energy. concentration of a solution of hydrogen peroxide in water, 30%; molar ratio C2H4:H2O2 = 1:1.7), an acetaldehyde yield of 34.6 wt% (ethanol 4.6 wt%). The selectivity of the process under the conditions of maximum ethyl alcohol yield and minimum acetaldehyde yield was virtually 100 wt%, recalculated for monooxygenase products. Selectivity in obtaining maximum acetaldehyde yield was somewhat lower (87 wt%) due to the production of CO2 as a by-product.
If the Michaelis-Menten equation is used, we thus make a number of assumptions; of course, these assumptions influence the kinetic model’s degree of adequacy: (1) an average value is taken in estimating the reaction rates for each temperature, and it cannot be understood from this average value whether the reaction rates in each experiment deviate from one another (the temperature is constant); (2) only one full reaction is described in the case of conjugation.
These disadvantages can be largely avoided if we employ the method of stationary concentrations, which is widely used in chemical kinetics [1]. In this method, we must propose one or a number of hypothetical mechanisms, of which only one fits the experimental data.
Using the average value of keff determined for each temperature, the Arrhenius equation was used to determine Eeff = 59.0 kJ/mol (Table 1). This value also agrees with the activation energy values for enzymatic reactions.
Note that the method of stationary concentrations has certain disadvantages: (1) the difference between the rates of accumulation and consumption of a highly active intermediate substance is equal to zero; (2) the coherent synchronous character of the primary and secondary reactions is not taken into account.
In this relation, the obtained kinetic information is incomplete: on the one hand, there is no kinetic estimate of the coherence between synchronous reactions (catalase and monooxygenase); on the other hand, the production of molecular oxygen is completely ignored (Fig. 3).
It follows from the proposed probabilistic mechanism (Fig. 3) of biomimetic ethylene oxidation by hydrogen peroxide that the monooxygenase reaction(the oxidation of ethylene into ethyl alcohol) takes place in conjugation with the catalase reaction (the decomposition of hydrogen peroxide).
It is known [1] that a necessary condition for achieving chemical conjugation in this system is its quantitative characteristic, determined by the equation
This ratio demonstrates that the rate constant of the catalase reaction exceeds the constant rate of the monooxygenase reaction by a factor of approximately 2 × 102, verifying the known data on the rates of these reactions [1].
By comparing the kinetic parameters obtained using the three different methods, we conclude that in kinetic descriptions of complex chemical reactions (including coherent synchronized reactions) the determinant equation yields a more complete description than other methods. Thus, for example, the method of stationary concentrations uses certain assumptions, while the determinant equation is free from them, which is the main advantage of this equation. Moreover, the determinant equation allows us to reveal interaction (coherence) between the synchronous chemical reactions and to quantitatively estimate this interaction.
synchronized catalase and monooxygenase reactions adequately describes the experimental data. The synchronous reactions (catalase and monooxygenase) consistently interact (i.e., are coherent) with each other, as is demonstrated by the determinant values (D = 0.1-0.4). As a result, chemical interference is observed in the studied catalytic system [1]: the primary reaction amplifies the secondary reaction; and the latter, in turn, slows down the primary reaction; and vice versa.
References
[1] T.M. Nagiev, Coherent Synchronized Oxidation Reactions by Hydrogen Peroxide, Elsevier, Amsterdam, 2007.
[2] L.M. Gasanova, C.A. Mustafaeva, I.T. Nagieva, in: Proceedings of the 14th International Congress on Catalysis, Jul. 13-18, 2008.
[3] U.V. Nasirova, L.M. Gasanova, I.T. Nagieva, in: Catalysis or a Sustainable World, Proceedings of the EuropaCat IX, Salamanca, Spain, Aug. 30-Sept. 4, 2009, p. 313.
[4] U.V. Nasirova, L.M. Gasanova, I.T. Nagieva, in: Proceedings of the 16th European Symposium on Organic Chemistry ESOC 2009, Prague, Czech Republic, Jul. 12-16, 2009, p. 2.055.
[5] T.M. Nagiev, Interaction of Synchronous Reactions in Chemistry and Biology, Elm, Baku, 2001. (in Russian).