Rate constants oxygen reactions

It is interesting to compare the rate constants of the oxygen-only ozone destruction reaction with those of the catalytic ozone destruction cycle. The rate constants for reactions 4-6 at 30 km are given below in units of cm molecules s . 

Furuyama, S., Atkinson, R., Colussi, A.J., Cvetanovic, R.J. (1974) Determination by the phase shift method of the absolute rate constants of reactions of oxygen ( ,P) atoms with olefins at 25°C. Int 7. J. Chem. Kinet. 6, 741. 

Rate Constants for Reactions of Oxygen-Centered Radicals with Silicon Hydrides... 

Scully FE, Jr, Hoigne JR. 1987. Rate constants for reactions of singlet oxygen with phenols and other compounds in water. Chemosphere 16 681-694. 

TABLE 13-3 Rate Constants for Reaction of Oxygen Species with trai 2-Butene"... 

Tratnyek, P.G. and Hoigne, J. Oxidation of substituted phenols in the environment a QSAR analysis of rate constants for reaction with singlet oxygen. Environ. Sci. Tecbnol., 25(9) 626-631, 1991. 

Bors, W., Michel C., and Saran, M., Flavonoid antioxidants rate constants for reactions with oxygen radicals. Methods Enzymol, 234, 420, 1994. 

In this paper the rate expressions have all been corrected for nitrogen evolution from the azo initiator, oxygen absorption by initiator radicals, and oxygen evolution in termination. It is assumed that the initiator which decomposes without starting oxidation chains does not react with oxygen (21). This correction involves the addition of (l-e)Ri/2e to the measured rate, where e is the efficiency of chain initiation, found to be 0.5 at 30 °C. and 0.6 at 56 °C. The rate constant for Reaction 7 has been written as 4ktCT in order that the three termination constants may be comparable (26, footnote 27).]... 

Oxygen has two possible interactions during the polymerization process [94], and these reactions are illustrated in Fig. 2. The first of these is a quenching of the excited triplet state of the initiator. When this quenching occurs the initiator will absorb the light and move to its excited state, but it will not form the radical or radicals that initiate the polymerization. A reduction in the quantum yield of the photoinitiator will be observed. The second interaction is the reaction with carbon based polymerizing radicals to form less reactive peroxy radicals. The rate constant for the formation of peroxy radicals has been found to be of the order of 109 1/mol-s [94], Peroxy radicals are known to have rate constants for reaction with methyl methacrylate of 0.241/mol-s [100], while polymer radicals react with monomeric methyl methacrylate with a rate constant of 5151/mol-s [100], This difference implies that peroxy radicals are nearly 2000 time less reactive. Obviously, this indicates that even a small concentration of oxygen in the system can severely reduce the polymerization rate. 

The results of determining absolute rate constants for reactions of oxygen atoms with various molecules are summarized in Table IV, A determination of every constant was made at various temperatures, it was possible to determine the activation energies, and the pre-exponential factors as well. The rate constants of some reactions given in Table IV were reported in the literature. 

According to this scheme, kx is the rate constant for Reactions 5 and 6 together, and a represents the fraction of these interactions that terminate. (The step represented by kx can be further broken down to include tert-BU2O4 as intermediate.) Reactions 3, 5, and 6 have also been studied at 25°C. in the gas phase by photogeneration of tert-butyl radicals in the presence of oxygen (24). The competition between Reactions 5 and 6 is demonstrated by product studies on our Experiment 91 and measured as indicated below. 

In the absence of laboratory measurements for the rate constants of reactions R5 and R6, and in order for these reactions to counterbalance the production of odd oxygen by reaction Rl, as rate constants the values... 

Here, rR is the oxidation rate of the reactant R, km the rate constant of oxygen adsorption, kml the rate constant of reaction between R and adsorbed oxygen, v the stoichiometric coefficient, equal to the moles of 02 necessary to oxidize one mole of R (v = 0.5 with R = H2). 

Reactions of the hydrated electron possibly may be somewhat relevant to the action of dose-modifying agents such as 02, NO, C02, and sulfhydryl compounds. It can safely be assumed that these exert their influence at the radiation-chemical level, and it is notable that many of them react rapidly with hydrated electrons. Table II, taken from a paper by Braams (6), compares the rate constant for reaction with the hydrated electron with the concentration at which certain compounds have been used as protective agents. It can be seen that, at the concentrations used in biological systems, those substances which are effective as protectors can compete favorably with oxygen for hydrated electrons. Penicillamine was not a good protector at the concentration used and did not compete as favorably as the other substances for hydrated electrons. Higher concentrations of penicillamine could not be... 

Nese C, Schuchmann MN, Steenken S, von Sonntag C (1995) Oxidation vs. fragmentation in radiosensitization. Reactions of a-alkoxyalkyl radicals with 4-nitrobenzonitrile and oxygen. A pulse radiolysis and product study. J Chem Soc Perkin Trans 2 1037-1044 Neta P, Huie RE, Mosseri S, Shastri LV, Mittal JP, Maruthamuthu P, Steenken S (1989) Rate constants for reduction of substituted methyl peroxyl radicals by ascorbate ions and N,N,N, N -tetrameth-yl-p-phenylenediamine. J Phys Chem 93 4099-4104 Neta P, Huie RE, Ross AB (1990) Rate constants for reactions of peroxyl radicals in fluid solutions. J Phys Chem Ref Data 19 413-513... 

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