Methyl radical formation

Acetylene Ion. No evidence for the contribution of ion-molecule reactions originating with acetylene ion to product formation has been obtained to date. By analogy with the two preceding sections, we may assume that the third-order complex should dissociate at pressures below about 50 torr. Unfortunately, the nature of the dissociation products would make this process almost unrecognizable. The additional formation of hydrogen and hydrogen atoms would be hidden in the sizable excess of the production of these species in other primary acts while the methyl radical formation would probably be minor compared with that resulting from ethylene ion reactions. The fate of the acetylene ion remains an unanswered question in ethylene radiolysis. 

The results of density functional theory (DFT) studies [90, 91] have suggested that the energy requirement via the C02 pathway is much less than that via the CO pathway, and thus the former is more thermodynamically favored. The methyl radical formation and dissociation of C02 are two rate-limiting steps for the synthesis of acetic acid directly from CH4 and C02. 

The spectra reported in Fig. 8, being unaffected by coadsorption of CO, are attributed to CH4 adsorbed on anions at low temperature. The methane molecule forms a weak CH 02 bond, which reduces its symmetry from Ta to C3V At elevated temperatures, methyl radical formation was reported (190-192). Ito et al. (192) reported a TPD study in the 220-600 K range of... 

The effect of addition of a UV stabilizer, 4,4 -butylidene bis(6-tert-butyl-m-cresol), on methyl radical formation was examined by Browning et al. (60) and it was found that a concentration of O. 1 % stabilizer is most effective in reducing the formation of methyl radicals on UV radiation. 

The pyrolysis of a diluted mixture of equimolar CH4 and CD4 was performed in a shock tube between 1500 and 1600 K and the products were quantitatively determined. From the hydrogen isotopic distribution of the products, methyl radical formation was confirmed as the initiation step of CH4 pyrolysis ... 

As displayed in Fig. 5, the specific surface area of the sample also declines in the order A, B, D, C, which is parallel to the sequence of methane conversion. Two aspects concerning the effect of the specific surface area on the catalytic properties have to be considered. (1) The larger the spedfic surface area, the higher the number of active centers by unit weifbf of the cataljwt and, of course, the faster the rate of methyl radical formation. (2) Lai e spedfic siirface areas may lead to an increase of e rate of formation of COx [4], due to the collision of methyl radicals with the surface. 

In addition, as it is well known, temperature is a very important factor which influences the catalytic properties. On the one hand, the increase of temperature may result in an increase of both the rate of formation and of desorption of methyl radical, which can obviously lead to an increase in the methane conversion and C2 selectivity on the other hand, the increase of temperature may also give rise to an increase of the rate of complete oxidation of methyl radicals and of the produced ethane and ethylene. As a result, there should be an optimum temperature at which the rate of methyl radical formation and its deep oxidation are equal to each other, leading to an optimum of methane conversion and of the selectivity of C2 formation. 

Model 1 The number of catalytic sites active in methyl radical formation depends on dissocia-tively adsorbed-type oxygen (T > 1013 K)... 

Basis of Simulation. It is basically assumed that the primary catalytic reaction step is the formation of methyl radicals which further react either on the catalytic surface or in the gas phase. The rate of catalytic methyl-radical formation was set equal to the rate of methane consumption. A power-law rate equation, valid for temperatures around 1020 K as reported earlier [27], was applied. 

Absorption of a quantum can promote an electron into the conduction band of Ti02. These electrons would tend to interact with the most electropositive carbon atoms in the polymer molecule, namely those in the methyl groups, leading to methyl radical formation and finally to methane ... 

Rosenthal, 1., Mosoba, M. M., and Riesz, P., Spin trapping with 2-methyl-2-nitrosopropane photochemistry of carbonyl-containing compounds. Methyl radical formation from dimethyl sulfoxide, Can. J. Chem., 60,1468, 1982. 

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