Radical chain nonselective

Write initiation, propagation, and termination steps for this radical-chain reaction. Estimate a AH0 for the overall reaction using the bond-dissociation energies of Table 4-6. Would you expect bromotrichloromethane to be a selective or nonselective brominating agent Explain. 

The decay of ozone, which can be initiated by the hydroxide ion, leads to a chain reaction and produces fast-reacting and thus nonselective OH-radicals. This also means that OH-radicals have a very short half-life, e.g. less than 10 ps at an initial concentration of I O 4 M. 

The autoxidation of organic substrates catalyzed by transition-metal salts has been used widely in the petrochemical industry for many years (32), but the oxidations are frequently nonselective since they operate by free-radical pathways that are sometimes initiated by the transition-metal ion. An example is the chain reaction of Reactions 2, 3, 4, and 5 (4). Propagation is maintained via Reactions 3 and 4, and any interaction between the metal ion and 02 would be incidental. 

Most of the current results on the selective oxidation of methane over metal oxide catalysts may be interpreted in terms of methyl radical chemistry. These radicals may either react with the oxides themselves to form methoxide ions or they may enter the gas phase. The methoxide ions on supported molybdena decompose to form formaldehyde or they react with water to yield methanol. On the basic oxides methoxide ions result in complete oxidation. Those radicals which enter the gas phase undergo typical free radical chemistry which includes coupling reactions to give ethane and chain branching reactions to give nonselective oxidation products. Secondary surface reactions, particularly with ethylene, also may result in complete oxidation. If further improvements in yields of partial oxidation products are to be achieved, ways must be found to more efficiently utilize the methyl radicals, both with respect to surface reactions and to gas phase reactions. In addition, if ethylene is the desired product, catalysts must be fine-tuned to the point where they will activate methane, but not ethylene. 

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