Oxidation products cage effect

The stepwise mechanism was also illustrated in terms of a temperature-dependent cage effect.23 Reaction of 24 with a mixture of lithium cyclo-hexyl-1-rf-oxide (48) and 3-pentyloxide (49) at 0°C, produced cross-over products 50 and 51, both in - and Z- forms, and the deuterium was scrambled in both isomers (89% in 50 and 6-12% in 51). In contrast, at —95—40°C, no... 

The oxidation of I2 in acetic anhydride in the presence of phosphoric acid was reported earlier to yield IPO4 however, the Mossbauer spectrum of the product clearly demonstrates that it should be treated as an iodine(i) compound.The yields of organic iodides produced in the reaction at 77 K of saturated aliphatic hydrocarbons with I and I2, generated by electron bombardment of I2 vapour, have been accounted for by a reaction mechanism involving cage effects. 

These results are at some variance with those of MacKay and Wolfgang (1962) who see no phase effect in acetylene yield and only a small effect on ethylene in comparing gaseous and liquid isobutane. They do, however, note that stabilization of the Cg build-up products may be going on since they observe an increase in both isopentane and 2-methyl-3-butene. The isopentane yield is probably enhanced because of stabilization of the methylene-insertion products. They also found a 25% decrease in acetylene from ethylene oxide on going from the gas to the solid which they ascribed to reaction of the intermediate with the cage. Ethylene in the gas, liquid, and solid phases was also studied. 

Few examples of this mechanism have been clearly demonstrated because of tfie difficulty in establishing that this path occurs from experimental data. The most well-established examples are reactions of nickel complexes with aryl halides Studied by Tsou and Kochi. The rate of the reaction of Ni(PEt3)jWith aryl halides was shown to be first order in nickel and in ArX and retarded by added PEtj, Ortho-methyl substituents had little effect on the rate. Because of the lack of steric effect, electron transfer was proposed to occur after formation of a TT-complex between Ni(PEt3)j and ArX, rather than by direct insertion of the metal into the carbon-halogen bond by a three-centered mechanism. Moreover, the products of the reaction included the Ni(I) species L3NiX and arene. Tliese products are likely to result from the pathway in Scheme 7.4, involving electron transfer from Ni(0) to the aryl halide and escape of the aryl radical from the solvent cage. Other studies of oxidative additions of aryl halides and sulfonates to Ni(0) complexes have been reported. " ... 

The practical value of the Fischer-H opsch reaction is limited by the unfavorable Schulz-Flory distribution of hydrocarbon products that is indicative of a chain growth polymerization mechanism. In attempts to increase the yields of lower hydrocarbons such as ethylene and propylene (potentially valuable as feedstocks to replace petrochemicals), researchers have used zeolites as supports for the metals in attempts to impose a shape selectivity on the catalysis [114] or to control the performance through particle size effects. [IIS] These attempts have been partially successful, giving unusual distributions of products, such as high yields of C3 [114] or C4 hydrocarbons. [116] However, the catalysts are often unstable because the metal is oxidized or because it migrates out of the zeolite cages to form crystallites, which then give the Schulz-Flory product distribution. 

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