Acetoxy radical, decomposition

When the decomposition is carried out in an inert solvent, methyl acetate and ethane are formed, whereas in the gas-phase decomposition methyl acetate is completely absent and ethane is produced in much smaller quantity, It was suggested that the dimers in solution represent the recombination of methyl, and the combination of methyl and acetoxy radicals, within the solvent cage. ... 

Thermal decomposition of lead tetraacetate gives rise to methyl radicals, again through the initial formation of acetoxy radicals. " An ionic mechanism for the decomposition has also been postulated, and it is possible that both mechanisms may occur, depending on the conditions. 

Let us assume that fci is equal to k9, the rate constant for the gas phase decomposition (15), where no cage effect is expected. This assumption does not always hold (15, 18). For example, it is known (18) that di-f erf-butyl peroxide (DPB) decomposes about 30% slower in the gas phase than in solution. We can calculate from our value of k8 and the known value of kg, from the work of Szwarc (7, 21), a value for the fraction of acetoxy radical pairs recombining, fR, where... 

The polyazophenylene units are formed from the polyrecombination of the decomposition products from bis(nitrosoacetyl)benzidine. Chain termination can occur by disproportionation of the polymer radicals and by recombination with acetoxy radicals. Despite the rate constant for the recombination of the phenyl and azophenyl radicals being much larger than that of the initiation reaction for isoprene, it is possible to synthesise copolymers from these materials by a careful choice of the various reaction parameters. However, block copolymers could only be obtained using emulsion techniques (see Table 4.11) and not in bulk or in solution. 

The acyl peroxide bonds (RCO2-OCR) are very weak (see Table 63), and the decomposition of the acetoxy radical is rather exothermic, viz. 

As was indicated previously, primary alkyl diacyl peroxides undergo decomposition to give two acyloxy radicals, which subsequently undergo rapid decarboxylation. The rate coefficient for decarboxylation of the acetoxy radical is calculated to be 1.6 X 10 sec at 60 °C in n-octane . The corresponding activation parameters were = 6.6 kcal.mole and A = 3.5 x 10 sec An earlier report estimated the activation energy to be about 5 kcal.mole . It was pointed out by... 

Martin et that attempts to trap the acetoxy radical with iodine, galvinoxyl or diphenylhydrazyl were either unsuccessful or ambiguous. However, isotopic labeling experiments show that cage recombination does occur and the mechanism of acetyl peroxide decomposition may be formulated as... 

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