Cage reaction diacyl peroxides

Observed rates of disappearance for diacyl peroxides show marked dependence on solvent and concentration.146 In part, this is a reflection of their susceptibility to induced decomposition (see 3.3.2.1.4 and 3.3.2.1.5). However, the rate of disappearance is also a function of the viscosity of the reaction medium. This is evidence for cage return (see 3.3.2.1.3).143 The observation144 of slow scrambling of the label in be.x LQy -carbonyl- %0 peroxide between the carbonyl and the peroxidic linkage provides more direct evidence for this process. 

The homolytic decomposition of diacyl peroxides proceeds via splitting of the weakest O—O bond. The acyloxy radicals formed are very unstable and a cascade of cage reactions follows this decomposition [4,42-46] ... 

The yield of cage reaction products increases with increasing viscosity of the solvent. The decomposition of diacyl peroxides was the object of intensive study. The values of rate constants of diacyl peroxides (diacetyl and dibenzoyl) decomposition (kf and initiation (ki = 2ekd) are collected in Tables 3.4 and Table 3.5. The values of e are collected in the Handbook of Radical Initiators [4]. 

Only a few diacyl peroxides see widespread use as initiators of polymerization. The reactions of the diaroyl peroxides (36, R=ai yl) will be discussed in terms of the chemistry of BPO (Scheme 3.25). The rate of p-scission of thermally generated benzoyloxy radicals is slow relative to cage escape, consequently, both benzoyloxy and phenyl radicals are important as initiating species. In solution, the only significant cage process is reformation of BPO (ca 4% at 80 °C in isooctane) " only minute amounts of phenyl benzoate or biphenyl are formed within the cage, fherefore, in the presence of a reactive substrate (e.g. monomer), the production of radicals can be almost quantitative (see... 

Knowledge of the cyclization rate of the 5-hexenyl radical has also been used to study cage reactions of alkyl radicals generated in solution from diacyl peroxides or to distinguish between intra- and intermolecular pathways in the Wittig rearrangement. It has also been used to study the mechanism of the deshalogenation of 1,4-, 1,5-, and 2,3-dihaloalkanes by alkali... 

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