Cage reaction dialkyldiazenes

I he hyponitrites generally appear somewhat more efficient with respect to radical generation than the dialkyldiazenes (see 3.3.1.1). However, a proportion of radicals is lost through cage reaction with formation of the corresponding dialkyl peroxides or ketone plus alcohol (Scheme The disproportionation... 

There have been numerous studies on the kinetics of decomposition of A IRK. AIBMe and other dialkyldiazenes.46 Solvent effects on are small by conventional standards but, nonetheless, significant. Data for AIBMe is presented in Table 3.3. The data come from a variety of sources and can be seen to increase in the series where the solvent is aliphatic < ester (including MMA) < aromatic (including styrene) < alcohol. There is a factor of two difference between kA in methanol and k< in ethyl acetate. The value of kA for AIBN is also reported to be higher in aromatic than in hydrocarbon solvents and to increase with the dielectric constant of the medium.31 79 80 Tlic kA of AIBMe and AIBN show no direct correlation with solvent viscosity (see also 3.3.1.1.3), which is consistent with the reaction being irreversible (Le. no cage return). 

The proportion of useful radicals generated from common dialkyldiazenes is never quantitative typically it is the range 50-70% in media of low viscosity i.e. in low conversion polymerizations).3 88 89 The main cause of this inefficiency is loss of radicals through self-reaction within the solvent cage. 

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