Cyclopropyl azoalkanes

The decomposition of four cyclopropyl azoalkanes has been reported in the literature . In the brief abstract of the work the reaction conditions are not specified but it may be assumed that the rate parameters listed in Table 4 refer to the homogeneous first order decomposition to nitrogen and the corresponding alkyl radicals. 

An inspection of the compilation of the rate data in Table 4 makes it evident that an abnormally high frequency factor and a relatively low activation energy are characteristic features of the thermal decomposition of azoalkanes. The data coming from different laboratories show considerable scatter but in spite of this it is clearly seen that the activation energy is related to the stability of the alkyl radicals formed in the decomposition and declines with the stability of the radicals. The same trend but even more conspicuously manifested can be observed in the reactions of cyano and aryl substituted azoalkanes. These kinetic features explain 

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The most fruitful group of reactions in this category, however, involves the 4,5-dihydro-3/f-pyrazol-4-ones 15 and 16. These are reluctant azoalkanes and difficult to deazetize under normal conditions, but this chemically robust nature enables them to be used in the synthesis of a wide variety of cyclopropyl derivatives. 

Alkyl radicals are conveniently generated by photodecomposition of azoalkanes. A kinetic study of the rearrangement of cyclopropyl radicals (1), obtained by photolysis of the azoalkanes (2), has been described. Particularly high radical concentrations leading to a dramatic change in the product ratio of tetrakis(pentafluoro-ethyl)hydrazine and perfluorobutane have been achieved in the pulsed laser excitation of perfluoroazoethane. On photolysis, azosulphonates also function as radical traps, with the formation of hydrazyl radicals as reactive intermediates. ... 

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