Pyrolysis of Aryl Azides. VIII. Hammett Correlations of Rates of Pyrolysis of Substituted 2-Azidobenzophenones

Abstract

Eight 2-azidobenzophenones with 4- or 5-substituents have been pyrolysed in decalin solution to yield 3-phenyl-2,1-benzisoxazoles. Rate values at 100° are correlated with the Hammett substituent constants, with respect to both the azido (A) and benzoyl (B) reaction centres , and yield the equation log k = -4.38 + 2.08σ^-/A -1.52σ_B. There is a similar equation for rates measured at 120°. Although nitro and benzoyl differ considerably in their neighbouring group abilities in azide pyrolyses, it is concluded that they exert their effects through the same mechanism.

The results are consistent with both published variants of an electrocyclic mechanism (Dyall; Smith, Budde and Chou).