Kinetics of the dehydration of N-(α-cyanobenzyl)-N-phenylhydroxylamines

Abstract

The rate of dehydration of N-(α-cyanobenzyl)-N-phenylhydroxylamines (I) catalysed by triethylamine and tri-n-butylamine were measured in 95% ethanol at 25°. The triethylamine catalysed rate of dehydration of α-cyano-p-chlorobenzyl derivative (Ic) was linearly correlated with the ionization ratio of p-cyanophenol in the same medium. Hammett ρ values of 2.90 and 1.57 were obtained for C- and N-phenyl substituents, respectively. The primary deuterium isotope effect for the reaction of (Ic) was ca. 6. An irreversible E1cB mechanism is suggested for the reaction except for the α-cyano-p-dimethylamino-derivative (Ie). The large positive deviation of (Ie) from the Hammett plot and its smaller deuterium isotope effect (ca. 3) are explained in terms of a transition to an E2 mechanism.