O-nucleophilic features of amidoximes in acyl group transfer reactions

Analysis of kinetic behavior of isomeric Z-amidoximes and their Z-ions in reactions with 4-nitrophenyl-4-toluenesulfonate, diethylphosphate, and diethylphosphonate was performed in the framework of Bronsted relationship. The reactivity of amidoximate anions with respect to the mentioned substrates is comparable to that of typical alpha-nucleophiles, oximate ions. The alpha-effect decreased with the growing basicity of amidoximate ions. and for compounds with pK(a) > 12.0 it was totally lacking. The high nucleophilic activity of neutral amidoximes and their anionic forms was ascribed to the cyclic structure of the transition state involving two kinds of assistance: general acidic, and basic catalysis. A unique feature of amidoximes as alpha-nucleophiles consists in their ability to perform efficient cleavage of ecotoxic substrates in a wide pH range, from basic to acid media.