Amine oxidation. Part VII. The effect of structure on the reactivity of alkyl tertiary amines towards alkaline potassium hexacyanoferrate(III)

Abstract

Kinetic studies on the oxidation of N-methyl- and N-deuteriomethyl-di-n-butylamine confirm that the rate-determining step is an electron-transfer from the nitrogen to the potassium hexacyanoferrate(III); the relative rate of reaction k_H/k_D is 1·04. The influence of deuteriation on the product distribution (isotope effect 3·6) indicates that the second step is a product-determining proton loss.

Further information about the electron-abstraction and the nature of the first transition state has been obtained from the rates of oxidation of a selection of cyclic tertiary amines. The results are in accord with the transition state occurring late on the reaction co-ordinate. Thus, in the transition state electron-transfer from the amine to the hexacyanoferrate(III) is almost complete and the configuration of the nitrogen resembles that of the intermediate aminium radical cation rather than that of the substrate.

The order of increasing ease of oxidation of bridgehead bicyclic amines, triethylenediamine monomethiodide, quinuclidine, and triethylenediamine is discussed in the light of these conclusions.