Studies in cyclophosphazenes. Part 9. Influence of the steric requirements of the amino-substituents on the rates of amination of 2-amino-2,4,4,6,6-pentachlorocyclotri(λ5-phosphazenes)

Abstract

Measurements of the rates of amination of a number of aminopentachlorocyclotriphosphazenes, N₃P₃Cl₅(NRR′)(R = Buⁿ, R′= H; R = R′= Buⁿ; R = Prⁱ, R′= H; RR′= C₅H₁₀), with dimethylamine to give non-geminal disubstituted products have been made at two temperatures in tetrahydrofuran with the aim of elucidating the steric effects of the amino-substituents in these reactions. The values of the rate constants and of the activation parameters determined showed that steric effects are only very small. To resolve the conflict between these findings and others in the literature in which appreciable steric influences were observed, the division of these amination reactions into three classes, each of which is affected by steric factors in its own way, is proposed. This enables much of the kinetic and preparative data on steric effects in these reactions to be rationalised in the framework of one general hypothesis.