Studies in cyclophosphazenes. Part 5. Influence of the steric requirements of the amines on the rate of amination of 2,2,4,4,6,6-hoxachlorocyclotri(λ5-phosphazene)

Abstract

The rates of reactions between the title compound and various straight-chain and branched primary and secondary amines to form the corresponding monoaminopentachlorocyclotriphosphazenes have been measured in tetrahydrofuran at different temperatures. The straight-chain primary amines all react at the same rate, but α-branched primary amines and secondary amines react more slowly. Although the entropy of activation makes the greatest contribution to the free energy of activation in all these reactions, the reduction of the rates is related to increases in the enthalpy of activation. Detailed analysis of the data supports a two-step mechanism. Comparison with data in the literature clarifies the steric course of the reaction and elucidates the role played by steric factors.