Solution chemistry of macrocycles. Part 3. Synthesis and thermodynamics of protonation of some tetra-azamacrocycles

Abstract

The synthesis of the tetra-aza-macrocycle 1,4,8,11-tetra-azacyclopentadecane is reported. The enthalpy and entropy contributions to the stepwise protonation of the three macrocycles, 1,4,8,11-tetra-azacyclopentadecane, 1,5,8,12-tetra-azacyclohexadecane, and 1,5,9,13-tetra-azacycloheptadecane, have been determined at 25 °C in 0.5M-KNO₃. A fully automatic potentiometric technique has been used to determine the basicity constants and a continuous titration calorimetric technique has been used to determine the corresponding enthalpy changes. The thermodynamic functions have been explained in terms of macrocyclic ring size and relative length of hydrocarbon chains between the nitrogen atoms. For large macrocycles the protonation behaviour is very similar to that of the corresponding open-chain tetramines.