Solution chemistry of macrocycles. Part 1. Basicity constants of 1,4,8,11-tetra-azacyclotetradecane, 1,4,8,12-tetra-azacyclopentadecane, and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane

Abstract

The four protonation constants of the macrocyclic tetra-amines 1,4,8,11-tetra-azacyclotetradecane ([14]aneN₄), 1,4,8,12-tetra-azacyclopentadecane ([15]aneN₄), and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (Me₄[14]aneN₄) have been determined in 0.5M-KNO₃ at 25 °C. Glass and silver/silver chloride electrodes were employed and the experimental e.m.f. values have been corrected for the liquid junction potential. The computer program MINIQUAD has been used for the calculation of the equilibrium constants. The values obtained are: [14]aneN₄, log K₁= 11.59, log K₂= 10.62, log K₃= 1.61, log K₄= 2.42; [15]aneN₄, log K₁= 11.08, log K₂= 10.38, log K₃= 5.28, log K₄= 3.60; Me₄[14]aneN₄, log K₁= 9.70, log K₂= 9.31, log K₃= 3.09, log K₄= 2.64. For the first two protonation steps the macrocyclic tetra-amines are more basic than the corresponding open-chain tetra-amines, even if the former exhibit a lower overall basicity.