Sodium ion exchange on the 1,4,7,10,13,16-hexaoxaoctadecanesodium(I) cation ([Na.18C6]+) in several solvents. A sodium-23 nuclear magnetic resonance study

Abstract

23 Na N.m.r. studies of Na+ exchange on the 1,4,7,10,13,16-hexaoxaoctadecanesodium(I) cation ([Na.18C6]+) in acetone, methanol and pyridine yield the respective decomplexation rate constants 10–2kd(265 K)= 606 ± 88, 42 ± 2 and 7.16 ± 0.30 s–1; and the corresponding activation parameters ΔH‡= 36.7 ± 0.7, 53.6 ± 0.8 and 50.5 ± 1.2 kJ mol–1; and ΔS‡=–14.0 ± 3.2, 27.8 ± 2.9, and 1.4 ± 4.2 J K–1 mol–1. These data are discussed in conjunction with data obtained from other n.m.r. and ultrasonic relaxation studies, and mechanistic aspects of the complexation of Na+ by 18C6 are considered.