Ultrasonic Absorption Kinetic Studies of the Complexation of Aqueous Li(+), Na(+), Rb(+), Tl(+), Ag(+), NH4(+), and Ca2(+) by 18-Crown-6.

摘要

The complexation-decomplexation reaction kinetics of the macrocyclic polyether 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) with the aqueous cations Li(+), Na(+), Rb(+), Tl(+), Ag(+), NH4(+), and Ca(2+) have been determined from acousto-optic ultrasonic absorption data covering the 15-205-MHz frequency range, at 25C. These data, together with a previously reported crown ether conformational change, were analyzed in terms of a multistep mechanism that admits the possibility of water loss or conformational changes but not diffusion as being rate limiting. The complexation rate constants follow the trend CA(2+) approx = Li(+)