Kinetic studies of the complexation of monovalent sodium, potassium, rubidium, thallium, and silver cations by aqueous 15-crown-5

Abstract

Abstract : A kinetic study of the rapid conformation equilibrium of aqueous 15-crown-5 (1,4,7,1+,13-pentaoxacyclopentadecane) and of its complexation of monovalent sodium, potassium, rubidium, thallium and silver cations at 25 degrees in aqueous solution has been carried out by ultrasonic absorption in the 15 to 205 MHz frequency range. A concentration independent absorption with a maximum at 22.9 + or - 0.5 MHz detected in aqueous solutions of 15-crown-5 with no cations added has been attributed to a conformational rearrangement of the crown ether. The kinetics of the complexation of the polyether with sodium, potassium, rubidium, silver and thallium(I) ions were then investigated at various polyether and metal concentrations with concentration dependent relaxations occurring between approx. 20 and approx. 50 MHz. These data, together with the conformational rearrangement data, were analyzed in terms of a two step mechanism with CR(1) rearranging to CR(2) and CR(2)+ M(+) rearranging to a complex in which CR(2) denotes the conformation of the ether which participates in the complexation reaction.