Cryptand Exchange Kinetics

Article abstract of DOI:10.1021/ja00373a017

The rate constants for some reactions between a metal cryptate MCry₁ⁿ⁺ and a free cryptand Cry₂ has been determined.For the case when Mⁿ⁺ = Tl⁺, Ca²⁺, Cry₁ = (2,2,2), (2_B,2,2) and Cry₂ = (2,2,1) in water or water-methanol mixtures, the observed rate constant correspond to that of the dissociation of MCry₁ⁿ⁺.However, the exchange reactions Pb(2,1,1)²⁺ + (2,2,1) and Pb(2,1,1)²⁺ + (2,2,2) in MeOH present rates that are much larger than the dissociation rate of Pb(2,1,1)²⁺.A mechanism involving a bimolecular reaction between cryptate and free cryptand is proposed.