Absolute rate constants for SN1-like ionization reactions in zeolites:: Determination of zeolite ionizing power

A kinetic probe molecule has been developed to investigate the absolute ionizing power of cation-exchanged (LiY, NaY, KY, RbY, and CsY) Y-zeolites. The probe, the 2-chloro-1-(4-methoxyphenyl)ethyl radical, was generated within the supercages of MY upon laser photolysis of 2-chloro-1-(4-methoxyphenyl)ethyl acetate under both dry and hydrated conditions. The ionizing power of the cation exchanged Y-zeolites depends on the nature of the counterion and increases upon going from CsY to LIY. In addition, the ionizing powers of the dry zeolites are weaker than that of neat water and are more similar to water/methanol mixtures containing from 30% to 70% water. A significant reduction in the absolute ionizing ability of the zeolite was found when the zeolite was hydrated by the coadsorption of water.