Mechanistic considerations for anation reactions in the solid state

Abstract The controversy regarding the mechanisms of anation reactions in the solid state is examined. Historically, these reactions have been considered as S N 2 since the nature of the anion affects the reaction. However, principles of reaction kinetics for solid state processes lead to as many as 17 possible rate laws. The role of free space, which increases as the difference between the sizes of the cation and anion increases, appears to be rate-determining in some cases. In most instances, the observed anion effect is readily explained in terms of free space (a defect-diffusion model) rather than S N 1 or S N 2. Consequently, rate laws based on nucleation or diffusion control appear to be more applicable to anation reactions. The review of a large number of anation reactions is presented to show the applicability of the defect-diffusion model.