INTERRELATIONSHIPS BETWEEN PHASE-TRANSFORMATIONS AND ORGANIC-CHEMICALREACTIVITY IN THE SOLID-STATE

A qualitative analysis is presented of the interrelationships between phase transformations and organic chemical reactivity in the solid sta te, taking into consideration general thermochemical relationships and the thermodynamics of heterophase equilibrium, Two cases, where isome rization reactions depend on the solid-state solubility of the reactan t and product, are considered and show that the formation of a new pha se can influence both the reaction yield and rate. For example, it is shown that crystallization of a new phase from a crystalline or amorph ous solid solution can supply the thermodynamic driving force for chem ical transformation. Formation of a new phase may influence solid-stat e kinetics depending on the solubility of a reactant in the new phase and the relative rates of chemical transformation and formation of the new phase. It is further shown that even for simple monomolecular rea ctions, kinetic curves for the overall process can consist of up to fi ve parts, depending on the type of phase diagram involved. These princ iples have been applied to some examples of solid-state isomerization in a way that allows the choice of a proper kinetic scheme and an expl anation of the direction and maximum yield observed for a particular r eaction.