Homogeneous Organic Reactions as Mechanistic Probes in Supercritical Fluids.

Abstract

An interesting and intriguing aspect of supercritical fluid solutions is their microscopic inhomogeneities. The most well-known of these are the long-range densities fluctuations that occur in a pure fluid at conditions close to the critical point. However, there are also short-range inhomogeneities around dissolved solutes in supercritical fluids, which are frequently referred to as local density augmentation and local composition enhancements. Many questions have arisen about the potential influences that short-range solvation and long-range density fluctuations might have on complex chemical reaction schemes. In attempts to answer these questions, researchers have sought to study the effect of supercritical fluid solvents on simple unimolecular and bimolecular reactions. In doing so, the reactions themselves have become probes of the molecular structure and the influence of solvation on reactivity in supercritical fluids (SCFs). In this paper, the authors attempt to review those studies that involve simple reactions as probes of molecular structure and its effect on reactivity in SCFs. The paper discusses (1) the potential ways for solvation in supercritical fluids to affect reactivity and (2) the reactions that probe solvation in supercritical fluids, including diffusion-controlled reactions, kinetically-controlled reactions, equilibrium reactions, SCF solvent cage effects, and other important reactions and directions.