Physical Organic Chemistry of Reactions in Dimethyl Sulphoxide

Abstract

Publisher Summary This chapter describes the use of dimethyl sulphoxide (DMSO) as an “inert” solvent in mechanistic investigations of heterolytic reactions and illustrates the methods developed for mechanistic study in dipolar aprotic media. The effect of DMSO on product distributions is discussed, and possible future uses of DMSO in mechanistic investigations are explained. The origin of the medium effect is considered, which is exhibited for reactions on changing from a hydroxylic solvent to a dipolar aprotic medium such as DMSO. The use of DMSO in organic chemistry has revealed the profound influence of solvent on the course and the rates of organic reactions but there is still a need to garner fundamental thermodynamic data relating to the transfer of solutes to DMSO from the aqueous state. Studies of simpler organic reactions in DMSO or its protic mixtures have revealed that this solvent can affect the outcome of a proton transfer process in a variety of ways. The stereochemical outcome of proton transfer can be retention, inversion, racemization, or a combination of these, depending on the presence or absence of DMSO. DMSO has unique molecular properties, which enable it to stabilize certain types of structures, such as the anionic intermediates in SNAR reactions. The two illustrative systems that are discussed to demonstrate the versality of this solvent in mechanistic studies are stabilization and catalytic decomposition of intermediates in SNAR reactions and the steric course of bimolecular Olefin-forming eliminations.