Class no. Acidity Basicity Dielectric comtmt

The importance of titrations in nonaqueous solvents as an analytical method is increasing; not only.has more sophisticated instrumentation become available, but theoretical knowledge about the physicochemical processes which govern titra-tions in nonaqueous solvents has extended very much in recent years. Especially the titrations of Brransted acids and bases have been the subject of numerous studiesla2, and most applications relate to these particular titrations. It is of great importance to make a proper choice of the solvent and the titrant when such titrations are applied to the analysis of a given compound, i.e. knowledge about acid-base strengths in the various solvents is an absolute necessity. Only when all equilibria occurring during a neutralization and their corresponding equilibrium constants are known, can one calculate whether this neutralization can be successfully used in an analytical titration. For the more common acids and bases in a number of solvents like acetonitrile3, dimethylsulfoxide4, dimethyl-formamide such is indeed the case. Empirically it has been found that solvents with a relatively low dielectric constant such as acetic acid6, 1,2-dichloroethane ’ and pyridine’, can also be effective-ly used as a medium for acid-base titrations. Some rules with regard to the choice of a solvent for a particular titration can be found from the classification of the solvent according to Brnrnsted g * lo. Here the solvents with a relatively low dielectric constant are classified as numbers 5-8 (cf: Table I)