Monograph - Metrohm

Remarks concerning solvents for non-aqueous titrations3 Remarks concerning solvents for non-aqueous titrations3.1 Amphiprotic solvents – acidic3.1.1 Glacial acetic acid (HAc)Solvent for bases in particular. The water content should be less than 1%. Insome cases acetic anhydride is added. However, this can lead to acetylation andtherefore to incorrect results (primary, secondary and tertiary amines). For thetitration of weak bases it is better to add an aprotic solvent, e.g. dioxane or toluene.3.1.2 Formic acidIs only used for the titration of the weakest bases, e.g. caffeine (pK B = 13.4) orurea (pK B = 13.8). The water content should not exceed 1%. Should not be usedwith short-chain alcohols – esterification!3.1.3 Trifluoroacetic acidSuitable as a solvent for the weakest bases, where acetic anhydride cannot beused because of acetylation. An expensive solvent!3.1.4 OthersPropionic acid, cresols and phenol are not very important. Cresols are used inmixtures, e.g. with chloroform, as solvents for determinations of terminal aminogroups in polyamides. As phenol has excellent solubilising properties for thesalts of organic bases, its use with a mixture of chloroform and acetonitrile hasbeen suggested for these applications.3.2 Amphiprotic solvents – basic3.2.1 EthylenediamineUsed as a solvent for weak acids. Has good solubilising properties. Has a levellingeffect for strong acids – carboxylic acids and phenols can nevertheless beseparated. It fumes when exposed to the air, is toxic and corrosive and also hasan unpleasant odour. Takes up water and carbon dioxide from the air (blank values).3.2.2 ButylamineSimilar properties to ethylene diamine, but has slightly smaller solubilising properties.Offensive odour.3.2.3 BenzylamineIf it has to be a solvent from this class (3.2), then this one. Similar to butylamine,but better solubilising properties and less offensive odour.Non-aqueous titration of acids and bases with potentiometric endpoint indication 5