Applications of Nonaqueous Acid-Base Titrations

If feasible, add-base titrations are best carried out in aqueous media. When, however, the add or base to be determined is too weak to be titrated in water or is insoluble, then nonaqueous titrations may be attractive. An enormous literature has developed 

From the practical point of view, nonaqueous solvents can be described broadly as acidic, basic, or neutral. For carrying out titrations, properties such as dielectric constant, melting point, boiling point, and (for amphiprotic solvents. Section 4-3) autoprotolysis constant are important (Table 6-1). 

Solvent purification has been discussed by many, and recommended procedures have been listed by Kratochvil. Molecular and volatilizable impurities are best measured by gas chromatography, and ionic impiuities by electrical conductivity. The commonest and most troublesome impurity, because of its leveling action, is water it can be measured by the Karl Fischer method (Section 19-8) among others. 

In general, a solvent selected for the titration of a weak acid should itself be a much weaker acid (or neutral) and usually should be basic enough compared with water as solvent to increase the extent of dissociation. Comparably, for a weak base the solvent should be a much weaker base and acidic enough to increase the extent of dissociation. For the possible differentiation of acids that are all strong in water, the choice of a solvent less basic than water is appropriate. The solvent should also dissolve the sample, and the reaction products should be either soluble or rapidly form 

The titrant base is generally a tetraalkylammonium hydroxide or an alkali metal alkoxide. Hiller used the sodium salt of methylsulfinyl carbanion as titrant base. 

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