Neuentwicklungen bei Titrationen in nichtwäßrigen Lösungsmitteln

Summary

The acidimetric titration of very weak bases, as for example carboxylic acid amides, with perchloric acid is so far only possible if the solvent, at least partly, consists of acetic anhydride. Many determinations, however, cannot be performed because of the acetylating and levelling effect of this compound. It is shown that acetonitrile can be used instead of acetic anhydride provided that no buffering substances, like glacial acetic acid or dioxane, are carried in together with the titrant. Thus, aliphatic and aromatic amines together with acid amides could be titrated in presence of each other for the first time.

The applicability of the combination of catalytic hydrogenation and titration has been extended. In addition to nitriles nitro and azo compounds and also pyrrole derivatives can be converted to amines by hydrogenation in glacial acetic acid and titrated with perchloric acid. Among the pyrrole compounds benzopyrroles (indole, carbazole) can be selectively determined by direct potentiometric titration with tributylmethylammonium hydroxide in pyridine; the acidity of simple pyrroles is not sufficient for such a titration.

Mixtures of aliphatic sulphonic acids and primary and secondary sulphonic acid amides have been analysed by alkalimetry. The differentiation between secondary sulphonic acid amides and sulphonic acids has only been possible by the use of glacial acetic acid as solvent. Sulphonic acids may be selectively determined by titration with sodium acetate solution in glacial acetic acid; when titrating potentiometrically with tributylmethylammonium hydroxide in tert.-butanol they are determined together with the secondary sulphonic acid amides; the second potential jump corresponds to the primary sulphonic acids amides.