The enthalpimetric titration of basic nitrogen compounds

Abstract

When aqueous solutions of bases are titrated enthalpimetrically with acid, it has been found that ammonia and aliphatic bases are titrated before pyridine and aniline bases. When aqueous solutions of the mineral acid salts of bases are titrated, the titration order is (i) the free acidity, (ii) the pyridine and aniline base salts and (iii) the ammonia and aliphatic base salts.

In non-aqueous solution, use has been made of the large endothermic heat of dilution when a strong hydrogen chloride solution in isopropyl alcohol is added to a wide range of organic solvents, excluding alcohols. As an enthalpimetric titrant, this solution first gives a temperature rise as a result of the neutralisation of the base in the solvent, followed by a sharp temperature drop that marks the end-point. In solvents other than acetic acid, aliphatic bases are titrated first and are distinguishable from aromatic bases, except those similar to diphenylamine, which are not titrated. In acetic acid solution, aliphatic and aromatic bases are titrated together first and are distinguishable from the weak bases like diphenylamine, which are titrated in this solvent.