Determination of primary and secondary amines alone and in mixtures with tertiary amines

Abstract

An iodatometric method has been developed for the determination of primary and secondary amines that is based on their quantitative reaction with phenyl isothiocyanate in dimethylformamide to form substituted thioureas. These are titrated with potassium iodate in an acidic medium at room temperature. The end-point is detected visually by the yellow colour imparted to the solution by the first drop of the iodate solution in excess, and potentiometrically by using a bright platinum-wire indicator electrode and a saturated calomel reference electrode. Methods have also been developed for the determination of primary (or secondary) amines and tertiary amines in the presence of each other. An excess of phenyl isothiocyanate, added to the mixture in solution in dimethylformamide, converts the primary (or secondary) amines into the corresponding di-(or tri-) substituted thioureas, whereas the tertiary amines are left unreacted. The conductimetric titration of tertiary amines with trichloroacetic acid, followed by the iodatometric titration of thioureas formed, enables the mixture to be analysed for both components. The methods described are simple, accurate and reliable.