Ionic polymerisation as a means of end-point indication in non-aqueous thermometric titrimetry. Part I. The determination of organic bases

Abstract

A method for the thermometric titration of organic bases in non-aqueous solution, in which ionic polymerisation is used to indicate the end-point, has been evaluated for a range of aliphatic and aromatic amines, including substituted and polyfunctional amines, heterocyclic nitrogen compounds, amides and some basic sulphur and phosphorus compounds. Perchloric acid and boron trifluoride were used as titrants and α-methylstyrene and isobutyl vinyl ether were the monomers used, respectively, in conjunction with them.

The precision of the method with titrants of molarities from 0·1 to 0·001 is of the order of 1·5 per cent. When a simple manual procedure involving the use of a thermometer to measure the temperature is adopted. More elaborate methods, in which the temperature is measured with a thermistor and recorded, give precisions better than 1 per cent.

Sample sizes down to about 0·0001 mequiv, e.g., about 10 µg of morpholine, which corresponds to 10 p.p.m. of morpholine in the volumes of sample solution titrated, can be determined with 0·001 M titrants. Calibration graphs show that the volume of titrant and amount of sample are linearly related in the range 0 to 3 ml of titrant.

It is suggested that comparison of the results obtained when a base is titrated with the two titrants, a Brønsted acid and a Lewis acid, can be used to investigate some of the properties of the base.