Ionic polymerisation as a means of end-point indication in non-aqueous thermometric titrimetry. Part V. The iodimetric determination of organic bases, hydrazine derivatives and water

Abstract

A thermometric titration method has been evaluated in which organic bases, hydrazines, phosphines and quaternary ammonium halides, and also water, have been titrated with iodine in non-aqueous solutions containing alkyl vinyl ethers. The latter polymerise with the excess of iodine evolving heat, which marks the end-point.

The ratio of the reactants in titrations of most of the amines examined, namely 3·6 to 4·6 atoms or 1·8 to 2·3 molecules of iodine to 1 molecule of amine, depending on the amine, is favourable to the titration. With hydrazine derivatives, the ratio ranges from 4·2 to less than 1 atom of iodine to 1 molecule of the hydrazine, depending on the hydrazine derivative.

Water can be titrated with iodine in the presence of alkyl vinyl ethers, about thirteen molecules of water consuming one atom of iodine.

The end-point in titrations of most of the compounds examined is marked by a sharp inflection in the titration graph when an automatic procedure is used. Precisions are usually better than 1 per cent. with 0·05 M and 2 per cent. with 0·01 M titrant solutions.

Sample sizes down to about 0·0005 mmol, depending on the iodine consumed in the reaction, can be determined with 0·01 M titrant solution. Calibration graphs show that, except in the titration of water, the volume of titrant and amount of sample are linearly related in the range 0 to 1 ml of titrant. The curvatures of calibration graphs for water depend on the rates of addition of iodine to the sample; linearity can almost be achieved at an appropriate titration rate.

It is suggested that the stoicheiometry, i.e., the iodine consumed per molecule of sample, is a quantitative measurement of the basic properties of the compounds investigated. The different stoicheiometries for different compounds make the iodimetric method useful for the selective determination of the constituents of binary mixtures of bases and hydrazine derivatives, but unsuitable for the determination of the total basic or hydrazine function in more complex mixtures.