Determination of organoisothiocyanates alone and in mixtures with organoisocyanates or thioureas

An iodatometric method for the determination of organoisothiocyanates is described. The isothiocyanates are quantitatively converted with n-butyl-amine in dimethylformamide medium into the corresponding symmetrical NN-disubstituted thioureas, which are titrated visually or potentiometrically in acidic medium with potassium iodate solution. Methods have also been developed for the analysis of isothiocyanate-isocyanate and isothiocyanate-thiourea mixtures on the same sample solution. A known excess of the standard n-butylamine solution added to the mixture in dimethyl-formamide converts the isothiocyanate and isocyanate into the corresponding disubstituted thiourea and urea, respectively. Acidimetric titration of the excess of amine, and iodatometric titration of the thiourea present and formed, enable the particular mixture to be analysed for both constituents. The end-points can be detected both visually and potentiometrically. The methods described are simple, accurate, reliable and widely applicable.