Studies on the existence of a tautomeric equilibrium in solutions of the analytical reagent dithizone

Abstract

The traditional view that solutions of dithizone in organic solvents comprise equilibrium mixtures of thiol and thione forms which are individually responsible for the characteristic strong visible absorption bands around 440 and 620 nm is examined critically. Fourier transform 1 H and 13 C NMR spectroscopic measurements on dithizone, seven of its alkyl-substituted homologues, and on its 13 C- and 15 N-labelled analogues point to the existence of only a single molecular species in chloroform, benzene or acetone. The marked solvatochromism, however, has yet to be explained. Modifications to established synthetic routes are reported which are especially suitable for the small-scale preparation of isotopically-labelled dithizone analogues.