Studies with dithizone: Part 35. A new look at the structure of dithizone in solution

The traditional view that solutions of dithizone in organic solvents comprise equilibrium mixtures of thione- and thiol-forms which are individually responsible for the characteristic strong absorption bands around 620 and 440 nm is examined critically. It is shown that experimental values of pH_{$\text{1}\text{2}$}, pK and R (the peak ratio) can legitimately be used in calculations although they are compounded of parameters (partition coefficients, acid dissociation constants, etc.) relating to both of the alleged tautomeric forms and the equilibrium constant, K_T governing the interconversion. Published attempts to calculate K_T from spectral data alone are shown to be unreliable.