A polarographic study of pyrocatechol violet

Abstract

In acidic medium the ring carbonyl group of pyrocatechol violet is reduced in a single reversible two-electron step at a dropping mercury electrode. At pH>6.5 the single step is split, two polarographic waves being obtained; the first corresponds to a reversible one-electron step, and the second to an irreversible one. The half-wave potentials of the two steps depend on the pH, but they are also influenced by the deprotonation of the electro-inactive part of the dye molecule. Boric acid interacts with the dye forming an ester with the phenolic OH groups in the ortho position. This results in two steps of equal height, as in the case of the alkalization of the solution.