Tetrahydroxyazon SCl as a new analytical reagent for determining copper(II)

2,2′,3,4-Tetrahydroxy-3′-sulfo-5-chloroazobenzene was synthesized from pyrogallol and 2-aminophenol-5-chlorobenzenesulfonic acid. The complexation of copper(II) with this reagent was studied. A homoligand compound of the stoichiometry 1: 1 was obtained at pH 2. The optimum conditions for complexation were found and the equilibrium constant of the reaction was calculated. The selectivity of the reaction was studied and the stability constant of the complex was evaluated. Procedures were developed for the photometric determination of copper in alloys and soils.