Electrochemical Reduction of Sodium 1,4-dihydroxy-9,10-anthraquinone-2-sulphonate in Aqueous and Aqueous Dimethyl Formamide Mixed Solvent: A Cyclic Voltammetric Study

The electrochemical behavior of sodium 1,4-dihydroxy-9,10-anthraquinone-2-sulphonate (sodium quinizarin-2-sulphonate), an analogue of the core molecule of anthracycline antibiotics, was studied using cyclic voltammetry. In pure and aqueous dimethyl formamide quinizarin-2-sulphonate undergoes successive two one- electron reductions and there is comproportionation between the quinone and its dianion to form a semiquinone radical. The apparent comproportionation constants in pure and aqueous dimethyl formamide mixtures were calculated. It was found at acidic, neutral and alkaline pH, when cyclic voltammetry is carried out in pure aqueous buffer the reduction of sodium quinizarin-2-sulphonate follows a one step two- electron reduction. In acidic buffer, it was found that the reduction involves two protons along with two electrons but at neutral and alkaline pH it is free from protons. It was found that at pH 9.0 there is also a comproportionation reaction.