Comparison of Electrochemical Behavior of Hydroxyl‐substituted and Nonhydroxyl‐substituted Azo Dyes at a Glassy Carbon Electrode

The voltammetric behaviour of four azo dyes has been compared at a glassy carbon electrode. It is shown that the azo dyes (e.g. Reactive Brilliant Red x‐3b (RBR x‐3b), Acid Red 6b (AR 6b)) with a hydroxyl group in the ortho position with respect to the azo bridge give rise to well defined, irreversible peaks for the oxidation and reduction process within a pH range of 2–12. In the case of the non‐hydroxyl azo dye (e.g. Reactive Yellow x‐rg (RY x‐rg)), or azo dye with a meta hydroxyl group (e.g. Reactive Orange x‐gn (RO x‐gn)), the oxidation was comparatively tougher, and the peak was not clear or even invisible in the accessible potential range. The mechanism of electrochemical oxidation of RBR x‐3b, as well as AR 6b is proposed. The reduction steps were only accessible when pH < 8 for RY x‐rg and RO x‐gn dye compounds. For the hydroxyl‐substituted dyes, re‐oxidation peaks were obtained in the subsequent scan, owing to the oxidation of reduction products‐amine or hydroazo intermediates.