Polarography of azo compounds and their metal complexes

Abstract

A study was made of the polarographic behaviour of a range of aromatic azo compounds, including hydroxy and nitro derivatives, in order to determine the effect of substituents on the reduction mechanism. The polarography of p-bis-azobenzene was also investigated in detail, and a mechanism suggested for its reduction at the DME. Ethanol depressed the limiting currents of hydroxy-substituted dyes in alkaline media, and this effect is believed to result from a decrease in adsorption of the dye on the electrode surface in the presence of high ethanol concentrations, and from electric repulsion by the electrode of the negatively-charged dye species. Nitro-substituted azo dyes, like pyridylazo compounds, produced hydrazo derivatives which were relatively stable in acid solution. The disproportionation of hydrazo intermediates can be either acid or base catalysed, depending on the nature of the substituent. Disproportionation rate constants were determined for several hydrazo compounds. Varying the type of chelating group and other substituents in azo compounds was studied for its effect on the polarographic determination of aluminium and nickel. Suggestions are made for improved reagents for the determination of these metal ions.