Abstract
Summary The polarographic behaviour of a wide range of pyridylazo and thiazolylazo dyes has been studied and several differences observed between the electrode reactions of these heterocyclic compounds and their benzene or naphthalene counterparts. The hydrazo derivatives of the heterocyclic dyes are more stable with respect to disproportionation, which is attributed to the strongly electron-attracting properties of the pyridyl and thiazolyl groups. In addition their disproportionation is base-catalyzed, whereas earlier studies showed that aromatic azo dyes undergo an acid-catalyzed reaction. Hammett substituent constants were calculated for a variety of heterocyclic groups. Half wave potential shifts were observed for several heterocyclic azo dyes in the presence of nickel and iron(III) ions, and the height of the metal-dye complex wave was proportional to metal concentration. Aluminium did not produce a shift with any of the dyes studied, which enables nickel or iron to be determined in the presence of an excess of aluminium.
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