R. M. Issa

Reduction of azo-compounds—I. Polarographic behaviour of some 4-hydroxymonoazo compounds at the dropping mercury electrode

Abstract The polarographic behaviour of some monoazo compounds has been studied in aqueous solutions of varying pH. The reduction current in alkaline media is almost half that of the limiting value in acid solution, indicating a change in the mechanism of reduction. A general mechanism for the reduction process in alkaline and acid media is suggested, which includes a rate-determining step involving one electron. The different kinetic parameters for the electrode reaction support the suggested mechanism. The effect of substituents is clarified.

The polarographic behaviour of cystine in solutions of varying pH at the dropping mercury electrode and effect of surface-active substances☆

The polarographic behaviour of cystine in solutions of varying pH was studied within the concentration range 0·06–1·3 mM at the dme. The polarograms each consist of a single wave in acid solutions of pH < 2 and two waves at higher pH, the first of which is apparently smaller than the second. Analysis of the waves proved that the first wave is less irreversible and exhibits a kinetic contribution whereas the second is irreversible and controlled by diffusion. The effect of pH on the limiting current and E12 as well as the reduction mechanism are discussed. The kinetic parameters are also determined in the absence and the presence of surface-active materials.

Polarography of eosin and erythrosin in solutions of varying pH at the DME

Abstract The polarographic behaviour of eosin and erythrosin in buffer solutions of pH 4–11 is discussed. The observed waves are assigned to the reduction of furan and pyrone rings of the molecule of erythrosin at pH 4–11 and for eosin at pH ⩽7. The nature of the waves is also investigated. In alkaline media the electrode reaction is essentially diffusion controlled whereas at pH

Polarography of dihalogen fluoresceins in solutions of varying pH at the dme

Abstract The polarographic behaviour of dichloro-, dibromo- and di-iodofluorescein has been studied in buffer solutions (pH 4–12) at the dme. The reduction of dichloro- and dibromo-derivatives involves the uptake of two electrons whereby the furane ring is reduced. At low pH (⩽7) a small wave appears, which is attributed to the partial reduction of the pyrone ring. In the case of diiodofluorescein, four electrons are consumed, corresponding to the reduction of both furane and pyrone rings at all pHs. The nature of the reduction waves is discussed.