Abstract
Polarography of 8-hydroxyquinoline, 8-hydroxyquinoline-5-sulphonic acid and 7-nitro-8-hydroxyquinoline-5-sulphonic acid has been carried out in aqueous buffers (pH 1·0 to 12·0) of constant ionic strength (0·54 M) at 25 ± 0·1°C. The observations with 8-hydroxyquinoline and 8-hydroxyquinoline-5-sulphonic acid were similar to those reported in the literature. The behaviour of the parent molecule of the 7-nitro derivative resembled that of 8-hydroxyquinoline-5-sulphonic acid. The nitro group gave a single step up to pH 8·5, above which it split into two. The number of electrons involved in the reduction of the nitro group over the whole pH range using the McBain—Dowson cell and applying the King—Cathcart equation was found to be six. A prewave, of adsorption characteristics, preceded the nitro group wave over the whole pH range. The kinetic parameters (α n a and −log k°) in the case of single step for the nitro group reduction have been calculated by Koutecky's method and a reduction mechanism is proposed.
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