Effect of Pyridine on the Extraction of the Ion-pair of Cobalt-Zincon Chelate Anion with Zephiramine

Abstract

Zincon(2-carboxy-2'-hydroxy-5'-sulfoformazyl benzene) reacts with cobalt(II) and forms a chelate anion which is extractable into chloroform by the presence of zephiramine (Z+Cr, benzyl-dimethyl-tetradecyl-ammonium chloride). When pyridine coexists with zephiramine, the quarternary complex, which is also extractable into chloroform, is formed. The molar absorptivity of the quarternary complex is about four times that of the ternary complex. The ternary complex shows the broad absorption band from 660 to 700 nm in the chloroform extract. On the other hand, the quarternary complex having blue coloration shows the absorption maximum at 675 nm in the chloroform extract. The optimum pH range for the extraction of the quarternary complex is 8.3-9.0. When the amou nts of zincon, zephiramine and pyridine are more than one and half times, ten times and a thousand times, respectively, that of cobalt, cobalt is extracted quantitatively into chloroform as the quarternary complex. Beer's law holds for the quarternary complex extracted under the optimum condition in the concentration range of 1.85--24.7 pg cobalt/10 ml. The molar absorptivity is (2.16+-0.O3) x 1O⁴ cm-2 mol-1 l.
Cobalt is oxidized to cobalt(III) in ammonia-buffered, aqueous media, and cobalt(1I) complex formed is extracted into chloroform as the quartenary complex. In the absence of pyridine, the ternary complex of cobalt(I11) is not extracted into chloroform. However, the absorption spectrum obtained for the extract of cobalt(II) in the presence of pyridine coincides with that of quarternary complex in which the oxidation state of cobalt was +3. The oxidation state of cobalt in the extractable ternary complex was, therefore, +2.