Analytical study of the reaction of phenothiazines with some oxidants, metal ions, and organic substances (review article)

Phenothiazines substituted in the 2 and 10 positions exhibit many valuable analytical properties. They are easily oxidized in acidic medium with a num ber of oxidants, e.g., K2Cr2O7. NH4VO3, Ce(SO4)(2), KBrO3, KIO3, KIO4, NaNO 2, H2O2. and chloramine T, with the formation of colored oxidation products . This property enable certain phenothiazines to be used as redox indicator s for the determination of Fe(II), Sn(II), U(IV), Mo(V), ascorbic acid, etc . Oxidation reactions of phenothiazines were also used for their determinat ion by spectrophotometric and flow injection methods. Some ions, such as ir on, vanadium, iodide, or nitrite have a catalytic effect on the oxidation o f phenothiazines. Owing to these properties several catalytic methods for t he determination of metals, iodide, and nitrite have been proposed. Phenoth iazines react in acidic media with platinum metals, e.g., Pd(II), Ru(III), and Pt(IV), the formation of colored complexes. They also react with thiocy anate anionic complexes of metals, e.g., Co(II), Pd(II), Fe(III), BI(III), Cr(III), Ti(IV), Nb(V), Mo(V), and U(VI). Some organic substances (e.g., pi cric acid, flavianic acid, alizarin S, titan yellow, brillant blue, pyrocat echol violet) form with phenothiazines colored ion-association compounds sp aringly soluble in water. These complexes are the basis for an extractive s pectrophotometic determination of some metals or phenothiazines.