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 number of oxidants, e.g., K2Cr2O7, NH4VO3, Ce(SO4)2, KBrO3, KIO3, KIO4, NaNO2, H2O2, and chloramine T, with the formation of colored oxidation products. This property enable certain phenothiazines to be used as redox indicators for the determination of Fe(II), Sn(II), U(IV), Mo(V), ascorbic acid, etc. Oxidation reactions of phenothiazines were also used for their determination by spectrophotometric and flow injection methods. Some ions, such as iron, vanadium, iodide, or nitrite have a catalytic effect on the oxidation of phenothiazines. Owing to these properties several catalytic methods for the determination of metals, iodide, and nitrite have been proposed. Phenothiazines 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 thiocyanate 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., picric acid, flavianic acid, alizarin S, titan yellow, brillant blue, pyrocatechol violet) form with phenothiazines colored ion-association compounds sparingly soluble in water. These complexes are the basis for an extractive spectrophotometic determination of some metals or phenothiazines.