6,7- AND 7,8-DIHYDROXYBENZOPYRYLIUM DERIVATIVES: SYNTHESIS, PROPERTIES AND ANALYTICAL APPLICATION (REVIEW)

The present review is devoted to a class of organic analytical reagents 6,7- and 7,8-dihydroxybenzopyrylium derivatives: their synthetic pathways, physicochemical properties, state in solutions, and analytical applications are described. Anion nature influence on spectral characteristics and some physico-chemical properties of 6,7-dihydroxybenzopyrylium derivatives was noted. Pathways of acid-base transformations in aqueous solutions of 6,7-dihydroxybenzopyrylium derivatives were described. It has been shown that derivatives of 6,7- and 7,8-dihydroxybenzopyrylium are capable for complexation with a number of p-, d-, and f-elements (Cu (II), Ga (III), In (III), Tl (III), Ge (IV), La (III), titanium subgroup, Bi (III), Mo (VI), W(VI) and others). Information on their composition, structure and analytical characteristics is summarized. It is noted that with the 6,7-dihydroxybenzopyrylium derivatives the simple and highly sensitive methods for the direct spectrophotometric and extraction-photometric determination of Ga(III), In(III), Tl(III), Ti(IV), Zr(IV), Hf(IV), Mo(VI), Ge(IV), Bi(III), Cu(II) have been developed. It is noted that 6,7-dihydroxybenzopyrilium derivatives complexes with Mo(VI) and Cu(II) are effectively extracted by Triton X‑100 micellar phase, which forms the basis for highly sensitive combined spectrophotometric and atomic absorption methods for their determination. The simplicity of targeted synthesis of 7,8- and 6,7-dihydroxybenzopyrylium derivatives opens the way to their use in the development of combined cloud point extraction and liquid-liquid microextraction with spectrophotometric or atomic absorption detection methods for the determination of a number of p- and d-elements.