Thin Layer Chromatography of Synthetic Dyes (VIII)

On the Decomposition Products of Xanthene Dyes (3) Tetrachlorofluorescein and Phloxine

Abstract

In continuation of the grevious work (Shokuhin Eiseigaku Zasshi, 8, 427, 434 (1967)), the decomposition products of tetrachlorofluorescein and phloxine were studied.
If the decomposition of these dyes is similar to that of fluorescein, resorcinol and 2- (2′, 4′-dihydroxybenzoyl) -tetrachlorobenzoic acid (2′, 4′-diOHB-tetra Cl-BA) may be yielded from tetrachlorofluorescein, and 2, 4-dibromoresorcinol and 2- (3′, 5′-dibromo-2′, 4′-dihydro-xybenzoyl) -tetrachlorobenzoic acid (2′, 4′-diOH-3′, 5′-diBrB-tetra Cl-BA) from phloxine. However, when tetrachlorofluorescein is hydrolyzed, it yields resorcinol, but 2′, 4′-diOHB-tetra Cl-BA could not be obtained. In the case of phloxine, it yielded 2, 4-dibromoresorcinol and 2-brornoresorcinol mainly, but 2′, 4′-diOH-3′, 5′-diBrB-tetra Cl-BA was not detected. Therefore, 2′, 4′-diOHB-tetra Cl-BA and 2′, 4′-diOH-3′, 5′-diBrB-tetra Cl-BA were synthe-sized and the behavior of these compounds in alkaline medium were studied. On heating in alkaline medium, these compounds transformed into fluorescent substances, alkaline solution of 2′, 4′-diOHB-tetra Cl-BA giving two spots of a greenish fluorescent product (Rf 0.20) and a bluish fluorescent product (Rf 0.06) on a thin layer chromatogram, using a solvent system of chloroform+glacial acetic acid (4: 1), while that of 2′, 4′-diOH-3′, 5′-diBrB-tetra Cl-BA gave a greenish fluorescent product (Rf 0.47) and a bluish fluorescent product (Rf 0.17). These greenish fluorescent products were isolated from these reaction solution and their structures were determined by infrared and nuclear magnetic resonance spectra, together with their analytical data. A greenish fluorescent product obtained from 2′, 4′-diOHB-tetra Cl-BA was 2, 3, 4-trichloro-6-hydroxyxanthone-1-carboxylic acid while that obtained from 2′, 4′-diOH-3′, 5′-diBrB-tetra Cl-BA was found to be 2, 3, 4-trichloro-5, 7-dibromo-6-hydroxyxanthone-1-carboxylic acid. From these results it became clear that 2′, 4′-diOHB-tetra Cl-BA was not obtained when tetrachlorofluorescein was hydrolyzed with 50% sodium hydroxide solution, and 2′, 4′-diOH-3′, 5′-diBrB-tetra Cl-BA, when phloxine was hydrolyzed.