Stability of the γ-Sultone Form of Bromcresol Green in the Organic Phase from Partitioning of the Dye between Water and Benzene

Abstract

In this study, bromcresol green, BCG, was partitioned between benzene and buffered aqueous solutions, pH 3.12 to 3.92. The colorless γ-sultone form of the dye in the organic phase was determined spectrophotometrically upon back-extracting into aqueous phosphate buffer at pH 6.7. The yellow monoanion (quinoid) form, BCG -, in the benzene phase prior to back-extraction was found to be practically negligible (e1 × 10 -6 mol dm -3 ). From the above, the equilibrium constant of the reaction (BCG -) w + (H + ) w a (sultone) organic is 373 ( 42 mol -1 dm 3 . Lithium chloride and/or 18-crown-6 only slightly increased the extractability of BCG under the experimental conditions.