Preparative Thin-Layer Chromatography of Semi-Xylenol Orange and Xylenol Orange by Development with Solvents Giving Discrete pH Change on the Plate

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Abstract
A new procedure is proposed to obtain pure Semi-Xylenol Orange (SXO) and Xylenol Orange (XO) from ca. 100 mg of synthetic mixture using preparative thin-layer chromatography on cellulose layer ca. 2 mm thick. Development with a composite solvent, 55–60 ml of 1-butanol saturated with 25% aqueous acetic acid-0.6–0.8 ml of 28% aqueous ammonia, forms two discrete zones of different pH values on the layer. The zones favor a sharp separation of polybasic Brønsted acids with structures similar to those of SXO and XO. SXO and XO are in the protonated forms corresponding to the pH values of the given zones. XO is located near the starting line in the lower zone of higher pH and SXO migrates through the layer in the upper part of the same zone. Both SXO and XO constitute the compact and concentrated bands. Each run takes only 3 hr. 18 mg of SXO and 36 mg of XO are obtained as sodium salts from 100 mg of the synthetic mixture.