Chlorobenzoic acids and derivatives: analysis of mixtures by thin-layer chromatography

Abstract

Thin-layer chromatographic (silica gel G)R_F values were obtained for the three isomeric monochlorobenzoic and two dichlorobenzoic acids. The p-bromophenacyl esters of benzoic, o-, m- and p-chlorobenzoic, and 3,4-dichlorobenzoic acids were prepared and R_F values obtained. The esters of benzoic, m-chlorobenzoic and 3,4-dichlorobenzoic acids were separated from the ternary mixture by thin-layer chromatography. When 2,4-dinitrophenyl-hydrazine in hydrochloric acid solution reacted with the esters spotted at the origin, subsequent thin-layer chromatography gave characteristic two-spot patterns for each, and this facilitated recognition of the type of mixture of monochlorobenzoic acids. An explanation is given of the formation of two hydrazones from each ester.