During an investigation of the biosynthesis of volatile branched-chain fatty acids in various papilionid species, it was necessary to develop a sensitive procedure for the detection of these acids as products of selected radioactive precursors. Colored nonvolatile derivatives were required for this purpose. In 1964, Churacek et al. (1) described a procedure for the synthesis of various azophenacyl esters of fatty acids and the separation of these esters in a reverse-phase paper chromatographic system. During the course of this work, Churacek and Pechova (2) demonstrated that these azophenacyl esters are conveniently separated on silica gel thin-layer plates. In this paper the thin-layer chromatographic separation of hydroxy acid azo esters is described, and a new solvent system for the separation of the esters of volatile fatty acids is also considered.
Purification of radioactive azophenacyl esters to constant specific activity can be achieved with minimal loss of material through successive purification steps, and t,he amounts of material recovered can be monitored photometrically. This technique was applied to the determination of the radiochemical purity of a volatile fatty acid isolated from a biological source. MATERIALS AND METHODS Preparation of Reagents N,N-Dimethyl-p-aminobenzolphenacyl chloride was prepared by a Friedel-Craft synthesis from p-aminophenacyl chloride according to the technique of Churacek et al. (1).