Friedel-Crafts acylation as a quality control assay for steroids.
The rapid Friedel-Crafts chromogenic acylation of alkene groups at ambient temperatures using a 25:1 mixture of 98% acetyl chloride and 70% perchloric acid is shown to have all the properties needed to serve as a potential quality control reagent that can be used to routinely discriminate among steroid analogs. Although ostensibly a non-selective reagent, from these and prior applications in terpenes and polyunsaturated acid esters, it is seen that the reaction is capable of discriminating bewteen geometric isomers and even enantiomers. The selectivity towards acylation of the alpha- over the beta-position at C-17 makes the method adaptable to screening for anabolic steroids. Reactions at that position produce the more unusual results, including a positive color reaction for alpha-methyltestosterone even though there is no alkene functional group in the vicinity of C-17. For molecules with more than one alkene, concurrent acylations are independent one from the other and, in the absence of any interferences, their spectral properties are found to be additive.