Structural Elucidation of Azo and Quinoneimine Products Formed in Diazonium-Based Color Reactions of Cannabinoids

Cannabis use is generally restricted worldwide because it contains the narcotic compound Δ9-tetrahydrocannabinol (Δ9-THC). Although cannabis is detected at crime scenes using color-based primary screening methods, the details of the reaction mechanism have not yet been elucidated. In this study, we isolated the products generated during the color reaction between the diazonium salt prepared from para-nitroaniline and nine cannabinoids and determined their structures. Azo compounds 6, 11, 16, and 17 were produced from cannabidiol, cannabigerol, cannabichromene, and cannabidiolic acid, respectively, while quinoneimines 7–10 and 12–15, which contained positional isomers, were produced from cannabinol, Δ9-THC, and hexahydrocannabinol. The reaction barely proceeded with Δ9-THC acetate and HHC acetate.