Isolating and Determining the Structures of Colored Products from the Reactions of Cannabinoids with Fast Blue RR

Although cannabis is used in a wide range of fields, including medicine and pharmacology, its use is prohibited in Japan because it contains Δ⁹-tetrahydrocannabinol (Δ⁹-THC), a compound that exhibits narcotic effects. While cannabis is primarily detected via color-based screening methods at crime scenes, the reaction products and mechanisms associated with these screening methods have not been fully elucidated. To address this issue, the colored products were isolated via the diazo-coupling reactions of the major cannabinoids (cannabidiol, cannabinol, and Δ⁹-THC) in cannabis with the Fast Blue RR diazonium salt, and their structures were determined using NMR spectroscopy. As expected, azo compound 2 was formed from cannabidiol, whereas cannabinol and Δ⁹-THC produced quinoneimines 3 and 4, respectively. This study is expected to lead to the future development of more sensitive color-based reagents that produce fewer false positives.