Hydrogenated Cardanol-Based Azo and Xanthene Dyes for Petroleum Authentication

Conventional petroleum markers used to prevent fuel smuggling and unauthorized mixing often involve complex dye synthesis and require inconvenient two-phase liquid-liquid extraction for detection. In this work, we developed two azo dyes (AzoHc, diAzoHc) and two xanthene dyes (FHc, RHc) based on hydrogenated cardanol (Hc). The dyes were synthesized in 50-70 % yields via one or two reaction steps. The hydrophobic Hc group significantly enhance the solubility of these dyes, enabling excellent compatibility with organic solvents and diesel fuel. These petroleum dye markers exhibit either colorimetric or fluorescent responses and remain miscible with diesel fuel upon treatment with appropriate bases or acids in common fuel-miscible organic solvents. This fuel miscibility allows simple one-phase detection without further extraction process. All dyes demonstrated high sensitivity, with detection limits as low as 0.02-0.68 ppm, and exhibited excellent stability in diesel fuel for at least one month without significant degradation.