Carbon Dots as Photoinitiators for Thiol–Ene Reactions

Thiol-ene reactions are highly valuable for the formation of C─S bonds, offering potential applications across various fields. This project presents several advantages over traditional synthesis methods, as a metal-free and eco-friendly approach for the anti-Markovnikov hydrothiolation of olefins, using carbon dots (CDs) as organic and bio-derived photo initiators. This process is characterized by mild conditions, it takes place in aqueous media under visible light, and it is compatible with a broad range of thiols (aliphatic, aromatic, and with different substituents on the ring), alkenes, and alkynes. CDs prepared from citric acid were used for the optimization of the reaction conditions and the scope. Subsequently, the reaction was performed using CDs synthesized with a hydrothermal treatment from industrial fruit waste (raspberries, blackberries, blueberries, pomegranate, and wild strawberries previously extracted with supercritical CO2). This protocol operates under mild conditions and aligns with the principles of a circular economy, focusing on waste valorization rather than simple recycling. The reaction mechanism was finally probed by performing Stern–Volmer quenching studies in the presence of increasing amounts of CCl3Br, as well as carrying out clock experiments.