Efficient Photooxygenation Process of Biosourced α-Terpinene by Combining Controlled LED-Driven Flow Photochemistry and Rose Bengal-Anchored Polymer Colloids
Robbie Radjagobalou, Jean‐François Blanco, Luca Petrizza, Mickael Le Béchec, Odile Dechy‐Cabaret, Sylvie Lacombe, Maud Save, Karine Loubière
Abstract
This work studies the reactivity of poly(N-vinylcaprolactam-co-vinyl acetate-co-vinylbenzyl Rose Bengal) microgels (VBRB@MG) as heterogeneous photosensitizers in a continuous-flow process for sustainable singlet oxygen-sensitized photooxygenation of a bio-based molecule. Experiments were carried out in a light-emitting diode (LED)-driven spiral-shaped microreactor in which slurry Taylor flows were generated, allowing accurate control of irradiation, light absorption, and gas–liquid flow conditions. The benchmark photooxygenation of α-terpinene was implemented in ethanol to provide a green solvent using air as a safe supply of oxygen. Swollen RB-grafted colloids formed an efficient substrate for converting α-terpinene into ascaridole, providing high conversion with high selectivity under continuous-flow conditions and within short residence times of a few minutes. The supported RB exhibited reactivity similar to that of free RB. The reactivity of the supported photosensitizer was maintained for several cycles with a reproducible level after 8 months of storage. Under experimental conditions favoring photobleaching of RB, the photobleaching level of RB was lower with the VBRB@MG colloids than with free RB, suggesting that grafting RB molecules onto the colloid can prevent their photodegradation.