Improved Reactor Productivity for the Safe Photo-Oxidation of Citronellol Under Visible Light LED Irradiation

A simple continuous flow photochemical reactor was optimized for the safe photo-oxidation of citronellol into precursors of rose oxide, a flagrance of commercial value. The reactor productivity was increased by a factor of 4 compared to the current literature for a conversion above 99 % and in safe conditions (up to 0.72 mM min(-1) mL(reactor)(-1)). The reactor was based on a classical design described by Booker-Milburn et al., i. e. multiple loops of perfluoroalkoxy (PFA) tubing wrapped tightly around a visible LED lamp under slug flow conditions. The influence of the type of visible white LED light (6500 K vs. 3000 K), of photosensitizers (tetraphenylporphyrin vs. methylene blue), of solvent (CH2Cl2 vs. MeOH), concentration of citronellol (0.1 M vs. 2 M) and of mass efficiency of the reactors (PFA tubing of 0.75 mm to 0.25 mm) was paramount to increase the productivity of the reactor.