Reconfigurable photoflow reactor for enhanced optimization of the aerobic oxidative coupling of 2-phenylbenzoic acid†

We tested eight configurations of a flat plate photoflow reactor, each with distinct photonic and mixing properties. The model reaction involved the photocatalytic oxidative cross-coupling of 2-arylbenzoic acid to form 6H-benzo[c]chromen-6-one, using air as an oxidant and visible light. Reactor designs included wide rectangular channels with varying depths and inclinations, two types of static mixers, and three serpentine-like channels with variable depths. All configurations outperformed a stirred batch photoreactor, with the 2 mm deep serpentine channel delivering the highest rate acceleration, reducing reaction time from 6 hours to less than 1.25 hours and increasing the apparent rate constant by over fourfold. The rate constant could not be correlated with the reactor illuminated area, but could be correlated with the inverse product of flow cross-section and light penetration depth. This correlation aids in optimizing similar reactions, with the optimum range influenced by light intensity and photocatalyst concentration, while the reconfigurable kit enables efficient empirical optimization without prior reaction kinetics knowledge.