An In-Depth Study of the Use of Eosin Y for the Solar Photocatalytic Oxidative Coupling of Benzylic Amines

The direct utilization of solar light for synthetic photochemistry is a sustainable and efficient technological goal. Herein we report the first in-depth study on the use of the inexpensive organic photocatalyst eosin Y for solar photocatalysis by demonstrating the oxidative coupling of benzylic amines to form imines, a class of valuable intermediates in chemical synthesis. By the use of a unique experimental setup with a custom-built variable-intensity solar light simulator, replication of a natural-sunlight environment was achieved. The relative significance of different variables on the reaction rate constant was quantitatively evaluated through comprehensive experimental design. Reaction kinetics and mechanistic information were obtained using both a batch reactor and a spinning-disc reactor. A maximum pseudo-first-order rate constant of 1.59 × 10–3 s–1 was obtained at a maximum turnover frequency of 192 h–1 through optimization of the reaction conditions. Experiments carried out using a spinning-disc reactor confirmed that the reaction was not mass-transfer-limited but rather photon-transfer-limited.