Synthesis of Juglone (5-Hydroxy-1,4-Naphthoquinone) in a Falling Film Microreactor

Photooxygenation of 1,5-dihydroxynaphthalene to Juglone was studied in a falling film microreactor. Moderate conversion rates of up to 31% were achieved after just 160 s of exposure to visible light. In contrast, batch reactions gave much lower conversions of up to 14% after a prolonged time period of 10 min. The difference in performance is explained by the superior light penetration in the microfilm and the large gas-liquid contact area.