Visible light catalyzed Anti-Markovnikov hydration of styrene to 2-phenylethanol: from batch to continuous

Abstract The 2-phenylethanol production by traditional chemical methods requires multi-step reactions, in which harsh conditions such as high temperature or strong acid/base are required and undesired by-products are easily produced. The visible light catalyzed anti-Markovnikov hydration of styrene is a single-step reaction using non-toxic catalyst under mild conditions. However, this reaction usually takes ten or even dozens of hours, facing the problem in scale up. The present work aims to intensify this reaction in continuous flow microreactor with comparison to traditional batch reactor. The effects of light source shape, reaction temperature, substrate concentration and catalyst concentration on the reaction were investigated. The continuous flow microreactor permitted to ensure more uniform light intensity and larger specific surface area, the reaction rate could thus be enhanced. The maximum productivity of 2-phenylethanol was 0.122 mol/(L.h), which was 2.5 times higher than that obtained in test tube under the same reaction conditions and 34 times higher than that reported in previous literature. The optimal photosensitizer concentration was 2%. The increase of substrate concentration would lead to the addition reaction between styrene cationic intermediates with styrene, thereby decreasing the selectivity of 2-phenylethanol.