Biphasic Catalytic Hydrogen Peroxide Oxidation of Alcohols in Flow: Scale-up and Extraction

We report continuous solvent-free biphasic alcohol oxidation with hydrogen peroxide and in-line separation of the tungsten polyoxometalate catalyst and phase transfer catalyst from the product. Zinc-substituted polyoxotungstate in combination with the selected phase transfer catalyst drives the oxidation reaction to completion within a short residence time (5–10 min) in a silicon Pyrex microreactor. This continuous and small-scale reactor allows for fast optimization of reaction conditions for each substrate and selection of the phase transfer catalyst. Scaling of the production rate (up to 650 times) is achieved with a Corning low flow reactor (LFR) and an advanced flow reactor (AFR). New scaled-up, in-line membrane-based liquid–liquid extraction units at the reactor outlet first separate the tungsten polyoxometalate catalyst with the aqueous waste stream from the organic product stream. A three-stage countercurrent liquid–liquid extraction then removes more than 90% of the phase transfer catalyst from the desired organic effluent stream while reducing the amount of extraction solvent required.