Science of Synthesis

Mortreux, A.; Sauthier, M.; Monflier, E.; Tilloy, S., Science of Synthesis: C-1 Building Blocks in Organic Synthesis, (2014) 1, 178.

The use of thermoregulated phase-transfer catalysts (TRPTC)[‌53‌,‌54‌] is an alternative to aqueous-phase biphasic catalysis, which often suffers from low reaction rates due to the limited solubilities of the substrates in the catalyst-containing aqueous phase. Polyoxyethylene is a water-soluble neutral compound. It has long been known that the solubility of polyoxyethylene arises from hydrogen bonding with water molecules. When elevating the temperature, the weak hydrogen bonds are broken and the polyoxyethylene chains become hydrophobic and no longer soluble in water. Thermoregulated phase-transfer catalysts take advantage of this property. Thermoregulated phase-transfer catalysts are obtained from the combination of a metal with a phosphorus-based ligand that bears polyoxyethylene chains. Depending on the number and size of the polyoxyethylene chains, the catalyst is soluble in an aqueous phase at room temperature and soluble in an organic phase at a higher temperature used to perform a catalytic reaction. Reaction rates can be high as both the reactants and the catalyst are in the same phase during the reaction. After completion of the reaction under homogeneous conditions at the appropriate temperature, the product mixture is cooled down, thus allowing the dissolution of the ligand and metal in the aqueous phase. Subsequent product separation and catalyst recycling can be accomplished by simple phase separation.

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