Key role of water for nucleophilic substitutions in phase-transfer-catalyzed processes: A mini-review

The fundamental role of water in anion-promoted reactions carried out under both liquid-liquid and solid-liqiud phase-transfer catalysis (LL- and SL-P TC:, respectively) conditions is reviewed. In particular, the hydration eff ect on the quaternary onium salt extraction constants, anion selectivity co efficients, and anion reactivity under LL-PTC conditions is reported. The e ffect of added water on SL-PTC reaction rates is also included. In addition , guidelines for optimizing the amount of water in the application of PTC t o organic synthesis are proposed.