Phase transfer catalysis: Chemistry and engineering

Phase transfer catalysis (PTC) uses catalytic amounts of phase transfer agents which facilitate interphase transfer of species, making reactions between reagents in two immiscible phases possible. PTC is used widely in the synthesis of various organic chemicals in both liquid-liquid and solid-liquid systems. Existing literature on PTC is chemistry-intensive and a mere handful of recent articles constitute the entire information on engineering analysis. This article reviews the field comprehensively by combining the existing knowledge from chemistry with insights into mechanistic and kinetic analysis and mathematical modeling of soluble and insoluble PTC. By its very nature, PTC involves a series of equilibrium and mass-transfer steps, beside the two main reactions. Neglect of mass-transfer effects can grossly overpredict the conversion of a PTC mediated reaction. A practical way of using PTC, which enables easy separation is to immobilize the catalyst on a solid support. Mass-transfer limitations and higher costs, however have precluded its commercial use so far, requiring further analysis of mass-transfer limitations in these complex three-phase systems. The use of PTC, combined with other rate enhancement techniques like sonochemistry, microwaves, electroorganic synthesis, and photochemistry, is being increasingly explored. Applications in this area in the manufacture of organic intermediates and fine chemicals seem almost unlimited.