An additive for improving the rate of catalysis in biphasic reaction systems is disclosed. The additive is an ionic molecule comprising an organic cation such as a heterocyclic compound or a quaternary ammonium or phosphonium cation, and an anion which may be organic or inorganic. A process for improved catalysis in an aqueous biphasic system wherein the catalyst is substantially dissolved in the aqueous phase and the substrate is substantially contained in the non-aqueous phase is also described. A suitable additive is 1-octyl-3-methylimidazolium halide. Examples of suitable catalytic reactions include the hydrogenation, hydrosilation, hydroboration, hydrovinylation, hydroformylation, oxidation and hydroxycarbonylation of alkenes, and Heck, Suzuki, Stille, and Sonigashira coupling.