what is phase transfer catalyst?

Phase-transfer catalysis is a special form of heterogeneous catalysis.It refers to the acceleration of the reaction upon the addition of the phase-transfer catalyst.A phase-transfer catalyst or PTC is a catalyst that facilitates the migration of a reactant from one phase into another phase where reaction occurs.Ionic reactants are often soluble in an aqueous phase but insoluble in an organic phase in the absence of the phase-transfer catalyst. This catalyst functions like a detergent for solubilizing the salts into the organic phase.
By using a PTC process,reactions can be achieved faster .They leads to obtain higher conversions or yields, make fewer byproducts and eliminate the need for expensive or dangerous solvents that will dissolve all the reactants in one phase,and also eliminate the need for expensive raw materials and/or minimize waste problems.Such catalysts are especially useful in green chemistry -as by allowing the use of water, the need for organic solvents is reduced.