Catalysts for PTC

Suitable catalysts for PTC are those which have a highly lipophilic cation (i.e. have strong affinity for an organic solvent). Catalysts used most extensively are quaternary ammonium or phosphonium salts (quats). Examples are  

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Although crown ethers were often found to be very effective catalysts, they have only found limited commercial application because of their high cost (10 to 100 times that of quats) and perceived toxicity. Cryptands are even more expensive than crown ethers. 

Most commonly used organic solvents in liquid/Uquid PTC are toluene and other hydrocarbons, chlorobenzene, and in the lab - chlorinated solvents such as CH2CI2 and CHCI3. For soUd/liquid PTC the more polar acetonitrile and even DMF are employed, too. 

Triphase catalysts (in which the catalyst is anchored to a polymer for ease of removal) 

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