Phase transfer catalysts soluble polyethers

Quaternary onium salts were the first phase-transfer catalysts used subsequently, a number of compounds (linear polyethers, polypodands, crown-ethers, cryptands, cage-compounds, etc.) were found effective for the anion activation in two-phase systems. These structurally different systems must satisfy at least two fundamental conditions in order to behave as phase-transfer catalysts i) solubility in the organic phase ii) steric hindrance around the cationic center leading to a good cation-anion separation within the ion-pair. 

It is known that the solubility of metal salts in nonpolar media is drastically increased if small amounts of crown ethers (cyclic polyethers) are used as complexation agents. Such a concept has been demonstrated in various areas of chemistry. For example, they are used as phase-transfer catalysts in organic synthesis. Moreover, Cheng27 and Schue28 have expanded this idea in the areas of anionic polymerization. 

Acyclic polyethers have not been reported to be phase-transfer catalysts, except for a few limited examples. They are only shown to be catalysts when present in large concentration and, ince they are very soluble in water, only under SL-PTC conditions. Under GL-PTC conditions on the contrary, they are able to mimic the functions of crown ethers in the absence of water and with relatively soft anions as phenoxide (or mercapdide), they can show effective complexing properties toward cations and consequently to increase the nucleophilic activity of reacting anions. 

A counter phase transfer catalysis effect was observed in reduction of allyl chloride with sodium formate in water/n-heptane systems with water soluble palladium(II) catalysts having phosphine ligands with polyether chains [274] it was demonstrated that the catalyst transported the substrate to the aqueous phase where it reacted with the formate. 

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