Phase transfer catalysis crown polyethers

In specific applications to phase transfer catalysis, Knbchel and his coworkers compared crown ethers, aminopolyethers, cryptands, octopus molecules ( krakenmole-kiile , see below) and open-chained polyether compounds. They determined yields per unit time for reactions such as that between potassium acetate and benzyl chloride in acetonitrile solution. As expected, the open-chained polyethers were inferior to their cyclic counterparts, although a surprising finding was that certain aminopolyethers were superior to the corresponding crowns. 

Phase transfer catalysis. As well as their use in homogeneous reactions of the type just described, polyethers (crowns and cryptands) may be used to catalyse reactions between reagents contained in two different phases (either liquid/liquid or solid/liquid). For these, the polyether is present in only catalytic amounts and the process is termed phase transfer catalysis . The efficiency of such a process depends upon a number of factors. Two important ones are the stability constant of the polyether complex being transported and the lipophilicity of the polyether catalyst used. 

Applications to Phase-transfer Methods.—Dehmlow has published a review on advances in phase-transfer catalysis (PTC) which discusses the introduction of crown ethers into this area. The full details are now available of a study of alkyl-substituted azamacrobicyclic polyethers (78a) as PT catalysts. When the alkyl chains are C14—C20, such molecules are very efficient catalysts in both liquid-liquid and solid-liquid phase-transfer modes, which contrasts with the lower catalytic ability of the less organophilic unsubstituted cryptand (78b). Crown ethers immobilized on polymeric supports have been demonstrated to possess increased PTC activity in 5n reactions, up to that of the non-immobilized systems, when the connection to the polymer involves long spacer chains [e.g. (79)]. 

The technique of phase-transfer catalysis has been extensively apphed to the two-phase polycondensation using various phase-transfer catalysts, such as quaternary ammonium and phosphonium salts, crown ethers and poly(ethylene glycol)s. 5 - 53,75,87,n9,i5i Various types of condensation polymers such as aromatic polysulfonates and polysulfides, aromatic polyethers, ahphatic and aromatic polysulfides, and carbon-carbon chain polymers of high molecular weights hy the phase-transfer catalyzed polycondensation fi-om combinations of aromatic disulfonyl chlorides, phosphonic dichlorides, activated aromatic dichlorides, and aliphatic dihahdes, with bisphenol, aliphatic and aromatic dithiols, and active ethylene compounds. The two-phase polycondensation was generally carried out in a water-immiscible organic solvent-aqueous alkaline solution system at room temperature. The method of polycondensation offers a highly versatile and convenient synthetic method for a variety of condensation polymers. 

The introduction of dipolar aprotic solvents " and the discovery of macrocyclic (crown ethers and macrobicyclic polyethers (cryptands represent some of the more significant steps. Dating from the late sixties, a new general technique was developed phase-transfer catalysis (PTC). PTC has the advantages of being extremely simple and economical and so met with immediate success in industrial applications. 

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