Polyethylene glycol phosphonium salts

It was a result of demand from industry in the mid-1960s for an alternative to be found for the expensive traditional synthetic procedures that led to the evolution of phase-transfer catalysis in which hydrophilic anions could be transferred into an organic medium. Several phase-transfer catalysts are available quaternary ammonium, phosphonium and arsonium salts, crown ethers, cryptands and polyethylene glycols. Of these, the quaternary ammonium salts are the most versatile and, compared with the crown ethers, which have many applications, they have the advantage of being relatively cheap, stable and non-toxic [1, 2]. Additionally, comparisons of the efficiencies of the various catalysts have shown that the ammonium salts are superior to the crown ethers and polyethylene glycols and comparable with the cryptands [e.g. 3, 4], which have fewer proven applications and require higher... 

The catalytic activity of polyethylene glycol (PEG) phosphonium salts has been evaluated, in phase-transfer dehydrohalogenation reactions, as slightly better than that of the corresponding PEG ammonium compounds886 (reaction 271). By comparison... 

Agents used as PT catalysts are onium salts (ammonium and phosphonium salts), macrocyclic polyethers (crown ethers), aza-macrobicyclic ethers (ciyptands), open chain polyethers (polyethylene glycols, PEGs, and their dimethyl ethers, glymes). Table 1 summarizes some of the properties of commonly used PT catalysts. 

Batch instruments are generally compatible with both Fmoc//Bu and Bck/ Bzl methods as well as polystyrene, polyethylene glycol-polystyrene graft (PEG-PS). and polyethylene oxide-polystyrene (PEO-PS) supports (for recent reviews see refs 31 and 32). For amino acid activation, protocols have been developed to include carbodiimide, aminium and phosphonium salts, and active esters (pcntafluorophenyl esters and acid halides). For batch instruments designed to monitor the Fmoc function, UV or conductivity detectors are used. 

Quaternary ammonium (3) and phosphonium ions (61), crown ethers such as (62), cryptands such as (63) and poly(ethylene glycol) ethers (64) bound to PS are catalysts for reactions of water insoluble organic compounds with organic insoluble inorganic salts. " Silica gel, alumina, polystyrene-polypropylene composite fibers, nylon capsule membranes, and polyethylene (Mn 1000-3000) have also been used as supports. The reactions are called phase-transfer-catalyzed because one or both of the reactants are transported from the normal liquid or solid phase into a polymer phase, where the reaction proceeds. 

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