Catalysis polyethers

THE can be polymerized by many strongly acidic catalysts, but not all of them produce the requked bitimctional polyether glycol with a minimum of by-products. Several large-scale commercial polymerization processes are based on fluorosulfonic acid, HESO, catalysis, which meets all these requkements. The catalyst is added to THE at low temperatures and an exothermic polymerization occurs readily. The polymerization products are poly(tetramethylene ether) chains with sulfate ester groups (8). 

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

See Antibiotics, polyethers Catalysis, phase-transfer Chelating agents. 

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. 

Acid anhydride-diol reaction, 65 Acid anhydride-epoxy reaction, 85 Acid binders, 155, 157 Acid catalysis, of PET, 548-549 Acid-catalyzed hydrolysis of nylon-6, 567-568 of nylon-6,6, 568 Acid chloride, poly(p-benzamide) synthesis from, 188-189 Acid chloride-alcohol reaction, 75-77 Acid chloride-alkali metal diphenol salt interfacial reactions, 77 Acid chloride polymerization, of polyamides, 155-157 Acid chloride-terminated polyesters, reaction with hydroxy-terminated polyethers, 89 Acid-etch tests, 245 Acid number, 94 Acidolysis, 74 of nylon-6,6, 568... 

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. 

Typical systems. A considerable number of immobilized polyether systems have been synthesized both for phase transfer catalysis as just discussed and for use in a number of analytical applications. Such immobilized systems are generally synthesized by either copolymerization of suitably functionalized macrocycles in the presence of cross-linking agents or by appending functionalized macrocycles to existing polymeric substrates. Structures (184)-(186) give examples of different... 

The technique now called fluorous biphasic catalysis was apparently first described in the Ph.D. thesis of M. Vogt in 1991 however, these studies did not become known to the community until sometime later. W. Keim, M. Vogt, P. Wasserscheid, B. Driessen-Holscher, Perfluorinated polyethers for the immobilization of homogeneous nickel catalysts , J. Mol. Catal A Chem. 1999,139,171. 

Zipse, H. Wang, L-H. Houk, K. N. Polyether Catalysis of Ester Aminolysis - A Computational and Experimental Study Liebigs Arm. 1996,1511-1522. 

Perfluorous polyethers in biphasic catalysis, 42 497 Performic acid, catalytic decomposition, 35 ... 

Polyenes, metathesis of, 24 134 Polyethers, perfluorous, in biphasic catalysis, 42 497... 

Liu et al. [18] investigated the possibility of catalyst recycling in the nonaqueous hydroformylation of 1-decene by using the thermomorphic polyether phosphite 2a described earlier under phase-transfer conditions. Catalyst recovery with the procedure of phase-separable catalysis was possible with 0.92% rhodium loss in the seventh cycle. Complete olefin conversion and aldehyde yields of 98% were reached, but linear and branched aldehydes were formed in almost equal amounts. 

Using a synthetic approach similar to that described above for the polyethers and based on liquid/liquid phase-transfer catalysis, the first furanic polycarbonate shown below was prepared (31) ... 

The physical properties of many macrocyclic polyethers and their salt complexes have been already described. - Dibenzo-18-crown-6 polyether is useful for the preparation of sharpmelting salt complexes. Dicyclohexyl-18-crown-6 polyether has the convenient property of solubilizing sodium and potassium salts in aprotic solvents, as exemplified by the formation of a toluene solution of the potassium hydroxide complex (Note 13). Crystals of potassium permanganate, potassium Lbutoxide, and potassium palladium(II) tetrachloride (PdClj + KCl) can be made to dissolve in liquid aromatic hydrocarbons merely by adding dicyclohexyl-18-crown-6 polyether. The solubilizing power of the saturated macrocyclic polyethers permits ionic reactions to occur in aprotic media. It is expected that this [)ropcrty will find practical use in catalysis, enhancement of... 

Polyether formation from ring opening forming poly(ethylene oxide) occurs through acid or base catalysis as shown below ... 

Keywords a,co-Alkanediamines, l,4 3,6-Dianhydrohexitols, Aldaric acids, Aldo-nolactones, Aminoalditols, o-Glucitol, Diaminoalditols, D-Mannitol, D-Xyhtol application, Erythritols, Isoidide, Isomannide, Isosorbide, L-Arabinitol, Lipase-catalysis, Polyamides, Polycarbonates, Polyesteramides, Polyesters, Polyethers, Polyureas, Polyurethanes, Super-acid, Tartaric acids... 

A series of polyphosphites, polyphosphates, polythiophosphates, and other polymers containing sulfone functions, based on 1, have also been described [17,119]. An efficient synthesis of polyethers from 1 and 1,8-dibromo or dimesyl octane by microwave-assisted phase transfer catalysis has been reported [120]. 

The affinity of the polymer-bound catalyst for water and for organic solvent also depends upon the structure of the polymer backbone. Polystyrene is nonpolar and attracts good organic solvents, but without ionic, polyether, or other polar sites, it is completely inactive for catalysis of nucleophilic reactions. The polar sites are necessary to attract reactive anions. If the polymer is hydrophilic, as a dextran, its surface must be made less polar by functionalization with lipophilic groups to permit catalytic activity for most nucleophilic displacement reactions. The % RS and the chemical nature of the polymer backbone affect the hydrophilic/lipophilic balance. The polymer must be able to attract both the reactive anion and the organic substrate into its matrix to catalyze reactions between the two mutually insoluble species. Most polymer-supported phase transfer catalysts are used under conditions where both intrinsic reactivity and intraparticle diffusion affect the observed rates of reaction. The structural variables in the catalyst which control the hydrophilic/lipophilic balance affect both activity and diffusion, and it is often not possible to distinguish clearly between these rate limiting phenomena by variation of active site structure, polymer backbone structure, or % RS. 

The findings that, both in ester and amide cleavage, an alkaline-earth metal ion is still catalytically active when complexed with a crown ether, and that a fraction of the binding energy made available by coordinative interactions with the polyether chain can be translated into catalysis, provide the basis for the construction of supramolecular catalysts capable of esterase and amidase activity. 

Calixcrown 5, featuring two diethylaminomethyl side-arms at the polyether bridge, testifies an attempt at a higher order multifunctional catalysis of ester cleavage, namely, from nucleophilic-electrophilic to nucleophilic-electrophilic-general acid catalysis [20]. 

The application of perfluorous polyethers in biphasic catalysis was first described by Vogt (133), who also synthesized ligands based on hexafluor-opropene oxide oligomers to create metal complexes that are soluble in the perfluorous polyethers. The solvophobic properties of the fluorous solvent were successfully incorporated in the metal complexes catalytic oligomerization and polymerization reactions with nickel and cobalt complexes were demonstrated. 

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