Phase-transfer catalysts Polyethylene glycol

Sawicki, R. A., Phase Transfer Catalysts Polyethylene Glycols Im-mohilized Onto Metal Oxide Surfaces, Tor. Lett., 23, 2249 ( 9Z2). 

Several microwave-assisted protocols for soluble polymer-supported syntheses have been described. Among the first examples of so-called liquid-phase synthesis were aqueous Suzuki couplings. Schotten and coworkers presented the use of polyethylene glycol (PEG)-bound aryl halides and sulfonates in these palladium-catalyzed cross-couplings [70]. The authors demonstrated that no additional phase-transfer catalyst (PTC) is needed when the PEG-bound electrophiles are coupled with appropriate aryl boronic acids. The polymer-bound substrates were coupled with 1.2 equivalents of the boronic acids in water under short-term microwave irradiation in sealed vessels in a domestic microwave oven (Scheme 7.62). Work-up involved precipitation of the polymer-bound biaryl from a suitable organic solvent with diethyl ether. Water and insoluble impurities need to be removed prior to precipitation in order to achieve high recoveries of the products. 

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... 

Lanthanide ions (La3+, Ce3+) were found to promote the cobalt-catalyzed reaction in a two-phase system with p-cyclodextrin or PEG-400 (polyethylene glycol 400) as phase-transfer catalysts.134... 

Oxidation of alkenes to ketones.3 Both internal and terminal alkenes are oxidized by PdCl2 (with CuCl2 as reoxidant) in water-polyethylene glycol (PEG), serving as the phase-transfer catalyst as well as the solvent (9, 360, 376). This oxidation is more facile than that catalyzed by quaternary ammonium salts, which is applicable only to terminal alkenes. 

Sauvagnat, B., Lamaty F., Lazaro, R. and Martinez, J., Polyethylene glycol (PEG) as polymeric support and phase-transfer catalyst in the soluble polymer liquid phase synthesis of ct-amino esters, Tetrahedron Lett., 1998, 39,821. 

Totten, G.E. and Clinton, N.A., Polyethylene glycol) derivatives as phase-transfer catalysts and solvents for organic-reactions, /. Macromol. Sci., Rev. Macromol. Chem. Phys., 1988, C28, 293. 

DBU DMC DMF EC EO EOS GSS ILs MBMTBP MEA MW PC PDMS PEG PEGda PEO PMPS PO PPG PPGda PTC PTHF PTMO PVP Diazabicyclo[5.4.0] -undec-7-ene Dimethylcarbonate Dimethylform amide Ethylene carbonate Ethylene oxide, oxyethylene Equation of state Gas-saturated solution Ionic liquids 2,2,-methylene-bis(4-methyl-6-tert-butylphenol) Monoethanolamine Molecular weight Propylene carbonate Polydimethylsiloxane Polyethylene glycol Poly(ethylene glycol) diacrylate Polyethylene oxide Poly(methylphenylsiloxane) Propylene oxide Poly(propylene glycol) Poly(propylene glycol) diacrylate Phase-transfer catalyst Poly(tetrahydrofuran) Polytetramethylene oxide Polyvinyl pyrrolidone... 

Keywords Carbon dioxide Polyethylene glycol Biphasic solvent system Phase-transfer catalyst Surfactant Radical initiator... 

N-Alkylation of 1,2,3-triazoles and benzotriazoles is readily achieved using (1) alkyl halides, dialkyl sulfates, diazoalkanes, and jS-tosylates or (2) the Mannich reaction. When alkyl halides are used, sodium alkoxide, sodium hydride, or sodium hydroxide is usually employed as the base. The N-alkylation of benzotriazole with alkyl halides proceeds efficiently using powdered NaOH as the base in DMF. The highest yields (80100%) of the alkylated benzotriazoles are obtained when a fourfold excess of NaOFl is employed. A-Alkylbenzotriazoles have been prepared from benzotriazole and alkyl halides using phase-transfer catalysts, e.g., KOFI, benzene, tetrabutyl-ammonium salts or KOH, benzene, polyethylene glycol. 

Benaglia M, Annunziata R, Cinquini M, Cozzi F, Tocco G (2000) A polyethylene glycol)-supported quaternary ammonium salt an efficient, recoverable, and recyclable phase-transfer catalyst. Qrg Lett 2 1737-1739... 

Xia, M., Wang, Y.-G. A novel microwave-activated Sonogashira coupling reaction and cleavage using polyethylene glycol as phase-transfer catalyst and polymer support. J. Chem. Res., Synop. 2002,173-175. 

Oxidations and reductions. Phase-transfer catalyst enables the oxidation of benzylamines to benzamides with KMnO in an organic solvent, whereas reduction of aldehydes can be carried out in toluene using NaBH and polyethylene glycol. ... 

In the case of acrylates mono- or disubstituted at C3, the adducts of dichlorocarbene, formed under phase-transfer catalysis conditions, react further to give the esters of 1,1,2,2-tetrachloro-spiro[2.2]pentanecarboxylic acid as the major products (Houben-Weyl, Vol. E19b, pp 1548-1549). Therefore, the catalyst(s) used for the selective cyclopropanation by phase-transfer catalysis of various acrylates vide supra) were examined. Dichlorocyclopropane 1 was formed from tert-butyl 3-methylbut-2-enoate and chloroform in the presence of 55% aqueous potassium hydroxide and a mixed catalyst polyethylene glycol ( Triton-N-lOl ) and tricapryl-methylammonium chloride ( Aliquat 336 ). The same reaction carried out in the presence of 18-crown-6 as a catalyst afforded three products, the cyclopropane as a minor product. 

The chloroform/base/phase-transfer catalyst method has proved to be useful for the preparation of 2,2-dichIorocyclopropyl ketones on condition that the double bond in the starting ketones is substituted in the a-position by an alkyl group. ° Both benzyltriethylammonium chloride and polyethylene glycol (PEG 1500, in the presence of powdered potassium hydroxide) are effective catalysts for these reactions. 

Cross-linked supports have also been made by copolymerization of polyethylene glycol terminated with methacrylate groups with cross-linking agents such as trimethylolpropane trimethacrylate.166 This type of resin has also been used as phase-transfer catalysts.167... 

NOTE Other phase transfer catalysts were evaluated and all were approximately equally as effective (PT-catalysts ranged from tetraalkylammonium halides to polyethylene glycols). In the same manner the bispropargyl ether of 4,4 -dihydroxydiphenyl sulfone (same as from preparation 6.2) gave a 96.2% yield, m.p. 184-186°C of light tan colored crystals. The NMR was consistent with its structure. 

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