Ethylene glycol, supported aqueous-phase

Initially, water was used as the hydrophilic liquid and these catalysts are therefore denoted as supported aqueous-phase catalysts (SAPCs) [7-10], Subsequently, we expanded this concept to other hydrophilic liquids such as ethylene glycol and glycerol [11], Reactions of liquid-phase, hydrophobic organic reactants take place at the film-organic interface. SAP catalysis differs significantly from SLP catalysis in that the latter is used for gas-phase reactants whereas the former is specifically designed for liquid-phase substrates. Additionally, with SLP catalysis, the reaction proceeds homogeneously in the supported film while in SAP catalysis it occurs at... 

The best example of supported aqueous phase catalysis, in which a homogeneous catalyst is embedded in an aqueous layer over silica, is the use of tetrasulfonated BINAP ligand to reduce 2-(6 -methoxy-2 -naphthyl)acrylic acid (31 Fig. 6.4). The ee is dependent on the supported organic phase, and in this case, ethylene glycol on a porous glass gave up to 95% ee for the hydrogenation product (naproxen). 

Shabaker, J. W. Davda, R. R. Huber, G. W. Cortright, R. D. Dumesic, J. A., Aqueous-phase reforming of methanol and ethylene glycol over alumina-supported platinum catalysts. Journal of Catalysis 2003, 215, 344. 

An extension of the combinatorial synthesis in solution is achieved by the use of soluble polymeric supports [80, 81], which combines some of the advantages of chemistry in solution and on solid phase. The so-called liquid-phase combinatorial synthesis is based on the physical properties of poly (ethylene glycol) monomethyl ether. The polymer is soluble in a variety of aqueous and organic solvents, which allows reactions to be conducted in homogeneous phase whereas the propensity to crystallize in appropriate solvents facilitates the isolation and purification of the compound at each step of the combinatorial synthesis. 

Even carbowax (a chemically and thermally stable poly(ethylene glycol), when adsorbed on an inorganic salt with no other solid support, may act as a very efficient gas-solid phase-transfer catalyst. This system has been employed, for example, in the Williamson synthesis of ethers and thioethers, starting from alkyl halides and phenols or thiols in the presence of potassium carbonate as a base Gas-solid PTC shows the advantage that pure products are obtained directly, due to the absence of aqueous and organic solvents. 

The success of aqueous techniques in catalysis initiated approaches that mimic their advantageous features while resolving immanent flaws of aqueous chemistry. Polyols (ethylene glycol, glycerol, etc.) and formamide resemble water in many aspects including solvent properties, immiscibility with hydrophobic liquids, and ability to support micel-lization and solubilization phenomena. Such liquids (e.g., ethylene glycol) are often used as a substitute for water in phase-separation techniques (biphasic, supported liquid phase. 

Efficient recyclable aqueous systems for the Heck reaction are yet to be discovered. Several biphasic and supported liquid phase systems using ethylene glycol as a substitute... 

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