Organic complexes hydrophilic

The allylation of aldehydes can be carried out using stannous chloride and catalytic cupric chloride or copper in aqueous media." In-situ probing provides indirect (NMR, CV) and direct (MS) evidence for the copper(I)-catalyzed formation of an allyltrihalostannane intermediate in very high concentration in water (Scheme 8.6). Hydrophilic palladium complex also efficiently catalyzes the allylation of carbonyl compounds with allyl chlorides or allyl alcohols with SnCl2 under aqueous-organic... 

This example illustrates a case of considerable analytical importance, especially for the determination of complex formation constants for hydrophilic complexes, as discussed in section 4.12, when the equilibrium constants for the stepwise metal-organic complexes are of secondary interest. values are tabulated in several reference works. is a conditional constant and only valid provided no other species are formed besides the extracted one. 

Solvent extraction has become a common technique for the determination of formation constants, P , of aqneons hydrophilic metal complexes of type MX , particularly in the case when the metal is only available in trace concentrations, as the distribntion can easily be measnred with radioactive techniques (see also section 4.15). The method reqnires the formation of an extractable complex of the metal ion, which, in the simplest and most commonly used case, is an nn-charged lipophilic complex of type MA. The metal-organic complex MA serves as a probe for the concentration of metal ions in the aqueous phase through its equilibrium with the free section 4.8.2. This same principle is used in the design of metal selective electrodes (see Chapter 15). Extractants typically used for this purpose are P-diketones like acetylacetone (HAA) or thenoyltrifluoroacteone (TTA), and weak large organic acids like dinonyl naph-talene sulphonic acid (DNNA). 

In using this technique accurately, it is necessary to consider possible sources of errors. A rather extensive summary of this technique applied to hydrophilic actinide complexation by practically all inorganic ligands, as well as a considerable number of weak organic acids, has recently been presented [33a,33b],... 

Scheme 5 Thin MIP composite films with high template affinity at low nonspecific background binding the matrix for MIP synthesis is a hydrophilic, low binding layer 1 on the support. Only the fraction of the functional monomer (grey dots) in the reaction mixture, which before polymerization had been involved in the pre-organized complex (dark grey dots) with the template (large dots), and which could not fully penetrate into layer 1, was during cross-linking polymerization in layer 1 (IPN formation) fixed in MIP sites on top of the hydrophilic, low binding layer 1.

One solution to reducing the complexity of chromatograms is the prior fractionation of samples and separate analysis of each fraction. This can be partially achieved by a combination of DEAE Sephadex chromatography and solvent extraction (see Part II, Section 7.2), the latter giving a simplified chromatogram which favours aromatic and hydrophobic constituents while the former a more quantitative extract containing the more hydrophilic organic acids which direct solvent extraction methods fail to extract. 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

Addition of a chiral carrier can improve the enantioselective transport through the membrane by preferentially forming a complex with one enantiomer. Typically, chiral selectors such as cyclodextrins (e.g. (4)) and crown ethers (e.g. (5) [21]) are applied. Due to the apolar character of the inner surface and the hydrophilic external surface of cyclodextrins, these molecules are able to transport apolar compounds through an aqueous phase to an organic phase, whereas the opposite mechanism is valid for crown ethers. 

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