Mandelic acid metal complexes

A different concept of chiral recognition was used by Lehn et al. (1978) for the differentiation between pairs of enantiomeric anions. Following the terminology used for metallo-enzymes, the chiral crown ether [309] acts as an apo-receptor, complexing a metal cation and thus becoming a chiral metal receptor that may discriminate between enantiomeric anions (cascade-type complexation). Extraction experiments with racemic mandelic acid dissolved in... 

Chiral di mination studies with the tetra-amine 54 were also performed with respect to racemic molecular anions via the formation of cascade complexes. Regulation of the chiral discrimination may be achieved to some extent by the nature of the cation initially complexed. Efficient ion pairing with molecular anions is favoured in solvents of low polarity. In this respect, aqueous solutions of alkali metal salts of ( )-mandelic acid or (+)-a-hydroxy-l-naphthaleneacetic acid were extracted into a CDCI3 phase where the ligand 54 is dissolved. In case of the mandelate anion, the anion ligand ratios in the CDCI3 layer were as follows Na (0.6 1), (1 1),... 

Some physical properties and structural features of the normal tetramandelate have been reported. The solubility of the 1 4 mandelato complex in 2 Jlf perchloric acid was determined to be 7.8 x 10" mole/ liter (444), and was found to fall slowly with increasing pH to a minimum of 4 X 10 at pH 3.1, after which it then rose. The change in solubility was accompanied by a change in composition which involved the formation of metal oxo species. In 1958, R. W. Stromatt (540) concluded on the basis of infrared spectroscopy, that the tetramandelates exist as discrete 8-coordinate molecular species. This would seem to be supported by the fact (24) that an organic-soluble species can be extracted from aqueous solutions containing (1.0 to 8) x 10 mole/liter zirconium(IV) in 1 M perchloric acid with an isopentyl alcohol solution of p-bromo-mandelic acid. The normal tetramandelate precipitated from aqueous solution at the usual concentration conditions, however, is very insoluble... 

In the companion paper (Hanna and Sarac 1977b) the oxidation of benzilic acid is reported with emphasis on learning the mechanistic imphcations with respect to Ce(TV). As is generally observed, the rates are much slower in sulfuric acid solutions and the existence of a stable precursor complex is doubtful. The authors calculate the equihbrium speciation of Ce among the first two hydrolysis products, free metal ion, and 1 1, 1 2, 1 3 Ce-S04 complexes and find that the rate of reaction is most strongly correlated with CeSO ". In the presence of sulfuric acid a precursor complex of the form CeSO HL is proposed. In perchlorate solutions there is some evidence for a reactive CeHL species and an unreactive Ce(HL) " species. The precursor complex stability constant and first-order oxidation rate parameter for the former intermediate are in excellent agreement with those reported by Amjad et al. (1977) for mandelic acid. 

The copper(II) complex with polyaniline exhibits a higher catalytic capability for the dehydrogenation of cinnamyl alcohol into cinnamaldehyde [18, 20]. The cooperative catalysis of both components is achieved. Iron(lll) chloride is similarly employed instead of copper(II) chloride. The catalytic system is applicable to the decarboxylative dehydrogenation of mandelic acid to benzaldehyde. In these oxidation reactions, a complex catalyst consisting of polyaniline and metal salt forms a reversible redox cycle under molecular oxygen (Scheme 3.10). The copper salt appears to play a role as a metallic dopant, which is monitored spectroscopically. 

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