Acids hydroxy, chelated

P-Keto esters and -keto amides, each substituted between the two carbonyl units with a 2-[2-(tri-methylsilyl)methyl] group, also undergo Lewis acid catalyzed, chelation-controlled cyclization. When titanium tetrachloride is used, only the product possessing a cis relationship between the hydroxy and ester (or amide) groups is product yields range from 65 to 88% (Table 8). While loss of stereochemistry in the product and equilibration of diastereomers could have occurred via a Lewis acid promoted retro aldol-aldol sequence, none was observed. Consequently, it is assumed that the reactions occur under kinetic, rather than thermodynamic, control. In contrast to the titanium tetrachloride promoted process, fluoride-induced cyclization produces a 2 1 mixture of diastereomeric products, and the nonchelating Lewis acid BF3-OEt2 leads to a 1 4.8 mixture of diastereomers. 

Humic adds. Chocolate brown, dust-like powder, poorly soluble in water with a large increase in volume, soluble in aqueous alkalis to give brown solutions, and in cone, nitric acid to give red solutions. H. forms a heteropolycondensate with Mr of 2000-500000 (mostly 20000-50000), mp. >300°C. They consist of a polycyclic core and loosely bound polysaccharides, proteins, simple phenols, and chelated metal ions which are linked to the core through carboxyl and carbonyl groups . The latter usually have aromatic character. The H. are strongly acidic (hydroxy- and polyhydroxycarboxylic acids) and mostly occur as salts. For analysis, see Lit.. ... 

A number of the plications also list L-tartaric acid and D-glucaric acid as having comparable properties, both being hydroxy acids and chelators. When inexpensive glucaric acid becomes commercially available on a significant scale, it has applications waiting for a supply and could overtake uses now dominated by tartaric acid. Additional applications unique to glucaric acid will also benefit fiom a dependable source. 

The Pechini method is a representative example of this approach as it is the most widely used polymer complex method. The original patent [47] describes the formation of a polymeric network by polyesterification of an a-hydroxy-carboxylic acid (e.g., citric add) and a polyhydroxy-alcohol (e.g., ethylene glycol). It is an effective method for the synthesis of multicomponent oxides by dissolving metal nitrates in water, adding an a-hydroxy-carboxyhc acid to chelate the metal cations, and adding ethylene glycol. Upon heating at moderate temperature (100 "C to 1500 °C), a poly-esterificahon reaction occurs that results in an ester which still contains two alco-... 

An aq. soln. of glycine, ca. 0.05 mole of cupric sulfate, and 4 moles of Na-carbonate treated with ca. 8 moles of isobutyraldehyde, refluxed 30 hrs. with efficient stirring, more aldehyde added, and refluxing continued ca. 0.5 hr. until most of the blue color of the cupric ions is discharged -hydroxy-leucine. Y 67%. F. e. s. T. T. Otani and M. Winitz, Arch. Biochem. Biophys. 102, 464 (1963) with the amino acid Gu-chelate and KOH cf. H. Mix and F.-W.Wilcke, H. 337, 40 (1964). 

In common with other hydroxy organic acids, tartaric acid complexes many metal ions. Formation constants for tartaric acid chelates with various metal ions are as follows Ca, 2.9 Cu, 3.2 Mg, 1.4 and Zn, 2.7 (68). In aqueous solution, tartaric acid can be mildly corrosive toward carbon steels, but under normal conditions it is noncorrosive to stainless steels (Table 9) (27). 

Chelated complexes such as sodium zirconium lactate [15529-67-6] or ammonium zirconium carbonate [22829-17-0] and acidic forms such as zirconium hydroxy oxide chloride [18428-88-1] have been used in preparations in deodorants or for treatment for poison oak and poison ivy dermatitis. In such occasions, when the skin had been cut or abraded, a few users developed granulomas which have been identified as a delayed hypersensitivity to zirconium (99). These may take several weeks to develop, and commonly persist for 6 months to over a year. 

The anions of 2-(arylsulfinylmethyl)oxazoles can be added to aldehydes to give 2-(l-aryl-sulfinyl-2-hydroxyalkyl)oxazoles which have been transformed into /1-hydroxy acids. With lithium bases, the enantioseleetivity could be increased to 50%. The use of a more chelating counter ion, such as magnesium, lowered the optical yields44. 

The complexes of aromatic hydroxy carboxylic acids (salicylic acid and its isomers) with [Bu2Sn(IV)] and [Ph3Sn(IV)] were obtained. The FT-IR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the O, O) atoms of the ligands. It was found that in most cases the -COO group chelated to the central atoms, but monodentate coordination was also observed. The complexes probably have polymeric structures. 

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