Salicylic acid chelation

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. 

In addition to the aforementioned types of intermolecular homoconjugates, there are also intramolecular homoconjugates, examples of which we have already mentioned with regard to the titrations of (a) ethylenediamine with acid (p. 248) and (b) of salicylic acid with base (p. 245). This phenomenon of intramolecular hydrogen bonding is usually called chelation, and so the conjugates concerned are preferably designated chelates. 

A third approach utilised copper salts, especially copper(II) sulphate, in conjunction with dyes containing chelatable groupings such as salicylic acid or o,o -dihydroxyazo moieties. Indeed, special ranges of copperable direct dyes, for which the treatment with copper(II) sulphate was really part of the dyeing process rather than an optional aftertreatment, were introduced. In the past the main use of this chelation treatment was to enhance light fastness, but it is little used for this purpose nowadays. 

Haapakka and Kankare have studied this phenomenon and used it to determine various analytes that are active at the electrode surface [44-46], Some metal ions have been shown to catalyze ECL at oxide-covered aluminum electrodes during the reduction of hydrogen peroxide in particular. These include mercu-ry(I), mercury(II), copper(II), silver , and thallium , the latter determined to a detection limit of <10 10 M. The emission is enhanced by organic compounds that are themselves fluorescent or that form fluorescent chelates with the aluminum ion. Both salicylic acid and micelle solubilized polyaromatic hydrocarbons have been determined in this way to a limit of detection in the order of 10 8M. 

The interaction of ligands derived from salicylic acid and its derivatives has been extensively investigated (83, 147, 149, 160, 170, 176, 183-205). A similar situation obtains with regard to l-hydroxy-2-naphthoic acid (185, 194, 196, 198, 206-215). Salicylic acid derivatives may be useful in chelation therapy for beryllium poisoning (2). 

In a bidentate ligand system, three molecules of a dye containing either a terminal salicylic acid unit (as in 5.2) or an o-nitrosonaphthol residue are able to chelate simultaneously with a trivalent metal ion of CN6, such as chromium (III) or iron(III), to form a 1 3 metal-dye complex (as in 5.8). Historically, the most important bidentate ligand system was alizarin (5.1). It has been suggested that both hydroxy groups and the keto group in the peri position are all involved with the metal atom in the chelation mechanism. 

The second example is the electro-oxidative polymerization of phenols bearing functional substituents. It is known that salicylic acid forms a stable chelate with copper ion, thus the copper catalyst is deactivated and the polymerization does not occur. On the other hand, salicylic acid was electro-oxidatively polymerized to produce the poly(phenyleneoxide) bearing carboxylic group. 

The product of step o is known as isochoris-mate.55 56 Isochorismate gives rise to a variety of products including vitamin K, salicylic acid,56a the iron chelator enterobactin (Fig. 16-1), and other siderophores. These are formed in E. coli via 2,3-dihy-droxybenzoate as indicated in Fig. 25-2.57-59a The genes (ent) for the requisite enzymes are clustered at 14 min on the E. coli chromosome map (Fig. 26-4). 

Terminally metallizable dyes (30) are obtained by the interaction of a diazonium salt and a coupling component containing a chelating system, for example salicylic acid, catechol, salicyl-aldoxime or 8-hydroxyquinoline, and their coordination chemistry is typical of these compounds. Such dyes were rarely used as preformed metal complexes but were usually applied to cotton and then converted to their copper complexes on the fibre to improve their fastness to wet treatments. A typical example is the blue dyestuff (31). 

It is more difficult to decide whether chelation plays any part in the activity of salicylic acid which is released in the biodegradation of aspirin and, especially in cases of abuse of this drug and in the therapy of rheumatic disease, may be present in appreciable quantities in the body. 

In general a phenol will undergo direct carboxylation of the nucleus when the dry sodium salt is heated under pressure with carbon dioxide (the Kolbe-Schmidt reaction). Addition of the weakly electrophilic carbon dioxide is promoted by electron release from the oxyanionic site. With phenol itself the ultimate product is salicylic acid (o-hydroxybenzoic acid) predominantly ortho attack may be attributable to stabilisation of the transition state through chelation. 

Using these agents, especially the particularly effective 1 2 complex 4 with salicylic acid, metallization can be carried out easily at high pH without precipitation of inert chromium hydroxide. In certain cases a 1 1 chromium complex that still contains chelating organic acid as ligand can also be obtained. 

Hydroxybenzoic acid (salicylic acid) does form a complex, although its formation is not favored when compared to that of the picolinato ligand. Presumably this, at least to an extent, reflects the fact that the chelate formed with salicylate has a six-membered ring, and six-membered chelates are much less favored than the five-membered analogue. 

Pseudomolecular systems. These involve species that are partly ionized in water and are molecular in an organic solvent. Examples include weak acids such as phenols, dithizone, salicylic acid, cupferron, and many neutral metal-chelate complexes. 

Humic substances, humic and fulvic acids, are essentially a mixture of compounds of different molecular weights. The total number of base-titratable groups is in the range of 10-20 meq per gram of carbon. Chelation by neighboring carboxyl and phenolic groups is the major mode of metal complexation. Compounds such as malonic acid, phthalic acid, salicylic acid, and catechol serve as convenient monomeric model compounds for estimating the coordi-native properties of humic substances. 

Hydroxyglutaric acid forms a ternary anionic complex with Fe and The complexes TiCl2L2 (L = ethyl-4-nitrobenzoylpyruvate, ethyl-4-phenylbenzoyl-pyruvate, ethyl-2,4-dimethoxybenzoylpyruvate, or ethyl-2-naphthylpyruvate) have been prepared.There has been a spectroscopic study of complex formation in the Ti -salicylate-aa-bipyridyl system,and a reinvestigation of the reaction between Ti and salicylic acid in concentrated sulphuric acid. The coloured TiO salicylic acid complex formed in the latter system is formulated as a 7t-compIex rather than a chelate. 

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