Copper complexes formation

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

Comparison117129 of the behaviour of bidentate, tridentate and tetradentate formazans with copper(II) salts has effectively demonstrated that two competing reactions occur copper complex formation (equation 16) and oxidation of the formazan to tetrazolium salt (equation 17). 

Copper complex formation. Add a few drops of aqueous copper(n) sulphate solution to an aqueous solution of the amino acid. A deep blue coloration is obtained. The deep blue copper derivative may be isolated by boiling a solution of the amino acid with precipitated copper(n) hydroxide or with copper(n) carbonate, filtering and concentrating the solution. These blue complexes are coordination compounds of the structure ... 

The Benzo Fast Copper (I.G. Farbenindustrie) and the Cuprophenyl (Geigy) dyes are converted to insoluble copper complexes on the fiber by treating the dyeings with a copper salt. Copper complex formation on the fiber has strongly lost technical significance due to the copper content in dyehouse effluents. The mostly copper-containing Indosol direct dyes recently launched by Sandoz are cross-linked on and with the fiber by aftertreatment with a special reactive agent [35],... 

Incorporation of metal ions into porphyrins is affected by other compounds in solution. Lowe and Phillips (25) found that copper(II) ions were chelated with dimethyl protoporphyrin ester 20,000 times faster in 2.5% sodium dodecylsulfate (SDS) than in 5% cetyl trimethyl ammonium bromide (CATB). The increased activity of SDS treated porphyrin was attributed to electrostatic attraction between anionic micelles formed around the tetrapyrrole nucleus and the metal cation. The authors also reported the influence of certain chelating agents on the rate of copper complex formation. Equimolar concentrations of copper and 8-hydroxyquinoline or sodium diethylthiocarbamate in 2.5% SDS increased the reaction rate 38 and 165 times, respectively, above the control. Secondary chelators may act by removing the hydration sphere on the metal ion increasing its attraction to pyrrole nitrogens (26). 

Copper Complex formation with 5,5-di-methyl-1,3-cyclohexanedione bis(4-phenyl-3-thiosemicarbazone) 0.8-8 Reaction medium 2.5-3.0moir HCI. Both fixed time and initial rate were used... 

Supplementing culture media, crude extracts, storage, and assay buffers with copper salts can assist copper complex formation in MCO preparations. In many cases, copper can be added to bacterial and fungal culture supernatants to increase MCO activity and holoenzyme yield [62-67]. Free copper ions are toxic to microorganisms, so copper concentrations must remain low enough during cultivation so that growth is not inhibited [61]. 

Hydantoin itself can be detected ia small concentrations ia the presence of other NH-containing compounds by paper chromatography followed by detection with a mercury acetate—diphenylcarba2one spray reagent. A variety of analytical reactions has been developed for 5,5-disubstituted hydantoias, due to their medicinal iaterest. These reactions are best exemplified by reference to the assays used for 5,5-diphenylhydantoiQ (73—78), most of which are based on their cycHc ureide stmcture. Identity tests iaclude the foUowiag (/) the Zwikker reaction, consisting of the formation of a colored complex on treatment with cobalt(II) salts ia the presence of an amine (2) formation of colored copper complexes and (3) precipitation on addition of silver(I) species, due to formation of iasoluble salts at N. ... 

Bonding Agents. These materials are generally only used in wire cable coat compounds. They are basically organic complexes of cobalt and cobalt—boron. In wire coat compounds they are used at very low levels of active cobalt to aid in the copper sulfide complex formation that is the primary adherance stmcture. The copper sulfide stmcture builds up at the brass mbber interface through copper in the brass and sulfur from the compound. The dendrites of copper sulfide formed entrap the polymer chains before the compound is vulcanized thus hoi ding the mbber firmly to the wire. 

The concentration of copper(I) ion remaining ia solution is not appreciable. However, aqueous copper(I) ion can be stabilized by complex formation with various agents such as chloride, ammonia, cyanide, or acetonitrile. 

Increased interest in the chemistry of ylides has produced X-ray structures for compounds 123 (R = OMe) (91T5277) and 138 (92H(34)1005), while possibilities of complex formation have led to structures for bidentate copper complex of 135 (94JCS(D)2651), monodentate copper complex of the 3-phenyltria-zolopyridine 139, monodentate (through N2) dinitrato ligand of 3-methyl-triazolopyridine 140 (99MI4), and dinitrato bidentate copper complex of... 

Amide groups interact with copper sulphate by the complex formation mechanism as mentioned previously. 

A similarly undesirable situation is brought about in unduly alkaline solutions caused by the indiscriminate use of amines which may lead to high dissolution rates of copper from its alloys owing to complex formation. The standards discussed in Section 5.5 are aimed at avoiding these undesirable situations. 

A further factor which must also be taken into consideration from the point of view of the analytical applications of complexes and of complex-formation reactions is the rate of reaction to be analytically useful it is usually required that the reaction be rapid. An important classification of complexes is based upon the rate at which they undergo substitution reactions, and leads to the two groups of labile and inert complexes. The term labile complex is applied to those cases where nucleophilic substitution is complete within the time required for mixing the reagents. Thus, for example, when excess of aqueous ammonia is added to an aqueous solution of copper(II) sulphate, the change in colour from pale to deep blue is instantaneous the rapid replacement of water molecules by ammonia indicates that the Cu(II) ion forms kinetically labile complexes. The term inert is applied to those complexes which undergo slow substitution reactions, i.e. reactions with half-times of the order of hours or even days at room temperature. Thus the Cr(III) ion forms kinetically inert complexes, so that the replacement of water molecules coordinated to Cr(III) by other ligands is a very slow process at room temperature. 

The bromo substituent in l-bromo-19-meLhyl-l,l9-dideoxybiladienes- c is not essential for porphyrin formation. When 1-methylbiladiene-ac dihydrobromide or the 1,19-dimethyl-biladienc-ac are heated in refluxing methanol or dimethylformamide in the presence of cop-per(II) salts, the porphyrin copper complexes 13 are formed by oxidative cyclization. The free porphyrins can then be obtained by removal of the copper with acid. A wide range of porphyrins 13 can be prepared by this method. However, a restriction is the accessibility of the starting material with special substitution patterns. 

Copper and brasses in the systems are more resistant to corrosion because of a stable oxide film however, if ammonia is present together with oxygen, corrosion of copper and copper oxide rapidly occurs. The corrosion is an oxidation process and results in the formation of the ammonia-copper complex [Cu(NH3)42+], Corrosion of nickel and zinc components also may occur in like fashion. 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

Some infrared data on these catalytic systems also support the intermediate complex formation (123). For a heterogeneous system of Cu metal and cyclohexyl isocyanide one observes, in solution, a vcn absorption at 2180 cm , compared to 2140 cm for the free isocyanide. Absorptions at 2181 and 2192 cm for the systems with CujO and CuCl, respectively, are measured. The solutions in each case have catalytic activity. The suggestion is made that either a copper(O) complex (from Cu metal) or copper(I) isocyanide complex (from CU2O or CuCl) is the catalytic species present. 

Copper complexes of sparteine have also been used for the catalysis of asymmetric carbon-carbon bond formation. The copper-catalyzed reaction... 

This group showed that isolable silver(I) diaminocarbene complexes can be use in situ instead of free carbenes, to generate the copper carbene complex. The silver salts that precipitates during the formation of the copper complex have not any negative effect on the conversion. This method is advantageous since most of the silver complexes are isolable, air-stable and easily obtained by treatment of the corresponding imidazohnium salt by 0.5 equiv of silver oxide (Scheme 53). The solid structure of 78 was analyzed by X-ray diffraction. 

The treatment of LB films of copper behenate (10-50 layers) with H2S gas resulted in formation of the semiconductor CU2S [177]. In this case, the LB films of behenic acid alone were formed and then exposed to solutions of copper chloride. Conversion of the carboxyl groups to carboxylate groups upon copper complexation was confirmed by infrared spectroscopy. Resistivity measurements versus temperature confirmed the formation of semiconducting CU2S in one case, and showed a linear increase in log(R) versus IT K). All of the samples became insulators on exposure to air maintaining the conductivity required storage under vacuum. The formation of CuiS sheets in some of the sample was concluded from optical microscopy and resistivity data. 

The degradation of tetrachloromethane by a strain of Pseudomonas sp. presents a number of exceptional features. Although was a major product from the metabolism of CCI4, a substantial part of the label was retained in nonvolatile water-soluble residues (Lewis and Crawford 1995). The nature of these was revealed by the isolation of adducts with cysteine and A,A -dimethylethylenediamine, when the intermediates that are formally equivalent to COClj and CSClj were trapped—presumably formed by reaction of the substrate with water and a thiol, respectively. Further examination of this strain classified as Pseudomonas stutzeri strain KC has illuminated novel details of the mechanism. The metabolite pyridine-2,6-dithiocarboxylic acid (Lee et al. 1999) plays a key role in the degradation. Its copper complex produces trichloromethyl and thiyl radicals, and thence the formation of CO2, CS2, and COS (Figure 7.64) (Lewis et al. 2001). 

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