Copper complexes oxalic acid

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. 

V to IX), the copper complexes of the imidazoles also precipitated from the reaction mixture, and were filtered off. Oxalic acid and 4(5)-imidazole (30) were determined in the filtrate.11 40,41 The complex was suspended in hot water,11,29 32-40,41,43 47 50 53,88 dilute sulfuric acid,48,49 or dilute hydrochloric acid,44 the copper was removed as the sulfide, with hydrogen sulfide or sodium sulfide,49 and the excess of hydrogen sulfide was removed with lead acetate.11 40 41,50 The clear... 

In ammoniacal solutions of copper salts, the oxidation products are likely to contain nitrogen thus, hexoses give oxalic acid, imidazoles, hydrogen cyanide, and urea. Kinetic studies have been reported for the reaction of Cu(II) in the presence of ammonia with maltose, lactose, melibiose, and cellobiose.190 For the oxidation by tetraamminecopper(II) in ammoniacal and buffered media the rate of reaction is first order in disaccharide concentration, order one-half in ammonia concentration, but it is independent of Cu(II) concentration. The reaction rate is decreased by the addition of ammonium chloride, because of the common ion effect. These kinetics suggested mechanisms involving an intermediate enediolate ion, with the rate of reaction being equal to the rate of enolization.191 A similar mechanism has been proposed for the oxidation of D-fructose by a copper-pyridine complex in an excess of pyridine.192... 

The compound is soluble in warm water but begins to decompose slowly into copper(II) oxalate, which precipitates shortly after dissolution of the complex. The decomposition is hastened by the addition of strong acid. The material is only very slightly soluble in the common organic solvents such as acetone, benzene, carbon tetrachloride, chloroform, ethanol, and methanol. The blue crystals lose water rapidly above 150° and the resulting compound decomposes at 260°. 

The use of oxalic acid as a complexing agent has been investigated using polishing and potentiodynamic studies [54]. Maximum removal rates were observed at pH 3. This is consistent with the fact that oxalic acid (HX) had the maximum concentration of X at pH = 3.00, which causes complexation with the positive copper surface at the acidic pH condition. 

Gorantla VRK, Babel A, Pandija S, Babu SV. Oxalic acid as complexing agent in CMP slurries of copper. Electrochem Solid State Lett 2005 8(5) G131-G134. 

There also exists a considerable number of ionic tris(thiourea) complexes. Thiourea is capable of reducing copper(II) salts to copper(I) complexes in acid solution to form [Cu(thiourea)3] salts. The following have been isolated chloride (194, 195), nitrate (194), oxalate (194, 195, 298), monohydrogen arsenate, and phosphate (298). 

Due to the anionic nature of rhamnolipids, they are able to remove metals from soil and ions such as cadmium, copper, lanthanum, lead and zinc due to their complexation ability [57-59], More information is required to establish the nature of the biosurfactant-metal complexes. Stability constants were established by an ion exchange resin technique [60], Cations of lowest to highest affinity for rhamnolipid were K+ < Mg + < Mn + < Ni " " < Co " < Ca2+ < Hg2+ < Fe + < Zn2+ < Cd2+ < Pb2+ < Cu2+ < M +. These affinities were approximately the same or higher than those with the organic acids, acetic, citric, fulvic and oxalic acids. This indicated the potential of the rhamnolipid for metal remediation. Molar ratios of the rhamnolipid to metal for selected metals were 2.31 for copper, 2.37 for lead, 1.91 for cadmium, 1.58 for zinc and 0.93 for nickel. Common soil cations, magnesium and potassium, had low molar ratios, 0.84 and 0.57, respectively. 

Other common transition metal corrosion products typically monitored at various sites within the plant include iron, copper, nickel, zinc, and chromium. More than 80% of BWR plants analyze for iron, nickel, copper, and zinc in reactor water, and nearly all of the BWR plants determine these metals in feed water. In addition, zinc is also an additive used in many plants to control the shutdown radiation dose rate. Nickel and chromium are corrosion products in BWR plants fi-om stainless-steel piping. The best selectivity and sensitivity for achieving low to submicrogram/Liter detection limits for transition metals can be obtained by separating transition metal complexes using pyridine-2, 6-dicarboxylic acid (PDCA) or oxalic acid as chelators in the eluent, followed by postcolumn derivatization with 4-(2-pyridylazo)resorcinol (PAR) and absorbance detection at 520 nm (see Section 8.2.1.2). This approach was successfully used to determine trace concentrations of iron, copper, nickel, and zinc in BWR and PWR matrices [197]. Figure 10.113 compares the chromatograms from the... 

Several additional formulations with EDTA (or citric acid) and other materials have been proposed. Martin patented a mixture of hydrogen peroxide, oxalic acid, and an EDTA or citric acid-type complexer for removing copper deposits (iron oxides are removed by using an additional stage). An unusual aspect of this process is that it is performed at a pH of 3.0-6.0. To allow passivation of the steel to be effective, oxidative copper-removal processes usually are conducted at pH values of >9.0. 

Binary systems synthesized consisted of Cu/Fe, Ni/Fe, Cu/Al and Ni/Al and Cu/Cr for 4-10 wt percent Cu or Ni in the calcined mixed oxide. Anionic complexing agents acetic, citric and oxalic acids and EDTA were used in molar ratios of 1 1 with the initial copper or nickel. Two stage precipitations were used starting with an initial formation of aluminum, chromium or ferric hydroxide by addition of NaOH to an aqueous solution of A1 nitrate, Cr nitrate or Fe chloride. In the second stage aqueous solutions of Cu sulfate or Ni nitrate were mixed with the initial precipitate with or without the presence of a 1 1 mole ratio of selected anionic complexing agents to complete the precipitation. A second mode of coprecipitation used was to preadsorb oxalic acid on the initially precipitated AI, Cr or Fe hydroxide. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

Several groups have been successful at the catalytic conversion of carbon dioxide, hydrogen, and alcohols into alkyl formate esters using neutral metal - phosphine complexes in conjunction with a Lewis acid or base (109). Denise and Sneeden (110) have recently investigated various copper and palladium systems for the product of ethyl formate and ethyl formamide. Their results are summarized in Table II. Of the mononuclear palladium complexes, the most active system for ethyl formate production was found to be the Pd(0) complex, Pd(dpm)2, which generated 10/imol HCOOEt per /rniol metal complex per day. It was anticipated that complexes containing more than one metal center might aid in the formation of C2 products however, none of the multinuclear complexes produced substantial quantities of diethyl oxalate. 

EDTA (ethylenediaminetetraacetic acid) forms stable metal chelates with a number of metal ions. Using this reagent as a complexing- agent, arsenic, bismuth, and selenium can be determined without any interference in the presence of nickel and cobalt. The cobalt-EDTA chelate is stable in 5 M HCl solution, whereas the corresponding bismuth complex is not. The influence of copper on the determination of arsenic can also be eliminated with EDTA, but not in the determination of selenium. Thiourea has been used to eliminate the influence of copper in the determination of antimony and sodium oxalate to eliminate the influence of copper and nickel in the determination of tin. An addition of thiosemicarbazide and 1,10-phenanthro-line reduces the interference of copper, nickel, platinum, and palladium in the determination of arsenic. 

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