Tervalent copper

Since the reactivity of the complex seems to depend primarily on the copper atom, the latter may be regarded as the temporary center for the positive charge in other words, tervalent copper is formally produced as an intermediate. 

Tervalent copper and nickel are involved in the autoxidation reactions of [Cu(H 3G4)] and [Ni(H 3G4)] respectively. In the case of nickel, decomposition of [Ni(H 3G4)] proceeds by decarboxylation of the terminal carboxy-group adjacent to the peptide nitrogen. - With copper, decomposition of [Cu-(H sG4)] proceeds through a carbon-centred free radical produced by abstraction of a hydrogen atom from the peptide backbone. Bulky carbon substituents assist the stabilization of the higher-oxidation state ions, and a study of the stabilities of leucyl tripeptide complexes with copper(ii) and nickel(u) has been reported. Copper(iii) and nickel(iii) tripeptide complexes of a-aminoisobutyric acid are thermally stable but are readily decomposed by photochemical pathways. Resonance Raman and other studies with copper(iii) peptide complexes have also been reported. ... 

A dark red color appears on warming very dilute alkaline solutions of copper salts with certain oxidizing agents (such as persulfate) in the presence of alkali periodate. The complex anion formed from tervalent copper and the periodiate radical is responsible for the color. ... 

The formation of this colored ion may be used as a spot test for periodate (Procedure I). Alternatively, the interference by periodate, with the catalytic effect of copper salts on the reaction between Mn+ ion and hypobromite may be utilized (Procedure II). This reaction normally proceeds with formation of manganese dioxide but, in the presence of even extremely small amounts of copper salts, permanganate is formed instead. The activation of the hypobromite is due to the intermediate formation of Cu oxide, which causes a further oxidation from MnOj to Mn04 ion, with regeneration of Cu oxide (see page 300). The formation of the stable complex ion of tervalent copper with periodate prevents the activation of the hypobromite. 

The production of stable complexes of tervalent copper, under the given conditions, is limited to periodic acid and telluric acid (see page 417). The test is therefore highly selective. 

If certain oxidizing agents (e.g. persulfate) are added to copper hydroxide suspended in an alkaline solution of an alkali tellurate, a dark red-brown color develops on heating. This is due to a stable complex anion formed from tervalent copper and the tellurate radical. ... 

The formation of a stable complex of tervalent copper under the given conditions is limited to telluric acid and periodic acid (see page 258). 

Interest is mounting in this state, promoted once again by its possible implication in biological systems. Galactose oxidase, for example, is a copper enzyme which catalyses the oxidation of galactose to the corresponding aldehyde. The tervalent oxidation state may be prepared from Cu(II) by chemical, anodic and radical oxidation. Cu(III) complexes of peptides and macrocycles have been most studied, particularly from a mechanistic viewpoint. The oxidation of I" by Cu(III)-deprotonated peptide complexes and by imine-oxime complexes have a similar rate law... 

A drop reaction for tervalent arsenic consists in treating a drop of the sample on filter paper with hydrochloric acid and a 0-5 per cent, aqueous solution of kairin (N-ethyl-8-hydroxytetrahydroquinoline hydrochloride) on adding a drop of aqueous ferric chloride and warming the test paper, a reddish-brown colour appears.3 The test is sensitive to 6 x 10 1° g. Mercury, lead and copper interfere. 

Fabbrizzi, L., Montagna, L., Poggi, A., Kaden, T.A. and Siegfried, L.C. 1986. Ditopic receptors for transition metal ions a heterobimetallic nickel(II)-copper(II) bis(macrocyclic) complex and its stepwise oxidation to the tervalent state. Inorg.Chem., 25,2671-2672. 

The reaction is not disturbed by silver or copper, or by iron(III), chromium or aluminium in the presence of ammoniacal tartrate solution if zinc is present, ammonium chloride should first be added cobalt(III) ions represss the sensitivity and should be oxidized to the tervalent state with hydrogen peroxide iron(II) interferes and should be oxidized and alkaline tartrate solution added before applying the test. 

A drop of the test solution is placed on filter paper and spotted with a (hrop of a saturated water solution of sodium azide. The fleck is exposed to the vapors of a saturated aqueous solution of sulfurous acid. A yellow color appears which changes to blue on treatment with a drop of a 2 % acetic acid solution of a-tolidine Idn, Limit 0.5 y Co). The test is based on the fact that the oxidation of complex Co azide to complex cobalt azide is catalyzed by the autoxidation of sulfurous acid. The color reaction with o-tolidine is due to the action of the tervalent cobalt formed. Copper and iron ions interfere and should be previously removed or masked. The test can be carried out in the presence of as much as 200 times the amount of nickel. 

When the following procedure is used the sensitivity of the test for copper is not decreased by foreign ions in the proportion 1 5000. Ions of the noble metals are reduced to the metal by the hydroxylamine hydrochloride, and thallium, silver, lead and mercurous ions are precipitated as chlorides. Such precipitates should be removed prior to the addition of the reagent, particularly if the quantity of copper to be detected is small. Tervalent iron, if present in high concentration, must be masked with tartaric acid and the pH then adjusted with ammonia. Colored ions in larger amounts impair the discernment of small quantities of (II). In such cases it is better to take advantage of the extractability of the copper salt in organic solvents. 

Further kinetic results relevant to the ligand replacement reactions discussed in this section are those for dissociation of lanthanide(m)-cydta complexes. Nearly all the tervalent rare-earth cations were included in this investigation, along with the closely related complexes of scandium(ra) and yttrium(m). Dissociation rates vary with pH, but are unaffected by the addition of copper(n) ions. Thus there is no direct transfer of cydta from Ln + to Cu + in the manner of equation (7) (next section). The rate constants for the acid-dependent dissociation path show a large variation with the nature of the lanthanide cation they vary from 1291 mol s (at 25 °C, fjb = 0.1 mol 1 ) for lanthanum(ra) to 0.0171 mols for lutecium(m) the trend of rate constants is one of regular decrease as the ionic radius decreases. The rate constant of 0.019 1 mol s for dissociation of the scandium(in) complex is, however, much higher than would be expected from the ionic radius of Sc +. Activation parameters for dissociation of these cydta complexes are reported for the La", Gd, Dy Tm ", Lu , and Y compounds. ... 

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