Cobaltic complexes hydroxide

Cobalt in steel Discussion. An alternative, but less sensitive, method utilises 2-nitroso-l-naphthol, and this can be used for the determination of cobalt in steel. The pink cobalt(III) complex is formed in a citrate medium at pH 2.5-5. Citrate serves as a buffer, prevents the precipitation of metallic hydroxides, and complexes iron(III) so that it does not form an extractable nitrosonaphtholate complex. The cobalt complex forms slowly (ca 30 minutes) and is extracted with chloroform. 

The rate showed a first-order dependence on the concentrations of both hydroxide and the cobalt complex, and Hogenkamp 89) suggested that the initial step was the removal of a proton from the /3-carbon, followed by the elimination of Co(I). Schrauzer, Weber, and Beckham 159) were subsequently able to show the formation of 7r-olefin-Co(I) complexes in... 

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

The XPS results do not indicate significant cobalt(II) hydroxide formation following complex sorption at pH 8 or 10 for... 

Hexaammineplatinum(IV) salts also undergo imine-forming reactions with acetylacetone (equation 49).172 A cobalt(III) acetylacetone complex can be formed as a result of intramolecular addition of cobalt-bound hydroxide ion to acetylacetone. The cobalt-bound oxygen atoms are retained in the new chelate ring (equation 50).173... 

Reductive decarboxylation of (20) yields C02, H+, and a Co(I) species at a measurable rate (94). In the presence of CO, the starting cobalt complex is regenerated, and a catalytic system for the oxidation of CO by ferricyanide is established. It is significant that in this system the metal-carbonyl bond is formed when the cobalt is in a reduced state. It is the subsequent oxidation of the cobalt by electron transfer that activated the carbonyl to attack by water or hydroxide. That this activation results in a weaker metal-carbonyl bond is evident since the Co(III)-carbonyl may be hydrolyzed in acidic solution with loss of the carbon monoxide ligand (94). 

Tris(phenylbiguanido)cobalt(III) hydroxide, [Co(C6-H5C2N6H5) 3]-3H20 or [Co(C6H6C2N6H6) 3] (OH) 3, forms rose-red crystals which melt with decomposition near 200° and are insoluble in water and alcohol. The compound absorbs carbon dioxide from the atmosphere and liberates ammonia from solutions of ammonium salts on boiling. Boiling water and alkali have no action upon the complex base, but concentrated acids decompose it. The anhydrous material may be obtained by heating the hydrate to 145 to 150° for 24 hours, but it readily absorbs water on exposure to air. The substance is preserved in an atmosphere free from carbon dioxide. 

With cobalt complex catalysts, in polar, aprotic solvents like DME it is often possible to get a-keto acids by controlled double carbonylation874-877. Alternatively, a-hydroxy acids are formed when benzyl halides are carbonylated in the presence of calcium hydroxide, in aqueous media878. Presumably the initially formed a-keto acid is reduced in the Meerwein-Ponndorf fashion to give the a-hydroxy group878. 

The base-catalyzed hydrolyses of cobalt complexes are generally first order in hydroxide—that is,... 

Finally, the hydroxide-catalyzed hydrolyses of cobalt complexes does not appear to be subject to steric hindrance (as a mechanism involving direct displacement should be), for when bulky organic groups are incorporated into the complex, basic hydrolysis is accelerated rather than retarded. 

The X-ray method was first applied (52) to a chelated inorganic molecule4) in the case of the most accessible product of the reaction of aqueous L(+)alanine with cobalt(III) hydroxide, the violet crystalline, a(+)-[Co(L-ala)s]. The absolute configuration of L(+)alanine is known and could be projected only on to the configuration shown. The configuration of the whole complex (IV) was thus established as D. 

Co(in) complexes promote similar reactions. When four of the six octahedral positions are occupied by amine ligands and two cis positions are available for further reactions, it is possible to study not only the hydrolysis itself, but the steric preferences of the complexes. In general, these compounds catalyze the hydrolysis of N-terminal amino acids from peptides, and the amino acid that is removed remains as part of the complex. The reactions apparently proceed by coordination of the free amine to cobalt, followed either by coordination of the carbonyl to cobalt and subsequent reaction with OH or H2O from the solution (path A in Figure 12-15) or reaction of the carbonyl carbon with coordinated hydroxide (path B). As a result, the N-terminal amino acid is removed from the peptide and left as part of the cobalt complex in which the a-amino nitrogen and the carbonyl oxygen are bonded to the cobalt. Esters and amides are also hydrolyzed by the same mechanism, with the relative importance of the two pathways dependent on the specific compoimds used. 

Boas et al. prepared and separated the meridional isomers of the [Co(ai-02)2] type complexes (oti-a2 represents the dianion of the dipeptide H2 i-a2> where ai is the N-terminal residue). Seven methods were used to prepare bis(dipeptidato)-cobaltate(III) complexes (i) by oxygenation of cobalt(II), (ii) from cobalt(II) carbonate, (iii) from sodium tricarbonatocobaltate(III), (iv) from hexaamminecobalt-(III) chloride, (v) from hexakis(urea)cobalt(III) perchlorate, (vi) from cobalt(III) hydroxide oxide, (vii) from triammine(glycylglycinato)cobalt(III). The methods starting from Co" gave more minor products, Na3[Co(C03)3] 3 H2O gave less, and cobalt(III) hydroxide oxide gave very little of these products. Thus, the method (vi) was prefered. The peptides used were gly-gly, L-ala-gly, gly-L-ala, L-leu-gly, gly-L-leu, L-phe-gly, gly-L-phe, L-ala-L-ala, L-ala-D-ala, L-leu-L-leu. 

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