Reduction Of Cobalt Research Articles

Kinetics of cobalt(III) reduction. 1. Reaction in aqueous solution of p-toluic acid

Kinetics of cobalt(III) reduction. 1. Reaction in aqueous solution of p-toluic acid

ChemInform Abstract: Kinetics of the Reduction of Cobalt(III) Amine Complexes by 1‐Hydroxy‐1‐methylethyl Radicals

In order to better understand the rate constants for the reduction of several cobalt complexes by 1-hydroxy-1-methylene radicals ({sup {sm bullet}}C(CH{sub 3}){sub 2}OH), the reactions of {sup {sm bullet}}(CH{sub 3}){sub 2}OH with several cobalt(III) complexes of bidentate amines have been studied. The Marcus-Hush theory was deemed the most appropriate for analysis of the kinetic data. The correlation between the kinetics of the reduction of the Co(III) amines by C(CH{sub 3}){sub 2}OH and the reduction of the first d-d band for Co(III) complexes is discussed. 21 refs., 2 figs., 1 tab.

Synthesis of C 2-oxygenates from syngas over cobalt catalysts promoted by ruthenium and alkaline earths

Silica-supported cobalt catalysts doubly modified with ruthenium and alkaline earths were active for the synthesis of C 2-oxygenates (C 2 O) from syngas. Triruthenium dodecacarbonyl was more effective than ruthenium trichloride as a ruthenium precursor. Ruthenium increased the catalytic activity by promoting the reduction of cobalt. Alkaline earths improved the selectivity of C 2 O by controlling the oxidation states of the cobalt catalysts. The chain-growth probabilities of hydrocarbons, oxygenates and total products in the Schultz-Flory equation on a Co Ru Sr/ SiO 2 catalyst were 0.48–0.49.

Kinetics of the reduction of cobalt(III) amine complexes by 1-hydroxy-1-methylethyl radicals

In order to better understand the rate constants for the reduction of several cobalt complexes by 1-hydroxy-1-methylene radicals ({sup {sm bullet}}C(CH{sub 3}){sub 2}OH), the reactions of {sup {sm bullet}}(CH{sub 3}){sub 2}OH with several cobalt(III) complexes of bidentate amines have been studied. The Marcus-Hush theory was deemed the most appropriate for analysis of the kinetic data. The correlation between the kinetics of the reduction of the Co(III) amines by C(CH{sub 3}){sub 2}OH and the reduction of the first d-d band for Co(III) complexes is discussed. 21 refs., 2 figs., 1 tab.

Vitamin B 12 and coenzyme B 12 models. II. An electrochemical investigation on alkyl- and (non-alkyl)cobalt(III) complexes of 3,8-dimethyl-5,6-benzo-4,7-diazadeca-3,7-diene-2,9-dione dioxime by cyclic voltammetry and polarography

An electrochemical investigation has been carried out by polarography and cyclic voltammetry to evaluate the suitability of a new coenzyme B 12 model built upon the quadridentate tetraza equatorial chelate, 3,8-dimethyl-5,6-benzo-4,7-diazadeca-3, 7-diene-2,9-dione dioxime [(DOH) 2bzo] as a non-biological mimic of coenzyme B 12 and to establish a quantitative electrochemical comparison with the cobaloxime and Costa-type models. The (non-alkyl) cobalt(III) complexes of (DOH) 2bzo exhibit two polarographic reduction waves corresponding to the reductions, Co(III)→Co(II) and Co(II)→ Co(I). The alkylcobalt(III) complexes exhibit adsorption/desorption phenomena, and the E 1/2 values have been obtained under conditions where the absorption/desorption processes and RCo decomposition have been suppressed by the externally added base. The cyclic voltammograms of both alkyl and (non-alkyl)cobalt(III) complexes consist of two cathodic waves corresponding to the reductions, Co(III)→Co(II) and Co(II)→Co(I) and two anodic waves corresponding to the oxidations, Co(I)→Co(II) and Co(Il)→Co(III). The Δ E p is large for the Co(III)/Co(II) redox couple indicating irreversible electron transfer. For the Co(II)/Co(I) couple, Δ E p is ∼ 60 mV indicating reversible one electron transfer, but the i pc/ i pa is ∼ 0.5 indicating irreversibility. The irreversibility of the Co(III)/Co(II) and Co(II)/Co(I) redox couples can be attributed to the breaking of the Co-ligand bond in the axial sites during the reduction processes and the generation of the five-coordinate cobalt(II) complex, [RCo II(DODOHbzo)] during the reduction of the organocobalt(III) complexes and the generation of the four-coordinate cobalt(I) complex, [Co I(DODOHbzo)] during the reduction of the five-coordinate cobalt(II) complex are envisioned. The i pa/ i pc ratio of 0.5 for the Co(II)/Co(I) redox couple indicates a 50% Co(I) yield probably due to the chemical reaction undergone by 50% of the electrogenerated Co(I). This suggests the involvement of a coupled chemical reaction such as an ECE mechanism. The near constancy of the E pc values for the Co(II)/Co(I) couple of all the complexes indicates that both the axial ligands are lost during the electrolytic conversion of Co(II) to Co(I). The E 1/2 values for both redox couples are more negative for the alkyl complexes than that of the (non-alkyl) complexes indicating the high basicity of the coordinated alkyl groups. The externally added base has a pronounced effect of increasing the rate of electron transfer and suppressing the RCo decomposition. The organocobalt(III) complexes undergo a quasireversible one electron oxidation without breaking either of the Co-ligand bonds in the axial sites. The E 1/2 value of the Co(IV)/Co(III) redox couple has a marked dependence on the nature of the organic ligand and is very sensitive even to the slight modifications of the Lewis base trans to the organic ligand. The results are discussed in the light of electrochemical studies of other models. of −0.8 which are very close to the Co(III)/Co(II) E 1/2 values of −1.47 V for methyl(solvent)cobinamide and the Co(II)/Co(I) E 1/2 value of −0.74 V for base off Co(II)cobalamin indicating the limitations of oxidation state formalism in deciding a suitable B 12 model. The study of Murakami. [15b] on the cobalt complexes of 1,19-dimethyl-AD-didehydrocorrin (BDHC) and its tetrahydro analogue (TDHC) indicates that the former is a closer electrochemical mimic of vitamin B 12, the E 1/2 being 0.47 V for the Co(III)/CO(II) couple and −0.71 V for the Co(II)/Co(I) couple. Their study also indicates a wide variation in the Co(III)/Co(II) E 1/2 values on the formal charge of the equatorial ligand. The Co(III)/Co(II) E 1/2 values of the cobalt (III) complexes of a family of closely related quadridentate tetraaza equatorial macrocyclic ligands such as (TDHC), aetioporphyrin and octaalkylcorrole, which carry 1−, 2− and 3− charges respectively, span over more than 1 V from +0.97 V for TDHC through +0.3 V for aetioporphyrin to −0.26 V for corrole.

Polarographic and spectrophotometric investigation of the reduction and deprotonation of (1,3,6,8,10,13,16,19-octa-azabicyclo-[6,6,6]-icosane)cobalt(III) ion, Co(sep)3+, in the presence of different anions

The reduction of the title compound has been studied polarographically in different aqueous media. Remarkable specific anion effects have been observed. In the presence of OH– ions there is a strong displacement of E1/2 towards negative values. This has been interpreted as due to a deprotonation of the Co(sep)3+ ion, which can be treated as an association with OH–. Using the DeFord–Hume equation, the association constants have been determined at a constant ionic strength (I) of 0.5 mol dm–3(NaCl). Values of 50 mol dm–3 and 2 × 103 mol3 dm–9 have been obtained for β1 and β3, whereas β2 appears to be too small to be measured. These results are supported by visible spectrophotometric and circular dichroism data. Analogous polarographic measurements were performed at I= 0.4, 1.0 and 2.0 mol dm–3. The differences between the results in the various media, as well as the changes in E1/2 in neutral solutions with different supporting electrolytes, are correlated with the effects of the different salts on the solubility in water of benzoic acid and of naphthalene (Setchenov coefficients). Hence, the hydrophobic character of the anions seems to be more relevant than the electrostatic effects.

Kinetics and mechanism of the reduction of cobalt(II) 4,4',4",4"'-tetrasulfophthalocyanine by 2-mercaptoethanol under anoxic conditions

The kinetics and mechanism of reduction of cobalt(II) 4,4’,4’’,4'’’-tetrasulfophthalocyanine by 2-mercaptoethanol to yield cobalt(I) tetrasulfophthalocyanine and 2-hydroxyethyl disulfide under anoxic conditions were investigated and the following rate law was found: v = -d[Co^(II)TSP]_T/dt = k_2K_1[RSH]_T[Co^(II)TSP]_T{2(1 + ɑ_H+ /Ka_1,+ Ka_2/ɑ_H+)(l+ ɑ[RSH]_T)}, where k_2 is a rate constant for the rate-limiting electron-transfer step, and K_1 is the equilibrium constant for the complexation of a CoTSP dimer with thioethanol; K_(a1) and K_(a2) are the apparent acid dissociation constants of HOC_2H_4SH and HOC_2H_4S^-, respectively; ɑ is K_1/(1 + ɑ_(H+)/K_(a1)+ K_(a2)/ɑ_(H+)):ɑ_H+ is the hydrogen ion activity. A nonlinear least-squares fit of the experimental data to the above rate law gave k_2 = 228 ± 3.8 s^(-l) and K_1 = 117 ± 2.5 M^(-1) at 27 oC at µ = 0.4 M.

Catalytic polarographic waves of cobalt(II) in the presence of sodium sulfide (SH− form) in borax – ammonium chloride

The presence of SH− ions in a medium containing ammonia (borax–NH4Cl) and cobalt(II) gives rise to a catalytic cobalt(II) prewave and a catalytic hydrogen wave, both of which manifest more positive potentials than the cobalt(II) reduction wave. The effects of time, sulfide and cobalt concentrations, mercury column height, and gelatine and neutral salts addition are discussed. In addition, the characteristics of the current–time and electrocapillary curves are shown. The results obtained suggest a mechanism whereby a cobalt(II) prewave is produced by a cobalt(II) complex with SH− in the 1:2 relationship. Hydrogen catalytic evolution is attributed to the reduction of a protonated complex.

Electrochemical reduction of cobalt(II), palladium(II), and copper(II) chelates with ?-hydroxylamine oximes at the dropping mercury electrode

1. The degree of oxidation of the metal ion in the chelates of Co, Pd, and Cu with α-hydroxylamine oximes is 2+ according to electrochemial and EPR data. 2. In the first stage of the electroreduction of the investigated chelates of Co with nioxime and of Cu with α-hydroxylamine oxime the degree of oxidation of the metal ion in the complex changes, while in the case of the other compounds the first electrons are probably accepted by mixed molecular orbitals, to which the ligand fragment makes the largest contribution. 3. The electrode reactions of the Co(II) and Pd(II) chelates with α-hydroxylamine oximes are complicated by the catalytic evolution of hydrogen from solutions containing proton donors.

Reducibility of laterite ores

The reducibility of several types of lateritic nickel bearing ores was investigated. The ores were reduced with hydrogen over a temperature range of 673 to 1273 K and reaction times from 5 to 80 minutes. The fraction of nickel, iron, and cobalt reduced to the metallic state was determined by leaching the reacted samples with a bromine-methanol solution followed by atomic absorption analysis for the individual elements. The reducibility of nickel increased with increasing iron concentration of the ore. Increased reduction temperature greatly raised the amount of nickel reduced for ores with high iron concentrations. The cobalt reducibility decreased with increasing iron concentration of the ore. Changes in reduction temperature affected cobalt reduction less than nickel reduction. The observed changes in reducibility have been attributed to the formation of phases which incorporate nickel and cobalt. The major ore components were plotted on the ternary phase diagram of the SiO2+(Al2O3)-MgO-FeO system. It is shown how this plot can be used to predict the reducibility of different types of lateritic ores.

ChemInform Abstract: Oscillations and Complex Mechanisms: O2 Oxidation of Benzaldehyde

The oxidation of benzaldehyde catalyzed by cobalt and bromine is an oscillating reaction in which the concentrations of Co(III) and of dissolved oxygen vary periodically with time. A mechanistic model is proposed in which the reaction alternates between two stages. In stage I the dissolved oxygen concentration is appreciable and benzoyl radicals combine with oxygen, ultimately oxidizing Co(II) to Co(III). In stage II dissolved oxygen is depleted, and benzoyl radicals are oxidized by Co(III). The model gives satisfactory agreement with a number of qualitative and quantitative features. These include the composition of the steady states and the amplitude and period of oscillation for different concentrations of cobalt, bromide, and benzaldehyde. Specific measurements were also made of the kinetics of the reduction of cobalt(III) by mixtures of benzaldehyde and sodium bromide, the stability of a cobalt-bromide complex, and the consumption of /sup 18/O/sub 2/. This last study demonstrates the presence of two major pathways to benzoic acid which differ in the source of oxygen.

Use of gas-diffusion electrodes for high-rate electrochemical reduction of carbon dioxide. II. Reduction at metal phthalocyanine-impregnated electrodes

The use of polytetrafluoroethylene-bonded, carbon gas-diffusion electrodes, prepared with carbon impregnated with metal phthalocyanines, for the electrochemical reduction of carbon dioxide in aqueous, acidic solution has been investigated. High rates of reduction of carbon dioxide to carbon monoxide were demonstrated at electrodes impregnated with cobalt (II) phthalocyanine. In contrast, formic acid, and not carbon monoxide, was produced at low rates at electrodes impregnated with either manganese, copper or zinc phthalocyanine. This marked variation in reaction product on changing the central metal ion of the organometallic complex is rationalized in terms of a reaction mechanism involving, as the first step, the electrochemical reduction of cobalt (II) to cobalt (I).

ChemInform Abstract: Phosphate‐Mediated Electron Transfer During the Reduction of Cobalt(III) Complexes by Titanium(III).

AbstractThe kinetics of the reduction of the well‐characterized complexes (I)‐(VI) by Ti(III) is investigated in LiCl/HCl solution at 25 °C. All the reactions are of first order with respect to each of the reactants.

Oscillations and complex mechanisms: O2 oxidation of benzaldehyde

The oxidation of benzaldehyde catalyzed by cobalt and bromine is an oscillating reaction in which the concentrations of Co(III) and of dissolved oxygen vary periodically with time. A mechanistic model is proposed in which the reaction alternates between two stages. In stage I the dissolved oxygen concentration is appreciable and benzoyl radicals combine with oxygen, ultimately oxidizing Co(II) to Co(III). In stage II dissolved oxygen is depleted, and benzoyl radicals are oxidized by Co(III). The model gives satisfactory agreement with a number of qualitative and quantitative features. These include the composition of the steady states and the amplitude and period of oscillation for different concentrations of cobalt, bromide, and benzaldehyde. Specific measurements were also made of the kinetics of the reduction of cobalt(III) by mixtures of benzaldehyde and sodium bromide, the stability of a cobalt-bromide complex, and the consumption of /sup 18/O/sub 2/. This last study demonstrates the presence of two major pathways to benzoic acid which differ in the source of oxygen.

Phosphate-mediated electron transfer during the reduction of cobalt(III) complexes by titanium(III)

Cinetique du transfert d'electrons entre les complexes de Ti(aq) 6 3+ et Co(dq) 6 3+ contenant des phosphates mono- ou bidentes

ChemInform Abstract: Mechanistic Information from the Effect of Pressure on Outer‐Sphere Electron‐ Transfer Reactions Involving the Reduction of Cobalt(III) by Iron(II) Complexes in Aqueous Solution .

Chemischer InformationsdienstVolume 17, Issue 40 Organoelement Compounds ChemInform Abstract: Mechanistic Information from the Effect of Pressure on Outer-Sphere Electron- Transfer Reactions Involving the Reduction of Cobalt(III) by Iron(II) Complexes in Aqueous Solution . I. KRACK, I. KRACKSearch for more papers by this authorR. VAN ELDIK, R. VAN ELDIKSearch for more papers by this author I. KRACK, I. KRACKSearch for more papers by this authorR. VAN ELDIK, R. VAN ELDIKSearch for more papers by this author First published: October 7, 1986 https://doi.org/10.1002/chin.198640271AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue40October 7, 1986 RelatedInformation

Metal substrate effects upon the kinetics of simple electrochemical reactions: The reduction of cobalt(III) ammines at single-crystal gold faces

The one-electron electroreduction kinetics of Co(NH 3) 3+ 6, Co(NH 3) 5F 2+, Co(NH 3) 5OSO + 3, Co(NH 3) 5NCS 2+, and c-Co(en) 2(NCS) + 2 (en = ethylenediamine) in aqueous perchlorate have been examined at gold (111), (100), (110), and polycrystalline surfaces and compared with those at mercury, silver (110), and polycrystalline silver surfaces. The first three, nominally outer-sphere, processes all exhibit rate constants that are substantially (ca. 10 3 − 10 4-fold) larger at each of the gold faces than at mercury and silver. This rate enhancement is well beyond that attributable to diffuse-layer effects. In contrast, the latter two, thiocyanate-bridged, reactions exhibited smaller variations with the electrode material which are attributable chiefly to differences in the extent of reactant adsorption. A stronger sensitivity of both the extent of adsorption and the electron-transfer kinetics within the adsorbed state was found, however, for c-Co(en) 2(NCS) + 2 reduction at the various single-crystal gold surfaces using very low (≲10 μ M) reactant concentrations, the adsorption being particularly extensive at gold (111). The observed rate variations with the substrate are discussed in terms of current models of heterogeneous kinetics and double-layer structure.

Mechanistic information from the effect of pressure on outer-sphere electron-transfer reactions involving the reduction of cobalt(III) by iron(II) complexes in aqueous solution

Etude des reactions entre Co(NH 3 ) 5 X 3+ (X=H 2 O, py, DMSO) et Fe(CN) 6 4− , entre 288 et 313 K. Parametres d'activation

ChemInform Abstract: Kinetics of Reduction of Cobalt(III) Porphyrins by Fe(II)‐EDTA2‐.

AbstractThe kinetic data of reduction of five water‐soluble ionic complexes (I) and (II) by the Fe(II) complexion of EDTA are determined.

ChemInform Abstract: Kinetics of Reduction of Cobalt(III) Complexes by Viologen Radicals.

ChemInform Abstract: Kinetics of Reduction of Cobalt(III) Complexes by Viologen Radicals.