Cobalt ions, oxidation

Oxidations of paraffins with high concentrations of cobalt catalyst have very special characteristics. Such oxidations will proceed at lower temperatures than in the case of lower concentrations of cobalt or with other catalysts, or in the absence of catalysts [10, 18, 60-66]. For example, the high-concentration cobalt-ion oxidation of -butane can be conducted at 100-110 °C compared with 150-180 °C for the other cases. Significantly higher efficiencies to acetic acid are reported (75-84 % vs. about 50-60 %). Co-reductants such as acetaldehyde, MEK, or p-xylene (especially p-xylene [65]) are reported to be useful, but not essential [66]. In high-concentration cobalt-ion catalyzed oxidations, rates are generally lower than in the conventional oxidations. 

These differences are explained by proposing that the high-concentration cobalt-ion oxidation involves a direct initial attack of Co on a electron transfer mechanism [60, 63] ... 

Following eq. (25), the high cobalt-ion oxidation of n-butane is hypothesized to proceed largely through MEK [63, 70]. A possible sequence is ... 

Various ways of overcoming the PTA oxidation problem have been incorporated into commercial processes. The predominant solution is the use of high concentrations of manganese and cobalt ions (2,248—254), optionally with various cocatalysts (204,255,256), in the presence of an organic or inorganic bromide promoter in acetic acid solvent. Operational temperatures are rather high (ca 200°C). A lesser but significant alternative involves isolation of intermediate PTA, conversion to methyl/)-toluate, and recycle to the reactor. The ester is oxidized to monomethyl terephthalate, which is subsequentiy converted to DMT and purified by distillation (248,257—264). 

It is worthwhile to point out that lithium extraction from inverse spinels V[LiM]04, such as V[LiNi]04 and V[LiCo]04 takes place at high voltage, typically between 4 and 5V [153]. Lithium is extracted from the octahedral 16d sites of these spinels with a concomitant oxidation of the divalent nickel or cobalt ions. From a structural point of view, this can be readily understood because lithium must be dislodged from the 16d octahedral sites, which are of low-energy, into neighboring energetically unfavorable 8b tetrahedra, which share all four faces with 16d sites that are occupied by nickel or cobalt and by lithium. Lithium extraction reactions... 

This method involves measurement of the oxidation rate of an aqueous sodium sulfite solution catalyzed by cupric or cobaltous ions. The oxygen absorbed reacts with the sulfite according to the equation ... 

The liquid-phase autoxidation of cyclohexane is carried out in the presence of dissolved cobalt salts. A lot of heterogeneous catalysts were developed for this process but most catalysts lacked stability. The incorporation of cobalt ions in the framework of aluminophosphate and aluminosilicate structures opens perspectives for heterogenization of this process. CoAPO (cobalt aluminophosphate) molecular sieves were found to be active heterogeneous catalysts of this oxidation.133 Site isolation was critical to get active catalysts.134... 

Mechanism 3 involves NiOH in at least three reactions, and Ni(OH)2 as the active Ni reactant in solution. Since increasing the concentration of the complex-ant(s) in solution will reduce the concentration of both unhydrolyzed and hydrolyzed metal ions, arguments of complexation cannot be readily employed to either support or discount this mechanism. However, it has been this author s experience in formulating electroless Co-P solutions with various complexants for Co2+ that improper complexation which results in even a faint precipitate of hydrolyzed cobalt ions yields an inactive electroless Co-P solution. Furthermore, anodic oxidation of hypo-phosphite at Ni anodes does not proceed at a significant rate under conditions where the surface is most probably covered with a passive film of nickel oxide [48], e.g. NiO.H20, which would be expected to oxidize the reducing agent via a cyclic redox mechanism. 

The flow-cell design was introduced by Stieg and Nieman [166] in 1978 for analytical uses of CL. Burguera and Townshend [167] used the CL emission produced by the oxidation of alkylamines by benzoyl peroxide to determine aliphatic secondary and tertiary amines in chloroform or acetone. They tested various coiled flow cells for monitoring the CL emission produced by the cobalt-catalyzed oxidation of luminol by hydrogen peroxide and the fluorescein-sensitized oxidation of sulfide by sodium hypochlorite [168], Rule and Seitz [169] reported one of the first applications of flow injection analysis (FTA) in the CL detection of peroxide with luminol in the presence of a copper ion catalyst. They... 

The question about the competition between the homolytic and heterolytic catalytic decompositions of ROOH is strongly associated with the products of this decomposition. This can be exemplified by cyclohexyl hydroperoxide, whose decomposition affords cyclo-hexanol and cyclohexanone [5,6]. When decomposition is catalyzed by cobalt salts, cyclohex-anol prevails among the products ([alcohol] [ketone] > 1) because only homolysis of ROOH occurs under the action of the cobalt ions to form RO and R02 the first of them are mainly transformed into alcohol (in the reactions with RH and Co2+), and the second radicals are transformed into alcohol and ketone (ratio 1 1) due to the disproportionation (see Chapter 2). Heterolytic decomposition predominates in catalysis by chromium stearate (see above), and ketone prevails among the decomposition products (ratio [ketone] [alcohol] = 6 in the catalytic oxidation of cyclohexane at 393 K [81]). These ions, which can exist in more than two different oxidation states (chromium, vanadium, molybdenum), are prone to the heterolytic decomposition of ROOH, and this seems to be mutually related. 

This expression is valid for oxidation with the excess of bromide ions over cobalt ions (the conditions of fast oxidation of Co3+). The experimental data agree with this dependence. The kp, kp, and Kkp values for three hydrocarbons (343 K, acetic acid) are presented below [206]... 

What is the structure of this Co-Mo-S phase A model system, prepared by impregnating a MoS2 crystal with a dilute solution of cobalt ions, such that the model contains ppms of cobalt only, appears to have the same Mossbauer spectrum as the Co-Mo-S phase. It has the same isomer shift (characteristic of the oxidation state), recoilfree fraction (characteristic of lattice vibrations) and almost the same quadrupole splitting (characteristic of symmetry) at all temperatures between 4 and 600 K [71]. Thus, the cobalt species in the ppm Co/MoS2 system provides a convenient model for the active site in a Co-Mo hydrodesulfurization catalyst. 

The actual schemes of these reactions are very complicated the radicals involved may also react with the metal ions in the system, the hydroperoxide decomposition may also be catalysed by the metal complexes, which adds to the complexity of the autoxidation reactions. Some reactions, such as the cobalt catalysed oxidation of benzaldehyde have been found to be oscillating reactions under certain conditions [48],... 

Miscellaneous Hepatotoxicity stored in 0.01% thymol light sensitive Coronary steal maintains renal blood flow Hepatotoxic avoid in renal impairment Renal toxicity Oxidizes cobalt ion in vitamin B12... 

Transition metals (iron, copper, nickel and cobalt) catalyse oxidation by shortening the induction period, and by promoting free radical formation [60]. Hong et al. [61] reported on the oxidation of a substimted a-hydroxyamine in an intravenous formulation. The kinetic investigations showed that the molecule underwent a one-electron transfer oxidative mechanism, which was catalysed by transition metals. This yielded two oxidative degradants 4-hydroxybenzalde-hyde and 4-hydroxy-4-phenylpiperidine. It has been previously shown that a-hydroxyamines are good metal ion chelators [62], and that this can induce oxidative attack on the a-hydroxy functionality. 

Photoreduction of cobalt(III) complexes can occur under a variety of conditions. Irradition of the charge transfer bands of these systems results only in decomposition with production of cobaltous ion and oxidation of one of the ligands. In some instances photoreduction can be initiated by irradiation of the ligand field transitions. Irradiation of ion pairs formed by these complexes with iodide ion with ultraviolet light also leads to reduction of the complexes. Finally, irradiation of iodide ion in the presence of the complexes leads to reduction. 

Several analogous systems which have been previously studied, may be reexamined in view of the mechanism suggested for the copper-catalyzed oxidative deamination. It was reported by Nyilasi that copper and cobalt ions catalyze the... 

The oxidation of cobaltioxalate by ceric and cobaltic ions which results in the quantitative reduction of the Co(III) to Co(II), simultaneously with the oxidation of the oxalate to CO2 (81), is an outstanding example of this type of reaction. Other analogous cases are the oxidations of cobalti-/>-aldehydo-benzoate by Co(III), MnOr and SsC -Ag (40), and of (NH3)6Co(III)(HCOO)+2 by MnOr yielding partially Co(III) (26). The last case is an example of an intermediate which is long lived enough to react with the oxidant if the latter is present in an appreciable excess. 

The oxidation of aromatic hydroxylamines with peracids in the presence of cupric ions produces nitroso compounds. In the rigorous absence of metallic ions, azoxy compounds are formed [32]. On the other hand, the air oxidation is strongly accelerated by metals, the approximate order of activity based on a kinetic study being cupric s ferric > manganous > nickel chromic > cobaltous ions. Silver and stannous ions appear to have no effect [33]. 

Oxidation of cobalt(ll) to cobalt(lll) by oxygen in the presence of N-hydroxyethylethylenediamine and carbon produces large amounts of ethylenediamine. Other products are formaldehyde, formic acid, and ammonia. The sum of the moles of ethylenediamine and ammonia produced is equal to the total number of moles of cobalt(ll) oxidized. A steady-state concentration of Co(ll)-Co(lll) is established in which the ratio Co(lll)/ Co(ll) = 1.207. Thus cobalt ion behaves as a true catalyst for cleavage of the N-hydroxyethyl-ethylenediamine. The total amount of cobalt(ll) oxidized per unit time, X, was calculated from the derived equation X = 3.8 + 7.0 k2 T — 3.8e-2-2k 1, where k2 = 0.65 hr.—1 The observed rate of formation of ethylenediamine plus ammonia also follows this equation. It is proposed that the cobalt ion serves as a center where a superoxide ion [derived from oxidation of cobalt-(II) by oxygen] and the ligand are brought together for reaction. 

Products of the reaction have been identified as ethylenediamine, formaldehyde, formic acid, and ammonia. A kinetic evaluation of rate experiments indicates that for each cobalt (II) ion oxidized either one molecule of ethylenediamine or one molecule of ammonia appears. 

To test the validity of the assumption that one cobalt (II) ion is oxidized to cobalt (III) for each ammonia or ethylenediamine molecule formed, a kinetic expression for the total amount of cobalt (II) oxidized was derived. The values of total cobalt (II) oxidized as calculated from this expression were compared with the experimentally determined sums of the amount of ethylenediamine and ammonia formed. 

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