Oxidizing agents cobalt compounds

A promising new battery now under development employs unusual iron(VI) compounds at the anode. Because iron(VI) is such a strong oxidizing agent, its compounds are normally very unstable, but these problems seem to have been solved by removing contaminants such as cobalt and nickel. These so-called super-iron batteries reportedly can furnish 50% more energy than conventional dry cell batteries. 

MetaUic cobalt dissolves readily in dilute H2SO4, HCl, or HNO to form cobaltous salts (see also Cobalt compounds). Like iron, cobalt is passivated by strong oxidizing agents, such as dichromates and HNO, and cobalt is slowly attacked by NH OH and NaOH. 

Beccalli et al. reported a new synthesis of staurosporinone (293) from 3-cyano-3-(lH-indol-3-yl)-2-oxo propionic acid ethyl ester (1464) (790). The reaction of 1464 with ethyl chlorocarbonate and triethylamine afforded the compound 1465, which, on treatment with dimethylamine, led to the corresponding hydroxy derivative 1466. The triflate 1467 was prepared from 1466 by reaction with trifluoromethanesulfonic anhydride (Tf20) in the presence of ethyldiisopropylamine. The palladium(O)-catalyzed cross-coupling of the triflate 1467 with the 3-(tributylstannyl)indole 1468 afforded the vinylindole 1469 in 89% yield. Deprotection of both nitrogen atoms with sodium ethoxide in ethanol to 1470, followed by photocyclization in the presence of iodine as the oxidizing agent provided the indolocarbazole 1471. Finally, reductive cyclization of 1471 with sodium borohydride-cobaltous chloride led to staurosporinone (293) in 40% yield (790) (Scheme 5.248). 

The effect is so pronounced that covalent compounds of cobalt(II) can decompose water with liberation of hydrogen, whereas the cobalt(III) ion decomposes water with liberation of oxygen, being one of the most powerful oxidizing agents know. The explanation is contained in Figure 6-3. In the ions CO++, Co+++, Fe++, and Fe H+ there is room for all unshared electrons in the 3d orbitals and inner orbitals. When octahedral bonds are formed in the covalent complexes, with use of two of the 3d orbitals, only three 3d orbitals are left for occupancy by unshared electrons. These are enough for bipositive and tripositive iron and for tripositive cobalt, but they can hold only six of the seven outer unshared electrons of bipositive cobalt. The seventh electron must... 

In aqueous solutions and in the absence of contplexing agents, cohalt compounds are stahlc only in the 2+ oxidation (cobaltous) state. In the complexcd state the cobaltous ion is relatively unstable, being readily oxidized to the 3+ oxidation (cohallic) slate. An extremely large number of 3-t- complex ions have been idenlilied. most of which are quite stable in aquenus media... 

Like silver, Co(III) is also a powerful oxidizing agent with E° = 1.82 V. Co(II) in HNO3 has been employed to degrade different organic compounds [70,71,73,74] by using separators to prevent Co electrodeposition. In acidic aqueous media, the oxidation of Co(II) to Co(III) has less than 100% current efficiency because it occurs at a more positive potential than water. Cobalt has the advantage over silver in that cobalt chloride complexes are... 

The cobalt-silicon compounds described here undergo reactions with protonic molecules such as hydrogen chloride, Lewis bases such as trimethylamine, and oxidizing agents. 

It is of interest that covalent compounds of bivalent cobalt can decompose H2O with liberation of H2, whereas the trivalent cobalt ion decomposes H2O, liberating O2, being one of the most powerful oxidizing agents known (5). These materials should have a use in modern aerospace problems. 

Diindenyl cobalt, Co (09117)2, may be produced by the interaction of indenyl potassium and the ammine [Co (NH ) 4] (SON) 2 in liquid ammonia (87). It forms black lustrous crystals which can be sublimed without decomposition they slowly sinter at 160° and melt rather gradually at about 180°. The compound is very soluble in benzene, ether, and alcohol but less soluble in petroleum ether, forming brown solutions. It is considerably less sensitive to oxidation than the dicyclopentadienyl, Co (05115)2, but powerful oxidizing agents convert it into the yellow [00(09117)2]+ ion (87), which may also be obtained by a Grignard reaction (151). 

E19.4 The oxides Fe04 and C02O9 contain iron and cobalt in oxidation states +8 and +9 respectively, which are not stable for either element. The massive amount of energy required to ionize either Fe to -t8 or Co to +9 cannot be offset by the lattice energy of the oxides, and the two compounds do not exist. Fe(+8) and Co(+9) would be a sufficiently strong oxidizing agent to oxidize some of the 0 anions back to O2. 

The first step in the GC determination of carbon and hydrogen is quantitative oxidation of the sample organic compounds, usually with a catalyst. Copper oxide is commonly used, but the reaction is relatively slow and elevated temperatures of about 900°C are required. With silver permanganate the reaction temperature is reduced to 550°C [34, 35] and with cobalt oxide to 750°C [36, 37] both compounds provide a shorter oxidation time. Other catalytic oxidizing agents, such as nickel oxide [38, 39] and cerium(IV) oxide [40], have been found promising. Platinum can also be used, especially when it is necessary to avoid the retention of any oxidation products by the solid catalyst. 

The first step is performed in liquid phase with air as oxidizing agent under pressures of 3.5-5 atm to maintain liquid conditions. With a cobalt naphthenate-catalyst, temperatures in the range of 120-130 C are adequate, whereas without catalyst the temperatures need to reach 145-150 0. An important feature of the process is the relatively low per-pass conversion of about 15 per cent of the cyclohexane charge. Water formed by the oxidation reaction and impurities in the feedstock such as sulfur-containing compounds and other hydrocarbons are removed azeotropically as reaction proceeds. Unless reaction water is removed, the air-oxidation ceases after about 25-30 per cent conversion. Removal of feed impurities and oxidation by-products results in a clean recycle stream. 

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