With Cobalt

In 2009, von Wangelin s group [185] demonstrated an operationally simple biaryl coupling reaction with CoClj to form functionalized biaryl compounds. In fact, the process involved in situ aryl Grig-nard formation from aryl bromides and subsequent homocoupling with the Co catalyst (5 mol%) with 1 atm of bottled air at 0 °C. 

As a final comment, although restricted in its essence to palladium chemistry - but which is nonetheless at the heart of modern cross-coupling arylation reactions - we quote from Astruc [12i], in conclusion, the field of palladium-catalyzed cross-coupling reactions for their work in which Heck, Negishi, and Suzuki were awarded the 2010 Nobel Prize in chemistry is extremely rich and productive and will continue to grow with major synthetic applications and green implications in the future.  

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As already noted, the simple salts in this oxidation state are powerful oxidising agents and oxidise water. Since, also, Co(III) would oxidise any halide except fluoride to halogen, the only simple halide salt is C0F3. Cobalt(lll) Jluoride, obtained by reaction of fluorine with cobalt(II) fluoride it is a useful fluorinating agent. 

Cobaltilll) nitrate Co(N03)3 has been prepared by the reaction of dinitrogen pentoxide with cobalt(III) fluoride. 

Solution polyacrylamides can also be prepared at high polymer soHds by radiation processes (80,81). Polyacrylamides with molecular weights up to 20 million can be prepared by inradiation of acrylamide and comonomers in a polyethylene bag with cobalt-60 gamma radiation at dose rates of 120-200 J/kg-h. The total dose of radiation is controlled to avoid cross-linking. 

Often the aldehyde is hydrogenated to the corresponding alcohol. In general, addition of carbon monoxide to a substrate is referred to as carbonylation, but when the substrate is an olefin it is also known as hydroformylation. The eady work on the 0x0 synthesis was done with cobalt hydrocarbonyl complexes, but in 1976 a low pressure rhodium-cataly2ed process was commerciali2ed that gave greater selectivity to linear aldehydes and fewer coproducts. 

Tetrafluorobenzene. This compouad has beea prepared by fluoriaatioa of hen2ene with cobalt trifluoride and subsequent combination of the dehydrofluoriaation and defluoriaation steps. Its ioni2ation potential is 9.01 V. Nitration gives 2,3,4,5-tetrafluoronitroben2ene [5580-79-0] ia 75% yield, an iatermediate to fluoroquinolone antibacterials (218). 

Pentafluorobenzene. Pentafluoroben2ene has been prepared by several routes multistage saturation—rearomati2ation process based on fluorination of ben2ene with cobalt trifluoride reductive dechlorination of chloropentafluoroben2ene with 10% pabadium-on-carbon in 82% yield (226,227) and oxidation of penta uorophenylbydra2ine in aqueous copper sulfate at 80°C in 77% yield (228). Its ioni2ation potential is 9.37 V. One measure of toxicity is LD q = 710 mg/kg (oral, mouse) (127). 

Hydantoin itself can be detected ia small concentrations ia the presence of other NH-containing compounds by paper chromatography followed by detection with a mercury acetate—diphenylcarba2one spray reagent. A variety of analytical reactions has been developed for 5,5-disubstituted hydantoias, due to their medicinal iaterest. These reactions are best exemplified by reference to the assays used for 5,5-diphenylhydantoiQ (73—78), most of which are based on their cycHc ureide stmcture. Identity tests iaclude the foUowiag (/) the Zwikker reaction, consisting of the formation of a colored complex on treatment with cobalt(II) salts ia the presence of an amine (2) formation of colored copper complexes and (3) precipitation on addition of silver(I) species, due to formation of iasoluble salts at N. ... 

Niobium carbide is used as a component of hard metals, eg, mixtures of metal carbides that are cemented with cobalt, iron, and nickel. Along with tantalum carbide, niobium carbide is added to impart toughness and shock and erosion resistance. The spiraling rise in the price of tantalum has spurred the development of a hafnium carbide—niobium carbide substitute for tantalum carbide (68). These cemented carbides are used for tool bits, drill bits, shovel teeth, and other wear-resistant components turbine blades and as dies in high pressure apparatus (see Carbides). 

The di(hydroxyaLkyl) peroxide (2) from cyclohexanone is a soHd which is produced commercially. The di(hydroxyaLkyl) peroxide (2) from 2,4-pentanedione (11, n = 1 X = OH) is a water-soluble soHd which is also produced commercially (see Table 5). Both these peroxides are used for curing cobalt-promoted unsaturated polyester resins. Because these peroxides are susceptible to promoted decomposition with cobalt, they must exist in solution as equihbrium mixtures with hydroperoxide stmctures (122,149). 

Acetaldehyde can be used as an oxidation-promoter in place of bromine. The absence of bromine means that titanium metallurgy is not required. Eastman Chemical Co. has used such a process, with cobalt as the only catalyst metal. In that process, acetaldehyde is converted to acetic acid at the rate of 0.55—1.1 kg/kg of terephthahc acid produced. The acetic acid is recycled as the solvent and can be isolated as a by-product. Reaction temperatures can be low, 120—140°C, and residence times tend to be high, with values of two hours or more (55). Recovery of dry terephthahc acid follows steps similar to those in the Amoco process. Eastman has abandoned this process in favor of a bromine promoter (56). Another oxidation promoter which has been used is paraldehyde (57), employed by Toray Industries. This leads to the coproduction of acetic acid. 2-Butanone has been used by Mobil Chemical Co. (58). 

Toluhydroquinone and methyl / fX butyUiydroquinone provide improved resin color retention 2,5-di-/-butyIhydroquinone also moderates the cure rate of the resin. Quaternary ammonium compounds, such as benzyl trimethyl ammonium hydroxide, are effective stabilizers in combination with hydroquinones and also produce beneficial improvements in color when promoted with cobalt octoate. Copper naphthenate is an active stabilizer at levels of 10 ppm at higher levels (150 ppm) it infiuences the cure rate. Tertiary butylcatechol (TBC) is a popular stabilizer used by fabricators to adjust room temperature gelation characteristics. 

Many forms of chromatography have been used to separate mixtures of quinoline and isoquinoline homologues. For example, alumina saturated with cobalt chloride, reversed-phase Hquid chromatography, and capillary gas chromatography (gc) with deactivated glass columns have all been employed (38,39). 

Other apphcations of sodium bromide iaclude use ia the photographic iadustry both to make light-sensitive silver bromide [7785-23-1] emulsions and to lower the solubiUty of silver bromides during the developing process use as a wood (qv) preservative in conjunction with hydrogen peroxide (14) as a cocatalyst along with cobalt acetate [917-69-1] for the partial oxidation of alkyl side chains on polystyrene polymers (15) and as a sedative, hypnotic, and anticonvulsant. The FDA has, however, indicated that sodium bromide is ineffective as an over-the-counter sleeping aid for which it has been utilized (16). 

Although an inherently more efficient process, the direct chemical oxidation of 3-methylpyridine does not have the same commercial significance as the oxidation of 2-methyl-5-ethylpyridine. Liquid-phase oxidation procedures are typically used (5). A Japanese patent describes a procedure that uses no solvent and avoids the use of acetic acid (6). In this procedure, 3-methylpyridine is combined with cobalt acetate, manganese acetate and aqueous hydrobromic acid in an autoclave. The mixture is pressurized to 101.3 kPa (100 atm) with air and allowed to react at 210°C. At a 32% conversion of the picoline, 19% of the acid was obtained. Electrochemical methods have also been described (7). 

Zirconium tetrafluoride [7783-64-4] is used in some fluoride-based glasses. These glasses are the first chemically and mechanically stable bulk glasses to have continuous high transparency from the near uv to the mid-k (0.3—6 -lm) (117—118). Zirconium oxide and tetrachloride have use as catalysts (119), and zirconium sulfate is used in preparing a nickel catalyst for the hydrogenation of vegetable oil. Zirconium 2-ethyIhexanoate [22464-99-9] is used with cobalt driers to replace lead compounds as driers in oil-based and alkyd paints (see Driers and metallic soaps). 

Of these dyes, Acid Yellow 151 (37) still has the greatest market among the yellows. As reported by USITC, production had increased to 1989 tons in 1985 from 706 tons in 1975. It is produced by coupling diazotized 2-amino-l-phenol-4-sulfonamide to acetoacetanilide followed by metallizing with cobalt to obtain a 1 2 cobalt complex. Acid Orange 24 (38), which is sulfanilic acid coupled to resorcinol to which diazotized mixed xyUdines have been coupled, is an unsymmetrical primary diasazo dye with a bihinctional coupling component. 

Cemented tungsten carbides also find use as a support for polycrystalline diamond (PCD) cutting tips, or as a matrix alloy with cobalt, nickel, copper, and iron, ia which diamond particles are embedded. These tools are employed ia a variety of iadustries including mineral exploration and development oil and gas exploration and production and concrete, asphalt, and dimension stone cutting. 

Sulfide Ores ores. In the Zairian ores, cobalt sulfide as carroUite is mixed with chalcopyrite and chalcocite [21112-20-9]. For processing, the ore is finely ground and the sulfides are separated by flotation (qv) using frothers. The resulting products are leached with dilute sulfuric acid to give a copper—cobalt concentrate that is then used as a charge in an electrolytic cell to remove the copper. Because the electrolyte becomes enriched with cobalt, solution from the copper circuit is added to maintain a desirable copper concentration level. After several more steps to remove copper, iron, and aluminum, the solution is treated with milk of lime to precipitate the cobalt as the hydroxide. 

Lateritic Ores. The process used at the Nicaro plant in Cuba requires that the dried ore be roasted in a reducing atmosphere of carbon monoxide at 760°C for 90 minutes. The reduced ore is cooled and discharged into an ammoniacal leaching solution. Nickel and cobalt are held in solution until the soflds are precipitated. The solution is then thickened, filtered, and steam heated to eliminate the ammonia. Nickel and cobalt are precipitated from solution as carbonates and sulfates. This method (8) has several disadvantages (/) a relatively high reduction temperature and a long reaction time (2) formation of nickel oxides (J) a low recovery of nickel and the contamination of nickel with cobalt and (4) low cobalt recovery. Modifications to this process have been proposed but all include the undesirable high 760°C reduction temperature (9). 

With cobalt historically being approximately twice the cost of nickel, cobalt-base alloys for both high temperature and corrosion service tend to be much more expensive than competitive alloys. In some cases of severe service their performance iacrease is, however, commensurate with the cost iacrease and they are a cost-effective choice. For hardfaciag or wear apphcations, cobalt alloys typically compete with iron-base alloys and are at a significant cost disadvantage. 

Several nonoccupational health problems have been traced to cobalt compounds. Cobalt compounds were used as foam stabilizers in many breweries throughout the world in the mid to late 1960s, and over 100 cases of cardiomyopathy, several followed by death, occurred in heavy beer drinkers (38,39). Those affected consumed as much as 6 L/d of beer (qv) and chronic alcoholism and poor diet may well have contributed to this disease. Some patients treated with cobalt(II) chloride for anemia have developed goiters and polycythemia (40). The impact of cobalt on the thyroid gland and blood has been observed (41). 

Cobalt as a Colorant in Ceramics, Glasses, and Paints. Cobalt(II) ion displays a variety of colors in soHd form or solution ranging from pinks and reds to blues or greens. It has been used for hundreds of years to impart color to glasses and ceramics (qv) or as a pigment in paints and inks (see CoLORANTS FOR CERAMICS). The pink or red colors are generally associated with cobalt(II) ion in an octahedral environment and the chromophore is typically Co—O. The tetrahedral cobalt ion, Co—chromophore, is sometimes green, but usually blue in color. 

Titanate Pigments. When a nickel salt and antimony oxide are calcined with mtile titanium dioxide at just below 1000°C, some of the added metals diffuse into the titanium dioxide crystal lattice and a yellow color results. In a similar manner, a buff may be produced with chromium and antimony a green, with cobalt and nickel and a blue, with cobalt and aluminum. These pigments are relatively weak but have extreme heat resistance and outdoor weatherabihty, eg, the yellow is used where a light cadmium could not be considered. They are compatible with most resins. 

Potassium. Potassium 2-ethyIhexanoate [3164-85-0] functions best in conjunction with cobalt. Potassium strongly activates cobalt in aqueous coatings and in high soHds paints based on low molecular-weight vehicles. 

Prepa.ra.tlon, There are several methods described in the Hterature using various cobalt catalysts to prepare syndiotactic polybutadiene (29—41). Many of these methods have been experimentally verified others, for example, soluble organoaluminum compounds with cobalt compounds, are difficult to reproduce (30). A cobalt compound coupled with triphenylphosphine aluminum alkyls water complex was reported byJapan Synthetic Rubber Co., Ltd. (fSR) to give a low melting point (T = 75-90° C), low crystallinity (20—30%) syndiotactic polybutadiene (32). This polymer is commercially available. 

Analogously, pyrazolyl-aluminate and -indate ligands have been prepared <75JCS(D)749) and their chelating properties evaluated with cobalt, nickel, copper and zinc. Gallyl derivatives of pyrazoles and indazoles have been extensively studied by Storr and Trotter e.g. 75CJC2944) who determined several X-ray structures of these compounds. These derivatives exist in the solid state as dimers, such as (212) and (288). A NMR study in acetone solution showed the existence of a slow equilibrium between the dimer (212) and two identical tautomers (289) and (290) (Section 4.04.1.5.1) (81JOM(215)157). 

The author is unaware of any commerical polymers that are specifically designed to degrade oxidatively, although oxidation may be involved in association with hydrolytic and biological degradation. It may be of interest to note that before World War II products known as rubbones were produced by degrading natural rubber with cobalt linoleate in the presence of cellulosic materials to produce low molecular weight, fluid oxidised natural rubber (Section 30.4). 

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