Cobalt carbonate, decomposition

The mauve colored cobalt(II) carbonate [7542-09-8] of commerce is a basic material of indeterminate stoichiometry, (CoCO ) ( (0 )2) H20, that contains 45—47% cobalt. It is prepared by adding a hot solution of cobalt salts to a hot sodium carbonate or sodium bicarbonate solution. Precipitation from cold solutions gives a light blue unstable product. Dissolution of cobalt metal in ammonium carbonate solution followed by thermal decomposition of the solution gives a relatively dense carbonate. Basic cobalt carbonate is virtually insoluble in water, but dissolves in acids and ammonia solutions. It is used in the preparation of pigments and as a starting material in the preparation of cobalt compounds. 

In view of the ready commercial availability and apparent stability of the hexahy-drate, it is probable that the earlier report of explosion on impact, and deflagration on rapid heating [1] referred to the material produced by partial dehydration at 100°C, rather than the hexahydrate [2], The caked crystalline hydrated salt, prepared from aqueous perchloric acid and excess cobalt carbonate with subsequent heated evaporation, exploded violently when placed in a mortar and tapped gently to break up the crystalline mass, when a nearby dish of the salt also exploded [3]. Subsequent investigation revealed the probable cause as heating the solid stable hexahydrate to a temperature ( 150°C) at which partial loss of water produced a lower and endothermic hydrate (possibly a trihydrate) capable of explosive decomposition. This hazard may also exist for other hydrated metal perchlorates, and general caution is urged [4,5],... 

Neither the thermal nor the cobalt-catalyzed decomposition of 3-butene-2-hydroperoxide in benzene at 100 °C. produced any acetaldehyde or propionaldehyde. In the presence of a trace of sulfuric acid, a small amount of acetaldehyde along with a large number of other products were produced on mixing. Furthermore, on heating at 100°C., polymerization is apparently the major reaction no volatile products were detected, and only a slight increase in acetaldehyde was observed. Pyrolysis of a benzene or carbon tetrachloride solution at 200°C. in the injection block of the gas chromatograph gave no acetaldehyde or propionaldehyde, and none was detected in any experiments conducted in methanol. 

Styrene derivatives can be selectively converted to the corresponding benzyl alcohols by molecular oxygen in the presence of bis(dimethylglyoximato)chloro(pyridine)cobalt(III) and sodium tetrahydroborate (equation 242).559 A likely mechanism for this reaction involves insertion of the alkene into the cobalt-hydride bond, followed by 02 insertion into the cobalt-carbon bond, as in equation (11), and decomposition of the peroxide adduct (168) to the ketone, which is reduced to alcohol by NaBH4 (equation 243). 

The decomposition of cobalt carbonate gives cobaltous oxide, C0CO3 —> CoO + C02, but this is easily oxidizable in the air to a higher oxide. The higher oxide reacts as an oxidizing agent towards HC1 and the chloride corresponding to CoO is obtained ... 

Potassium Cobalti-nitrite, K3Co(N02)6. H20, is the most familiar example of this type. It is also known as cobalt yellow and Fischer s salt in honour of its discoverer.1. It is readily prepared by adding potassium nitrite to an aqueous solution of a soluble cobalt salt acidified with acetic acid. It results in a very pure condition when cobalt carbonate is suspended in an aqueous solution containing an equivalent amount of potassium carbonate or nitrite, and treated with nitrous fumes (resulting from the action of nitric acid upon arsenious oxide) until it has suffered complete decomposition.2 The amount of combined water varies from 0 to 4 molecules according to circumstances. 

Ammonium Cobalti-nitrite, 4(NH4)3Co(N02)s.3Ha0, was first prepared in 1856 by Gibbs and Genth. Erdmann 2 obtained it by the action of ammonium nitrite upon cobalt chloride solution acidulated with acetic acid. It may also be obtained by adding semicarbazide to a solution of sodium cobalti-nitrite 3 and by double decomposition of solutions of ammonium chloride and sodium cobalti-nitrite or by addition of nitrous acid to a suspension of cobalt carbonate in the requisite quantity of ammonium nitrite solution.4 In all three cases the salt is precipitated out. 

Cobalt Tetra-carbonyl, Co(C0)4 or Co2(CO)g.—This compound may be prepared by passing carbon monoxide at a pressure of 40 atmospheres over reduced cobalt at 150° C. The higher the pressure the more rapid is the formation of the earbonyl.7 It forms as fine, orange-coloured transparent crystals, which are best preserved by hermetically sealing them in a glass tube in an atmosphere of hydrogen or of carbon monoxide. Upon exposure to air decomposition takes place resulting in the formation of a basic cobalt carbonate. With bromine it yields cobalt bromide and carbon monoxide ... 

The thermal decomposition of cobalt carbonate fitted the Avrami-Erofeev equation with n = 1.37 at 493 K and 2.54 at 543 K [74]. These data were later reanalyzed by Engberg [75] who allowed for an initial reaction, 0.02 and found , = 95 kJ mol, which is close to the Co-O bond dissociation energy (91 kJ mol ). 

Ardizzone. S.. Spinolo, G., and Trasatti, S., The point of zero charge of CO3O4 prepared by thermal decomposition of basic cobalt carbonate, Electrochim. Acta, 40, 2683, 1995. 

The activities of the C03O4 catalysts for N2O decomposition are shown in Fig. 3. The C03O4 catalyst obtained from cobalt carbonate exhibited higher activity than the catalysts obtained from the KBL and HTL phases. The T50 value of the catalyst obtained firm cobalt carbonate (precipitation temperature, 35 °C) was about 180 °C, while those of the catalysts obtained from IfflL (80 °C) and HTL (0 °C) were 302 and 378 °C, respectively. 

Cobalt(II) alkoxides are known and monomeric forms are part of a wider review.413 The interest in these compounds pertains to a potential role in catalysis. For example, a discrete cobalt(II) alkoxide is believed to form in situ from a chloro precursor during reaction and performs the catalytic role in the decomposition of dialkyl pyrocarbonates to dialkyl carbonates and carbon dioxide.414 A number of mononuclear alkoxide complexes of cobalt(II) have been characterized by crystal structures, as exemplified by [CoCl(OC(t-Bu)3)2 Li(THF)].415 The Co ion in this structure and close relatives has a rare distorted trigonal-planar coordination geometry due to the extreme steric crowding around the metal. 

Delpeux S., Szostak K., Frackowiak E., Bonnamy S., Beguin F. High yield of pure multiwalled carbon nanotubes from the catalytic decomposition of acetylene on in-situ formed cobalt nanoparticles. J. Nanosc. Nanotech. 2002 2 481-4. 

The order of addition is important. This procedure affords a solution of high cobalt concentration (approximately 0.2 M) which promotes decomposition of the excess hydrogen peroxide at a desirable rate. Substitution of sodium for potassium hydrogen carbonate makes it impossible to obtain such a high concentration of cobalt in solution. 

The formation of bulk cobalt carbide is quite a slow process since it requires the diffusion of carbon into the cobalt bulk. It was reported that the full conversion of unsupported and reduced Co to Co2C only occurred after 500 h of exposure to pure CO at 230°C. Increasing the reaction temperature resulted in a faster rate of carburization.81 Bulk cobalt carbides are considered to be thermodynamically metastable species, and therefore Co2C will decompose to hep cobalt and graphite, while Co3C will decompose to fee cobalt and methane. Thermal decomposition of bulk carbides under an inert atmosphere is believed to occur at 400°C.81 Hydrogenation of the bulk carbides is believed to be a fast process and occurs around 200°C.82 83... 

A high carbon monoxide pressure ( 5 atmos.) favours the formation of the butane. Possible mechanisms for its formation include homolytic cleavage of the benzyl-cobalt tetracarbonyl complex and recombination of the radicals to generate 2,3-diphenylbutane and dicobalt octacarbonyl, or a base-catalysed decomposition of the benzylcobalt tetracarbonyl complex (Scheme 8.4). The ethylbenzene and styrene could arise from the phenylethyl radical, or from the n-styrene hydridocobalt tricarbonyl complex. 

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