Cobalt hydrocarbonyl

Light yellow gas or liquid unstable, decomposes rapidly at ambient temperature solidifies at —26°C (—14°F) boils at 10°C (SOT) slightly soluble in water (0.05%), dissolves in organic solvents. 

The toxic effects are similar to those of nickel tetracarbonyl or iron pentacarbonyl. The acute toxicity, however, is lower than that of these two carbonyls. Inhalation of the gas can cause dizziness, giddiness, and headache. It readily decomposes at room temperature producing toxic carbon monoxide. A 30-minute LC50 in rats is 165 mg/m (Palmes et al. 1959). 

Flammable gas the liquid form can explode when heated in a closed container due to rapid decomposition and heavy pressure buildup. 

---

The cobalt catalyst can be introduced into the reactor in any convenient form, such as the hydrocarbon-soluble cobalt naphthenate [61789-51 -3] as it is converted in the reaction to dicobalt octacarbonyl [15226-74-17, Co2(CO)g, the precursor to cobalt hydrocarbonyl [16842-03-8] HCo(CO)4, the active catalyst species. Some of the methods used to recover cobalt values for reuse are (11) conversion to an inorganic salt soluble ia water conversion to an organic salt soluble ia water or an organic solvent treatment with aqueous acid or alkah to recover part or all of the HCo(CO)4 ia the aqueous phase and conversion to metallic cobalt by thermal or chemical means. 

Rhodium Ca.ta.lysts. Rhodium carbonyl catalysts for olefin hydroformylation are more active than cobalt carbonyls and can be appHed at lower temperatures and pressures (14). Rhodium hydrocarbonyl [75506-18-2] HRh(CO)4, results in lower -butyraldehyde [123-72-8] to isobutyraldehyde [78-84-2] ratios from propylene [115-07-17, C H, than does cobalt hydrocarbonyl, ie, 50/50 vs 80/20. Ligand-modified rhodium catalysts, HRh(CO)2L2 or HRh(CO)L2, afford /iso-ratios as high as 92/8 the ligand is generally a tertiary phosphine. The rhodium catalyst process was developed joindy by Union Carbide Chemicals, Johnson-Matthey, and Davy Powergas and has been Hcensed to several companies. It is particulady suited to propylene conversion to -butyraldehyde for 2-ethylhexanol production in that by-product isobutyraldehyde is minimized. 

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. 

The mechanism of the cobalt-cataly2ed oxo reaction has been studied extensively. The formation of a new C—C bond by the hydroformylation reaction proceeds through an organometaUic intermediate formed from cobalt hydrocarbonyl which is regenerated in the aldehyde-forrning stage. The mechanism (5,6) for the formation of propionaldehyde [123-38-6] from ethylene is illustrated in Figure 1. 

The earhest modification of the Oxo process (qv) employed cobalt hydrocarbonyl, HCo(CO)4, as catalyst. The reaction was carried out in the Hquid phase at 130—160°C and 10—20 MPa (1450—2900 psi) to give a ratio of n- to isobutyraldehyde of between 2 1 to 4 1. / -Butyraldehyde, the straight-chain isomer and the precursor of 2-ethylhexanol, was the more valuable product so that a high isomer ratio of n- to isobutyraldehyde was obviously advantageous. 

Hydroformylation, or the 0X0 process, is the reaction of olefins with CO and H9 to make aldehydes, which may subsequently be converted to higher alcohols. The catalyst base is cobalt naph-thenate, which transforms to cobalt hydrocarbonyl in place. A rhodium complex that is more stable and mnctions at a lower temperature is also used. 

Cobalt hydroformylation of butadiene produced low yields (24%) of an equimolar mixture of n- and isovaleraldehyde (40). It has been established that the cobalt hydrocarbonyl adds to form a stable 7r-allyl complex (93, 94). 

Cobalt hydrocarbonyl is a volatile substance of limited stability at or above ambient temperature. Its tendency to decompose at undesirable sites in a process has posed a severe problem for commercial operations. Consequently, the patent literature contains numerous references to a variety of schemes for selectively removing cobalt from product and converting it to a form suitable for catalytic reuse. 

Extraction of the highly acidic cobalt hydrocarbonyl by aqueous base then phase separation from product, followed by acidification to reform the hydrocarbonyl catalyst. 

X-PetUent + Cobalt Hydrocarbonyl—Effect of Carbon Monoxide 30 Minutes)... 

Toxicology. Cobalt hydrocarbonyl is expected to be a pulmonary irritant. 

Definitive toxicity data for cobalt hydrocarbonyl do not exist because of the rapid decomposition in air of the chemical to a solid particulate. In most cases, exposures are primarily to inorganic cobalt compounds. 

By analogy to nickel carbonyl, acute effects from animal exposures are expected to be pulmonary edema, congestion, and hemorrhage. In humans, nickel carbonyl causes an acute flulike syndrome that subsides and is followed after 12-36 hours by an acute respiratory syndrome. Exposure to cobalt hydrocarbonyl may be expected to produce similar effects. 

Palmes ED, Nelson N, Lasldn S, Kuschner M Inhalation toxicity of cobalt hydrocarbonyl. Am Ind Hyg Assoc J 20 453 68, 1959... 

Occupational safety and health guidelines for chemical hazards—Supplement IV-OHG. Cobalt Hydrocarbonyl, pp 1-8. Publications Dissemination, EID, National Institute for Occupational Safety and Health, Cincinnati, OH, 1995... 

Silca, crystalline-quartz, 628 Chromyl chloride, 175 Fthylidene norbornene, 335 Methomyl, 443 Cobalt hydrocarbonyl, 182 Decaborane, 203 Benomyl, 67 Diborane, 211 Pentaborane, 555 Osmium tetroxide, 546 Cesium hydroxide, 131 Alumina trihydroxide, 38 Aluminum oxyhydroxide, 38 Vinyl toluene, 738 Nonylphenol, 541 2,4-Dinitrotoluene, 279 Trimethyl benzene, 712 Methylcyclohexanol, 465 Terphenyls, 656 Isooctyl alcohol, 409 Anisidine, 52... 

The formation of formate esters in the hydroformylation reaction (90, 64) may be explained by a CO-alkoxide insertion reaction as well as by the CO-hydride insertion mechanism mentioned above. Aldehydes formed in the hydroformylation reaction can be reduced by cobalt hydrocarbonyl (27) presumably by way of an addition of the hydride to the carbonyl group (90, 2). If the intermediate in the reduction is an alkoxycobalt carbonyl, carbon monoxide insertion followed by hydrogenation would give formate esters (90, 64). 

The addition of cobalt hydrocarbonyl to olefins has been investigated and information on the detailed mechanism of the reaction obtained. The reaction of 1-pentene with cobalt hydrocarbonyl to produce a mixture of 1- and 2-pentylcobalt tetracarbonyls was shown to be inhibited by carbon monoxide (46). The inhibition very likely arises because the reactive species is cobalt hydrotricarbonyl rather than the tetracarbonyl. The carbon monoxide, by a mass action effect, reduces the concentration of the reactive species. 

Cobalt hydrocarbonyl is a very reactive compound. It reacts extremely rapidly with triphenylphosphine, probably by a first-order dissociation mechanism, producing cobalt hydrotricarbonyl triphenylphosphine (44). This demonstrates the very ready replacement of one ligand by another. Cobalt hydrocarbonyl also catalyzes the isomerization of olefins. Under conditions of the hydroformylation reaction, olefin isomerization is observed. But there is controversy as to whether or not rearranged aldehydes (aldehydes which cannot be produced by simple addition to the starting olefin) are produced mainly by rearrangement of an intermediate in the reaction (28, 75, 55) or by reaction of isomerized olefins (55). 

Manganese hydrocarbonyl, though much less reactive than cobalt hydrocarbonyl, does add to some activated olefins. Tetrafluoroethylene for example reacted to give tetrafluoroethylmanganese pentacarbonyl (95). 

Cobalt hydrocarbonyl reacts rapidly with conjugated dienes, initially forming 2-butenylcobalt tetracarbonyl derivatives. These compounds lose carbon monoxide at 0°C. or above, forming derivatives of the relatively stable l-methyl-ir-allyl-cobalt tricarbonyl. As with normal alkylcobalt tetracarbonyls, the 2-butenyl derivatives will absorb carbon monoxide, forming the acyl compounds but these acyl compounds also slowly lose carbon monoxide at 0°C. or above, forming 7r-allyl complexes. The acyl compounds can be isolated as the monotriphenylphosphine derivatives (47). 

Metal Hydrides. Metal hydrides generally react readily with acetylenes, often by an insertion mechanism. Cobalt hydrocarbonyl gives complicated mixtures of compounds with acetylenes. The only products which have been identified so far are dicobalt hexacarbonyl acetylene complexes (34). Greenfield reports that, under conditions of the hydroformy lation reaction, acetylenes give only small yields of saturated monoaldehydes (30), probably formed by first hydrogenating the acetylene and then reacting with the olefin. Other workers have identified a variety of products from acetylene, carbon monoxide, and an alcohol with a cobalt catalyst, probably cobalt hydrocarbonyl. The major products observed were succinate esters (74,19) and succinate half ester acetals (19). 

Metal Hydrides. It is likely that the reduction of aldehydes to alcohols by cobalt hydrocarbonyl (27) is an example of a carbonyl insertion reaction with a metal hydride. It is not clear which way the hydrocarbonyl adds to the carbonyl groups —whether it forms a cobalt-carbon bond (2), or a cobalt-oxygen bond (90). 

RCH2OH + Co2(CO)7 (72) A known reaction of cobalt hydrocarbonyl suggests that the cobalt-carbon bond may be preferred. It has been reported that, under rather vigorous conditions, acetaldehyde or formaldehyde react with CO and a cobalt catalyst to give o -hydroxy acids or esters in alcohol solution (7). The intermediate with the carbon-cobalt bond probably is undergoing a CO insertion reaction, folllwed by a hydrolysis or... 

If the formation of formate esters under hydroformylation conditions involves the carbonylation of an alkoxycobalt carbonyl as suggested previously (90), this would be evidence that cobalt hydrocarbonyl adds the reverse way to acyl groups. Since the formation of formate esters can be explained as well by a CO insertion into a cobalt-hydrogen group followed by alcoholysis, however, the data would be explained best if a cobalt-carbon bond was formed in the hydride reduction of acyl compounds. 

Figure C shows carbon monoxide insertion reactions. There are a number of reduction reactions of carbon monoxide catalyzed by transition metals, and these, I believe, all involve an insertion of carbon monoxide into a metal hydride as an initial step. Cobalt hydrocarbonyl reacts with carbon monoxide to give formate derivatives. This is probably an insertion reaction also.

Figure D shows some olefin insertion reactions. Hydride additions to olefins have been known for a long while. Among these many examples, manganese hydrocarbonyl, and cobalt hydrocarbonyl, magnesium hydride, diborane, alkylalu-minum hydrides, germanium and tin hydrides all add quite readily to olefins. These last two cases are questionable because the mechanism is not clear. Some of these additions occur without a catalyst some are speeded up by ultraviolet light some are catalyzed by Group VIII metals. So it is not clear whether all these reactions are the same or whether there are several different mechanisms.

Figure F shows some acetylene insertion reactions. These, too, are similar to the olefin insertion reactions. The manganese and cobalt hydrocarbonyls again add. Chloronickelcarbonyl hydride, which I believe is an intermediate in many of the nickel carbonyl-catalyzed reactions, adds to olefins. Diborane and the aluminum hydrides also add.

Cobalt hydrocarbonyl, diborane, and aluminum hydrides add, I think, to all of these carbonyl compounds. Of course, there is the well known Grignard reagent and the alkyllithium additions to carbonyl compounds. Aluminum alkyls add, and we could have listed all the other alkali metal alkyls. Recent work has shown that the tin alkoxides add readily to all these derivatives, and similarly, a tin amide adds to most of these carbonyl compounds. 

---