Metal carbonyls carbon monoxide

Pyrolysis plant safety - carbon monoxide, metal carbonyls, carcinogens. 

Caution. The following syntheses involve the use or evolution of carbon monoxide, metal carbonyls, and tertiary phosphines. These are toxic materials, and the syntheses must therefore be carried out in a well-ventilated fume hood. 

Metals having a zero oxidation state can still be complexed by a similarly soft bonding ligand such as carbon monoxide. Nickel carbonyl, Ni(CO)4, is a gas used in the nickel refining industry in order to volatilize and purify nickel from its ores. It is interesting to note that... 

In I, the electron pair base character of CO can arise from donation of the lone pair on carbon, while its acid character can arise from utilization of an empty p-orbital on carbon. In MO terms the ir-acidity of CO originates from the interaction of filled orbitals of appropriate symmetry with empty, antibonding orbitals, (iTy ) or (.if ), of CO. Despite lone pairs located formally at both the carbon and the oxygen ends, carbon monoxide behaves as a base only at carbon in metal carbonyls . However, spectroscopic evidence points to the existence of linkage isomerism for carbon monoxide in Au(CO)(OC) obtained by cocondensation of gold vapors and CO at approximately lOK. ... 

Now warm the tube C gently with a flame until it is just too hot to touch—between 60 and 100 —and increase the flow of carbon monoxide. Nickel carbonyl vapor is carried over and decomposes in C, depositing a mirror of nickel on the surfaces. The principle of the Mond process for purifying nickel is to pass carbon monoxide over the metal and then to decompose the nickel carbonyl on the surface of heated nickel balls. Cobalt, the main impurity to be removed, does not react with carbon monoxide under these conditions, and in any case its carbonyl is not volatile. Nickel completely free from cobalt is thus obtained. 

The electron configurations for the transition metals discussed here and in Appendix B are for individual metal atoms in the gas phase. Most chemists work with the transition metals either in the metallic state or as coordination compounds (see Chapter 25). A solid transition metal has a band structure of overlapping d and s orbital levels (see Section 13-7). When transition metal atoms have other types of atoms or molecules bonded to them, however, the electronic configuration usually becomes simpler in that the d orbitals fill first, followed by the next higher s orbital. This is illustrated by Cr, which has a 4s 3d electronic configuration as a free atom in the gas phase. But in the compound Cr(CO)5, chromium hexacarbonyl, which contains a central Cr atom surrounded by six neutral carbon monoxide (or carbonyl) groups, the chromium atom has a 3d electronic configuration. 

The term decarbonylation encompasses all methods of removing carbon monoxide from carbonyl compounds, and several methods of decarbonylation are known. Transition-metal-catalyzed decarbonylation is one of them.[ii... 

During vapometallurgical refining, impure metal obtained by the reduction of nickel oxide is subjected to the action of carbon monoxide forming volatile nickel carbonyl [Ni(CO)4] (carbonyl or Mond process). This reaction is reversed by heat, and the nickel carbonyl decomposes to pure nickel metal and carbon monoxide. The carbonyl process produces the purest nickel (99.97% or more) [47-51]. 

A related version of great economic interest is the Fischer-Tropsch process for reductive conversion of carbon monoxide to hydrocarbons. This reaction is catalyzed by a number of metals but cobalt and iron have been most closely studied. The key reaction steps are reduction of metal-complexed carbon monoxide and carbonyl insertion reactions. The hydrocarbon chain is built up by a series of successive carbonyl insertion and reduction steps. 

CO. Alkynes will react with carbon monoxide in the presence of a metal carbonyl (e.g. Ni(CO)4) and water to give prop>enoic acids (R-CH = CH-C02H), with alcohols (R OH) to give propenoic esters, RCH CHC02R and with amines (R NH2) to give propenoic amides RCHrCHCONHR. Using alternative catalysts, e.g. Fe(CO)5, alkynes and carbon monoxide will produce cyclopentadienones or hydroquinols. A commercially important variation of this reaction is hydroformyiation (the 0x0 reaction ). 

Cobalt has an odd number of electrons, and does not form a simple carbonyl in oxidation state 0. However, carbonyls of formulae Co2(CO)g, Co4(CO)i2 and CoJCO),6 are known reduction of these by an alkali metal dissolved in liquid ammonia (p. 126) gives the ion [Co(CO)4] ". Both Co2(CO)g and [Co(CO)4]" are important as catalysts for organic syntheses. In the so-called oxo reaction, where an alkene reacts with carbon monoxide and hydrogen, under pressure, to give an aldehyde, dicobalt octacarbonyl is used as catalyst ... 

Nickel tetracarbonyl Ni(CO)4 was the first metal carbonyl to be discovered, by Mond in 1890 it is obtained by passage of carbon monoxide over nickel metal heated to 320 K. It is a volatile, toxic liquid (b.p. 315 K), and has a tetrahedral structure. It has considerable stability, but inflames in air it is believed that in the structure... 

The unit has virtually the same flow sheet (see Fig. 2) as that of methanol carbonylation to acetic acid (qv). Any water present in the methyl acetate feed is destroyed by recycle anhydride. Water impairs the catalyst. Carbonylation occurs in a sparged reactor, fitted with baffles to diminish entrainment of the catalyst-rich Hquid. Carbon monoxide is introduced at about 15—18 MPa from centrifugal, multistage compressors. Gaseous dimethyl ether from the reactor is recycled with the CO and occasional injections of methyl iodide and methyl acetate may be introduced. Near the end of the life of a catalyst charge, additional rhodium chloride, with or without a ligand, can be put into the system to increase anhydride production based on net noble metal introduced. The reaction is exothermic, thus no heat need be added and surplus heat can be recovered as low pressure steam. 

The addition of alcohols to form the 3-alkoxypropionates is readily carried out with strongly basic catalyst (25). If the alcohol groups are different, ester interchange gives a mixture of products. Anionic polymerization to oligomeric acrylate esters can be obtained with appropriate control of reaction conditions. The 3-aIkoxypropionates can be cleaved in the presence of acid catalysts to generate acrylates (26). Development of transition-metal catalysts for carbonylation of olefins provides routes to both 3-aIkoxypropionates and 3-acryl-oxypropionates (27,28). Hence these are potential intermediates to acrylates from ethylene and carbon monoxide. 

Ca.rbonylProcess. Cmde nickel also can be refined to very pure nickel by the carbonyl process. The cmde nickel and carbon monoxide (qv) react at ca 100°C to form nickel carbonyl [13463-39-3] Ni(CO)4, which upon further heating to ca 200—300°C, decomposes to nickel metal and carbon monoxide. The process is highly selective because, under the operating conditions of temperature and atmospheric pressure, carbonyls of other elements that are present, eg, iron and cobalt, are not readily formed. 

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

Use of alcohol as a solvent for carbonylation with reduced Pd catalysts gives vinyl esters. A variety of acrylamides can be made through oxidative addition of carbon monoxide [630-08-0] CO, and various amines to vinyl chloride in the presence of phosphine complexes of Pd or other precious metals as catalyst (14). 

Carbon monoxide was discovered in 1776 by heating a mixture of charcoal and 2inc oxide. It provided a source of heat to industry and homes as a component of town gas and was used as a primary raw material in German synthetic fuel manufacture during World War II its compounds with transition metals have been studied extensively (see Carbonyls). Most recently, carbon monoxide emission from vehicle exhausts has been recognized as a primary source of air pollution (qv). 

Carbon monoxide [630-08-0] (qv), CO, the most important 7T-acceptor ligand, forms a host of neutral, anionic, and cationic transition-metal complexes. There is at least one known type of carbonyl derivative for every transition metal, as well as evidence supporting the existence of the carbonyls of some lanthanides (qv) and actinides (1) (see AcTINIDES AND THANSACTINIDES COORDINATION COMPOUNDS). 

Garbonylation of Olefins. The carbonylation of olefins is a process of immense industrial importance. The process includes hydroformylation and hydrosdylation of an olefin. The hydroformylation reaction, or oxo process (qv), leads to the formation of aldehydes (qv) from olefins, carbon monoxide, hydrogen, and a transition-metal carbonyl. The hydro sdylation reaction involves addition of a sdane to an olefin (126,127). One of the most important processes in the carbonylation of olefins uses Co2(CO)g or its derivatives with phosphoms ligands as a catalyst. Propionaldehyde (128) and butyraldehyde (qv) (129) are synthesized industrially according to the following equation ... 

Easily decomposed, volatile metal carbonyls have been used in metal deposition reactions where heating forms the metal and carbon monoxide. Other products such as metal carbides and carbon may also form, depending on the conditions. The commercially important Mond process depends on the thermal decomposition of Ni(CO)4 to form high purity nickel. In a typical vapor deposition process, a purified inert carrier gas is passed over a metal carbonyl containing the metal to be deposited. The carbonyl is volatilized, with or without heat, and carried over a heated substrate. The carbonyl is decomposed and the metal deposited on the substrate. A number of papers have appeared concerning vapor deposition techniques and uses (170—179). 

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