Reversible carbon monoxide

Bennett B, Lemon BJ, Peters JW. 2000. Reversible carbon monoxide binding and inhibition at the active site of the Fe-only hydrogenase. Biochemistry 39 7455-60. 

Estabrook, R.W., Cooper, D.Y. and Rosenthal, O. (1963) The light reversible carbon monoxide inhibition of the stroid C21-hydrolase system of the adrenal cortex. Biochemische Zeitschrfi, 338, 741-755. 

In summary, chain propagation involves alternating reversible carbon monoxide insertion in Pd-alkyl species and irreversible insertion of the olefin in the resulting Pd-acyl intermediates. The overall exothermicity of the polymerization is caused predominantly by the olefin insertion step. Internal coordination of the chain-end s carbonyl group of the intermediate Pd-alkyl species, together with CO/olefin competition, prevents double olefin insertion, and thermodynamics prevent double CO insertions. The architecture of the copolymer thus assists in its own formation, achieving a perfect chemoselectivity to alternating polyketone. 

The first reversible carbon monoxide insertion into the manganese-carbon bond of MnMe(CO)5 and MnPh(CO)5 ... 

Winter A, Shatin L Hyperbaric oxygen in reversing carbon monoxide coma neurologic and psychologic study. New York State Journal of Medicine 70 880-884, 1970... 

The data on the adsorption of carbon monoxide (Table 2) show that as the amount of substitution of Fe for Cr in Cu(FexCr2-x)04 increases the amount of reversible carbon monoxide adsorption decreases and that of irreversible adsorption increases. Increasing Fe content in the catalyst beyond 0.4 brings down the irreversible adsorption of CO. 

Low temperature carbon monoxide sensors based on the reversible carbon monoxide adsorptive poisoning of precious metal electrodes are also being developed by Los Alamos National Laboratory. The addition of metals such as ruthenium to the platinum electrode material greatly improves the hydrogen oxidation kinetics in the presence of CO. An amperometric sensor that senses the CO inhibition of the hydrogen oxidation can be fabricated from a platinum electrode, a proton conductor and a platinum ruthenium alloy electrode. While the... 

All of the above results indicate that ionic copper species are active in the methanol synthesis over Cu-ZnO-AbOs catalysts. Contrary to that, in the dehydrogenation of cyclohexanol to cyclohexanone over reduced Cu-ZnO-AbOa catalysts a correlation was found between activity and reversible carbon monoxide uptake measured by IR spectroscopy, therefore, it was proposed that metallic copper species are the probable active sites in this dehydrogenation reaction. ... 

The water gas shift reaction involves the conversion of water and carbon monoxide into hydrogen and carbon dioxide, typically using a heterogeneous transition metal-oxide catalyst (Scheme 12.1). The reaction is reversible, and under certain conditions the reaction can operate in either the forwards (hydrogen production) or reverse (carbon monoxide production) direction. Promoted iron-oxide catalysts are most prevalent in WGS chemistry, although, by comparison, platinum-group metals exhibit a greater catalytic activity. ... 

Now suppose that in our system only the reversible carbon monoxide adsorption step occurs, that is, the reversible interaction between gaseous carbon monoxide and empty catalyst sites. Then at equilibrium, which also is the steady state. 

Coordinatively Unsaturated Cobalt Carbonyls Relevant to Hydro-formylation. The negative effect of carbon monoxide partial pressure on the rate of hydroformylation was the first indication of the participation of coordinatively unsaturated cobalt carbonyls in the catalysis of aldehyde formation and of the accompanying olefin isomerization. The retarding effect of carbon monoxide has also been observed in cobalt-catalyzed olefin and aldehyde hydrogenation and in various other reactions of cobalt carbonyls as well. It was assumed that in these reactions in fast reversible carbon monoxide dissociation highly reactive coordinatively unsaturated complexes are formed in very low concentrations, undetectable by conventional analytical methods. By using sophisticated new methods, in some cases the detection and characterization of these elusive species has become possible. 

Iron Sulfur Compounds. Many molecular compounds (18—20) are known in which iron is tetrahedraHy coordinated by a combination of thiolate and sulfide donors. Of the 10 or more stmcturaHy characterized classes of Fe—S compounds, the four shown in Figure 1 are known to occur in proteins. The mononuclear iron site REPLACE occurs in the one-iron bacterial electron-transfer protein mbredoxin. The [2Fe—2S] (10) and [4Fe—4S] (12) cubane stmctures are found in the 2-, 4-, and 8-iron ferredoxins, which are also electron-transfer proteins. The [3Fe—4S] voided cubane stmcture (11) has been found in some ferredoxins and in the inactive form of aconitase, the enzyme which catalyzes the stereospecific hydration—rehydration of citrate to isocitrate in the Krebs cycle. In addition, enzymes are known that contain either other types of iron sulfur clusters or iron sulfur clusters that include other metals. Examples include nitrogenase, which reduces N2 to NH at a MoFe Sg homocitrate cluster carbon monoxide dehydrogenase, which assembles acetyl-coenzyme A (acetyl-CoA) at a FeNiS site and hydrogenases, which catalyze the reversible reduction of protons to hydrogen gas. 

This is the reverse of the water-gas shift reaction in the production of hydrogen and ammonia (qv). Carbon dioxide may also be reduced catalyticaHy with various hydrocarbons and with carbon itself at elevated temperatures. The latter reaction occurs in almost all cases of combustion of carbonaceous fuels and is generally employed as a method of producing carbon monoxide. 

Very recently, considerable effort has been devoted to the simulation of the oscillatory behavior which has been observed experimentally in various surface reactions. So far, the most studied reaction is the catalytic oxidation of carbon monoxide, where it is well known that oscillations are coupled to reversible reconstructions of the surface via structure-sensitive sticking coefficients of the reactants. A careful evaluation of the simulation results is necessary in order to ensure that oscillations remain in the thermodynamic limit. The roles of surface diffusion of the reactants versus direct adsorption from the gas phase, at the onset of selforganization and synchronized behavior, is a topic which merits further investigation. 

Catalytic methanation is the reverse of the steam reforming reaction. Hydrogen reacts with carbon monoxide and carbon dioxide, converting them to methane. Methanation reactions are exothermic, and methane yield is favored at lower temperatures ... 

The first and rate-determining step involves carbon monoxide dissociation from the initial pentacarbonyl carbene complex A to yield the coordinatively unsaturated tetracarbonyl carbene complex B (Scheme 3). The decarbonyla-tion and consequently the benzannulation reaction may be induced thermally, photochemically [2], sonochemically [3], or even under microwave-assisted conditions [4]. A detailed kinetic study by Dotz et al. proved that the initial reaction step proceeds via a reversible dissociative mechanism [5]. More recently, density functional studies on the preactivation scenario by Sola et al. tried to propose alkyne addition as the first step [6],but it was shown that this... 

Although the reverse of this reaction cannot be carried out directly, carbon monoxide does react with hydroxide ions in hot alkali to produce formate ions ... 

Some insertion reactions, particularly those of carbon monoxide, are reversible, but many are not. Reactions have also been reported which result in extrusion of Y from M—Y—X, even though the reverse of this process [Eq. (1)] is not known to occur. Elimination of Nj from arylazo... 

Whereas some acyl products, especially RCOMn(CO)5 and RCOCo-(CO)4, easily eliminate carbon monoxide via the reverse of the insertion, others decarbonylate through a different route. For example, the reaction... 

In contrast, dissimilation of acetate may take place by reversal of the pathway used by organisms snch as Clostridium thermoaceticum for the synthesis of acetate from COj. In the degradation of acetate, the pathway involves a dismutation in which the methyl group is successively oxidized via methyl THF to COj while the carbonyl group is oxidized via bound carbon monoxide. Snch THF-mediated reactions are of great importance in the anaerobic degradation of pnrines, which is discussed in Chapter 10, Part 1. 

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