Active carbon dioxide

He mechanism of the reaction appears to involve the attack by an activated carbon dioxide molecule at the activated ortho position in the phenoxide ion ... 

G. Prakash, G. K. S. Efficient Chemoselective Carboxylation of Aromatics to Arylcarboxylic Acids with Superelectrophilically Activated Carbon Dioxide-Al2CI6/Al System. J. Am. Chem. Soc. 2002, 124, 11379-11391. (d) Klumpp, D. A. Rendy, R. McElrea, A. Superacid Catalyzed Ring-opening Reactions Involving 2-Oxazolines and the Role of Superelectrophilic Intermediates. Tetrahedron Lett. 2004, 45, 7959-7961. 

As seen, the transformation into the anion-radical is a very effective way to activate carbon dioxide. 

Biotin reacts with an oxidized carbon fragment (denoted as CO2) and an energy-rich compound, adenosine triphosphate (ATP), to form carboxy biotin, which is activated carbon dioxide. Biotin is firmly bound to its enzyme protein by a peptide linkage. Biotin and carboxy biotin are ... 

The difficulty to transform CO2 into other organic compounds lies in its high thermodynamic stability. Typical activation energies for the dissociation and recombination ofC02 are of 535 and 13 kJ/mol, respectively [5], The activation can occur by photochemical or electrochemical processes, by catalytic fixation or by metal-ligand insertion mechanisms. As documented in different reviews, organometallic compounds, metallo-enzyme sites and well defined metallic surfaces are able to activate carbon dioxide [6-16],... 

To activate carbon dioxide for chemical reactions, it is advantageous to fix and destabilize this rather inert molecule. An important strategy to control and influence the reactivity of CO2 is its coordination to amines, metal-bound imido moieties, or metal centers (144), which leads to a decrease of the CO bond order, while the molecule in most cases becomes considerably bent. In biochemical pathways, the CO2 adduct of the coenzyme biotin (17) is involved in various carboxylation and transcarboxylation reactions (146). Similar structural motifs could become important functional building blocks for bioinspired photoreactions involving carbon dioxide activation steps (Fig. 18). 

The quantities of carbon stored in the form of atmospheric carbon dioxide, CO2 in the hydrosphere and carbonates in the terrestrial environment, substantially exceed those of fossil fuels. In spite of this, the industrial use of carbon dioxide as a source of chemical carbon is presently limited to preparation of urea and certain carboxylic acids as well as organic carbonates and polycarbonates. However, the situation is expected to change in the future, if effective catalytic systems allowing to activate carbon dioxide will become available. In this connection, the electrochemical reduction of CO2, requiring only an additional input of water and electrical energy, appears as an attractive possibility. 

Ryan B. Prince was born in Robbinsdale, MN, in 1972. He graduated from Southeast Missouri State University in 1995 with his B.S. degree in Chemistry, where he worked for Professor Jin K. Gong on the synthesis and characterization of transition-metal complexes that bind and activate carbon dioxide. He then went to the University of Illinois and worked with Professor Jeffrey S. Moore on the synthesis and study of oligo(m-phenylene ethynylene) foldamers. He completed his Ph.D. degree in Organic Chemistry in 2000 and is currently a senior research chemist at 3M Company in St. Paul, MN. 

Scheme 16.16 Electrochemically activated carbon dioxide in the synthesis of cyclic carbonates and unsymmetiical carbonates and carbamates (Reprinted from Ref. [132] and [133] with kind permission of Elsevier)...

The synthesis of cyclic carbonates in RTILs, via cycloaddition of cathodically activated carbon dioxide to epoxide, has been reported by Deng et al. [139]. Ionic liquids, saturated with CO by bubbling at normal pressure and containing the epoxidic substrate, were electrolyzed in an undivided cell (Cu as cathode. Mg or Al as sacrificial anode). The electrolyses were carried out under potentiostatic conditions at a potential negative enough to the selective reduction of CO to CO (E=-2.4 V vs. 

Scheme 16.17 Synthesis of cyclic carbonates in RTILs, via cycloaddition of cathodiceilly activated carbon dioxide to epoxide (Reprinted from Ref. [139] with kind permission of The Royal Society of Chemistry)...

Scheme 16.18 Synthesis of carbamates, from amines and electrochemicaUy activated carbon dioxide, in ionic liquid solutions (Reprinted from Ref [140] with kind permission of The American Chemical Society)...

A non-catalyzed method to activate carbon dioxide is conversion with methane to synthesis gas using an argon plasma (Equation 3.6) [89-91]. 

Long-term oxygen therapy has been shown to improve the client s quality of life and survival. The oxygen must be kept between 1 and 3 L/min to prevent respiratory failure, which occurs when the oxygen level is increased and the client s hypoxic drive is no longer active. Carbon dioxide narcosis occurs in clients with COPD and eliminates that stimulus for breathing. 

The facultative microorganisms which become dominant as the oxygen is depleted by the aerobes are commonly called acid formers. As the name implies, organic acids are major products of their activity. Carbon dioxide remains the major major gaseous product, and less heat is generated. Due to the similarity of products generated in this phase and the aerobic phase, it is extremely difficult to distinguish between the two in practice. In many cases, this phase may actually never become dominant. However, its transitory function is very relevant to the overall decomposition process. 

Activated carbon dioxide. Copper(I) cyanoacetate transfers carbon dioxide... 

It is the control of the reactivity of this carbamate anion which has allowed us to generate in quantitative yields either urethanes or isocyanates directly. By understanding those factors which promote the nucleophilicity of the carbamate oxygen, we have discovered how to generate urethanes directly from either primaiy or secondary amines (Activated Carbon Dioxide Chemistry-I (ACDC-I) (12, 13, 15-18). A key aspect of this chemistry was our discovery that carbamate anions can serve as excellent nucleophiles, when a suitable tertiary amine base is utilized to generate the carbamate anion in the reaction of carbon dioxide with a primary or secondary amine (equation 4). By proper choice of the tertiary amine co-base, which in general does not react with CO2 under the mild conditions employed. 

Ammonium sulfate Calcium acetate Calcium chloride Calcium hydroxide Calcium sulfate Candida guilliermondii Candida lipolytica Carbohydrase Carbon, activated Carbon dioxide... 

In this catalytic reaction the nickel plays a dual role first, it activates the aryl halide and makes its r uction more easy, and then it activates carbon dioxide. In such reactions, the carboxylation steps are found to occur within the coordination shell of the metal. 

Subsequently, the Monsanto researchers developed a variation of this activated carbon dioxide chemistry process whereby activated carbamate anions derived from primary amines could be reacted rapidly with electrophilic dehydrating agents, such as acid halides, to produce the corresponding isocyanates in excellent yields, according to the following reaction ... 

This has proven to be a very versatile reaction, which can start with a variety of electrophilic dehydrating agents and organic bases. Furthermore, the mild reaction conditions allow for the use of amine precursors, which can possess a number of different functional groups. Thus the Monsanto activated carbon dioxide process not only eliminates the use of phosgene as a starting material, but also provides additional benefits, including milder reaction conditions, urethane and isocyanate products in quantitative yields, reductions in problem impurities and by-products, and broader possibilities in choice of amine feedstock. 

Casadei MA, Moracci FM, Zappia G, Inesi A, Rossi L (1997) Electrogenerated superoxide-activated carbon dioxide. A new mild and safe approach to organic carbamates. J Org Chem 62 6754-6759... 

Pyruvate carboxylase is a mitochondrial enzyme which requires Mg and biotin as a carrier of activated carbon dioxide. In addition, it has an absolute requirement for acetyl-CoA, which acts as an allosteric activator (page 340). In this way the accumulation of acetyl-CoA normally triggers the formation of oxaloacetate. If ATP is in short supply, oxaloacetate will combine with some of the acetyl-CoA to form citrate, and so be drawn into the citrate cycle. On the other hand, if there is a surplus of ATP, both this and the oxaloacetate will be used for gluconeogenesis. 

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