Carbon dioxide proton production from

The reaction was second order in acid and first order in substrate, so both rearrangements and the disproportionation reaction proceed via the doubly-protonated hydrazobenzene intermediate formed in a rapid pre-equilibrium step. The nitrogen and carbon-13 kinetic isotope effects were measured to learn whether the slow step of each reaction was concerted or stepwise. The nitrogen and carbon-13 kinetic isotope effects were measured using whole-molecule isotope ratio mass spectrometry of the trifluoroacetyl derivatives of the amine products and by isotope ratio mass spectrometry on the nitrogen and carbon dioxide gases produced from the products. The carbon-12/carbon-14 isotope... 

Because of thetr electron deficient nature, fluoroolefms are often nucleophihcally attacked by alcohols and alkoxides Ethers are commonly produced by these addition and addition-elimination reactions The wide availability of alcohols and fliioroolefins has established the generality of the nucleophilic addition reactions The mechanism of the addition reaction is generally believed to proceed by attack at a vinylic carbon to produce an intermediate fluorocarbanion as the rate-determining slow step The intermediate carbanion may react with a proton source to yield the saturated addition product Alternatively, the intermediate carbanion may, by elimination of P-halogen, lead to an unsaturated ether, often an enol or vinylic ether These addition and addition-elimination reactions have been previously reviewed [1, 2] The intermediate carbanions resulting from nucleophilic attack on fluoroolefins have also been trapped in situ with carbon dioxide, carbonates, and esters of fluorinated acids [3, 4, 5] (equations 1 and 2)... 

Hydrogen transfer reactions are highly selective and usually no side products are formed. However, a major problem is that such reactions are in redox equilibrium and high TOFs can often only be reached when the equilibria involved are shifted towards the product side. As stated above, this can be achieved by adding an excess of the hydrogen donor. (For a comparison, see Table 20.2, entry 8 and Table 20.7, entry 3, in which a 10-fold increase in TOF, from 6 to 60, can be observed for the reaction catalyzed by neodymium isopropoxide upon changing the amount of hydrogen donor from an equimolar amount to a solvent. Removal of the oxidation product by distillation also increases the reaction rate. When formic acid (49) is employed, the reduction is a truly irreversible reaction [82]. This acid is mainly used for the reduction of C-C double bonds. As the proton and the hydride are removed from the acid, carbon dioxide is formed, which leaves the reaction mixture. Typically, the reaction is performed in an azeotropic mixture of formic acid and triethylamine in the molar ratio 5 2 [83],... 

The carbon dioxide anion-radical was used for one-electron reductions of nitrobenzene diazo-nium cations, nitrobenzene itself, quinones, aliphatic nitro compounds, acetaldehyde, acetone and other carbonyl compounds, maleimide, riboflavin, and certain dyes (Morkovnik and Okhlobystin 1979). The double bonds in maleate and fumarate are reduced by CO2. The reduced products, on being protonated, give rise to succinate (Schutz and Meyerstein 2006). The carbon dioxide anion-radical reduces organic complexes of Co and Ru into appropriate complexes of the metals(II) (Morkovnik and Okhlobystin 1979). In particular, after the electron transfer from this anion radical to the pentammino-p-nitrobenzoato-cobalt(III) complex, the Co(III) complex with thep-nitrophenyl anion-radical fragment is initially formed. The intermediate complex transforms into the final Co(II) complex with the p-nitrobenzoate ligand. 

Carbon dioxide reduction is thought to proceed via metallocarboxylate intermediate (s) formed by coordination of CO2 to the electron-rich Re center, although discrete steps in the process cannot be unambiguously assigned. The timing of Cl displacement from and CO2 adduction to the Re(bpy) (CO)3 unit are important mechanistic parameters. Most interpretations are based on a one-electron pathway, involving the interaction of CO2 with the product of Eq. (5) a two-electron pathway, involving interaction of CO2 with the product of Eq. (6) or a combination of these steps. Additional mechanistic considerations are the role dimeric rhenium intermediates and likely proton sources. 

In biochemical decarboxylation reactions where the reactant contains a 3-keto group, the e-amino group of a lysyl side chain of the protein backbone can form an iminium derivative with the substrate.82 Upon loss of carbon dioxide, the delocalized, weakly basic product will not react faster than carbon dioxide can separate. Benner83 showed that the stereochemical consequence of decarboxylation of acetoacetate by acetoacetate decarboxylase involves protonation of the product from either face, consistent with a passive, uncatalyzed step, which is consistent with the view we have presented. 

The mechanism of CDI-mediated acylation of amines is well understood. The first step involves a partial protonation of the basic imidazole-nitrogen, protonated A-acetylimidazole has a p a of 3.6,f l leading to an activated species which is then attacked by the carboxylate. The resulting mixed anhydride extrudes carbon dioxide giving rise to A-acylimidazole which on treatment with an amine compound leads to the desired anoide (Scheme 1). An important advantage of this method over the carbodiimide method is that the byproducts carbon dioxide and imidazole are readily and quantitatively separated from the reaction product by simple washing procedures. 

The a-exomethylene-y-lactone framework has been successfully constructed via two electrosynthetic pathways, that is, both by the direct and by the concerted decarboxylation processes as mentioned earlier [Eq. (45)] [151]. The electrodecarboxylation of XCa is probably initiated by a one-electron oxidation of the sulfur atom, giving first the cation radical (XCb) and subsequently a concerted elimination of the thiyl radical and carbon dioxide to LXXXIX. On the other hand, the electrochemical decarboxylation of LXXXVIIIa involves an El-type elimination of a proton from the cation intermediate (LXXXVIIIb) generated from direct two-electron oxidation of the carboxyl group. The latter method generally requires a higher oxidation potential than that required for the concerted method. Therefore, the concerted electrodecarboxylation method becomes more advantageous, especially when the substrates or products are unstable under oxidative conditions. 

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