Carbon dioxide, electron acceptor

Hypothesis 2. Diffusion of DOC and sulfate from confining bed pore waters provides sources of electron donor (organic carbon) and electron acceptor (sulfate). Carbon dioxide produced by this reaction drives shell material dissolution/ calcite cement precipitation which can explain the major ion and carbon isotope composition of Black Creek aquifer water. 

Chemical Properties The formation of salts with acids is the most characteristic reaction of amines. Since the amines are soluble in organic solvents and the salts are usually not soluble, acidic products can be conveniendy separated by the reaction with an amine, the unshared electron pair on the amine nitrogen acting as proton acceptor. Amines are good nucleophiles reactions of amines at the nitrogen atom have as a first step the formation of a bond with the unshared electron pair of nitrogen, eg, reactions with acid anhydrides, haUdes, and esters, with carbon dioxide or carbon disulfide, and with isocyanic or isothiocyanic acid derivatives. 

The second type of biological process is a direct treatment process, in which bacteria oxidize the sulfur species. This oxidative desulfurization reaction is carried out in the presence of an electron acceptor (such as nitrate, NOs ), a source of carbon (such as carbon dioxide or I ICO, ), and a source of reduced nitrogen (such as ammonia). The... 

Concerning the reduction step of the redox reaction, the heterotrophic microorganisms may use different electron acceptors. If oxygen is available, it is the terminal electron acceptor, and the process proceeds under aerobic conditions. In the absence of oxygen, and if nitrates are available, nitrate becomes the electron acceptor. The redox process then takes place under anoxic conditions. If neither oxygen nor nitrates are available, strictly anaerobic conditions occur, and sulfates or carbon dioxide (methane formation) are potential electron acceptors. Table 1.1 gives an overview of these process conditions related to sewer systems. 

In the case of fermentation, the carbon and energy source is broken down by a series of enzyme-mediated reactions that do not involve an electron transport chain. In aerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which oxygen serves as an external electron acceptor. In anaerobic respiration, the carbon and energy source is broken down by a series of enzyme-mediated reactions in which sulfates, nitrates, and carbon dioxide serve... 

For anion-radicals, air (i.e., oxygen, carbon dioxide, and water [moisture]), on the whole, is an active component of the medium and so it should be removed before conducting reactions. Understandably, air inhibits anion-radical reactions The anion-radicals primarily formed are consumed at the expense of oxidation, carboxylation, and protonation. Certainly, oxidation can take place only if the acceptor organic molecule possesses a lower affinity for an electron than oxygen does or if one-electron oxidation of the anion-radical by oxygen proceeds more rapidly than the anion-radical decomposition into a radical and an anion (RX R + X ). 

The radical-anions from from alkenes with electron withdrawing substituents will add to carbon dioxide [28]. This process involves the alkene radical-anion, which transfers an electron to carbon dioxide for which E° = -2.21 V vs. see [29]. Further reaction then occurs by combination of carbon dioxide and alkene radcal-anions [30]. The carbanion centre formed in this union may either be protonated or react with another molecule of carbon dioxide. If there is a suitable Michael acceptor group present, this carbanion undergoes an intramolecular addition reaction... 

Anaerobic CP degradation involves sequential reductive dehalogenations with MCPs or DCPs as final metabolites, or degradation may proceed to complete dechlorination to phenol, further transformation to benzoate and, ultimately, conversion to methane and carbon dioxide. Reductive dechlorination of PCP, for example, results in the formation of meta- or para-CPs as the end-products (e.g., Woods et al., 1989 Madsen Aamand, 1992), or anaerobic degradation may continue to complete mineralization (Boyd Shelton, 1984 Mohn Kennedy, 1992 Wu et al., 1993). In reductive dechlorinations, CPs serve as electron acceptors and need a suitable electron donor. 

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