Halide ion, oxidation

Huang L, Wojciechowski G, Ortiz de Montellano PR (2005) Prosthetic heme modification during halide ion oxidation. Demonstration of chloride oxidation by horseradish peroxidase. J Am Chem Soc 127 5345-5353... 

Therefore, the chemical modification of the tin dioxide surface during halide ion oxidation (Equations 10.1 and 10.2) is due to the reaction of hypohalogenous acid with the protein side-chains. Actually, during the process, two types of reaction occur i) the oxidation of sulfur atoms and ii) the substitution of the hydrogen (H) of some amine/imine/amide groups, i.e., oxidation and halogenation of the protein side-chains occurs. 

Transition-metal-alkyl bonds can be formed by a variety of reactions that include metathetical replacement of a halide ion, oxidative addition, and insertion of an alkene into a metal-hydride bond. " A similar set of reactions is available for the synthesis of transition-metal-aryl bonds, although the analogous insertion of a benzyne intermediate into a metal-hydride bond is not particularly viable as a synthetic route. For alkyl complexes that have longer chains than methyl, thermal decomposition to give the metal-hydride complex by a j5-hydrogen transfer reaction is frequently observed at ambient temperature. 

From the data available, it appears that for Br, Cl, HN3, and SCN, the rates of reaction with Co +(aq) are influenced by the water-exchange rate on the oxidant, whereas those for I and hydroquinone occur too rapidly ( 2 X 10 and 8 x 10 faster) for this to be a rate-determining factor. The results on the hydrogen peroxide system appear to contrast markedly with those in another studyin which evidence is suggested from stopped-flow traces for two intermediate complexes of the type CoHaOg " and (Co", -HOa ). Studies of the halide ion oxidations have also been carried out in... 

A chain mechanism is proposed for this reaction. The first step is oxidation of a carboxylate ion coordinated to Pb(IV), with formation of alkyl radical, carbon dioxide, and Pb(III). The alkyl radical then abstracts halogen from a Pb(IV) complex, generating a Pb(IIl) species that decomposes to Pb(II) and an alkyl radical. This alkyl radical can continue the chain process. The step involving abstraction of halide from a complex with a change in metal-ion oxidation state is a ligand-transfer type reaction. 

In the arylations of enamines with very reactive aryl halides (352,370) such as 2,4-dinitrochlorobenzene, the closely related mechanistic pathway of addition of the enamine to the aromatic system, followed by elimination of halide ion, can be assumed. The use of n-nitroarylhalides furnishes compounds which can be converted to indolic products by reductive cycliza-tion. Less reactive aryl halides, such as p-nitrochlorobenzene, lead only to N-arylation or oxidation products of the enamines under more vigorous conditions. 

It oxidizes halide ions (except F ) to free halogen. Soluhons of S, Se, Te and Po in H2Se04 are brightly coloured (cf. p. 664). 

Such solutions are necessarily contaminated with halide ions and with the products of any subsequent decomposition of the hypohalite anions themselves. Alternative routes are the electrochemical oxidation of halides in cold dilute solutions or the chemical oxidation of bromides and iodides ... 

It must be noted that impurities in the ionic liquids can have a profound impact on the potential limits and the corresponding electrochemical window. During the synthesis of many of the non-haloaluminate ionic liquids, residual halide and water may remain in the final product [13]. Halide ions (Cl , Br , I ) are more easily oxidized than the fluorine-containing anions used in most non-haloaluminate ionic liquids. Consequently, the observed anodic potential limit can be appreciably reduced if significant concentrations of halide ions are present. Contamination of an ionic liquid with significant amounts of water can affect both the anodic and the cathodic potential limits, as water can be both reduced and oxidized in the potential limits of many ionic liquids. Recent work by Schroder et al. demonstrated considerable reduction in both the anodic and cathodic limits of several ionic liquids upon the addition of 3 % water (by weight) [14]. For example, the electrochemical window of dry [BMIM][BF4] was found to be 4.10 V, while that for the ionic liquid with 3 % water by weight was reduced to 1.95 V. In addition to its electrochemistry, water can react with the ionic liquid components (especially anions) to produce products... 

The critical breakdown potential, which is the positive potential limit of stability of the oxide film. At this potential and more positive potentials, the oxide film is unstable with respect to the action of anions, especially halide ions, in causing localised rupture and initiating pitting corrosion. 

When aluminium is immersed in water, the air-formed oxide film of amorphous 7-alumina initially thickens (at a faster rate than in air) and then an outer layer of crystalline hydrated alumina forms, which eventually tends to stifle the reaction In near-neutral air-saturated solutions, the corrosion of aluminium is generally inhibited by anions which are inhibitive for iron, e.g. chromate, benzoate, phosphate, acetate. Inhibition also occurs in solutions containing sulphate or nitrate ions, which are aggressive towards iron. Aggressive anions for aluminium include the halide ions F ,... 

Au(diphos)2 and Au(diars)2 can be oxidized to gold(III) species [127]. These tend to add halide ions so that Au(diars)2lJ has a distorted octahedral structure with very weakly bound iodides (section 4.12.5). 

Monatomic anions, such as the Cl- ions in sodium chloride and the O2- ions in quicklime (CaO), are named by adding the suffix -ide and the word ion to the first part of the name of the element (the stem" of its name), as shown in Table D.l thus, S2 is a sulfide ion and O2 is an oxide ion. There is usually no need to specify the charge, because most elements that form monatomic anions form only one kind of ion. The ions formed by the halogens are collectively called halide ions and include fluoride (F ), chloride (Cl-), bromide (Br-), and iodide (I ) ions. 

The reaction between Fe(IlI) and Sn(Il) in dilute perchloric acid in the presence of chloride ions is first-order in Fe(lll) concentration . The order is maintained when bromide or iodide is present. The kinetic data seem to point to a fourth-order dependence on chloride ion. A minimum of three Cl ions in the activated complex seems necessary for the reaction to proceed at a measurable rate. Bromide and iodide show third-order dependences. The reaction is retarded by Sn(II) (first-order dependence) due to removal of halide ions from solution by complex formation. Estimates are given for the formation constants of the monochloro and monobromo Sn(II) complexes. In terms of catalytic power 1 > Br > Cl and this is also the order of decreasing ease of oxidation of the halide ion by Fe(IlI). However, the state of complexing of Sn(ll)and Fe(III)is given by Cl > Br > I". Apparently, electrostatic effects are not effective in deciding the rate. For the case of chloride ions, the chief activated complex is likely to have the composition (FeSnC ). The kinetic data cannot resolve the way in which the Cl ions are distributed between Fe(IlI) and Sn(ll). 

OXIDATION OF INORGANIC COVALENT SPECIES 2.2.1 Halide ions... 

There are related reactions in which the sulfur is at the sulfoxide or sulfilimine oxidation level. Another example of the addition-cyclization route involves a-haloesters, which react to form epoxides by displacement of the halide ion. 

Another useful oxidative reaction in aqueous medium is the cleavage of cyclic ketones by hydrogen peroxide in the presence of Fe(II) salts (Eq. 8.25). The reaction proceeds through an a-hydroxy hydroperoxide, leading to a variety of products.50 The presence of Fe(II) salts decomposes the intermediate, generating a radical. In the presence of halide ions, the radical leads to synthetically useful halocarboxylic acids.51... 

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