Halogens anions

The quaternary ammonium salts (QAS) are widely used as ionofores of ion-selective electrodes and extractants of metals halogenic anion complexes. The influence of the QASes nature with various methyl groups contents on the cadmium extraction from bromide media has been investigated. 

Dipping solution II Halogen anions Dissolve 100 mg bromocresol purple in 100 ml ethanol and add a few drops of 10% ammonia solution until the color changes. 

Habituating drugs 76 Halate anions 45 Halide anions 45 Halogen anions 231, 232 Halogen acids 189... 

Similar conclusions concerning the effect of the anion and impurities in the ionic liquid on the cyclopropanation reaction have been drawn in a recently published study [47]. Ionic liquids with the formula [bmim][X], where X = OTf, NTf2, PFe, and BF4, were used. The catalyst used in this study was 6b-Cu(OTf). In all cases, good enantioselectivities (89-97% ee) were obtained and these are similar to those obtained in chloroform. The influence of the presence of halogen anions was tested by the addition of 5% [bmim] [Cl] or [bmim][Br] to [bmim][BF4]. In both cases, a catalytically inactive solution was obtained, showing the detrimental effect of these anions on the reaction. 

As base B several electron donors can be employed, e.g. amines 127), hydrazines128), amine oxides129, ethers126, phosphanes 130>131, and even charged ligands such as halogen anions 126) and many others 126). There may be formed either 1 1 or 1 2 adducts as in Eq. (7), an equilibrium being assumed to be established between these two adducts ... 

When the counterion is complex, for example metal-halogen anions such as BF4-, the most electronegative portion of the counterion becomes attached to the silicon center. Because of this attachment, it is natural to consider the intermediacy of a silicenium cation (silylium or silylenium ion) intermediate in such reactions (Eq. 4). Bond energies derived from electron impact studies indicate that Eq. 4 is exothermic in the gas phase by about 8 kcal/mol.26,29 There seems little doubt that trivalent silicon-centered cationic species do exist in the gas phase30,31 or that processes similar to that shown in Eq. 4 do occur there.32,33... 

A one-electron reduction of the bond between an aliphatic carbon and a halogen leads to a halogen anion and a carbon-free radical. A good example is the reduction of carbon tetrachloride as discussed earlier in this chapter. The first product in the reduction is the trichloromethyl-free radical. Carbon-centered radicals are not very reactive with biological molecules, but they react very rapidly with molecular oxygen (a diradical) to form a peroxy-free radical (Fig. 5.15), which is quite toxic (10). 

In electrochemistry, the effect of acidic anions on the electrode interface is important. The interaction of the adsorbed water molecules is relatively weak with perchlorate ions (Cl04 ) and fluoride ions (F ), intermediate with chloride ions (Cl ) and sulfate ions (S04 "), and relatively strong with phosphate ions (P04 ") and bromide ions (Br ). In a series of halogen anions, fluoride ions (F ), which interact weakly with the metal surface, are adsorbed as hydrated ions (H3O F ) chloride and bromide ions (Cl and Br ), which interact strongly with the metal surface, are adsorbed as dehydrated ions (Cl M and Br M). 

In general, the contact adsorption of deh3drated anions changes the interfacial lattice structure of adsorbed water molecules, thereby changing the interfadal property. For example, the clean surfaces of metallic gold and silver, which are hydrophobic, become hydrophilic with the contact adsorption of dehydrated halogen anions. 

Dysprosium has an oxidation state of +3, which forms the Dy metallic ion that is hmited to a small group of compounds. A general example that demonstrates how the ion of dysprosium combines with halogen anions follows Dy + 3C1 — DyCl. ... 

Treatment of complex 11 in NCMe with H2SO4 and dihalogen equivalents results in hydride abstraction and formation of B-halogenated anions (Chart 9). Thus, with N-chlorosuccinimide (2 equiv) or iodine (1 equiv), the species [N(PPh3)2][7-X-2,2,2-(CO)3-c/o50-2,l-FeCBioHio] [X = Cl (40), I (41)] are formed. Use of 4 equiv of... 

The nature of bonding of the adsorbed species to the model cluster of metal surfaces can be analyzed in terms of the so-called constrained space orbital variation (CSOV) method. For halogen anions adsorbed on various silver surfaces, it has been found that Pauli repulsion, metal polarization, and charge transfer to the metal surface mainly contribute to the binding energy of the ions [104, 301]. 

Phenothiazine is readily oxidized when irradiated in solution with chlorinated hydrocarbones (8). The reaction has been shown to be an electron transfer generating the phenothiazine (PTH) radical cation (PTH+ ) and the halogen anion as shown in equation 1. hv. ... 

Generation of electrophilic species from organic polyfluorinated materials usually requires direct interaction of a strong Lewis acid with a substrate, which can result in formation of a cation either by abstraction of a halogen anion (usually F ) from a substrate (Eq. 8) or by formation of a zwitterionic intermediate as a result of coordination of the Lewis acid with an unshared electron pair on a multiply bonded heteroatom (Eq. 9) [12] ... 

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