Halogens anions formed

The tendency of the halogens to form chain-like polyanions that are stabilized by delocalization of the negative charge [15,34] is a basic chemical principle. Donor-acceptor interactions between Lewis-acidic Br2 and halide anions, but also with polyhalides acting as Lewis bases, give rise to the formation of a variety of homo and heteroatomic adducts. The maximum number of atoms in these chains increases with the atomic weights... 

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. 

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 ... 

Reactions of P-halogen-NHPs with Lewis acids leading to halide abstraction, or metathetic replacement of the halide by a nucleofugic, noncoordinating anion form by far the most important routes to access phosphenium ions in general [51, 52] and also 1,3,2-diazaphospholenium cations in particular. As Lewis acid assisted P-X... 

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). 

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... 

To obtain an estimate of the combined enthalpies of hydration of such cations and anions, the thermodynamic cycle shown in Figure 2.6 is helpful. In Figure 2.6 it is assumed that the element X is a halogen and forms a uni-negative ion. 

The complex anions formed with the other halogens are all of the form [MX ]2", with... 

An unusual radical halogenation of hydrocarbons by phase-transfer catalysis may be performed by reacting alkanes with tetrahalomethanes. The reaction is initiated by single-electron oxidation of OH- by CHlg4. The tetrahalomethane radical anion formed decomposes to the 12 trihalomethyl radical [Eq. (10.56)], which is then involved in C—H activation and propagation steps 286... 

Bromoethylamine may undergo two reaction pathways in its modification of sulfhydryl groups in proteins (Fig. 84). In the first scheme, the thiolate anion of cysteine attacks the No. 2 carbon of 2-bromoethylamine to release the halogen and form a thioether bond (Lindley, 1956). This straightforward reaction mechanism is similar to the modification of sulfhydryls with iodoacetate (Section 4.2). In a two-step, secondary... 

Bromide or chloride anions can now be oxidized to X+ by p-nitrobenzenesulphonyl peroxide. The positive halogen thus formed reacts with olefins via halonium ions183. Similarly, PhSe+ can be generated from PhSeSePh184. 

The overall reaction involves replacing the halogen atom of the alkyl halide with an NH, unit. Another method is the Gabriel synthesis of amines. This involves treating phthalimide with KOH to abstract the N-H proton. The N-H proton of phthalimide is more acidic (pK9) than the N-H proton of an amide since the anion formed can be stabilised by resonance with both neighbouring carbonyl groups. The phthalimide ion can then be alkylated by treating it with an alkyl halide in nucleophilic substitution. 

Radical anions formed from halogen-containing aromatic systems. . 321... 

Coal and many coal-derived liquids contain polycyclic aromatic structures, whose molecular equivalents form radical cations at anodes and radical anions at cathodes. ESR-electrolysis experiments support this (14). Chemically, radical cations form by action of H2SO4 (15,19), acidic media containing oxidizing agents (15,20,21,22), Lewis acid media (18,23-35) halogens (36), iodine and AgC104 (37,38), and metal salts (39,40). They also form by photoionization (41,42,43) and on such solid catalytic surfaces as gamma-alumina (44), silica-alumina (45), and zeolites (46). Radical anions form in the presence of active metals (76). 

Iodine heptafluoride reacts with AsF5 or SbF5 to form products containing the IF6+ cation. 16.4.3 Polyatomic Halogen Anions... 

A number of other, but minor primary photoproducts was also found, among them the products expected from a radical (photo-Claisen) rearrangement and from photohydrolysis of the ortho chlorine 2- and 4-chlorophenol were detected too, but their formation remained unexplained. The photodegradation quantum yield of dichlorprop did not depend on pH and was 50 times smaller than that of the anionic form of the related monohalo-genated compound mecoprop (see above) [77]. This is another example of the marked influence of the pattern of ring halogen substitution on the course and on the efficiency of photodegradation. 

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