Halogens oxyanions

More detailed consideration of these various equilibria and other redox reactions of the halogen oxoacids will be found under the separate headings below. As expected, the rates of redox reactions of the halogen oxyanions will depend, sometimes crucially, on the precise conditions used. However, as a very broad generalization, they tend to become progressively faster as the oxidation state of the halogen decreases, i.e. ... 

The photodecomposition mechanism of BrO has been elucidated by flash photolytic studies in aqueous solutions containing NaOH and also from e.s.r. and optical absorption measurements in aqueous NaOH glasses after photolysis at 77 K. The sole primary reaction was decomposition to 0( D) and BrOj, and is therefore unlike the additive primary processes for the other halogen oxyanions. The radiolytic reduction of KBr04 in aerated and deaerated aqueous solutions has been investigated. In acidic medium the only reaction is to give H (or HO2) and Br04, with G(—BrO ) = 3.5. In neutral solution BrO is reduced by the... 

Hot atom chemistry of salts of halogen oxyanions has been studied by many authors (Owens 1979) since the Roman group led by Fermi (Amaldi et al. 1935) dealt with it. Boyd and Larson (1968) noticed that the BrOs retention is little dependent on its partner cation but the yield of Br02 and BrO are strongly dependent on the cation. It was found in a variety of bromates that the retention of ° Br, Br, and Br was in a good correlation with the electron affinity of the cations (Saito et al. 1965). 

I itro-DisplacementPolymerization. The facile nucleophilic displacement of a nitro group on a phthalimide by an oxyanion has been used to prepare polyetherimides by heating bisphenoxides with bisnitrophthalimides (91). For example with 4,4 -dinitro monomers, a polymer with the Ultem backbone is prepared as follows (92). Because of the high reactivity of the nitro phthalimides, the polymerkation can be carried out at temperatures below 75°C. Relative reactivities are nitro compounds over halogens, Ai-aryl imides over A/-alkyl imides, and 3-substituents over 4-substituents. Solvents are usually dipolar aprotic Hquids such as dimethyl sulfoxide, and sometimes an aromatic Hquid is used, in addition. 

Under aerobic conditions, S -adenosyhnethionine is the methyl donor for methylation of meth-anethiol and methaneselenol (Drotar et al. 1987), and probably for the bacterial methylation of halogenated phenols and thiophenols (Neilson et al. 1988). It is also the probable methyl donor for fungal methylation of the oxyanions of As and Sb (Bentley and Chasteen 2002). 

For nucleophiles of different atomic numbers, nucleophilicity usually does no parallel basicity. For example, for the halogens the reactivity sequence I > Br > Cl is opposite to the sequence of basicity Cl > Br > I . Similarly, sulfur anions such as HS are better nucleophiles but weaker bases than corresponding oxyanions such as HO . 

The topics covered in this book include the above kinds of information for oxyanions of the elements which form discrete anions carbon, sulfur, nitrogen, and the halogens including ... 

All of the halogens except fluorine, which is more electronegative than oxygen, form oxyanions in which the valence of the halogen varies, e.g., chlorite, chlorate, perchlorate. 

In contrast to other classes of salts with oxyanions, high-temperature thermodynamic data are largely lacking e.g., HSC only lists data for four. These have been listed as well as AHf° and S° from Wagman et al.3 In this chapter thermodynamic data for the three halogen gases have been listed (Tables 6.1 to 6.3)... 

There are only three oxyanions that form anhydrous salts chlorites (C102), chlorates (C10(), and perchlorates (C104). Their stability increases with the increasing oxidation state of the halogen. There is no clear evidence for the existence of stoichiometric, anhydrous hypochlorites (CIO). Even for the few reported salts (NaCIO, Ca(C10)2) one finds reports of smell of chlorine, indicating continuous decomposition at ambient temperature. 

As outlined in Scheme 5, tertiary cyclopropanol salts are also subject to the oxyanion-accelerated VCP rearrangement. In this sequence the requisite vinylcyclopropanol salts are conveniently prepared from readily available 1,1-dibromocyclopropanes by sequential halogen-metal exchanges, followed first by alkylation, and then by oxygenation. Products resulting from alternative 1,5-hydrogen shift (retro-ene) pathways were not detected in these reactions. 

Chlorine in group 7A, the halogens, forms four oxyanions. These oxyan-ions are named according to the number of oxygen atoms present. The following conventions are used to name these oxyanions. 

Other halogens form oxyanions that are named similarly to the oxyanions chlorine forms. Bromine forms Br03, the hromate ion. Iodine forms the periodate ion (104 ) and the iodate ion (IO3 ). 

As shown in Table 7.11, chlorine forms four oxyanions that are named according to the number of oxygen atoms present. Names of similar oxyanions formed by other halogens follow the rules used for chlorine. For example, bromine forms the bromate ion (BrOs"), and iodine forms the periodate ion (I04 ) and the iodate ion (I03 ). 

Prefixes are used when the series of oxyanions of an element extends to four members, as with the halogens. The prefix per- indicates one more O atom than the oxyanion ending in -ate hypo- indicates one O atom fewer than the oxyanion ending in -ite ... 

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