Halogen ions

In the case of the halogens, fluorine only forms one ion—f . Chlorine, bromine, and iodine, however, have several ions. The following list shows the ions for chlorine, bromine, and iodine  

Notice the prefixes per, from hyper, meaning above, and hypo, meaning below or beneath. There are other ions that have the prefix per, but this is probably the only use in chemistry of hypo. 

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The enthalpies for the reactions of chlorine and fluorine are shown graphically in Figure 11.2 as the relevant parts of a Born-Haber cycle. Also included on the graph are the hydration energies of the two halogen ions and hence the enthalpy changes involved in the reactions... 

In the case of electrochemical reactions the partial anodic reaction results in the formation of a solvated metal cation, a charged or uncharged metal complex MX or a solid compound MX, where AT is a halogen ion, organic acid aninn, etc. 

In the CeSI (115) and NdSBr (334) type of structure, bromine and iodine are coordinated to five metal ions (four of the same layer, and one of the opposite layer) and four halogen ions of the double layer. In the SmSI type (335), iodine is coordinated to three metal ions of a [LS] layer and three other iodine ions of the double layer. In the FeOCl type of compound, such as ErSCl (355) and LuSBr (85), the halogen is surrounded by a polyhedron formed by six sulfur and four halogenide ions. 

The effect of TOS on the product distribution during the pyrolysis of R22 over CU-AIF3 catalyst is shown in Fig. 3. The amoimt of halogen ion trapped in NaOH solution was determined by IC. The concentration of Cl formed during the pyrolysis of R22 was higher than the concentration of F at all TOS. This result is a consequence of the facile cleavage of the C-Cl bond in comparison to the C-F bond. Bond dissociation energy for the C-element of R22 is followed by the order C-C1[Pg.235]

Halides Metal ion(s) + halogen ion Common salt (sodium chloride), a component of animal diets Fluorite (calcium fluoride), a lapidary material and flux... 

Marquis and Lebel [534] precipitated potassium from seawater or marine sediment pore water using sodium tetraphenylborate, after first removing halogen ions with silver nitrate. Excess tetraphenylborate was then determined by silver nitrate titration using a silver electrode for endpoint detection. The content of potassium in the sample was obtained from the difference between the amount of tetraphenyl boron measured and the amount initially added. 

In general, halogen ions have a decreasing effect upon the CL intensity. Salt concentration and buffer pH are also known to affect the CL reaction. The choice of buffer and its pH suited to each CL reaction system are hence very important to obtain intense CL. 

Interaction of a light photon with a halogen ion in the AgBr crystal. The energy from the photon (hv) liberates an electron from this ion ... 

The catalyst is reported to be a true solid acid without halogen ion addition. In the patent describing the process (239), a Pt/USY zeolite with an alumina binder is employed. It was claimed that the catalyst is rather insensitive to feed impurities and feedstock composition, so that feed pretreatment can be less stringent than in conventional liquid acid-catalyzed processes. The process is operated at temperatures of 323-363 K, so that the cooling requirements are less than those of lower temperature processes. The molar isobutane/alkene feed ratio is kept between 8 and 10. Alkene space velocities are not reported. Akzo claims that the alkylate quality is identical to or higher than that attained with the liquid acid-catalyzed processes. 

The halogen ions produced during the combustion of an organic substance can naturally be determined in the usual way also—gravi-metrically by precipitation with Ag. ... 

This discussion of the energetics of the halogenate ions is in no way a digression. In the first place, when the reaction coordinate within a series is the same, a connection between driving force and rate can be expected. In the second place, it is important to realize that, if we are unable to understand the equilibrium stability in a basic way, we are hardly in position to deal effectively with the stabilities of the activated complexes. Increased concern with the stabilities of this important family of molecules, both at the experimental and theoretical levels, is justified. 

More often the passive layer is broken down locally and then the steel is said to be attacked by localized corrosion, the most important forms being pitting, crevice corrosion, and corrosion cracking. Most often the localized corrosion is caused by halogen ions such as chloride, bromide, and iodide. Pitting or pitting corrosion is seen as small pinholes on the surface of the steel. This section describes electrochemical instrumental methods to investigate and measure this form of corrosion attack. 

Aldoximes (7) are converted into the corresponding nitriles (8) by using halogen ions as mediators (Scheme 3). Sodium chloride affords the best result among the supporting electrolytes (Cl > Br > r > CIO4- > TsO ) [37]. 

The gaseous dichlorocarbene radical cation reacted with alkyl halides via a fast electrophilic addition to form a covalently bonded intermediate (CI2C—X—R)+ in a Fourier transform ion cyclotron resonance mass spectrometer. This intermediate fragments either homolytically or heterolytically to produce net halogen atom or halogen ion transfer product. Addition of carbonyls to the carbene ion is followed by homolytic cleavage of the C-O bond to yield a new carbene radical cation. 

It is these reactions that are thought to provide some justification for equation (vii) [in Section VI B3] according to which p-phenethylbi-guanide in methanol exists to some extent as biguanidium methoxide. This being so, the reaction with alkyl halides is the nucleophihc displacement of the halogen ion by methoxide with formation of the methyl ether and the salt of the biguanide. 

Indirect electro-oxidation of primary amines to nitriles is achieved using halogen ion as mediator [93]. The reaction is typically carried out in an undivided cell... 

Vanadates For the isostructural strontium and barium ortho-vanadates the V-—0 vibrational frequencies decrease with increasing effective nuclear charge [51]. Similar orthovanadates with the apatite structure have for a given halogen ion decreasing frequencies of the VO4 ion in the order Ca>Sr >Ba ((62) and Table 4]. However, it is impossible to see any trend towards the tiivalent lanthanide cations (59). The IR bands are so wide in this case that small changes cannot be measured. 

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