Ions in halides

The interactions of 1,3,2-diazaarsolium and 1,3,2-diazastibolium ions in halides and in complexes have been calculated <2005HAC327, 2005ZFA1403>. 

Olah GA, Welch J (1975) Onium ions. XII. Heterolytic dediazoniation of benzenediazonium ions in halide ions in pyridinium polyhydrogen fluoride solution giving isomeric haloben-zenes reflecting ambident reactivity of benzenediazonium ions and intermediate phenyl cation as well as subsequent aryne formation. J Am Chem Soc 97 208—210... 

Ishii T (2005) Eirst-principles calculations for the cooperative transitions of Yb dimer clusters in Y3AI5O12 and Y2O3 crystals. J Chem Phys 122 024705-1-024705-6 Rubio O (1991) Doubly-valent rare-earth ions in halide crystals. J Phys Chem Solids 52 101-174... 

This situation can however be overcome through the analysis of standard optical and EPR parameters which can be measured for much lower impurity concentrations. For instance in the case of d , d and d ions in halide lattices with octahedral coordination it has been pointed out that Re can be derived from the experimental isotropic superhyperfine constant, As. A general view on this method is given in Ref [4]. 

The heats of formation of the gaseous atoms, 4, are not very different clearly, it is the change in the bond dissociation energy of HX, which falls steadily from HF to HI, which is mainly res ponsible for the changes in the heats of formation. 6. We shall see later that it is the very high H—F bond energy and thus the less easy dissoeiation of H—F into ions in water which makes HF in water a weak aeid in comparison to other hydrogen halides. 

Cobalt II) halides can be obtained by direct combination of the elements, or by dehydration of their hydrates. Anhydrous cobalt(II) chloride is blue, and the solid contains octahedrally-coordinated cobalt the hydrated salt C0CI2. bHjO is pink, with each cobalt surrounded by four water molecules and two chloride ions in a distorted octahedron. 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

The summation is over the different types of ion in the unit cell. The summation ca written as an analytical expression, depending upon the lattice structure (the orij Mott-Littleton paper considered the alkali halides, which form simple cubic lattices) evaluated in a manner similar to the Ewald summation this typically involves a summc over the complete lattice from which the explicit sum for the inner region is subtractec... 

Sulphur, as sulphide ion, is detected by precipitation as black lead sulphide with lead acetate solution and acetic acid or with sodium plumbite solution (an alkaLine solution of lead acetate). Halogens are detected as the characteristic silver halides by the addition of silver nitrate solution and dilute nitric acid the interfering influence of sulphide and cyanide ions in the latter tests are discussed under the individual elements. 

Alkyl azides prepared by nucleophilic substitution by azide ion in primary or secondary alkyl halides are reduced to primary alkylamines by lithium aluminum hydride or by catalytic hydrogenation... 

Silver chloride crystals are face-centered cubic (fee), having a distance of 0.28 nm between each ion in the lattice. Silver chloride, the most ionic of the halides, melts at 455°C and boils at 1550°C. Silver chloride is very ductile and can be roUed into large sheets. Individual crystals weighing up to 22 kg have been prepared (10). 

A very useful procedure for introducing a cyano group into a pyridazine ring is the Reissert-type reaction of the A/-oxide with cyanide ion in the presence of an acyl halide or dimethyl sulfate. The cyano group is introduced into the a-position with respect to the A-oxide function of the starting compound. The yields are, however, generally poor. In this way, 6-cyanopyridazines (111) can be obtained from the corresponding pyridazine 1-oxides (Scheme 33). 

One of the most required methods of determination of iodide-ions in praetiee of ehemieal analysis is photometrie determination of produets of iodination of organie eompounds. The oxidation of iodide to iodine ean be earned out suffieiently seleetively. But in ease of presenee of great abundanee of bromide-ions the seleetive oxidation of iodide-ions is problematie. The variants of determination of iodide-ions with different organie reagents are known, but the absenee of bromide-ions in a system is supposed in most of them. In natural objeets these halides are present simultaneously. 

The mobilities of ions in molten salts, as reflected in their electrical conductivities, are an order of magnitude larger than Arose in Are conesponding solids. A typical value for diffusion coefficient of cations in molten salts is about 5 X lO cm s which is about one hundred times higher Aran in the solid near the melting point. The diffusion coefficients of cation and anion appear to be about the same in Are alkali halides, wiAr the cation being about 30% higher tlrair Are anion in the carbonates and nitrates. 

The transport of charged ions in alkali halides and, later on, in (insulating) ceramics is a distinct parepisteme, because electric fields play a key role. This large field is discussed in Schmalzried s 1995 book, already mentioned, and also in a review by one of the pioneers (Nowick 1984). This kind of study in turn led on to the developments of superionic conductors, in which ions and not electrons carry substantial currents (touched on again in Chapter 11, Section 11.3.1.1). 

Nucleophilic substitution reactions that occur imder conditions of amine diazotization often have significantly different stereochemisby, as compared with that in halide or sulfonate solvolysis. Diazotization generates an alkyl diazonium ion, which rapidly decomposes to a carbocation, molecular nitrogen, and water ... 

Some instances of incomplete debromination of 5,6-dibromo compounds may be due to the presence of 5j5,6a-isomer of wrong stereochemistry for anti-coplanar elimination. The higher temperature afforded by replacing acetone with refluxing cyclohexanone has proved advantageous in some cases. There is evidence that both the zinc and lithium aluminum hydride reductions of vicinal dihalides also proceed faster with diaxial isomers (ref. 266, cf. ref. 215, p. 136, ref. 265). The chromous reduction of vicinal dihalides appears to involve free radical intermediates produced by one electron transfer, and is not stereospecific but favors tra 5-elimination in the case of vic-di-bromides. Chromous ion complexed with ethylene diamine is more reactive than the uncomplexed ion in reduction of -substituted halides and epoxides to olefins. ... 

The reactions of alcohols with hydrogen halides to give alkyl halides (Chapter 4) are nucleophilic substitution reactions of alkyloxonium ions in which water is the leaving group. Primary alcohols react by an Sn2-like displacement of water from the alkyloxonium ion by halide. Secondary and tertiary alcohols give alkyloxonium ions which fonn caibo-cations in an SNl-like process. Reanangements are possible with secondary alcohols, and substitution takes place with predominant, but not complete, inversion of configuration. 

The other halides of Zn and Cd are in general hygroscopic and very soluble in water ( 400g per lOOcm for ZnXa and 100g per lOOcm for CdXa). This is at least partly because of the formation of complex ions in solution, and the anhydous forms are best prepared by... 

TBAF has been used as a source of fluoride ions in a number of substitution reactions studied by Cox et al. [23]. Allcyl and acyl halides react with TBAF to give the corresponding allcyl or acyl fluoride in good yield. In the reaction between (R)-2-tosyloctane and TBAF, the product was (S)-2-fluorooctane, confirming an Sn2 mechanism for the reaction (Scheme 5.1-5) [18, 23]. 

Nucleophilic displacement reactions One of the most common reactions in organic synthesis is the nucleophilic displacement reaction. The first attempt at a nucleophilic substitution reaction in a molten salt was carried out by Ford and co-workers [47, 48, 49]. FFere, the rates of reaction between halide ion (in the form of its tri-ethylammonium salt) and methyl tosylate in the molten salt triethylhexylammoni-um triethylhexylborate were studied (Scheme 5.1-20) and compared with similar reactions in dimethylformamide (DMF) and methanol. The reaction rates in the molten salt appeared to be intermediate in rate between methanol and DMF (a dipolar aprotic solvent loiown to accelerate Sn2 substitution reactions). 

As well as viscosity, other factors to be aware of include the purity of the ionic liquids. The presence of residual halide ions in neutral ionic liquids can poison transition metal catalysts, while different levels of proton impurities in chloroalumi-... 

The aggressivity of halides varies, with bromide and chloride being most aggressive. Increasing concentration of the halide also depresses the pitting potential as demonstrated for two steels in Fig. 3.16. Certain ions in solution act as inhibitors (e.g. nitrate) raising the pitting potential while others depress it (e.g. sulphide). Temperature and pH also have effects as illustrated... 

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. 

The theory of the structure of ice and water, proposed by Bernal and Fowler, has already been mentioned. They also discussed the solvation of atomic ions, comparing theoretical values of the heats of solvation with the observed values. As a result of these studies they came to the conclusion that at room temperature the situation of any alkali ion or any halide ion in water was very similar to that of a water molecule itself— namely, that the number of water molecules in contact with such an ion was usually four. At any rate the observed energies were consistent with this conclusion. This would mean that each atomic ion in solution occupies a position which, in pure water, would be occupied by a water moldfcule. In other words, each solute particle occupies a position normally occupied by a solvent particle as already mentioned, a solution of this kind is said to be formed by the process of one-for-one substitution (see also Sec. 39). 

Although the viscosity B-coefficients for the fluorides are not known, we see. that the value for the ionic entropy of F" listed in Table 45 is — 2.3 + 2, very different from the value +13.5 for Cl". The value for F- is, in fact, very near the value —2.49 for (OH)-. We have then the very interesting question, whether the activities of the fluorides will fall in line with the other halides. In structure the ion F" certainly resembles Cl" and the other halide ions but according to the tentative scheme proposed above, we should perhaps focus attention on the solvent in the co-sphere of each ion. In this case we should expect to obtain for the fluorides a family of curves similar to that of the hydroxides, in contrast to that of the chlorides. The activities are known as a function of concentration for NaF and KF only. It is found that the curve for NaF lies below that of KF—that is to say, the order is the same as that of NaOH and KOII, in contrast to that of NaCl and KC1. 

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