Chloride, bromide and iodide

The standard potentials [ns N.H.E. (see Section 2.28)] of the fundamental couples involving uncomplexed mercury(I) and mercury(II) ions are  

The oxidation of Hg to Hg2 + requires a smaller (less oxidising) potential than 

Reagents. Supporting electrolyte. For chloride and bromide, use 0.5 M perchloric acid. For iodide, use 0.1M perchloric acid plus 0.4M potassium nitrate. It is recommended that a stock solution of about five times the above concentrations be prepared (2.5M perchloric acid for chloride and bromide 0.5M perchloric acid + 2.0A f potassium nitrate for iodide), and dilution to be effected in the cell according to the volume of test solution used. The reagents must be chloride-free. 

Catholyte. The electrolyte in the isolated cathode compartment may be either the same supporting electrolyte as in the cell or 0.1 M sulphuric acid the formation of mercury(I) sulphate causes no difficulty. 

Chloride. Experience in this determination may be obtained by the titration of, say, carefully standardised ca 0.005 M hydrochloric acid. 

Mack and Grimsrud [790] have described a photochemical modulated pulsed electron capture detector suitable for the gas chromatographic determination of chloride, bromide and iodide in rainwater. 

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Wadsd I 1968 Heats of vaporization of organic compounds II. Chlorides, bromides and iodides Acta Chem. Scand. 22 2438... 

Chlorides, bromides and iodides Covalent when anhydrous. Soluble in Soluble in water ... 

While the chloride, bromide and iodide are insoluble in water, the fluoride, AgF, is very soluble. 

Ammonium chloride [12125-02-9] NH Q, ammonium bromide [12124-97-9] NH Br, and ammonium iodide [12027-06-4] NH I, are crystalline, ionic compounds of formula wts 53.49, 97.94, and 144.94, respectively. Their densities d systematically foUow the increase in formula weight 1.53, 2.40, and 2.52. AH three exist in two crystal modifications (10) the chloride, bromide, and iodide have the CsQ stmcture below temperatures of 184.5, 137.8, and — 17.6°C, respectively each reversibly transforms to the NaQ. stmcture at higher temperatures. 

Halide Complexes. Silver hahdes form soluble complex ions, AgX and AgX , with excess chloride, bromide, and iodide. The relative stabihty of these complexes is 1 > Br > Cl. Complex formation affects solubihty greatiy. The solubihty of silver chloride in 1 A/ HCl is 100 times greater than in pure water. 

Physica.1 Properties. Physical properties of some typical diorganotin compounds are shown in Table 6. The diorganotin chlorides, bromides, and iodides are soluble in many organic solvents and, except for dimethyltin dichloride, are insoluble in water. 

Beryllium Halides. The properties of the fluoride differ sharply from those of the chloride, bromide, and iodide. BeryUium fluoride is essentiaUy an ionic compound, whereas the other three haUdes are largely covalent. The fluoroberyUate anion is very stable. 

It is known that the order of acidity of hydrogen halides (HX, where X = F, Cl, Br, I) in the gas phase can be successfully predicted by quantum chemical considerations, namely, F < Cl < Br < I. However, in aqueous solution, whereas hydrogen chloride, bromide, and iodide completely dissociate in aqueous solutions, hydrogen fluoride shows a small dissociation constant. This phenomenon is explained by studying free energy changes associated with the chemical equilibrium HX + H2O + HjO in the solu-... 

Enamino ketones can protonate not only on nitrogen or carbon but also on oxygen to give 12,13, and 14, respectively. Enamino ketones form stable perchlorates, chlorides, bromides, and iodides, and examination of their infrared (21,22), ultraviolet (23), and nuclear magnetic resonance (24,25) spectra show these salts to be O protonated. The salts of 4-dialkylamino-... 

A detailed discussion of individual halides is given under the chemistry of each particular element. This section deals with more general aspects of the halides as a class of compound and will consider, in turn, general preparative routes, structure and bonding. For reasons outlined on p. 805, fluorides tend to differ from the other halides either in their method of synthesis, their structure or their bond-type. For example, the fluoride ion is the smallest and least polarizable of all anions and fluorides frequently adopt 3D ionic structures typical of oxides. By contrast, chlorides, bromides and iodides are larger and more polarizable and frequently adopt mutually similar layer-lattices or chain structures (cf. sulfides). Numerous examples of this dichotomy can be found in other chapters and in several general references.Because of this it is convenient to discuss fluorides as a group first, and then the other halides. 

The method may be applied to those anions (e.g. chloride, bromide, and iodide) which are completely precipitated by silver and are sparingly soluble in dilute nitric acid. Excess of standard silver nitrate solution is added to the solution containing free nitric acid, and the residual silver nitrate solution is titrated with standard thiocyanate solution. This is sometimes termed the residual process. Anions whose silver salts are slightly soluble in water, but which are soluble in nitric acid, such as phosphate, arsenate, chromate, sulphide, and oxalate, may be precipitated in neutral solution with an excess of standard silver nitrate solution. The precipitate is filtered off, thoroughly washed, dissolved in dilute nitric acid, and the silver titrated with thiocyanate solution. Alternatively, the residual silver nitrate in the filtrate from the precipitation may be determined with thiocyanate solution after acidification with dilute nitric acid. 

Discussion. The theory of the titration of cyanides with silver nitrate solution has been given in Section 10.44. All silver salts except the sulphide are readily soluble in excess of a solution of an alkali cyanide, hence chloride, bromide, and iodide do not interfere. The only difficulty in obtaining a sharp end point lies in the fact that silver cyanide is often precipitated in a curdy form which does not readily re-dissolve, and, moreover, the end point is not easy to detect with accuracy. 

The zinc chloride is acting here as a Lewis acid. Similarly, thiirane dioxides react with metal halides such as lithium and magnesium chlorides, bromides and iodides in ether or THF to give the halo-metal sulfmates (130) in fair yields157. 

The radii in the lowest row of the table were obtained by a number of approximate considerations. For instance, if we assume the bismuth radius to bear the same ratio to the interatomic distance in elementary bismuth as in the case of arsenic and antimony, we obtain (Bi) = 1.16— 1.47 A. A similar conclusion is reached from a study of NiSb and NiBi (with the nickel arsenide structure). Although the structures of the aurous halides have not been determined, it may be pointed out that if they are assumed to be tetrahedral (B3 or Bi) the interatomic distances in the chloride, bromide, and iodide calculated from the observed densities1) are 2.52, 2.66, and 2.75 A, to be compared with 2.19, 2.66, and 2.78 A, respectively, from pur table. 

The experimental values for the lithium halides are high. This is due to two different phenomena. In the case of the chloride, bromide and iodide the anions are in mutual contact, that is, the repulsive forces operative are those between the anions, and the anion radius alone determines the inter-atomic distances. The geometry of the sodium chloride structure requires that, for less than 0.414, the anions come into contact... 

These considerations also explain the occurrence of cases of dimorphism involving the sodium chloride and cesium chloride structures. It would be expected that increase in thermal agitation of the ions would smooth out the repulsive forces, that is, would decrease the value of the exponent n. Hence the cesium chloride structure would be expected to be stable in the low temperature region, and the sodium chloride structure in the high-temperature region. This result may be tested by comparison with the data for the ammonium halides, if we assume the ammonium ion to approximate closely to spherical symmetry. The low-temperature form of all three salts, ammonium chloride, bromide and iodide, has the cesium chloride structure, and the high-temperature form the sodium chloride structure. Cesium chloride and bromide are also dimorphous, changing into another form (presumably with the sociium chloride structure) at temperatures of about 500°. 

In lithium chloride, bromide and iodide, magnesium sulfide and selenide and strontium chloride the inter-atomic distances depend on the anion radius alone, for the anions are in mutual contact the observed anion-anion distances agree satisfactorily with the calculated radii. In lithium fluoride, sodium chloride, bromide and iodide and magnesium oxide the observed anion-cation distances are larger than those calculated because of double repulsion the anions are approaching mutual contact, and the repulsive forces between them as well as those between anion and cation are operative. 

Cuprous iodide catalyzes the reaction of various alkyl chlorides, bromides, and iodides in hexamethylphosphoric triamide (HMPT), to give the complexed product RaSnXj, which can then be further alkylated with a Grignard reagent, or can be hydrolyzed to the oxide and converted into various other compounds, R2SnY2 (43). This promises to be a useful laboratory method, e.g.,... 

Tertiary halides undergo elimination most easily. Eliminations of chlorides, bromides, and iodides follow Zaitsev s rule, except for a few cases where steric effects are important (for an example, see p. 1316). Eliminations of fluorides follow Hofmann s rule (p. 1316). 

Primary alkyl halides (chlorides, bromides, and iodides) can be oxidized to... 

In a KI matrix the electronic absorption maximum of 82 - is observed at 400 nm, and the 88 stretching vibration by a Raman line at 594 cm k 83 shows a Raman line at 546 cm and an infrared absorption at 585 cm which were assigned to the symmetric and antisymmetric stretching vibrations, respectively. The bromides and iodides of Na, K, and Rb have also been used to trap 82 - but the wavenumbers of the 88 stretching vibration differ by as much as 18 cm- from the value in KI. The anion S3- has been trapped in the chlorides, bromides and iodides of Na, K, and Rb [120]. While the disulfide monoanion usually occupies a single anion vacancy [116, 122], the trisulfide radical anion prefers a trivacancy (one cation and two halide anions missing) [119]. 

The nature of the group X determines the type of reaction which is the most important. For X = azide, thiocyanate, hydroxide, chloride bromide and iodide the inner-sphere bath operates while for X = ammonia or oxyanions (including carboxylates) the main pathway is the outer-sphere reaction. For X = fluoride or nitrite the concentration of the cyanide ion present determines which is the major reaction pathway. 

Attempts have been made to trap the intermediate radical with a monomer, particularly in the reduction of benzyl chloride by Cr(II) to benzylchromium ion (and ultimately to toluene and dibenzyl). The results were ambiguous, however, as benzylchromium ion itself reacts with butadiene and acrylonitrile. This reduction shows second-order kinetics with E — 14.6 kcal.mole and = 14.3 eu. The rate coefficients for benzyl chloride, bromide and iodide follow the expected sequence ... 

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