Chloride ion, 1.28

The term acid was extended by Lewis to include substances which are electron acceptors. Thus AICI3 can accept electrons from a chloride ion forming the [AICI4] ion and is a Lewis acid. 

The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

Thiis, when tables report the starrdard emf or starrdard free errergy of the chloride ion. 

Modestov A D, Zhou G-D, Ge FI-FI and Loo B FI 1995 A study by voltammetry and the photocurrent response method of copper electrode behavior in acidic and alkaline solutions containing chloride ions J. Electroanal. Chem. 380 63-8... 

The strongly electronegative (p. 49) chlorine atom becomes a chloride ion, the proton accepting the electron pair donated by the nitrogen atom. A similar reaction occurs when ammonia is passed into water, but to a much lesser extent as oxygen in water is a poorer donor of the electron pair ... 

A/ij the lattice energy of sodium chloride this is the heat liberated when one mole of crystalline sodium chloride is formed from one mole of gaseous sodium ions and one mole of chloride ions, the enthalpy of formation of sodium chloride. 

When either hydrogen ions or hydroxide ions participate in a redox half-reaction, then clearly the redox potential is alTected by change of pH. Manganate(Vir) ions are usually used in well-acidified solution, where (as we shall see in detail later) they oxidise chlorine ions. If the pH is increased to make the solution only mildly acidic (pH = 3-6), the redox potential changes from 1.52 V to about 1.1 V, and chloride is not oxidised. This fact is of practical use in a mixture of iodide and chloride ions in mildly acid solution. manganate(VII) oxidises only iodide addition of acid causes oxidation of chloride to proceed. 

Thus chloride ions are oxidised to chlorine by manganate( VIl) under standard conditions... 

Thus under standard conditions chloride ions are not oxidised to chlorine by dichromate(Vr) ions. However, it is necessary to emphasise that changes in the concentration of the dichromate(VI) and chloride ions alters their redox potentials as indicated by the Nernst equation. Hence, when concentrated hydrochloric acid is added to solid potassium dichromate and the mixture warmed, chlorine is liberated. 

Most chlorine-containing compounds can be converted to give chloride ions, for example covalent chlorides by hydrolysis, chlorates by reduction. The chloride ion is then tested for thus ... 

If excess chloride ion is added to a blue solution containing... 

Iron(III) chloride forms numerous addition compounds, especially with organic molecules which contain donor atoms, for example ethers, alcohols, aldehydes, ketones and amines. Anhydrous iron(III) chloride is soluble in, for example, ether, and can be extracted into this solvent from water the extraction is more effective in presence of chloride ion. Of other iron(III) halides, iron(III) bromide and iron(III) iodide decompose rather readily into the +2 halide and halogen. 

For this reaction, charcoal is a catalyst if this is omitted and hydrogen peroxide is used as the oxidant, a red aquopentammino-cobalt(lll) chloride, [Co(NH3)jH20]Cl3, is formed and treatment of this with concentrated hydrochloric acid gives the red chloro-p0itatnmino-coba. t(lll) chloride, [Co(NH3)5Cl]Cl2. In these latter two compounds, one ammonia ligand is replaced by one water molecule or one chloride ion it is a peculiarity of cobalt that these replacements are so easy and the pure products so readily isolated. In the examples quoted, the complex cobalt(III) state is easily obtained by oxidation of cobalt(II) in presence of ammonia, since... 

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. 

These are of two general kinds octahedral, pink complexes and tetrahedral, blue complexes. If cobalt(II) chloride is dissolved in aqueous solution, the predominant species is the hexaaquo-ion [ColHjO) ] (pink). If this solution is heated, it becomes blue, and the same effect is observed if chloride ion is added in excess. This colour change is associated with the change... 

The anhydrous chloride is prepared by standard methods. It is readily soluble in water to give a blue-green solution from which the blue hydrated salt CuClj. 2H2O can be crystallised here, two water molecules replace two of the planar chlorine ligands in the structure given above. Addition of dilute hydrochloric acid to copper(II) hydroxide or carbonate also gives a blue-green solution of the chloride CuClj but addition of concentrated hydrochloric acid (or any source of chloride ion) produces a yellow solution due to formation of chloro-copper(ll) complexes (see below). 

Zincill) chloride. ZnCl2, is the only important halide—it is prepared by standard methods, but cannot be obtained directly by heating the hydrated salt. It has a crystal lattice in which each zinc is surrounded tetrahedrally by four chloride ions, but the low melting point and solubility in organic solvents indicate some covalent... 

Gravimetrically, silver nitrate is used to determine the chloride ion. 

The ion can be regarded as (CK ->AuCI, ). and coordinaiion by the chloride ion brings the covalency from three (in AuClj) to four (in [AUCI4] ), oxidation state remaining as + 3. 

Mercury(I) compounds in solution give a white precipitate with chloride ion. blackened by ammonia (p. 437) alkalis and reducing agents generally produce black or grey mercury from mercury(I) compounds. 

Chandrasekhar, J., Smith, S,F,m Jorgensen, W.L. Theoretical examonation of the Stv2 reaction involving chloride ion and methyl chloride in the gas phase and aqueous solution. J. Amer. Chem. Soc. 107 (1985) 154-163. 

Figure 5.21 reprinted with permission from Chandrasekhar J, S F Smith and W L Jorgensen. Theoretical Examination of the 5 2 Reaction Involving Chloride Ion and Methyl Chloride in the Gas Phase and Aqueous Solution. The Journal of the American Chemical Society 107 154-163. 1985 American Chemical Society. 

Stuart S J and B J Berne 1996. Effects of Polarisability on the Hydration of the Chloride Ion. Journal of Physical Chemistry 100 11934-11943. 

When hydrochloric acid is cautiously added to an aqueous solution containing both sodium nitrite and the sodium salt of sulphanilic acid, NaOsSCgH NH, the amino group of the latter undergoes normal diazotisation, giving the diazonium chloride (A). The latter, however, ionises in solution, giving sodium and chloride ions and the internal salt (B), which possesses two opposite charges and is therefore neutral this internal salt is stable under... 

Phenyldiazonium chloride and other similar diazonium compounds are very soluble in water, are completely insoluble in ether and other organic solvents, and are completely dissociated in aqueous solution to organic cations and inorganic anions (e.g., chloride ions) a convenient formulation is therefore, for example, CjHjNj+CP. 

An uneventful coupling of two hemispherical cavitand molecules — a tetrameth-anethiol and a tetrakis(chloromethyl)precursor (see p. 169) — yielded D.J. Cram s (1988) carcerand . ft entraps small molecules such as THF or DMF, cesium or chloride ions, or argon atoms as permanently imprisoned guests . Only water molecules are small enough to pass through the two small pores of this molecular (prison) cell. 

In the Wacker process, the reaction is actually carried out in dilute HCl at a high concentration of chloride ion and an elevated temperature. The high concentration of CUCI2 shifts the equilibrium further to the right. 

Diacetoxylation of various conjugated dienes including cyclic dienes has been extensively studied. 1,3-Cyclohexadiene was converted into a mixture of isomeric l,4-diacetoxy-2-cyclohexenes of unknown stereochemistry[303]. The stereoselective Pd-catalyzed 1,4-diacetoxylation of dienes is carried out in AcOH in the presence of LiOAc and /or LiCI and beiizoquinone[304.305]. In the presence of acetate ion and in the absence of chloride ion, /rau.v-diacetox-ylation occurs, whereas addition of a catalytic amount of LiCl changes the stereochemistry to cis addition. The coordination of a chloride ion to Pd makes the cis migration of the acetate from Pd impossible. From 1,3-cyclohexadiene, trans- and ci j-l,4-diacetoxy-2-cyclohexenes (346 and 347) can be prepared stereoselectively. For the 6-substituted 1,3-cycloheptadiene 348, a high diaster-eoselectivity is observed. The stereoselective cij-diacetoxylation of 5-carbo-methoxy-1,3-cyclohexadiene (349) has been applied to the synthesis of dl-shikimic acid (350). 

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