Chloride-ion transfer reactions

Despite this, they are good solvents for chloride-ion transfer reactions, and solvo-acid-solvo-base reactions (p. 827) can be followed conductimetri-cally, voltametrically or by use of coloured indicators. As expected from their constitution, the trihalides of As and Sb are only feeble electron-pair donors (p. 198) but they have marked acceptor properties, particularly towards halide ions (p. 564) and amines. 

As was previously mentioned, Artephius described the process of the Philosophers Stone using Antimony in about 1120 or 1150 CE. It rapidly became the divine Wet Method of producing the Philosophers Stone used by all the great alchemists. Antimony Trichloride is today widely used as an excellent non-aqueous solvent, especially for chloride-ion transfer-reactions. It avoids troublesome nitrates altogether by using chloride ion transfer. 

Self-ionization equilibria have been assumed to exist in the pure liquids. Davies and BaughanI have shown that the self-ionization in molten antimony (III) chloride is hkely to be principally due to the presence of small amounts of impurities, but the results are still at least partially in accord with the following equations, which have been regarded as due to chloride ion transfer reactions between solvent molecules ... 

The extent of chloride ion transfer reactions has been extensively studied by spectrophotometric techniques. One of the approaches has been based on the pronounced differences in spectra between solvent-coordinated and fully chloride-coordinated ferric chloride in phosphorus oxychlorideio and phenylphosphonic... 

In agreement with the results of preparative work it was concluded that the solvent cations replace phenolic hydrogens in the indicator molecules on dissolution in phosphorus oxychloride with formation of hydrogen chlorideii Colour changes are regarded as due to chloride ion transfer reactions ... 

Colour indicators, such as crystal violet may be used to follow chloride ion transfer reactions, the reactions being analogous to those described in phosphorus oxychloride (p 124 and 125). 

Here AI2CI7" is the characteristic acidic ion and Cl" the characteristic basic ion. This is again the chloride-ion transfer reaction. Addition of AICI3 increases the acidity of the solution while the addition of CP increases the basicity. In molten sulphates an analogous equilibrium is set up ... 

Metal deposition is an example of a more general class of electrochemical reactions, ion transfer reactions. In these an ion, e.g. a proton or a chloride ion, is transferred from the solution to the electrode surface, where it is subsequently discharged. Many ion-transfer reactions involve two steps. The hydrogen-evolution reaction, for example, sometimes proceeds in the following way ... 

Further, we consider an ion transfer reaction at a multiphase silver-silver chloride electrode in an aqueous chloride solution as shown in Fig. 6-7. The ion transfer reactions at the AgCl/Cl u, interface tmd at the Ag/AgCl interface are, respectively, given in Eqn. 6-19 ... 

Reaction 9 shows that the major portion of the reacting ethylene ions interact with ethyl chloride by discrete transfer steps including H" transfer, H2" transfer, and possibly Cl" transfer. Also, as discussed later, the total cross section for reaction of ethylene ions in this system is quite large (> 100 sq. A.). This may be compared with the corresponding reaction of ethylene ions with ethane, for which extremely small cross-sections have been found (44). In the latter case, however, the H" transfer reaction is endothermic, and the H2" transfer process would not have been detected in the previous experiments. These facts may explain the low reactivity reported. With ethyl chloride, H" transfer to ethylene ions is also indicated to be endothermic by the usual calculations. This suggests that the reactant ethylene ions in this system may well be vibra-tionally excited. It would also account for the chloride ion transfer to this ion, mentioned above. The ratio of rate constants observed for C2H4+ reaction with ethyl chloride is kU2-/ku- = 1.4. In addition to the reactions just discussed, part of the ethylene ion reactant forms a complex intermediate with CoH5C1, and elimination of HC1 and DC1 from this intermediate occurs with about equal probability. 

Chloride and fluoride ion-transfer reactions in halomethanes and haloethanes have also been studied by Dawson, Henderson, O Malley, and Jennings... 

An electrode of the second kind results, when a simple metal eleetrode is coupled to a precipitation equilibrium of a metal salt. The silver/silver chloride electrode is an example of this kind of electrodes (Fig. II.9.3b). Hence, the electrode reaction consists of the ion-transfer reaction and the precipitation of silver chloride... 

Due to the high donor properties of the solvent molecules halide ion-transfer reactions are limited in solutions of dimethyl sulphoxide. Although in the system C0CI2—TiCU chloride ion transfer gives in acetonitrile Co++ and [Tide]" and in trimethylphosphate [CoCla]" and [TiCla], no halide transfer is observed in dimethyl sulphoxide Complex iodides and complex bromides of class (a)... 

Now let us look at the electrolysis cell, which is also referred to as the electrolytic cell. An electrolysis cell contains three elements an electrolyte, a cathode, and an anode. The electrolyte is typically a solution of water or other solvent in which ions are dissolved or molten salts such as potassium chloride. Charge-transferring reactions take place at electrodes when an external voltage is applied to the electrodes the ions in the electrolyte flow to and from the electrodes. The decomposition of a normally stable or inert chemical compound in the solution takes place only if the applied external electrical potential is of correct polarity and large enough magnitude. 

One-electron oxidation of carboxylate ions generates acyloxy radicals, which undergo decarboxylation. Such electron-transfer reactions can be effected by strong one-electron oxidants, such as Mn(HI), Ag(II), Ce(IV), and Pb(IV) These metal ions are also capable of oxidizing the radical intermediate, so the products are those expected from carbocations. The oxidative decarboxylation by Pb(IV) in the presence of halide salts leads to alkyl halides. For example, oxidation of pentanoic acid with lead tetraacetate in the presence of lithium chloride gives 1-chlorobutane in 71% yield ... 

Since the rate was independent of acidity even over the range where H0 and pH differ, and the concentration of free amine is inversely proportional to the acidity function it follows that the rate of substitution is proportional to h0. If the substitution rate was proportional to [H30+] then a decrease in rate by a factor of 17 should be observed on changing [H+] from 0.05 to 6.0. This was not observed and the discrepancy is not a salt effect since chloride ion had no effect. Thus the rate of proton transfer from the medium depends on the acidity function, yet the mechanism of the reaction (confirmed by the isotope effect studies) is A-SE2, so that again correlation of rate with acidity function is not a satisfactory criterion of the A-l mechanism. 

Another two-phase system using phase-transfer catalysis for the oxidation of diaryl-iV-arylsulphonyl sulphilimines to sulphoximines has also been described188. In this reaction the oxidizing reagent is sodium hypochlorite and yields are in excess of 90% in most cases (equation 70). This reaction presumably occurs by initial attack by the nucleophilic hypochlorite ion on the sulphur atom followed by chloride ion elimination. 

Although widely used in the past and still used in special cases, the industrial sulfation with chlorosulfonic acid presents several problems which have caused the decline of this technique in favor of the more advantageous sulfation method with sulfur trioxide. These problems consist of evolution of the highly corrosive hydrogen chloride, heat transfer characteristics of the reaction, and the comparatively high level of chloride ion in the sulfated product compared with alcohol and alcohol ether sulfates obtained with sulfur trioxide. 

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