Oxidation-reduction reactions sodium chloride

In solution, NaOCl dissociates into sodium ions (Na+) and hypochlorite ions (OC1). Bleaching involves an oxidation-reduction reaction in which the Cl in the OC1 ion (oxidizing agent) is reduced to the chloride ion (Cl ). The reducing agent is either a dye, which fades, or the stain being removed. 

If a chemical reaction can make electricity it should not be surprising to learn that electricity can make a chemical reaction. Using an electric current to cause a chemical reaction is called electrolysis, a technique widely used to win elements from their compounds. For example, pure sodium metal (Na) and chlorine gas (CI2) are obtained by passing electricity through molten sodium chloride (NaCl). The study of the interplay of electricity and oxidation-reduction reactions is called electrochemistry. 

An oxidation-reduction reaction occurs when sodium and chlorine react to form sodium chloride, as shown in Figure 11.1. The equation for this reaction is... 

Stannous hydroxide, Sn(OH)2, is formed by adding dilute sodium hydroxide solution to stannous chloride. It is readily soluble in excess alkali, producing the stannite ion, Sn(OH)g . When a solution containing stannite ion is boiled an auto-oxidation-reduction reaction occurs, with deposition of metallic tin and production of the stannate ion, Sn(OH)g- ... 

Sodium metal and chlorine gas react violently to form sodium chloride. Oxidation and reduction happen together in this reaction. 

The concept of oxidation states (sometimes called oxidation numbers) lets us keep track of electrons in oxidation-reduction reactions by assigning charges to the various atoms in a compound. Sometimes these charges are quite apparent. For example, in a binary ionic compound the ions have easily identified charges in sodium chloride, sodium is +1 and chlorine is -1 in magnesium oxide, magnesium is +2 and oxygen is -2 and so on. 

We have discussed the formation of sodium chloride before and have noted that it is an oxidation-reduction reaction uncharged sodium atoms lose electrons to form Na ions, and uncharged chlorine atoms gain electrons to form Cl ions. The synthesis of magnesium fluoride is also an oxidation-reduction reaction because Mg and F ions are produced from the uncharged atoms. 

Voltaic cells are based on spontaneous oxidation-reduction reactions. Conversely, it is possible to use electrical energy to cause nonspontaneous redox reactions to occur. For example, electricity can be used to decompose molten sodium chloride into its component elements ... 

To reverse this half-reaction and bring about the oxidation of water, we need an applied potential difference of at least 0.82 V. Suppose the added salt is sodium chloride. When Cl ions are present at 1 mol-L 1 in water, is it possible that they, and not the water, will be oxidized From Table 12.1, the standard potential for the reduction of chlorine is Cl.36 V ... 

The large cell used for the electrolysis of sodium chloride in industry is known as a Downs cell. To decrease heating costs, calcium chloride is added to lower the melting point of sodium chloride from about 800°C to about 600°C. The reaction produces sodium and calcium by reduction at the cathode, and chlorine by oxidation at the anode. 

Electrochemical oxidation of aldoximes using halide ions as mediators afforded the corresponding nitrile oxides in the anode compartment, which were simultaneously reduced to nitriles by cathodic reduction (equation 15). Sodium chloride affords the best result among the supporting electrolytes (Cl > Br > 1 > C104 > TsO ). Accordingly, the electrochemical reaction of oximes carried out in the presence of dipolephiles yielded isooxazolines (equation 16). 

Synthetically useful routes to dibenzo[c,e J[l,2]dithiins are normally based on cyclizations of biphenyI-2,2 -disulfonyl chlorides. A method applied successfully to the parent compound reduces the precursor with zinc in acetic acid to generate the bis thiol, which is then gently oxidized to the dithiin using iron(II) chloride (66HC(21-2)952). An alternative one-step reductive cyclization, which has been applied to the preparation of the 2,9- and 3,8-dinitro derivatives, involves reduction of the appropriate bis sulfonyl chlorides with hydriodic acid in acetic acid (68MI22600). Yet another reductive cyclization uses sodium sulfite followed by acidification, and these conditions lead to dibenzo[c,e][1,2]dithiin 5,5-dioxide. The first step of the reaction is reduction to the disodium salt of biphenyl-2,2 -disulfinic acid which, on acidification, forms the anhydride, i.e. dibenzo[c,e][l,2]dithiin 5,5,6-trioxide. This is not isolated, but is reduced by the medium to the 5,5-dioxide (77JOC3265). Derivatives of dibenzo[c,e] [1,2]dithiin in oxidation states other than those mentioned here are obtainable by appropriate oxidation or reduction reactions (see Section 2.26.3.1.4). 

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