Oxidation-reduction chlorine

The manufacture of a dye from primary raw materials involves a number of prior synthetic stages and transformations, commonly referred to as unit processes. Such processes include nitration, sulfona-tion, diazotization, oxidation, reduction, chlorination, and others. The products, precursors of the dyes themselves, are collectively known as intermediates. Intermediates are produced by a variety of reactions. Many dye intermediates are manufactured by repeated, and often difficult, chemical reactions to obtain the desired product. Such conversion may be exemplified by the manufacture of a relatively simple intermediate, for example, N,-N-diabenzylaniline disulfonic acid. This conversion requires a number of unit processes, namely the nitration of benzene, the reduction of nitrobenzene, to give aniline, the alkylation of aniline leading to N,N-dibenzylaniline the sulfonation of which gives, finally, the disulfonic acid [11]. 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Both the Toth and Alcoa processes provide aluminum chloride for subsequent reduction to aluminum. Pilot-plant tests of these processes have shown difficulties exist in producing aluminum chloride of the purity needed. In the Toth process for the production of aluminum chloride, kaolin [1332-58-7] clay is used as the source of alumina (5). The clay is mixed with sulfur and carbon, and the mixture is ground together, pelletized, and calcined at 700°C. The calcined mixture is chlorinated at 800°C and gaseous aluminum chloride is evolved. The clay used contains considerable amounts of silica, titania, and iron oxides, which chlorinate and must be separated. Silicon tetrachloride and titanium tetrachloride are separated by distillation. Resublimation of aluminum chloride is requited to reduce contamination from iron chloride. 

The reddish brown pentachloride, uranium pentachloride [13470-21 -8], UCl, has been prepared in a similar fashion to UCl [10026-10-5] by reduction—chlorination of UO [1344-58-7] under flowing CCl, but at a lower temperature. Another synthetic approach which has been used is the oxidation of UCl by CI2. The pentachloride has been stmcturaHy characterized and consists of an edge-sharing bioctahedral dimer, U2CI2Q. The pentachloride decomposes in H2O and acid, is soluble in anhydrous alcohols, and insoluble in benzene and ethers. 

Va.na.dlum(III) Oxide. Vanadium(III) oxide (vanadium sesquioxide, V2O2) is a black soHd, having the comndum (AI2O2) stmcture. It can be prepared by reduction of the pentoxide by hydrogen or carbon. Air oxidation proceeds slowly at ambient temperatures, but oxidation by chlorine at elevated temperatures to give VOCl and V20 is rapid. 

The semiregenerative procedure for catalyst regeneration varies slightly between catalyst vendors however, it typically follows these general steps plant shutdown, carbon bum, oxidation and chlorination, nitrogen purge, reduction, and plant start-up. During the plant shutdown, Hquid hydrocarbons... 

Oxidation and chlorination of the catalyst are then performed to ensure complete carbon removal, restore the catalyst chloride to its proper level, and maintain full platinum dispersion on the catalyst surface. Typically, the catalyst is oxidized in sufficient oxygen at about 510°C for a period of six hours or more. Sufficient chloride is added, usually as an organic chloride, to restore the chloride content and acid function of the catalyst and to provide redispersion of any platinum agglomeration that may have occurred. The catalyst is then reduced to return the metal components to their active form. This reduction is accompHshed by using a flow of electrolytic hydrogen or recycle gas from another Platforming unit at 400 to 480°C for a period of one to two hours. 

Chloride Reductant. Processes prior to 1945 used hydrochloric acid as both the acid and reducing agent. Hydrochloric acid is oxidized to chlorine gas and chlorate is reduced to chlorine dioxide. The overall stoichiometry produces a 2 1 molar ratio of chlorine dioxide to chlorine. Sodium chloride is a by-product ... 

When chlorine gas is bubbled into a solution of NaOH, self-oxidation-reduction occurs to give hypochlorite ion, CIO-, by the reaction... 

In quantitative analysis we are chiefly concerned with reactions which take place in solution, i.e. ionic reactions. We shall therefore limit our discussion of oxidation-reduction to such reactions. The oxidation of iron(II) chloride by chlorine in aqueous solution may be written ... 

Similiar problems of regioselectivity as in reduction reactions are encountered in oxidation reactions of porphyrins and chlorins. The oxidation of chlorins to isobacteriochlorins can be directed by insertion of zinc(II) or nickel(II) into the macrocycle. Again here, the metal-free chlorins give the bacteriochlorins whereas the metal chlorins, e.g. 1, give isobacteriochlorins, e.g. 3.15a,b I 7... 

Phenanthridine (74) was converted by NBS into the 2-bromo derivative (40%) (55JA6379), but the bromine-sulfuric acid-silver sulfate reagent gave low yields of 1-, 4-, and 10-bromophenanthridines in the ratio (1 6.4 9.5), a reactivity order which contrasts with that found in nitration (1 > 10 > 4 > 2) (69AJC1105). Phosphoryl chloride converted phenanthridine 5-oxide into the 6-chloro derivative, but when that position was blocked by a phenyl substituent, the reductive chlorination process gave a 2-chloro compound (84MI2). 

The formation of carbon monoxide aids chlorination in exactly the same way as does the formation of carbon dioxide which of the two oxides of carbon would found in the reaction depends on the temperature at which reduction-chlorination is carried out. Below 600 °C carbon dioxide forms while above 700 °C carbon monoxide is formed. This changeover results from the variation in the free energies of formation of these two oxides with temperature. For example, at 900 °C the situation as regards the formation of titanium tetrachloride from titanium dioxide is guided by the reactions ... 

An extension of the reduction-chlorination technique described so far, wherein reduction and chlorination occur simultaneously, is a process in which the oxide is first reduced and then chlorinated. This technique is particularly useful for chlorinating minerals which contain silica. The chlorination of silica (Si02) by chlorine, in the presence of carbon, occurs above about 1200 °C. However, the silica present in the silicate minerals readily undergoes chlorination at 800 °C. This reaction is undesirable because large amounts of chlorine are wasted to remove silica as silicon tetrachloride. Silica is, therefore, removed by other methods, as described below, before chlorination. Zircon, a typical silicate mineral, is heated with carbon in an electric furnace to form crude zirconium carbide or carbonitride. During this treatment, the silicon in the mineral escapes as the volatile oxide, silicon monoxide. This vapor, on contact with air, oxidizes to silica, which collects as a fine powder in the furnace off-gas handling system ... 

Titanium tetrachloride is produced on an industrial scale by the chlorination of titanium dioxide-carbon mixtures in reactors lined with silica. During the reactor operation, the lining comes into contact not only with chlorine but also with titanium tetrachloride. There appears to be no attack on silica by either of these as the lining remains intact. However, the use of such a reactor for chlorinating beryllium oxide by the carbon-chlorine reduction chlorination procedure is not possible because the silica lining is attacked in this case. This corrosion of silica can be traced to the attack of beryllium chloride on silica. The interaction of beryllium chloride with silica results in the formation of silicon tetrachloride in accordance with the reaction... 

This reaction is also an oxidation-reduction process whereby the oxygen atom is oxidized from the —2 oxidation state to the zero oxidation state as the chlorine atom is reduced from the +1 to —1 oxidation state. As diatomic oxygen is an effective disinfectant, pool owners should avoid the loss of O2 via the decomposition of the hypochlorite ion. Adding hypochlorite-containing disinfectant in the evening hours reduces the loss of the ion from photochemical decomposition. 

The reactions that this sodium-chlorine case typifies are called oxidation-reduction reactions. The term oxidation refers to the loss of electrons, while the term reduction refers to the gain of electrons. A number of oxidation-reduction reactions (nicknamed redox reactions) are useful in titrimetric analysis, and many are encountered in other analysis methods. 

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. 

Chlorine reactions may be classified broadly under two types (i) oxidation-reduction and (ii) substitution reactions. The standard electrode potential for Cr — V2CI2 + e in aqueous solution is -1.36 V. Some examples of both types are highlighted briefly below ... 

In situ redox manipulation (ISRM) is an in situ, groundwater remediation technology for manipulating the oxidation-reduction (redox) potential of an unconfined aquifer to immobilize inorganic contaminants (metals, inorganic ions, and radionuclides) and to destroy organic contaminants (primarily chlorinated hydrocarbons). 

Treatment of 6-phenylphenanthridine N-oxide with phosphorus oxychloride results in reductive chlorination, the chlorine entering at position 2 (Scheme 12). 

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