Preparation and General Properties of the Halogens

Because fluorine and chlorine are strong oxidizing agents, they must be prepared by electrolysis rather than by chemical oxidation of the fluoride and chloride ions. Electrolysis does not work for aqueous solutions of fluorides, however, because fluorine is a stronger oxidizing agent than oxygen. From Table 19.1. we find that 

Chlorine gas (CI2) is prepared industrially by the electrolysis of molten NaCl or by the chlor-alkali process, the electrolysis of a concentrated aqueous NaCl solution (called brine). (Chlor denotes chlorine, and alkali denotes an alkali metal, such as sodium.) Two of the common cells used in the chlor-alkali process are the mercury cell and the diaphragm cell. In both cells, the overall reaction is 

As you can see, this reaction yields two useful by-products, NaOH and H2. The cells are designed to separate the molecular chlorine from the sodium hydroxide solution and the molecular hydrogen to prevent side reactions such as 

These reactions must be prevented because they consume the desired products and can be dangerous because a mixture of H2 and CI2 is explosive. 

Anode (oxidation) Cathode (reduction) Overall reaction  

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General Properties of Compounds of Niokel—Preparation of Nickel Salts free from Cobalt—Niokel and the Halogens—Oxides of Niokel—Nickel and Sulphur—Niokel and Selenium, Tellurium, Chromium, and Molybdenum—... 

Structural modifications of polyaniline have mainly been exploited to achieve improved processability and environmental stability. In general, the substituted polyanilines can be obtained via oxidative polymerization of the corresponding monomer. However, inductive and steric effects can make such monomers difficult to polymerize [42]. Several substituted polyanilines have been prepared by varying the nature (alkyl, alkoxy, halogen, etc.) and the position (2- vs 3-, 5-positions) of the substituent [24, 27-32, 34, 37, 43, 44]. These studies have shown that regardless of the nature and position of the substituent group, there is an adverse effect on polymerization and the properties of the polymer such as conductivity and electroactivity. To overcome these limitations, various synthetic methods have been developed to prepare self-doped sulfonated polyanilines. These methods involve controlled postpolymerization modifications by synthetic reactions on the whole polymer and copolymerization of less reactive monomers with aniline as described below. 

In addition to this work on charcoal- and silica-supported catalysts and on evaporated platinum films, a number of studies have been made on alumina-supported platinum catalysts (e.g., 111-114, 81,115) in which the aim has been the study of reactions at the platinum alone. In these cases, one cannot automatically dismiss the possibility of participation of the alumina support (i.e., of dual function behavior of the catalyst) because it is known that alumina may have acidic properties, particularly when retained halogen is present. In general terms, there is no immediate answer to this problem because the nature of this sort of catalyst wall be much dependent on the details of catalyst history, preparation, and use. However, there can be little doubt that in many experimental studies using plati-num/alumina, and in which the assumption has been made that the alumina support is inert, this assumption is essentially valid. For instance, one may note the inert alumina used by Davis and Venuto (111) and the justification provided by Gault et al. (116) for the inertness of the alumina used in a substantial body of previous work irrespective of whether the catalyst was... 

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