Halogens and Their Compounds

The first large-scale use of chlorine was for bleaching paper and cotton textiles it also is widely used as a germicide for public water supplies. Presently it is used principally in production of the chemical compounds sulfur chloride, thionyl chloride, phosgene, aluminum chloride, iron(ni) chloride, titaniura(IV) chloride, tin(IV) chloride, and potassium chlorate. 

Organic chemicals made directly from chlorine include derivatives of methane methyl chloride, methylene chloride, chloroform, carbon tetrachloride, chlorobenzene ortho- and para-dichlorobenzenes ethyl chloride, and ethylene chloride. 

The oldest process for chlorine production used hydrochloric acid reacting with manganese 

The fluorine industry is intimately related to aluminum production. Aluminum oxide, (AljOj) is electrolyzed to metallic aluminum with a flux of sodium fuoroaluminate (Na AlF,), called cryolite - a rare mineral found in commercial quantities only in Greenland with other uses glass, enamels, and as a filler for resin-bonded grinding wheels. 

Synthetic cryolite solved the supply problem, but synthetic cryolite requires fluorine which is actually more abundant in the Earth s crust than chlorine, but dispersed in small concentrations in rocks. Until the 1960s, fluorspar (CaFj) a mineral long known and used as a flux in various metallurgical operations was the source. A source is phosphate rock that contains fluorine i.s 3% quantity, 

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Table 17.1 Early history of the halogens and their compounds...

In the works of Bray (28) and Abel (29) on the reactions between hydrogen peroxide and the halogens and their compounds many examples of branched sequences can be found. 

Reaction conditions for the oxidation of secondary alcohols by halogens and their compounds are shown in equations 265-268. 

Applications of the halogens and their compounds are widespread in industry, health care, and other areas. One is fluoridation, the practice of adding small quantities of fluorides (about 1 ppm by mass) such as NaF to drinking water to reduce dental caries. 

Asbestos (suspended particulate matter and fibers), glass fibers, and mineral fibers Halogens and their compounds, phosphorus and its compounds, and particulate matter... 

Organic compounds and partial oxidation compounds (rubber and plastics, organic solvents, chlorinated hydrocarbons and fluorocarbons, volatile organic compounds, CH, etc.) Organometallic compounds Halogens and their compounds (As, AsH, etc.)... 

The relationship between the efficiency of the substances inhibitor action and the nature of the halogen and the effect of small concentration of additives confirm that the inhibitor mechanism of halogens and their derivatives on the ignition and combustion of model systems has a chemical origin. It was discovered that halogens and their compounds do not affect the oxidation of carbon to carbon dioxide [63]. At the same time, they essentially inhibit the oxidation of CO to CO2 [64] and the formation of formaldehyde during combustion of methane. 

Fluorine, found at the top of Group 17, is the most reactive of all the non-metallic elements and is a powerful oxidising agent. The next element in Group 17 is chlorine, also a toxic gas, but its compounds, such as trichlorophenol, are important disinfectants. Compounds of carbon, fluorine and chlorine are known as CFCs and have been responsible for most of the damage to the Earth s ozone layer. You can read more about uses of the halogens and their compounds on page... 

Recall important items of information and generalizations about the halogens and their compounds, and combine them with others to gain new insights into the chemistry of the elements. (Questions 6.1-6.10)... 

Metals in the platinum family are recognized for their ability to promote combustion at lowtemperatures. Other catalysts include various oxides of copper, chromium, vanadium, nickel, and cobalt. These catalysts are subject to poisoning, particularly from halogens, halogen and sulfur compounds, zinc, arsenic, lead, mercury, and particulates. It is therefore important that catalyst surfaces be clean and active to ensure optimum performance. 

Chemical properties of iodine are quite similar to those of other halogens, especially chlorine and bromine. However, being less electronegative than chlorine and bromine, its reactivity towards most metals, nonmetals, and their compounds may differ vastly. All iodine reactions occur in vapor phase or aqueous media. Vapor phase reactions require elevated temperatures. 

The rules discussed so far allow us to make educated guesses about possible compounds formed by elements. However, not all compounds deduced by application of the rules actually exist. Moreover, some elements have more oxidation numbers than the rules identify. Nitrogen, for example, exhibits every integral oxidation number from -3 to +5, as well as a fractional oxidation number, -5, in HN3 and its salts. Except for fluorine, the halogens also exhibit most of the integral oxidation numbers from -1 to +7. Detailed study of the chemistry of the elements and their compounds is necessary to know which compounds actually exist. 

Everyday uses of halogens or their compounds are well known, such as the use of chlorine in purifying drinking water, the use of iodine as an antiseptic, and the use of bromine in photographic films as the compound silver bromide. 

Halogens and their covalent compounds Metal carbonyls Organometallic compounds Oxidizing agents Polychlorinated dibenzofuran Polychlorinated dibenzo-p-dioxin... 

At first sight there seems to be an anomaly in the reactions involving the free halogens and their oxygen compounds. Thus, although chlorine is able to liberate iodine from iodide ion, icxiine is able to liberate chlorine from chlorate ion,.according to the reaction... 

Halogens and their oxygen-containing compounds are useful and selective oxidants for secondary alcohols. The addition of a chlorine solution in carbon tetrachloride to a chloroform solution of 5a-cholestane-3p,19-diol below 30 °C gives a 77% yield of 5a-cholestan-19-ol-3-one after 15 min [681]. 

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