Chlorine dioxide

Reaction of chlorine dioxide with chloride ion to form chlorite was found to obey the rate expression  

The reaction with iodide has been examined using a rapid-mixing device . Two slow steps were detected in the pH range 5.5-8.S. The first may be ascribed to formation of the species CIO2I and the second to its decomposition, yielding chlorite and iodine. Both reactions have small activation enthalpies, 7.4 and 0.8 kcal.mole , respectively. The intermediate is probably related closely to the species CI2O2 previously proposed (p. 376). 

Of the chlorine oxides only chlorine dioxide has achieved industrial significance. It is a gas at room temperature. As a result of its explosive properties, it can only utilized in situ and even then has to be diluted with inert gases (nitrogen, carbon dioxide) to 10 to 15% (by volume). 

When large quantities are required, it is manufactured from sodium chlorate, for smaller quantities from sodium chlorite. 

Sodium chlorate is reacted with hydrochloric acid  

The gaseous, explosive chlorine dioxide has to be immediately diluted with inert 

The most important side-reaction is the augmented formation of chlorine  

The physical process of filtration is rather effective in removing pathogens from water. During the 1800s, before chlorine came into widespread use, filtration with simple sand filters employed in just a few cities cut down significantly on the incidence of waterborne cholera in those cities. With modern membrane technology (see Section 5.10), ultrafiltration can remove even viruses from water. Small amounts of chlorine or chloramines (see Section 5.11.3) can be added to maintain sterile water in distribution systems, but much less of these agents are required for membrane-filtered water than are required for total disinfection. 

Chlorine is the most commonly used disinfectant employed for killing bacteria in water. When chlorine is added to water, it rapidly hydrolyzes 

The two chemical species formed by chlorine in water, HOCl and OCl , are known as free available chlorine and are very effective in kilting bacteria and other pathogens. In the presence of ammonia, HOCl reacts with ammonium ion to produce monochloramine (NH2CI), dichloramine (NHCI2), and trichloramine (NCI3), three species collectively called combined available chlorine. Although weaker disinfectants than chlorine and hypochlorite, the chloramines persist in water distribution systems to provide residual disinfection. 

A major problem with the use of chlorine as a disinfection agent is by-product production from the reaction of chlorine or bromine generated from chlorine with organics in water. The most common such by-products are the trihalomethanes including chloroform, HCCI3, and dibromochlo-romethane, HCBr2Cl, noted as water pollutants in Chapter 4, Section 4.13. Humic substances are common precursors to chlorinated by-products their removal before water chlorination prevents the formation of organochlorine by-products. 

Chlorine is used to treat water other than drinking water. It is employed to disinfect effluent from sewage treatment plants, as an additive to the water in electric power plant cooling towers, and to control microorganisms in food processing. 

The oxidation by Co(III) to chlorate in an acidic perchlorate medium has a simple stoichiometry 

Vol % of C102 in gas phase Weight of C102, grams per liter of solution  

Enthalpy and phase-equilibrium data for the binary system HC1-H20 are given by Van Nuys, Trans. Am. Inst. Chem. Engrs., 39, 663 (1943). 

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Lengyel I, Rabai G and Epstein I R Experimental and modelling study of oscillations in the chlorine dioxide-iodine-malonic acid reaction J. Am. Chem. See. 112 9104-10... 

Liquid chlorine dioxide, ClOj, boils at 284 K to give an orange-yellow gas. A very reactive compound, it decomposes readily and violently into its constituents. It is a powerful oxidising agent which has recently found favour as a commercial oxidising agent and as a bleach for wood pulp and flour. In addition, it is used in water sterilisation where, unlike chlorine, it does not produce an unpleasant taste. It is produced when potassium chlorate(V) is treated with concentrated sulphuric acid, the reaction being essentially a disproportionation of chloric(V) acid ... 

Industrially an aqueous solution of chlorine dioxide can be prepared by passing nitrogen dioxide up a packed tower down which sodium chlorate(V) flows ... 

The aqueous solution is safe to handle, the dissolution being essentially physical. On standing in sunlight the solution slowly decomposes to a mixture of acids. In alkaline solution a mixture of chlorate(lll), CIO2, and chlorate(V), CIO J, ions is rapidly produced. Chlorine dioxide is paramagnetic, the molecule containing an odd electron and having a structure very like that of NOj (p. 231). 

Dichlorine hexoxide. CKO, is formed when chlorine dioxide is... 

Only chloric(III) acid, HCIO2, is definitely known to exist. It is formed as one of the products of the reaction of water with chlorine dioxide (see above). Its salts, for example NaClOj, are formed together with chlorates)V) by the action of chlorine dioxide on alkalis. Sodium chlorate(III) alone may be obtained by mixing aqueous solutions of sodium peroxide and chlorine dioxide ... 

Chlorine dioxide Ammonia, carbon monoxide, hydrogen, hydrogen sulflde, methane, mercury, nonmetals, phosphine, phosphorus pentachloride... 

Phosphorus pentachloride Aluminum, chlorine, chlorine dioxide, chlorine trioxide, fluorine, magnesium oxide, nitrobenzene, diphosphorus trioxide, potassium, sodium, urea, water... 

Chlorine oxygen acids and salts, chlorous acid, chlorites, and chlorine dioxide... 

Cm ORINE OXYGEN ACIDS AND SALTS - DICTD ORINE MONOXIDE, HYPOCTD.OROUS ACID, AND HYPOCm ORITES] (Vol 5) Chlorous acid, chlorites, and chlorine dioxide... 

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