Chlorine dioxide dissociation

Tratnyek and Hoigne (1994) investigated 25 substituted phenoxide anions for QSARs that can be used to predict rate constants for the reaction of additional phenolic compounds oxidized by chlorine dioxide (OCIO). Correlating oxidation rates of phenols in aqueous solution is complicated by the dissociation of the phenolic hydroxyl group. The undissociated phenol and the phenoxide anion react as independent species and exhibit very different properties. The correlation analysis should be performed on the two sets of rate constants separately. 

Perhaps the first significant experiments on transfer of vibrational energy were performed in Norrish s laboratory at Cambridge29. When chlorine dioxide is exposed to radiation of the appropriate wavelength it dissociates... 

The oxidation of tris-(l,10-phenanthroline)iron(ii) by chlorite, chlorate, and chlorine dioxide has been investigated, " and the mechanism compared with that for the reaction of chlorine. In the case of QOa" and Qa, the reaction rate is controlled by the first dissociation step of the [Fe(phen)a] ... 

Solid chlorine dioxide polyhydrate cem be handled safely at low temperatures, usually in the form of blocks encased in ice coatings (227), and it is frequently shipped cold and regenerated as a gas (228) for bleaching flour. Stable liquid mixtures of chlorine dioxide with chlorine at low temperatures are also reported (212). It has been alleged that pyridine and chlorine dioxide form a stable solid complex that can be used to furnish free chlorine dioxide on addition of water (216). Chlorine dioxide is reported (2) to form a complex of low volatility in solution with neutral or basic perborate, which supposedly can be again dissociated by acidification of the solution with release of chlorine dioxide. In fact, the stabilized solutions have all the properties of neutral or slightly basic solutions of chlorite ion, which disproportionate upon the addition of acid. 

These chlorine radicals are the ozone-removing agents. They react with ozone to form chlorine monoxide radicals and molecular oxygen. The chlorine monoxide radical then reacts with more ozone to form chlorine dioxide, which dissociates to regenerate a chlorine radical. These three steps—two of which each destroy an ozone molecule— are the propagating steps that are repeated over and over. It has been calculated that a single chlorine atom destroys 100,000 ozone molecules ... 

Chemical Properties. The chemistry of the sulfur chlorides has been reviewed (141,142). Sulfur monochloride is stable at ambient temperature but undergoes exchange with dissolved sulfur at 100°C, indicating reversible dissociation. When distilled at its atmospheric boiling point, it undergoes some decomposition to the dichloride, but decomposition is avoided with distillation at ca 6.7 kPa (50 mm Hg). At above 300°C, substantial dissociation to S2 and CI2 occurs. Sulfur monochloride is noncombustible at ambient temperature, but at elevated temperatures it decomposes to chlorine and sulfur (137). The sulfur then is capable of burning to sulfur dioxide and a small proportion of sulfur trioxide. 

Chemical Properties. The chemistry of sulfuryl chloride has been reviewed (170,172,195). It is stable at room temperature but readily dissociates to sulfur dioxide and chlorine when heated. The equiUbrium constant has the following values (194) ... 

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

Physical Properties.—Sulphuryl chloride is a colourless, fuming liquid, with an extremely pungent odour. Z)2 = 1-6074 ->t " = l-4437. It boils at 69-1° C. at 760 mm. pressure, and freezes at —46° C.5 The vapour density is normal at first, but when the chloride is kept, even at 100° C., its vapour commences to dissociate into sulphur dioxide and chlorine. At 200° C. dissociation is almost complete.6 When dissolved in benzene the substance shows a molecular- weight corresponding with S02C12. At ordinary temperatures the specific heat is 0-233, the latent heat of evaporation 32-4 calories per gram, and the heat of formation from the elements approximately 89,540 calories per gram-molecule.7 The dielectric constant at 20° C. is 8-5. As a solvent, the ebullioscopic constant of sulphuryl chloride has been found to have... 

At 200° C. sulphuryl chloride converts sulphur into monochloride, this result probably being preceded by dissociation of the sulphuryl chloride into chlorine and sulphur dioxide. In the presence of aluminium chloride this reaction can be effected even at the ordinary temperature, and aluminium chloride is known to favour the dissociation of sulphuryl chloride ... 

The next step, addition (equation 83) of molecular oxygen to C1CO, involves the intermediacy of the unstable chloroformylperoxy radical, which may readily dissociate (equation 84) to chlorine monoxide and carbon dioxide. 

The implication of this mechanism is that the most ideal catalyst under the most optimum conditions would transform six ethylene molecules into EO and one ethylene molecule into water and carbon dioxide. Hence, according to this theory, the selectivity can never exceed 6/7. This theory also explains the favourable influence of chlorine. It was known that chlorine selectively poisons sites on Ag which can adsorb O2 dissociatively. As atomic oxygen was considered to be... 

Chemically much more inert than chlorine, phosgene is a very stable compound and is not dissociated by cxplo. bursting charges. When dry, phosgene does not attack iron ami may, therefore, be kept indefinitely in iron and steel containers. It is, however, extremely sensitive to water, in contact with which it quickly breaks down into hydroehlorii acid and carbon dioxide, according to the equation... 

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