Oxides of the Halogens

Over a dozen oxides of the halogens have boon characterized, many of them quite unstable. Perhaps the most important are chlorine dioxide, CJ02, and iodine pentoxide, I2O5. Chlorine dioxide (boiling point 11° C) is an odd molecule (p. 62), but apparently it shows no tendency to dimerize. Although it has been used as an antiseptic in water purification and as a bleach, it must be handled in diluted form for it is explosive when alone. It is formed, along with HCIO4, when chlorates are treated with concentrated sulfuric acid, but a safer preparation involves reduction of a chlorate with oxalic acid. 

The hypohalite ions, OCl, OBr, and OI, are formed (along with equivalent quantities of the corresponding halide ions) when the elemental halogens are hydrolyzed in basic solution. Two solid hypobromites and several solid hypochlorites have been isolated. The so-called bleaching powder or chloride of lime, prepared by treatment of calcium hydroxide with chlorine, is often described as a mixed salt Ca(OCl)Cl (however, 

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During the past 20 y numerous other highly coloured halogen cations have been characterized by Raman spectroscopy. X-ray crystallography, and other techniques, as summarized in Table 17.18. Typical preparative routes involve direct oxidation of the halogen (a) in the absence of solvent, (b) in a solvent which is itself the oxidant (e.g. AsFs) or (c) in a non-reactive solvent (e.g. SO2). Some examples are listed below ... 

Electron transfer to the metal centre results in oxidation of the halogen and the complex then dissociates. The relative quantum yields are high (0.1 to 1) when irradiation is made in the GT band in complexes with Br or I this reaction is still observed with irradiation in the d-d bands, but the quantum yields are then lower. 

There are ten oxides of the halogens. Chlorine forms the greatest and iodine the least number. 

F and Cl atoms react readily in this manner. Br atoms can abstract hydrogen atoms only from H02 or aldehydes I atoms are even less reactive. The alternative to the Cl + RH reaction is oxidation of the halogen atom (X = Cl, Br, I) by ozone ... 

Iodine pentoxide, I2O5, is the most stable oxide of the halogens [8]. It has found some practical application as a mild oxidant, especially useful in analytical chemistry. Iodine pentoxide is one of the few chemicals that can oxidize carbon monoxide rapidly and completely at room temperature. The reaction forms the basis of a useful analytical method for determining the concentration of CO in the atmosphere or in other gaseous mixtures [8]. 

The oxides of the halogens are generally highly reactive compounds. Chlorine oxide has been extensively studied due to its role in the destruction of stratospheric ozone. Chlorine dioxide is a powerful chlorinating and bleaching agent. Iodine pentoxide is used to quantitatively determine carbon monoxide concentrations. 

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