Reactions with Halate Ions

Several studies have been published in which bromate ion has been used as an oxidant. In the rections with cyano(bipyridyl)iron(ii) complexes and [Fe(bipy)3] + autocatalysis is observed. The reaction stoicheiometry in excess BrOa is considered to be in accord with the reaction 

The reaction with [Fe(CN)2(bipy)2] is similar in mechanism. In both cases the first electron-transfer step is rate determining although there are probably parallel pathways having different dependencies. In the reaction as written, comparison of oxidation rates with those of Ce and V suggests the process to be outer-sphere in nature. For the complex [Fe(bipy)s] +, however, under 

In this case, the slow step is though to proceed via an inner-sphere process with rate-limiting loss of a water molecule from the bromine(v) ion. The mono-protonated species HBr02 has been proposed as the oxidant in the reaction with [Fe(phen)s] + in sulphuric acid solution. A variety of reduction products, from Br to Br, has been suggested in the reaction of cerium(iii) with bromate ions in sulphate media. At high acid concentrations Br and Br are favoured whereas at low acid Br- is formed. 

In the oxidation of hexachloroiridate(iii) by iodate ion the stoicheiometry is identical to that of the corresponding bromate system. The rate law is of the form 

XO3- + [IrOG] - + 2H+[H2X03-Irae]2-is a common feature. The calculated values for are of the order 5 x 10 , 50, and 

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As with FCIO2 and FIO2, hydrolysis regenerates the halate ion, the reaction with FBr02 being of explosive violence. Hydrolysis in basic solution at 0° can be represented as... 

Reaction of hypochlorite with bromide and iodide leads to formation first of the other hypohalite and then, more slowly, of the halates. With bromide ion, between pH 10 and 14, formation of hypobromite is the only significant process , although the halates were detected at lower pH. The rate equation... 

This method, very common in the analytical literature, gives an amplification factor of 6 and is the basis of a large number of amplification reactions. It can be applied using different oxidants, such as chlorine or bromine wateq or sodium hypochlorite. A method has been proposed for the simultaneous determination of iodide and bromide ions, and also for the determination of iodine and bromine in organic compormds. The method is based on the oxidation of both ions to their halates and titration of the iodate and bromate after reaction with iodide for... 

Studies of the oxidations of oxovanadium(iv) by halate ions have been reported. In the reaction with bromate ... 

The rate of oxidation of thiosulphate ion by chlorate and bromate is not small by comparison with other reactions of these halates. The chlorate reaction appears to have received only very fragmentary kinetic examination. The latter has been studied , but only reported as having a rate equal to fc[ ][BrOJ ] ]. The iodate reaction has been reported to have the stoichiometry... 

The halides Cr, Br" and I" react with [S20g] to form the elements, although r is partly oxidized to lOs . (Iodide in excess, however, is suitable to determine [S208] when followed by back titratioa) The ions Fe and markedly accelerate the reactions, a mixture of the two apparently being more effective than either alone. With Ag as a catalyst in the presence of HNO3, the halides are oxidized not to the free elements but to halates r lOa etc. 

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