Formation of halates

Second-order reactions in this region have been reported by a number of other authors -and also in more strongly alkaline solution - . Whether the reaction under the latter conditions has rates dependent on alkalinity has been contested. The earlier independence claimed may be an accident arising from the particular experimental temperature (50 °C) used. In any case, the rate in alkaline solutions is much greater than would be predicted from results near neutrality. A different mechanism is doubtless operative. The following rate parameters are reported  

Weiss represented the rates of reaction in alkaline solution by the equation 

The authors suggest that the activated complexes may have structures (Cl-O-O-Cr) and (O-Cl-O-Cl ), or, conceivably, be cyclic. Some earlier reports indicated first-order dependence of rate on hypochlorite concentration. Whilst this could reflect an undetected kinetic dependence on a catalyst concentration, probably the observations are spurious and arise from delays in the evolution of oxygen due to supersaturation. 

The decomposition in acidic solution may be second- or third-order in hypo-chlorous acid. A series of studies by Skrabal et o/. , with the evaluation of the value of the acid dissociation constant for HOCl by kinetic measurements as their goal, noted that the reaction order decreases from three to two as the acidity decreases . It was claimed that, in almost neutral solution, the rate equation 

The third-order dependence reported by Foerster and Dolch , 

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The formation of halate(V) and halide ions by reaction (11.4) is favoured by the use of hot concentrated solutions of alkali and an excess of the halogen. 

As mentioned in Section I, disproportionation occurs most rapidly at a pH corresponding to the pKa value [Eq. (12). The velocity of formation of halate increases greatly in the order C103 < Br03 < 107 this order correlates directly with the leaving-group tendencies of the respective halide ion (see Table I). 

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