Bromate

The nature of chemical oscillations, especially those involving bromate ion, are currently of considerable interest. Many of these processes involve oxidation of malonic acid, and the conditions for the onset of chemical oscillation have been described,following accumulation of bromomalonic acid (BrMA). The extent of formation which is critical is dependent on [Br03 ]o and on the 

Further details of the mechanism have been described/ In the simplest outline, the dynamic features of the system may be defined by the kinetics of the oxidation of Ce(III) by BiOf, while reduction of cerium(IV) by BrMA provides a linear feedback. Studies on the manganese(II)-catalyzed reaction in orthophosphoric acid have been published.A kinetic study has also been made of the bromate-malonic-acid-ascorbic acid system.A very slow reaction between ascorbic acid and Br03 (k2 3 x 10 M s ) is identified and a rapid process between Br and the same substrates. The resultant variations of ascorbic acid concentration show maxima and minima with time. 

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In the bromate-iron clock reaction, there is an autocatalytic cycle involvmg the species intennediate species HBrO. This cycle is comprised of the following non-elementary steps ... 

The bromate-ferroin reaction has a quadratic autocatalytic sequence, but in this case the induction period is detennined primarily by the time required for the concentration of the hiliibitor bromide ion to fall to a critical low value tlirough the reactions... 

Field R J, Koros E and Noyes R M 1972 Csoillations in ohemioal systems, part 2 thorough analysis of temporal osoillations in the bromate-oerium-malonio aoid system J. Am. Chem. Soo. 94 8649-64... 

Zhabotinsky A M, Buohholtz F, Kiyatin A B and Epstein I R 1993 Csoillations and waves in metal-ion oatalysed bromate osoillating reaotion in highly oxidised states J. Phys. Chem. 97 7578-84... 

The existence of chaotic oscillations has been documented in a variety of chemical systems. Some of tire earliest observations of chemical chaos have been on biochemical systems like tire peroxidase-oxidase reaction [12] and on tire well known Belousov-Zhabotinskii (BZ) [13] reaction. The BZ reaction is tire Ce-ion-catalyzed oxidation of citric or malonic acid by bromate ion. Early investigations of the BZ reaction used tire teclmiques of dynamical systems tlieory outlined above to document tire existence of chaos in tliis reaction. Apparent chaos in tire BZ reaction was found by Hudson et a] [14] aiid tire data were analysed by Tomita and Tsuda [15] using a return-map metliod. Chaos was confinned in tire BZ reaction carried out in a CSTR by Roux et a] [16, E7] and by Hudson and... 

The stability of the halate(I) ion decreases, as expected, from C10 to 10 and only the chlorate(I) ion can be considered reasonably stable even in aqueous solution. Solid sodium bromate(I). NaBrO (with five or seven molecules of water of crystallisation) can be obtained, but on standing or warming it disproportionates ... 

Chlorine, bromine and iodine form halic(V) acids but only iodic(V) acid, HIO3, can be isolated. Solutions of the chloric) V) and bromic) V) acids can be prepared by the addition of dilute sulphuric acid to barium chlorate(V) and bromate(V) respectively, and then filtering (cf. the preparation of hydrogen peroxide). These two acids can also be prepared by decomposing the corresponding halic(I) acids, but in this case the halide ion is also present in the solution. 

Unexpectedly we find that the bromate(V) ion in acid solution (i.e. effectively bromic(V) acid) is a more powerful oxidising agent than the chlorate(V) ion, CIO3. The halates(V) are thermally unstable and can evolve oxygen as one of the decomposition products. Potassium chlorate(V), when heated, first melts, then resolidifies due to the formation of potassium chlorate(VII) (perchlorate) ... 

The ability of the solid chlorates(V) to provide oxygen led to their use in matches and fireworks. Bromates(V) and iodates(V) are used in quantitative volumetric analysis. Potassium hydrogen diiodate(V), KHflOjlj, is used to standardise solutions of sodium thiosulphate(Vf) since in the presence of excess potassium iodide and acid, the reaction... 

Xhe existence of chloric(VII), (perchloric), HCIO4, and several periodic(VII) acids has long been established. Bromic(VlI) acid and the bromate(VII) ion have only recently been discovered. 

Principle. An organic compound which contains chlorine is mixed with sodium peroxide and ignited in a closed metal bomb. The chlorine is thus converted to sodium chloride, and after acidification the chloride is estimated by the Volhard volumetric method. Bromine and iodine, when constituents of organic compounds similarly treated, are converted largely into sodium bromate and iodate respectively these ions are therefore subsequently reduced by hydrazine to bromide and iodide ions, and estimated as before. 

Benzilic acid may be obtained in a high state of purity by the action of an alkaline bromate solution upon benzoin at 85-90° ... 

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