Bromates, alkali

Alkali bromates are mainly manufactured by the electrochemical oxidation of bromide in a process similar to that for the manufacture of sodium chlorate (see Section 1.7.4.2.3)  

Alternatively they can be manufactured by passing bromine into alkali hydroxide solutions, whereupon disproportionation takes place with the formation of a mixture of bromide and bromate (see Section 1.7.5.2.1), from which the more poorly soluble bromate is separated. 

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Lead Bromate (Monohydrate). Pb(Br03)2.H20 mw 481.06, colorless crysts, mp (decomp at 180°), d 5.53g/cc si sol in cold w, moderately in hot w. Poisonous Pure Pb bromate is not dangerous, but when prepd by the action of Pb acetate on an alkali bromate, the unstable diaceto-diplumbo-bromate is always present. This complex explodes violently on heating, striking or rubbing... 

The alkali bromates.—According to C. F. Rammelsberg,28 lithium bromate,... 

Another method for preparing alkali bromates is by electrolysis of bromine in alkali solutions. Anodes coated with Pb02 are used and a small amount of dichromate is added to prevent reduction of BrO- at the cathode (76). 

Imaeda S9) investigated the chlorine and the bromine NQR in alkali chlorates and alkali bromates at 0 °C as a function of impurity concentration. Brom-ates, chlorates, and nitrates served as impurities. The results of Imaeda s investigation are given in Table VI.2. There is a considerable frequency shift, which is mostly negative (decrease in frequency) if the impurity ions are larger in size than the host ions. In cases where the impurity is smaller than the host ion, the frequency increases. Imaeda assumes that the distortion of the electronic wave functions about the impurities is responsible for the frequency shift. Temperature effects are ruled out since the impurity shift in the bromates... 

Alkali bromates are sensitive to heat and shock. They are utilized e.g. in the treatment of flour and in hair. setting lotions. 

Note Pure lead bromate is not dangerous, but when made by pptng lead acetate with an alkali bromate, it may detonate or explode on heating, striking or rubbing because some acetate is occluded. 

The modes of thermal decomposition of the halates and their complex oxidation-reduction chemistry reflect the interplay of both thermodynamic and kinetic factors. On the one hand, thermodynamically feasible reactions may be sluggish, whilst, on the other, traces of catalyst may radically alter the course of the reaction. In general, for a given cation, thermal stability decreases in the sequence iodate > chlorate > bromate, but the mode and ease of decomposition can be substantially modified. For example, alkali metal chlorates decompose by disproportionation when fused ... 

The classical methods used to separate the lanthanides from aqueous solutions depended on (i) differences in basicity, the less-basic hydroxides of the heavy lanthanides precipitating before those of the lighter ones on gradual addition of alkali (ii) differences in solubility of salts such as oxalates, double sulfates, and double nitrates and (iii) conversion, if possible, to an oxidation state other than -1-3, e g. Ce(IV), Eu(II). This latter process provided the cleanest method but was only occasionally applicable. Methods (i) and (ii) required much repetition to be effective, and fractional recrystallizations were sometimes repeated thousands of times. (In 1911 the American C. James performed 15 000 recrystallizations in order to obtain pure thulium bromate). 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

Intimate mixtures of chlorates, bromates or iodates of barium, cadmium, calcium, magnesium, potassium, sodium or zinc, with finely divided aluminium, arsenic, copper carbon, phosphorus, sulfur hydrides of alkali- and alkaline earth-metals sulfides of antimony, arsenic, copper or tin metal cyanides, thiocyanates or impure manganese dioxide may react violently or explosively, either spontaneously (especially in presence of moisture) or on initiation by heat, friction, impact, sparks or addition of sulfuric acid [1], Mixtures of sodium or potassium chlorate with sulfur or phosphorus are rated as being exceptionally dangerous on frictional initiation. 

Reaction 12.21 illustrates the trend toward lower electronegativity (less oxidizing power) as one descends a periodic group. The bromine vapor is trapped in aqueous Na2C03 (in effect, a mild source of alkali) as bromide and bromate ions... 

Hydrofluoric acid like water is an associated liquid, and even the gas, as we shall soon see, is associated. It has the power of uniting with fluorides. It also seems to be an ionizing solvent for a soln. of potassium fluoride in liquid hydrogen fluoride is an excellent conductor it also possesses marked solvent powers. According to E. C. Franklin,7 the liquid readily dissolves potassium fluoride, ehloride, and sulphate sodium fluoride, bromide, nitrate, chlorate, and bromate acetamide and urea. The solvent action is not so marked with barium fluoride, cupric chloride, and silver cyanide while calcium and lead fluorides copper sulphate and nitrate ferric chloride, mercuric oxide, and magnesium metal, are virtually insoluble in this menstruum. Glass also is not affected by the liquid if moisture be absent. The liquid scarcely acts on most of the metals or non-metals at ordinary temp., though it does act on the alkali metals at ordinary temp., much the same as does water, with the simultaneous production of flame. 

By shaking bromine water with finely divided magnesia, C. Lowig obtained a yellow liquid which at first behaved like an alkali towards litmus, but a more protracted action removed the colour, and when treated with weak acids gave off bromine. It is therefore supposed to be a soln. of magnesium hypobromite. A. J. Balard found that the soln. is decomposed by exposure to light, heat, or by evaporation in vacuo, and with an excess of bromine is converted into magnesium bromide and bromate. 

The violence of the explosion is feebler with iodates than it is with chlorates or bromates. The chlorates transform lead oxide to the dioxide manganese oxide in fused alkalies to manganates etc. Ammonium iodate explodes when heated alone. Chloric, bromic, and iodic acids with their salts are energetic oxidizing agents. 

Cerous iodates and the iodates of the other rare earths form crystalline salts sparingly soluble in water, but readily soluble in cone, nitric acid, and in this respect differ from the ceric, zirconium, and thorium iodates, which are almost insoluble in nitric acid when an excess of a soluble iodate is present. It may also be noted that cerium alone of all the rare earth elements is oxidized to a higher valence by potassium bromate in nitric acid soln. The iodates of the rare earths are precipitated by adding an alkali iodate to the rare earth salts, and the fact that the rare earth iodates are soluble in nitric acid, and the solubility increases as the electro-positive character of the element increases, while thorium iodate is insoluble in nitric acid, allows the method to be used for the separation of these elements. Trihydrated erbium iodate, Er(I03)3.3H20, and trihydrated yttrium iodate, Yt(I03)3.3H20,... 

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