Alkali metal bromides

Interaction of lead oxide with bromide salts in phenol at the ratio Br PbO less than 2 yields the precipitation of white sediments with the general formula PbnOm(OPh)(2.z)(n-m)Brz(n-m), where n = 4 - 10, m = 1 - 4, z = 0 - 1 and formation of (n-m) moles of water. Reaction takes place in the presence of a variety of bromide salts including quaternary and alkali metal bromides. In the latter case, the presence of acoordinating solvent, e.g. MeCN, is necessary. The composition of product lead bromophenoxides depends on the Br PbO ratio, bromide salt and solvent. These complexes usually have Pb 0 ratio of 4 1 or 3 1, and variable levels of bromide (including some bromide-free complexes) (Table 3). 

It also may be obtained by double decompostion reactions between a ferric salt and a bromide (alkali metal bromide) in aqueous solution followed by evaporation and crystallization ... 

Investigations by Illuminati and Mandolini [103] also hint at a participation of ion pair effects on the particular properties of the cesium compounds. These authors studied the inhibition of cyclization reactions by the formation of contact ion pairs. They found that increasing additions of alkali metal bromides inhibit the cyclization of 104 to various extents. Addition of LiBr effects the strongest inhibition of the reaction, whereas CsBr leads to the highest reaction rate (Fig. 6). 

Zhukov, A.N. and Fedorova, I.L., The effect of water addition on the electrosurface properties of quartz in solutions of alkali metal bromides in ethanol. Colloid J, 66, 292, 2004. 

The results of investigations performed in molten individual alkali-metal halides show that the complexation ability of bromide ions is minimal as compared with the other halides considered. This means that molten alkali-metal bromides, with constituent potassium and caesium cations, contain a relatively large quantity of free cations, and for this reason their oxoacidic properties are stronger. The increase in the melt acidity is the factor causing the increase in metal-oxide solubilities. 

Figure 8 A schematic plot showing the dominant effects on the bromine chemical shifts as one changes the alkali metal from Li to Cs in the alkali metal bromides. See text for discussion (NN = nearest neighbours NNN = next nearest neighbours). From Ref. 147. Reproduced by permission of Elsevier Ltd.

Doping alkali metal bromides and other simple salts... 

Figure 22 Br MAS NMR spectra of powdered alkali metal bromides. All experiments were carried outat Bq = 11.7T and used v,ot = 10 kHz. (A) a mixture of LiBr and KBr (B) a mixture of CsBr, RbBr, KBr and NaBr (C) 0.03 M NaBr in D2O. For (B), the single, double and triple primes correspond to the rotational sidebands of NaBr, KBr and CsBr, respectively. The sidebands for RbBr were not fully resolved due to overlap with the KBr sidebands, which are shown for comparison in (A). Inset measured bromine chemical shift values (errors).

Besides alkali metal bromides, quaternary ammonium salts can be employed as promoters, e.g., methyltri-n-octylammonium chloride. The nature of the metal bromide promoter is not particularly critical. Other promoters, such as diphenylguanidine may be employed in combination with the bromide or quaternary ammonium salt. 

The polymerization takes place slightly above room temperature, from 35°C to about 55°C, with the higher reaction temperature near the end of reaction. The reaction is terminated by the removal of the catalyst from the reaction mixture. To the reaction mixture, an inorganic alkali metal bromide or an alkaline earth metal bromide is added as a promoter. 

Iodine bromide and arsenic(III) bromide resemble closely as solvents iodine monochloride and arsenic(III) chloride respectively, and stable acids have not been isolated in the bromo-systems. Molten mercury(II) bromide is an excellent solvent for various classes of compounds. Alkali metal bromides form solvated anionic species which appear to contain the ions [IBr2] , [AsBr4] and [HgBr3] respectively and phosphorus(V) bromide gives PBr4+IBr2 in iodine bromide where it behaves as a base. Other basic substances are nitrogenous bases such as pyridine. 

Antonov BD (1975) The x-ray diffraction study of molten alkali metal bromides and iodides. J Struct Chem 16 474-476... 

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