Bromine perbromates

The structure has recently been shown by EXAFS to be bromine perbromate BrOBrOs with Br -0 186.2pm, Br -0 160.5 pm and angle BrOBr 110 3° d °) (cf. CIOCIO3 and Br0C103). Br0Br03 is thermally unstable above —40°C and decomposes violently to the elements at 0°C slower warming yields B1O2 (see above). Alkaline hydrolysis leads to disproportionation ... 

Chlorine, bromine, and iodine each form four different oxoanions that are distinguished by prefixes and suffixes. The nomenclature of these ions is illustrated for bromine, but it applies to chlorine and iodine as well BrO, hypohromite Br02, bromzte Br03, bromate and Br04, perbromate. 

The solid produced at —5°C by interaction of bromine and ozone is only stable at —80°C or in presence of ozone, and decomposition may be violently explosive in presence of trace impurities [1], The structure may be the dimeric bromyl perbromate, analogous to Cl206 [2],... 

A qualitative similarity to the aqueous chemistry of chlorine will be evident. For each oxoanion of chlorine, there is a corresponding bromine species, although perbromate salts form only under certain strongly oxidizing conditions (e.g., oxidation of bromate ion in alkaline solution with F2 or XeF2) and in fact were unknown until 1968. 

The best known exceptions to the general reluctance of bromine to accept a + 7 oxidation stale are perbroinic acid and the perbromate ion, which were unknown prior to 1968 (see Chapter 17). Their subsequent synthesis has made their nonexistence" somewhat less crucial as a topic of immediate concern to inorganic chemists, but bromine certainly continues the trend started by arsenic and selenium Thus the perbromate ion is a stronger oxidizing agent than either perchlorate or periodate. 

Bromates.—The bromates are white salts soluble in water they do not, however, decompose into bromide and perbromate when heated the perbromate is unstable, and bromide and oxygen are the only products. Bromic acid, too, when warmed changes to water, hydrobromic acid, bromine, and oxygen as no compound analogous to C102 is produced, bromous acid is unknown. 

Less is known about the anhydrous bromine-containing oxysalts than about the corresponding compounds of chlorine and iodine. This is true both with respect to the total number of such salts, as well as the information available on each salt. Since 1974, when the last review of these compounds was published,1 the situation has changed only slightly, with the number of known bromites increasing from 2 to 3, bromates from 15 to 17, and perbromates from 3 to 8. There are still no thermodynamic data above 298 K. Consequently, this chapter is fairly brief, includes no high-temperature equilibrium calculations, and updates qualitative and semi-quantitative information using material published since 1972. 

Perbromic acid is a strong monobasic acid. Its aqueous solutions are stable up to about 6 M (55% HBr04), even at 100°. Fairly concentrated solutions may develop a yellow bromine color from the decomposition of traces of bromate ion and hypobromous acid. If a 6 M perbromic acid solution is allowed to stand for several months, the bromate and hypobromite will have all decomposed, and the resulting bromine can be flushed out with pure nitrogen, leaving a colorless solution. 

TABLE 12 Bromine-79/81 solid-state NMR data for perbromates ... 

As is the case with the perchlorates, the bromine atom in the perbromate series is in a nearly tetrahedral environment and hence the EFG at the bromine will be nearly zero. Therefore, it should be possible to observe Br SSNMR signals in these systems. The cesium member of this series, CsBr04, belongs to the tetragonal Hi/a space group, while the others (M = K, Rb, NH4) belong to the orthorhombic group Pntm. 

There is some reason to think that bromine forms bleaching compounds, which, like those of chlorine, contain peculiar acids bromons or hypobromous acids and it is also probable that there exists a perbromic acid, analogous to perchloric acid. Our knowledge of these compounds, however, is very limited. 

Pyridine Complexes. The addition of a halogen to pyridine affords a molecular complex The bromine complex Is capable of the halogen— atlon of olefins as reported by Lloyd and Durocher and Zupan et al (61-63). Anti stereoselectivity Is observed and a nucleophilic solvent can replace the second halogen, thus Implicating a bromonlum Ion. A similar complex with polyvinyl pyrldlne-N-oxlde acts In a similar fashion. The polymer-bound pyrldlnlum hydrobromide perbrom-Ide has also been formed by Frechet, Farrall and Nuyens. It reacts with olefins In the same fashion but has also been shown to halogenate ketones (64). 

---