Perbromic acid

The quest for perbromic acid and perbromates and the various reasons adduced for their apparent non-existence make fascinating and salutary reading. " The esoteric radiochemical synthesis of Br04 in 1968 using the /3-decay of radioactive Se, whilst not providing a viable route to macroscopic quantities of perbromate. 

Per-aciditat, /. superaeidity. -ameisensaure, /. performic (peroxyformie) acid, -benzoe-s ure, /. perbenzoic (peroxybenzoic) acid, -borsaure, /. perboric acid, -bromsiure, /. perbromic acid, -buttersaure, /. perbutyrie (peroxybutyric) acid. 

Perbromic acid was first prepared in 1969 in a very unusual way that made use of the conversion of... 

Perbromic acid HBr04 aq Colorless Slow decomp 158.0... 

Perchloric and perbromic acids are very strong, having b = 3 in the general formula (HO)aXOfc. Periodic acid in an excess of water is a weak acid because the HIO4 initially present reacts with water to give H5I06 ... 

If potassium perbromate is the desired product, neutralize the solution potentiometrically with 4 M potassium hydroxide, using 0.1 M potassium hydroxide to reach the precise end point. It is advisable to keep a little of the perbromic acid solution in reserve in case the end point is overshot. Glassware may be used for this and subsequent steps. 

Heat the potassium perbromate slurry to 100° and add enough water to bring all the solid into solution at this temperature. Allow to cool gradually to room temperature. Then chill in an ice bath for an hour and decant the supernatant solution. Redissolve the solid in a minimum of water at 100° and again cool, chill, and decant. Dry the solid at 100°. Transfer to an agate mortar, crush, and dry to constant weight at 110° in vacuum. The yield of potassium perbromate is 80% of the perbromic acid taken. If the recrystallization step is omitted, the yield is 90%. 

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. 

Above 6 M, perbromic acid solutions tend to be erratically unstable, although the decomposition is not explosive. Concentration in vacuum at room temperature produces an azeotrope consisting of about 80% perbromic acid (ca. 12 M), which usually decomposes during or shortly after preparation. Molec-... 

The bromate-perbromate electrode potential is about 1.76 volts in acid solution,3 making perbromic acid a potent oxidant. However, dilute solutions react sluggishly at room temperature. Bromide and iodide are oxidized slowly and chloride not at all. The 6 M acid attacks stainless steel at room temperature, and at 100° it oxidizes chloride ion to chlorine, Cr(III) to Cr(VI), Mn(II) to Mn02, and Ce(III) to Ce(IV) in nitrate solution. The 12-M acid is a vigorous oxidizing agent even at room temperature. 

Perbromic acid and perbromates are most readily assayed by determination of their oxidizing power after reduction with hydrogen bromide, as described earlier in this article. Traces of fluoride in the acid or salts may be determined potentio-metrically, using a fluoride-sensitive electrode (Orion Research, Inc.) and an expanded-scale pH meter. Acid or alkaline solutions should be neutralized or buffered with acetic acid and sodium acetate before the determination. The electrode response should be calibrated against similar solutions of known fluoride content. 

M hydrogen bromide. The tribromide can be determined spectrophotometrically at 275 nm. At this wavelength, perbromic acid has an extinction coefficient of only about 5.8... 

Small amounts of perbromic acid or perbromates can be obtained by oxidation of Br03 electrolytically or by the action of XeF2. The best preparation involves oxidation of Br03" by fluorine in 5 M NaOH solution by a rather complicated procedure, pure solutions can be obtained ... 

EXAMPLE 6.16. Write formulas for the following acids (a) nitric acid, (h) chloric acid, (c) hypophosphorous acid, and (d) perbromic acid. 

The oxoacids and their salts are very stable, in contrast to the lack of stability of the halogen oxides themselves. A large number of these acids exist at the representative oxidation states of the halogens, namely, +1, +3, +5, and +7. Even perbromic acid, HBr04, has been synthesized by fluorination ofbromates. 

The existence of perbromic acid and perbromates were once considered an impossibility on the basis of thermodynamic considerations. Recently, however, these have been prepared on a regnlar laboratory scale. Perbromic acid or perbromates are synthesized by oxidation of BrOs" electrolytically or by fluorination of bromate with elemental flnorine (equation 120) or other strong fluorination agents such as Xep2 (equation 121). 

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