Bromous acid
| Bromous acid | |
|---|---|
| IUPAC name | Bromous acid[note 1] |
| Other names | Bromic(III) acid Hydroxy-λ3-bromanone Hydroxidooxidobromine |
| Identifiers | |
| InChI | InChI=1/BrHO2/c2-1-3/h(H,2,3) |
| InChIKey | DKSMCEUSSQTGBK-UHFFFAOYAC |
| Standard InChI | InChI=1S/BrHO2/c2-1-3/h(H,2,3) |
| Standard InChIKey | DKSMCEUSSQTGBK-UHFFFAOYSA-N |
| CAS number | [] |
| ChemSpider | |
| Properties[2][3] | |
| Chemical formula | HBrO2 |
| Molar mass | 112.91 g mol−1 |
| Acidity (pKa) | 3.43(11) |
| Related compounds | |
| Other halous acids | Chlorous acid |
| Other compounds | Hydrobromic acid Hypobromous acid Bromic acid Perbromic acid |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
Bromous acid, HBrO2, is an oxoacid of bromine. Its existence as a molecular species has been considered doubtful[4][5] but, although it is unstable with respect to disproportionation, its lifetime in aqueous solution is sufficient for spectroscopic study.[3][6] It is an intermediate in the Belousov–Zhabotinskii reaction.[6] Some salts (bromites) are known.[4]
Contents
Disproportionation
Bromous acid is unstable with respect to disproportionation: at acid pH, the thermodynamic products are bromine and bromate.
- 5 HBrO2 → Br2 + 3 BrO−3 + 3 H+ + H2O
The initial mechanism is simpler than that for chlorous acid, as the production of bromine dioxide and the oxidation of water to oxygen are negligible. Hence, there are just two significant initial steps:[3]
HBrO2 + HBrO2 → HBrO + BrO−3 + H+ k = 800(100) dm3 mol−1 s−1 HBrO2 + BrO−2 → HBrO + BrO−3 k = 39.1(26) dm3 mol−1 s−1
The hypobromous acid then disproportionates further to give the final products. There is no evidence of any catalysis of the disporportionation of HBrO2 by bromide ions (unlike the case of chlorous acid and chloride ions).[3]
Acidity
The acid dissociation constant of bromous acid can be calculated from the observed kinetics of its disproportionation:[3] Ka = 3.7(9) × 10−4 (pKa = 3.43). This is consistent with that which would be expected from periodic trends.
| pKa | ||
|---|---|---|
| HClO 7.47 |
HBrO 8.80 |
HIO 10.70 |
| HClO2 1.96 |
HBrO2 3.43 |
HIO2 — |
| HClO3 < 0 |
HBrO3 < 0 |
HIO3 0.80 |
Notes and references
Notes
- ↑ Bromous acid is a retained name in IUPAC nomenclature.[1]
References
- ↑ Nomenclature of Inorganic Chemistry; IUPAC Recommendations 2005; Royal Society of Chemistry: Cambridge, 2005; p 287. ISBN 0-85404-438-8, <http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf>.
- ↑ Faria, Roberto de Barros; Epstein, Irving R.; Kustin, Kenneth Systematic design of chemical oscillators. Part 84. Determination of the pKa of bromous acid. J. Phys. Chem. 1992, 96 (17), 6861–63. DOI: 10.1021/j100196a003.
- ↑ 3.0 3.1 3.2 3.3 3.4 Faria, R. B.; Epstein, Irving R.; Kustin, Kenneth Kinetics of Disproportionation and pKa of Bromous Acid. J. Phys. Chem. 1994, 98 (4), 1363–67. DOI: 10.1021/j100055a051.
- ↑ 4.0 4.1 Ukeles, S. D.; Freiberg, M. Bromine, Inorganic Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley: New York, 2002. DOI: 10.1002/0471238961.021815131001031.
- ↑ Cotton, F. Albert; Wilkinson, Geoffrey Advanced Inorganic Chemistry, 5th ed.; Wiley-Interscience: New York, 1988; pp 566–67. ISBN 0-471-84997-9.
- ↑ 6.0 6.1 Ariese, Freek; Ungvarai-Nagy, Zsuzsanna The disproportionation of bromous acid (HBrO2), key species of the Belousov-Zhabotinskii oscillating reaction. J. Phys. Chem. 1986, 90 (1), 1–4. DOI: 10.1021/j100273a001.
External links
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