Perbromate

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Perbromate
Other names Tetraoxidobromate(1−)
Identifiers
InChI InChI=1/BrHO4/c2-1(3,4)5/h(H,2,3,4,5)/p-1
InChIKey LLYCMZGLHLKPPU-REWHXWOFAT
Standard InChI InChI=1S/BrHO4/c2-1(3,4)5/h(H,2,3,4,5)/p-1
Standard InChIKey LLYCMZGLHLKPPU-UHFFFAOYSA-M
CAS number [16474-32-1]
ChemSpider 4574125
Structure[1]
Molecular geometry tetrahedral: r(Br–O) = 161 pm
Thermochemistry[2][3]
Std enthalpy of formation ΔfHo298 +12.1 kJ mol−1 (aq)
Std Gibbs energy of formation ΔfGo298 +120.8 kJ mol−1 (aq)
Standard molar entropy So298 187 J K−1 mol−1 (aq)
Related compounds
Other anions Perchlorate
Periodate
Hypobromite
Bromite
Bromate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

A perbromate is a salt or ester of perbromic acid. Perbromates, including perbromic acid,[note 1] are the only well-characterized compounds of bromine in the +7 oxidation state.

Perbromates are thermodynamically more oxidizing than perchlorates or periodates, and eluded preparation for more than 100 years until 1968.[5][6][7] However, they are kinetically quite inert, especially in dilute solution.[6][7][8]

History

Although perchlorates and periodates have been known since the early nineteenth century, perbromates proved far more elusive.[9][10] The first claim of preparation came in 1863,[11] but proved unrepeatable.[12][13] Several later attempts to prepare perbromates were equally unsuccessful.[14][15] Some authors surmised that perbromates were fundamentally unstable.[16][17]

The first clear evidence of the existence of the perbromate anion came from "hot-atom" techniques. A sample of the β−-emittor selenium-83 (t½ = 25 min) was prepared in the form of the selenate anion SeO2−4 and allowed to decay into bromine-83. Approximately 14% of the 83Br activity (β−, t½ = 2.4 h) coprecipitated with rubidium perchlorate, as expected for a perbromate species.[5]

Electrolysis of lithium bromate at a platinum anode gave a yield of about 2% perbromate.[5] Small amounts of perbromate (1–4% yield) were also formed by the xenon difluoride oxidation of bromates, while perxenate, peroxodisulfate and ozone were ineffective as oxidizing agents.[5]

Preparation

The preparation of macroscopic quantities of perbromates relies on the oxidation of sodium bromate[note 2] in alkaline solution (5 M sodium hydroxide) by gaseous fluorine:

BrO−3 + F2 + 2 OH− → BrO−4 + 2 F− + H2O

The yield is about 20%, and the reaction can be operated on a 100-gram scale. Perbromic acid can be prepared from the resulting sodium perbromate by ion exchange, and used to prepare other perbromates.[19]

Structure

  r(Br–O)/pm Ref.
CsBrO4 159.1 [20]
NaBrO4·H2O 160.2 [21]
[Co(H2O)6](BrO4)2 160.5 [22]
LiBrO4·3H2O 160.6 [23]
Ca(BrO4)2·3H2O 160.7 [24]
Ba(BrO4)2·3H2O 160.8 [25]
solution (EXAFS) 161 [1]
[Ni(H2O)6](BrO4)2 162.9 [26]

The perbromate ion has Td symmetry, although this may be slightly lowered in crystal structures. Bromine–oxygen bond distances are in the range 159–163 pm.

Properties

Perbromate esters

Isopropyl perbromate has been prepared by the reaction of silver perbromate with 2-bromopropane at −20 °C: it is stable in solution at −20 °C, but decomposes to acetone with a half-life of 30 minutes at room temperature.[27]

Notes and references

Notes

  1. ↑ Perbromic acid is fully dissociated in solution. By analogy with perchloric acid,[4] the solid HBrO4·2H2O is expected to contain [(H2O)2H]+[BrO4]−.
  2. ↑ Sodium bromate is used as the resulting sodium perbromate is very soluble in water; potassium perbromate is much less soluble (as is the case with the corresponding perchlorates).[18]

References

  1. ↑ 1.0 1.1 Levason, William; Ogden, J. Steven; Spicer, Mark D.; Young, Nigel A. Characterisation of the oxo-anions of bromine BrOx− (x = 1–4) by infrared, Raman, nuclear magnetic resonance, and bromine K-edge extended X-ray absorption fine structure techniques. J. Chem. Soc., Dalton Trans. 1990 (1), 349–53. DOI: 10.1039/DT9900000349.
  2. ↑ Johnson, Gerald K.; Smith, Peter N.; Appelman, Evan H.; Hubbard, Ward N. Thermodynamic properties of the perbromate and bromate ions. Inorg. Chem. 1970, 9 (1), 119–25. DOI: 10.1021/ic50083a025.
  3. ↑ Lee, C. L.; Lister, M. W. The Decomposition of Aqueous Sodium Bromite. Can. J. Chem. 1971, 49 (17), 2822–26. DOI: 10.1139/v71-470.
  4. ↑ Olovsson, Ivar Hydrogen-Bond Studies. XXIX. Crystal Structure of Perchloric Acid Dihydrate, H5O2+ClO4−. J. Chem. Phys. 1968, 49 (3), 1063–67. DOI: 10.1063/1.1670193.
  5. ↑ 5.0 5.1 5.2 5.3 Appelman, Evan H. The Synthesis of Perbromates. J. Am. Chem. Soc. 1968, 90 (7), 1900–1. DOI: 10.1021/ja01009a040. Appelman, Evan H. Perbromic acid and perbromates: synthesis and some properties. Inorg. Chem. 1969, 8 (2), 223–27. DOI: 10.1021/ic50072a008.
  6. ↑ 6.0 6.1 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1020–22. ISBN 0-08-022057-6.
  7. ↑ 7.0 7.1 Cotton, F. Albert; Wilkinson, Geoffrey Advanced Inorganic Chemistry, 5th ed.; Wiley-Interscience: New York, 1988; pp 568–69. ISBN 0-471-84997-9.
  8. ↑ Kjaer, A. M.; Ulstrup, J. Electron-transfer reactions between the perbromate ion and iron(II) complexes of 2,2'-bipyridine and substituted 1,10-phenanthrolines. Inorg. Chem. 1982, 21 (9), 3490–94. DOI: 10.1021/ic00139a044.
  9. ↑ Herrell, A. Y.; Gayer, K. H. The elusive perbromates. J. Chem. Educ. 1972, 49 (9), 583. DOI: 10.1021/ed049p583.
  10. ↑ Appelman, Evan H. Nonexistent compounds. Two case histories. Acc. Chem. Res. 1973, 6 (4), 113–17. DOI: 10.1021/ar50064a001.
  11. ↑ Kämmerer, Hermann Notizen. J. Prakt. Chem. 1863, 90, 190. DOI: 10.1002/prac.18630900126. Kaemmerer, Hermann Studien über die Sauerstoffverbindungen der Halogene. Ann. Phys. (Berlin) 1869, 214 (11), 390–417. DOI: 10.1002/andp.18692141104.
  12. ↑ Pattison Muir, M. M. Note on the perbromates. J. Chem. Soc. 1876, 30, 469. DOI: 10.1039/JS8763000469.
  13. ↑ Wolfram, Guido Ueber die Darstellung der Perbromsäure. Justus Liebigs Ann. Chem. 1879, 198 (1–2), 95–98. DOI: 10.1002/jlac.18791980107.
  14. ↑ Cook, Ernest H. Effect of heat on iodates and bromates. I. Potassic iodate and bromate. J. Chem. Soc., Trans. 1894, 65, 802–14. DOI: 10.1039/CT8946500802.
  15. ↑ Bancroft, G. M.; Gesser, H. D. The search for perbromate—I: The thermal decomposition of bromates. J. Inorg. Nucl. Chem. 1965, 27 (7), 1545–56. DOI: 10.1016/0022-1902(65)80016-1.
  16. ↑ Hugus, Z. Z., Jr. The Possible Use of 4f Orbitals in Bonding: the Enhanced Stability of the Higher Oxidation States of Iodine, Tellurium and Antimony; the Non-existence of Perbromic Acid. J. Am. Chem. Soc. 1952, 74 (4), 1076–77. DOI: 10.1021/ja01124a502.
  17. ↑ Urch, D. S. The perbromate problem. J. Inorg. Nucl. Chem. 1963, 25 (7), 771–78. DOI: 10.1016/0022-1902(63)80360-7.
  18. ↑ 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.
  19. ↑ Appelman, E. H. Perbromic acid and potassium perbromate. Inorg. Synth. 1972, 13, 1–9. DOI: 10.1002/9780470132449.ch1.
  20. ↑ Gebert, Elizabeth; Peterson, Selmer W.; Reis, Arthur H., Jr.; Appelman, Evan H. The crystal structure of cesium perbromate. J. Inorg. Nucl. Chem. 1981, 43 (12), 3085–89. DOI: 10.1016/0022-1902(81)80067-X.
  21. ↑ Blackburn, A. C.; Gallucci, J. C.; Gerkin, R. E.; Reppart, W. J. Structure of sodium perbromate monohydrate. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1992, 48 (3), 419–24. DOI: 10.1107/S0108270191010818.
  22. ↑ Blackburn, A. C.; Gerkin, R. E. Structure of hexaaquacobalt(II) perbromate. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1993, 49 (7), 1271–75. DOI: 10.1107/S0108270192013465.
  23. ↑ Blackburn, A. C.; Gallucci, J. C.; Gerkin, R. E.; Reppart, W. J. Structure of lithium perbromate trihydrate. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1993, 49 (8), 1437–39. DOI: 10.1107/S0108270193000538.
  24. ↑ Blackburn, A. C.; Gerkin, R. E. Structure of tetraaquacalcium perbromate. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1993, 49 (8), 1439–42. DOI: 10.1107/S0108270193001714.
  25. ↑ Gerkin, R. E.; Reppart, W. J.; Appelman, E. H. The structure of barium perbromate trihydrate Ba(BrO4)2.3H2O. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1988, 44 (6), 960–62. DOI: 10.1107/S0108270188002215.
  26. ↑ Gallucci, J. C.; Gerkin, R. E.; Reppart, W. J. Structure of nickel(II) perbromate hexahydrate at 296 K. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1990, 46 (9), 1580–84. DOI: 10.1107/S0108270189013533.
  27. ↑ Baum, Kurt; Beard, Charles D.; Grakauskas, Vytautas Preparation of an alkyl perbromate. J. Am. Chem. Soc. 1975, 97 (2), 267–68. DOI: 10.1021/ja00835a005. Baum, Kurt; Beard, Charles D.; Grakaukas, Vitautas (U.S. Dept. of the Navy) Preparation of alkyl perbromates. US Patent 4022811, published 5 October 1977.

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