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Perrhenic acid

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Perrhenic acid
Perrhenic acid
Ball-and-stick model of the perrhenic acid molecule
Names
IUPAC name
Perrhenic(VII) acid
Other names
Hydrated rhenium(VII) oxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.033.968 Edit this at Wikidata
RTECS number
  • TT4550000
  • InChI=1S/2H2O.7O.2Re/h2*1H2;;;;;;;;; checkY
    Key: JOTGKJVGIIKFIQ-UHFFFAOYSA-N checkY
  • InChI=1/2H2O.7O.2Re/h2*1H2;;;;;;;;;/rH4O9Re2/c1-10(2,3)9-11(4,5,6,7)8/h4-5H2
    Key: JOTGKJVGIIKFIQ-SEUCOXMMAB
  • [OH2][Re](=O)(=O)(=O)([OH2])O[Re](=O)(=O)=O
Properties
H4O9Re2 (solid)
HReO4 (gas)
Molar mass 251.2055 g/mol
Appearance Pale yellow solid
Density ?
Melting point °C (? K)
Boiling point sublimes
Soluble
Acidity (pKa) -1.25[1]
Structure
octahedral-tetrahedral (solid)
tetrahedral (gas)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Corrosive
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability (red): no hazard codeInstability (yellow): no hazard codeSpecial hazards (white): no code
3
Flash point Non-flammable
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Perrhenic acid is the chemical compound with the formula Re2O7(OH2)2. It is obtained by evaporating aqueous solutions of Re2O7. Conventionally, perrhenic acid is considered to have the formula HReO4, and a species of this formula forms when rhenium(VII) oxide sublimes in the presence of water or steam.[2] When a solution of Re2O7 is kept for a period of months, it breaks down and crystals of HReO4.H2O are formed, which contain tetrahedral ReO4− [3] For most purposes, perrhenic acid and rhenium(VII) oxide are used interchangeably.

Properties

The structure of solid perrhenic acid is [O3Re-O-ReO3(H2O)2].[4] This species is a rare example of a metal oxide coordinated to water - most often metal-oxo-aquo species are unstable with respect to the corresponding hydroxides:

M(O)(H2O) → M(OH)2

Gaseous perrhenic acid is tetrahedral, as suggested by its formula HReO4.

Reactions

Perrhenic acid or the related anhydrous oxide Re2O7 converts to dirhenium heptasulfide upon treatment with hydrogen sulfide:

Re2O7+ 7 H2S → Re2S7 + 7 H2O

The heptasulfide, which has a complex structure,[5] catalyses the hydrogenation of double bonds and is useful because it tolerates sulfur compounds, which poison noble metal catalysts. Re2S7 also catalyses the reduction of nitric oxide to N2O.

Perrhenic acid in the presence of HCl undergoes reduction in the presence of thioethers and tertiary phosphines to give Re(V) complexes with the formula ReOCl3L2.[6]

Perrhenic acid combined with platinum on a support gives rise to a useful hydrogenation and hydrocracking catalyst for the petroleum industry.[7] For example, silica impregnated with a solution of perrhenic acid is reduced with hydrogen at 500 °C.[citation needed] This catalyst is used in the dehydrogenation of alcohols and also promotes the decomposition of ammonia.

Catalysis

Perrhenic acid is a precursor to a variety of homogeneous catalysts, some of which are promising in niche applications that can justify the high cost of rhenium. In combination with tertiary arsines, perrhenic acid gives a catalyst for the epoxidation of alkenes with hydrogen peroxide.[8] Perrhenic acid catalyses the dehydration of oximes to nitriles.[9]

Other uses

Perrhenic acid is also used in the manufacture of x-ray targets.

See also

References

  1. ^ http://www.iupac.org/publications/pac/1998/pdf/7002x0355.pdf
  2. ^ Glemser, O.; Müller, A.; Schwarzkopf, H. (1964). "Gasförmige Hydroxide. IX. Über ein Gasförmiges Hydroxid des Rheniums". Zeitschrift für anorganische und allgemeine Chemie. 334: 21–26. doi:10.1002/zaac.19643340105.{{cite journal}}: CS1 maint: multiple names: authors list (link).
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  4. ^ Beyer, H.; Glemser, O.; Krebs, B. “Dirhenium Dihydratoheptoxide Re2O7(OH2)2 - New Type of Water Bonding in an Aquoxide” Angewandte Chemie, International Edition English 1968, Volume 7, Pages 295 - 296. doi:10.1002/anie.196802951.
  5. ^ Schwarz, D. E.; Frenkel, A. I.; Nuzzo, R. G.; Rauchfuss, T. B.; Vairavamurthy, A. (2004). "Electrosynthesis of ReS4. XAS Analysis of ReS2, Re2S7, and ReS4". Chemistry of Materials. 16: 151–158. doi:10.1021/cm034467v.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ Parshall, G. W.; Shive, L. W.; Cotton, F. A. (1997). "Phosphine Complexes of Rhenium". Inorganic Syntheses. 17: 110–112. doi:10.1002/9780470132487.ch31.
  7. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  8. ^ van Vliet, M. C. A.; Arends, I. W. C. E.; Sheldon, R. A. (1999). "Rhenium Catalysed Epoxidations with Hydrogen Peroxide: Tertiary Arsines as Effective Cocatalysts". J. Chem. Soc., Perkin Trans. 1: 377–80. doi:10.1039/a907975k.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ Ishihara, K.; Furuya, Y.; Yamamoto, H. (2002). "Rhenium(VII) Oxo Complexes as Extremely Active Catalysts in the Dehydration of Primary Amides and Aldoximes to Nitriles". Angewandte Chemie, International Edition. 41: 2983–2986. doi:10.1002/1521-3773(20020816)41:16<2983::AID-ANIE2983>3.0.CO;2-X.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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