Perrhenic acid

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Perrhenic acid
Perrhenic acid
Ball-and-stick model of the perrhenic acid molecule
Names
IUPAC name
Tetraoxorhenic(VII) acid
Other names
Hydrated rhenium(VII) oxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.033.968
RTECS number TT4550000
Properties
H
4
O
9
Re
2
(solid)
HReO
4
(gas)
Molar mass 251.2055 g/mol
Appearance Pale yellow solid
Boiling point sublimes
Soluble
Acidity (pKa) -1.25[1]
Conjugate base Perrhenate
Structure
octahedral-tetrahedral (solid)
tetrahedral (gas)
Hazards
Main hazards Corrosive
R-phrases (outdated) R34
S-phrases (outdated) S26, S36/37, S39, S45
NFPA 704
Flammability (red): no hazard codeHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity (yellow): no hazard codeSpecial hazards (white): no codeNFPA 704 four-colored diamond
3
Flash point Non-flammable
Related compounds
Related compounds
Re
2
O
7
, Mn
2
O
7
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Perrhenic acid is the chemical compound with the formula Re
2
O
7
(OH
2
)
2
. It is obtained by evaporating aqueous solutions of Re
2
O
7
. Conventionally, perrhenic acid is considered to have the formula HReO
4
, and a species of this formula forms when rhenium(VII) oxide sublimes in the presence of water or steam.[2] When a solution of Re
2
O
7
is kept for a period of months, it breaks down and crystals of HReO
4
·H
2
O
are formed, which contain tetrahedral ReO
4
[3] For most purposes, perrhenic acid and rhenium(VII) oxide are used interchangeably. Rhenium can be dissolved in nitric or concentrated sulfuric acid to produce perrhenic acid.

Properties[edit]

The structure of solid perrhenic acid is [O
3
Re-O-ReO
3
(H
2
O)
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)(H
2
O)
M(OH)
2

The two rhenium atoms have different bonding geometries, with one being tetrahedral and the other octahedral, and with the water ligands coordinated to the latter. Gaseous perrhenic acid is tetrahedral, as suggested by its formula HReO
4
.

Reactions[edit]

Perrhenic acid or the related anhydrous oxide Re
2
O
7
converts to dirhenium heptasulfide upon treatment with hydrogen sulfide:

Re
2
O
7
+ 7 H
2
S
Re
2
S
7
+ 7 H
2
O

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. Re
2
S
7
also catalyses the reduction of nitric oxide to N
2
O
.

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 ReOCl
3
L
2
.[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[edit]

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]

Perrhenic-acid-nitrile-formation.png

Other uses[edit]

Perrhenic acid is also used in the manufacture of x-ray targets.[10][11]

See also[edit]

References[edit]

  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 (in German). 334: 21–26. doi:10.1002/zaac.19643340105..
  3. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
  4. ^ Beyer, H.; Glemser, O.; Krebs, B. “Dirhenium Dihydratoheptoxide Re
    2
    O
    7
    (OH
    2
    )
    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 ReS
    4
    . XAS Analysis of ReS
    2
    , Re
    2
    S
    7
    , and ReS
    4
    ". Chemistry of Materials. 16: 151–158. doi:10.1021/cm034467v.
  6. ^ Parshall, G. W.; Shive, L. W.; Cotton, F. A. (1997). "Phosphine Complexes of Rhenium". Inorganic Syntheses. 17: 110&ndash, 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 (3): 377–80. doi:10.1039/a907975k.
  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 (16): 2983–2986. doi:10.1002/1521-3773(20020816)41:16<2983::AID-ANIE2983>3.0.CO;2-X.
  10. ^ http://www.gehealthcare.com/usen/service/time_material_support/docs/Radplus2100.pdf[permanent dead link]
  11. ^ X-ray#Sources