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
13768-11-1 N
ChemSpider 21106462 YesY
Jmol 3D model Interactive image
RTECS number TT4550000
Properties
H
4
O
9
Re
2
(solid)
HReO
4
(gas)
Molar mass 251.2055 g/mol
Appearance Pale yellow solid
Melting point °C (? K)
Boiling point sublimes
Soluble
Acidity (pKa) -1.25[1]
Structure
octahedral-tetrahedral (solid)
tetrahedral (gas)
Hazards
Main hazards Corrosive
R-phrases R34
S-phrases S26, S36/37, S39, S45
NFPA 704
Flammability (red): no hazard code Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity (yellow): no hazard code Special hazards (white): no codeNFPA 704 four-colored diamond
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).
N verify (what is YesYN ?)
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

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

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: 110–112. 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
  11. ^ X-ray#Sources