sensagent's content
- definitions
- synonyms
- antonyms
- encyclopedia
Dictionary and translator for handheld
New : sensagent is now available on your handheld
Advertising ▼
Webmaster Solution
Alexandria
A windows (pop-into) of information (full-content of Sensagent) triggered by double-clicking any word on your webpage. Give contextual explanation and translation from your sites !
SensagentBox
With a SensagentBox, visitors to your site can access reliable information on over 5 million pages provided by Sensagent.com. Choose the design that fits your site.
Business solution
Improve your site content
Add new content to your site from Sensagent by XML.
Crawl products or adds
Get XML access to reach the best products.
Index images and define metadata
Get XML access to fix the meaning of your metadata.
Please, email us to describe your idea.
Lettris
Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.
boggle
Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !
English dictionary
Main references
Most English definitions are provided by WordNet .
English thesaurus is mainly derived from The Integral Dictionary (TID).
English Encyclopedia is licensed by Wikipedia (GNU).
Copyrights
The wordgames anagrams, crossword, Lettris and Boggle are provided by Memodata.
The web service Alexandria is granted from Memodata for the Ebay search.
The SensagentBox are offered by sensAgent.
Translation
Change the target language to find translations.
Tips: browse the semantic fields (see From ideas to words) in two languages to learn more.
last searches on the dictionary :
CRESSIDA BELL ·
Bud Adams ·
Barmecide ·
(Ashcan ·
Bud Houser ·
Grumman F-14 ·
Graphism ·
(Arthur, ·
COUNT SQL ·
permission slip ·
4666 online visitors
computed in 0.062s
Wikipedia
Perrhenic acid
| Perrhenic acid | |
|---|---|
 |
|
 |
|
|
Perrhenic(VII) acid |
|
|
Other names
Hydrated rhenium(VII) oxide |
|
| Identifiers | |
| CAS number | 13768-11-1  |
| ChemSpider | 21106462  |
| RTECS number | TT4550000 |
| Jmol-3D images | Image 1 |
|
|
|
|
| Properties | |
| Molecular formula | H4O9Re2 (solid) HReO4 (gas) |
| Molar mass | 251.2055 g/mol |
| Appearance | Pale yellow solid |
| Density | ? |
| Melting point |
°C (? K) |
| Boiling point |
sublimes |
| Solubility in water | Soluble |
| Acidity (pKa) | -1.25[1] |
| Structure | |
| Coordination geometry |
octahedral-tetrahedral (solid) tetrahedral (gas) |
| Hazards | |
| R-phrases | R34 |
| S-phrases | S26, S36/37, S39, S45 |
| Main hazards | Corrosive |
| NFPA 704 |
 0
3
0
|
| Flash point | Non-flammable |
| Related compounds | |
| Related compounds | Re2O7, Mn2O7 |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
|
| Infobox references | |
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. Rhenium can be dissolved in nitric or concentrated sulfuric acid to produce perrhenic acid.
Contents |
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
- ^ http://www.iupac.org/publications/pac/1998/pdf/7002x0355.pdf
- ^ 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..
- ^ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419.
- ^ 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.
- ^ 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.
- ^ Parshall, G. W.; Shive, L. W.; Cotton, F. A. (1997). "Phosphine Complexes of Rhenium". Inorganic Syntheses 17: 110–112. DOI:10.1002/9780470132487.ch31.
- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ^ 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.
- ^ 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.
|
|||||||||||||||||||||||||||||
