Chloroplatinic acid

Chloroplatinic acid
Structural formulas of the component ions of chloroplatinic acid
Two rough red crystals in a glass tube
Names
IUPAC name
Dihydrogen hexachloroplatinate(2–)
Other names
Hexachloroplatinic acid
Identifiers
16941-12-1 YesY
3D model (Jmol) Interactive image
ChemSpider 55731 YesY
ECHA InfoCard 100.037.267
EC Number 241-010-7
PubChem 61859
RTECS number TP1510000
UNII Q65224GJ7F YesY
Properties
H2PtCl6
Molar mass 409.81 g/mol
Appearance Reddish brown solid
Density 2.431 g/cm3
Melting point 60 °C (140 °F; 333 K)
Boiling point decomposes
highly soluble
Structure
Anti-fluorite.
octahedral
0 D
Hazards
Safety data sheet External MSDS
Toxic (T)
Corrosive (C)
R-phrases R25, R34, R42/43
S-phrases (S1/2), S22, S26, S36/37/39, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
0
2
1
Related compounds
Other anions
 Hexachloropalladic acid
Other cations
 Potassium hexachloroplatinate,
Ammonium hexachloroplatinate,
Rubidium hexachloroplatinate,
Caesium hexachloroplatinate
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

Chloroplatinic acid or hexachloroplatinic acid is an inorganic compound with the formula [H3O]2[PtCl6](H2O)x. A red solid, it is an important commercial source of platinum, usually as an aqueous solution. Although often written in shorthand as H2PtCl6, it is the hydronium (H3O+) salt of the hexachloroplatinate anion (PtCl2−
6).[1][2][3] The compound is also available as the hexahydrate.

Production

Orange liquid containing bubbles
Platinum is being dissolved in hot aqua regia

Chloroplatinic acid is produced by dissolving platinum metal sponge in aqua regia. Brownish red crystals can be isolated by evaporating this solution to a syrup.[4]

Pt + 4 HNO3 + 6 HCl → "H2PtCl6" + 4 NO2 + 4 H2O

A related procedure gives the hexahydrate, H2PtCl6(H2O)6.[5]

Alternative methods have been heavily investigated, but the older literature can be unreliable.[6]

Reactions

When heated, hexachloroplatinic acid decomposes first to platinum(IV) chloride, and for this reason heating of hexachloroplatinic acid can result in insoluble platinum compounds.[1]

(H3O)2PtCl6·nH2O → PtCl4 + 2 HCl + (n + 2) H2O

Applications

Potassium determination

Chloroplatinic acid was popularized for the determination of potassium. The potassium is selectively precipitated as potassium chloroplatinate. Determinations were done in 85% (v/v) alcohol solutions with excess platinate ions, and the precipitated product was weighed. Potassium could be detected for solutions as dilute as 0.02 to 0.2% (m/v).[7]

This method for determination of potassium was advantageous vs. the sodium cobaltinitrite method used previously, since it required a single precipitation reaction. Today, the concentration of potassium is determined with an ion-selective electrode. These modern methods remain subject to interference.

Purification of platinum

Treatment with an ammonium salt, such as ammonium chloride, precipitates solid ammonium hexachloroplatinate,.[4] Heating the ammonium salt in hydrogen reduces it to elemental platinum. Platinum is often isolated from ores or recycled from residues thus.[8]

Catalysis

Like many platinum compounds, chloroplatinic acid is used in catalysis. This compound was first reported by John Speier and colleagues from Dow Corning Corporation to catalyze the addition of silyl hydrides to olefins, hydrosilylation. Early test reactions used isopropanol solutions of trichlorosilane (SiHCl3) with pentenes. Prior work on the addition of silanes to alkenes required radical reactions that were inefficient.[9][10] As well as with Karstedt's catalyst, Speier's catalyst enjoys widespread use for hydrosilylation, the main drawback is that the deliquescent properties of the catalyst.[11]

It is generally agreed that chloroplatinic acid is a precursor to the actual catalyst. A possible role for colloidal platinum or zero-valent complexes has also been considered.[12]

Chloroplatinic acid prepared from aqua regia is occasionally contaminated with nitrosonium hexachloroplatinate, (NO)2PtCl6. This species is obtained by the reaction of nitrosyl chloride (NOCl) and platinum metal.[13]

References

  1. 1 2 Schweizer, A. E.; Kerr, G. T. (1978). "Thermal Decomposition of Hexachloroplatinic Acid". Inorg. Chem. 17 (8): 2326–2327. doi:10.1021/ic50186a067.
  2. ↑ Holleman; Wiberg (2001). Inorganic Chemistry (First ed.). New York: Academic Press. ISBN 0-12-352651-5.
  3. ↑ The related palladium compound, [H3O]2[PdCl6], is extremely unstable and has not been isolated in pure form.Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (Second ed.). New York: Elsevier Butterworth-Heinemann. ISBN 978-0-7506-3365-9.
  4. 1 2 Kauffman, George B. (1967). "Ammonium Hexachloroplatinate(IV)". Inorganic Syntheses. 9: 182–185. doi:10.1002/9780470132401.ch51.
  5. ↑ Grube, H. (1963). "Hexachloroplatinic(IV) Acid". In Brauer, G. Handbook of Preparative Inorganic Chemistry. 2 (2nd ed.). New York: Academic Press. p. 1569.
  6. ↑ Rudnick, Paul; Cooke, R. D. (1917). "The Preparation of Hydrochloroplatinic Acid by means of Hydrogen Peroxide". J. Am. Chem. Soc. 39 (4): 633–635. doi:10.1021/ja02249a011.
  7. ↑ Smith, G. F.; Gring, J. L. (1933). "The Separation and Determination of the Alkali Metals Using Perchloric Acid. V. Perchloric Acid and Chloroplatinic Acid in the Determination of Small Amounts of Potassium in the Presence of Large Amounts of Sodium". J. Am. Chem. Soc. 55 (10): 3957–3961. doi:10.1021/ja01337a007.
  8. ↑ Cotton, S. A. (1997). Chemistry of Precious Metals. London: Chapman and Hall. ISBN 0-7514-0413-6.
  9. ↑ Speier, J. L.; Webster, J. A.; Barnes, G. H. (1957). "The Addition of Silicon Hydrides to Olefinic Double Bonds. Part II. The Use of Group VIII Metal Catalysts". J. Am. Chem. Soc. 79 (4): 974–979. doi:10.1021/ja01561a054.
  10. ↑ Saam, John C.; Speier, John L. (1958). "The Addition of Silicon Hydrides to Olefinic Double Bonds. Part III. The Addition to Non-terminal Olefins in the Presence of Chloroplatinic Acid". J. Am. Chem. Soc. 80 (15): 4104–4106. doi:10.1021/ja01548a073.
  11. ↑ Mukund P. Sibi,"Hydrogen Hexachloroplatinate(IV)" Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons. doi:10.1002/047084289X.rh038
  12. ↑ Lewis, L. N.; Sy, K. G.; Bryant, G. L.; Donahue, P. E. (1991). "Platinum-catalyzed hydrosilylation of alkynes". Organometallics. 10 (10): 3750–3759. doi:10.1021/om00056a055.
  13. ↑ Moravek, R. T.; Kauffman, G. B.; Mahmood, T. (1967). "Nitrosyl Hexachloroplatinate(IV)". Inorganic Syntheses. 9: 217–220. doi:10.1002/9780470132555.ch63.
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