Chloroplatinic acid

Chloroplatinic acid
IUPAC name Dihydrogen hexachloroplatinate(2–)
Other names Hexachloroplatinic acid
Identifiers
CAS number	16941-12-1 Y
PubChem	61859
ChemSpider	55731 Y
UNII	Q65224GJ7F Y
EC number	241-010-7
RTECS number	TP1510000
Jmol-3D images	Image 1
SMILES [H+].[H+].Cl[Pt-2](Cl)(Cl)(Cl)(Cl)Cl
InChI InChI=1S/6ClH.Pt/h6*1H;/q;;;;;;+4/p-4 Y Key: GBFHNZZOZWQQPA-UHFFFAOYSA-J Y InChI=1/6ClH.Pt/h6*1H;/q;;;;;;+4/p-4/rCl6Pt/c1-7(2,3,4,5)6/q-2/p+2 Key: GBFHNZZOZWQQPA-DUMOQKOKAQ
Properties
Molecular formula	H2PtCl6
Molar mass	409.81 g/mol
Appearance	Reddish brown solid
Density	2.431 g/cm3
Melting point	60 °C (333 K)
Boiling point	decomp
Solubility in water	highly soluble
Structure
Crystal structure	Anti-fluorite.
Coordination geometry	octahedral
Dipole moment	0 D
Hazards
MSDS	External MSDS
EU Index	078-009-00-4
EU classification	Toxic (T) Corrosive (C)
R-phrases	R25, R34, R42/43
S-phrases	(S1/2), S22, S26, S36/37/39, S45
NFPA 704	0 2 1
Related compounds
Other anions	Hexachloropalladic acid
Other cations	Potassium hexachloroplatinate, Ammonium hexachloroplatinate, Rubidium hexachloroplatinate, Caesium hexachloroplatinate
Y acid (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chloroplatinic acid or hexachloroplatinic acid is the chemical compound usually found as the hexahydrate with the formula H₂PtCl₆·(H₂O)₆. This is one of the most readily available soluble compounds of platinum. It is rarely obtained in the pure state. The commercial product is the oxonium salt of the hexachloroplatinate(IV) anion. Therefore, the correct formula is [H₃O]₂[PtCl₆]·4H₂O.^[1][2] The related palladium compound, [H₃O]₂[PdCl₆] is extremely unstable and has not been isolated in pure form.^[3]

Production

Platinum is being dissolved in hot aqua regia

Chloroplatinic acid is produced by dissolving platinum metal sponge in aqua regia. This reaction is rumored to produce nitrogen-containing platinum compounds, but the product is H₂PtCl₆. Chloroplatinic acid is brownish-red, and can be isolated by evaporating this solution to a syrup.^[4]

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

Alternative methods have been heavily investigated, but the older literature can be unreliable.^[5]

Reactions

When hexachloroplatinic acid is heated, it decomposes through platinum(IV) chloride, platinum(II) chloride, to elemental platinum, although the reactions do not occur stepwise, cleanly:^[1]

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

PtCl₄ PtCl₂ + Cl₂

PtCl₂ Pt + Cl₂

All three reactions are reversible.

Applications

Potassium determination

See also: Potassium hexachloroplatinate

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).^[6]

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

Purification of platinum

See also: Ammonium hexachloroplatinate

Treatment with an ammonium salt, such as ammonium chloride, gives ammonium hexachloroplatinate,^[7] which is very insoluble in ammonium solutions. 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 reaction of silyl hydrides with olefins, hydrosilylation.(3) Typical of his reactions, Speier used isopropanol solutions containing trichlorosilane (SiHCl₃), and methyldichlorosilane (CH₃HSiCl₂), with pentenes. Prior work on the addition of silanes to alkenes required radical reactions that were inefficient.^[9][10] It is generally agreed that chloroplatinic acid is a catalyst precursor, and more recent discussions have considered a possible role for colloidal platinum or zero-valent complexes.^[11]

Related compounds

Chloroplatinic acid prepared from aqua regia is occasionally contaminated with (NO)₂PtCl₆. This species is obtained by the reaction of nitrosyl chloride and Pt metal.^[12]

References

1. ^ ^{a b} A. E. Schweizer, G. T. Kerr (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 0123526515. 
3. ^ Greenwood, N.N.; Earnshaw, A. (1997). Chemistry of the Elements (Second ed.). New York: Elsevier Butterworth-Heinemann. ISBN 978-0750633659. 
4. ^ George B. Kauffman; Thurner, Joseph J.; Zatko, David A. (1967). "Ammonium Hexachloroplatinate(IV)". Inorganic Syntheses 9: 182–185. doi:10.1002/9780470132401.ch51. 
5. ^ Paul Rudnick and R. D. Cooke (1917). "The Preparation of Hydrochloroplatinic Acid by means of Hydrogen Peroxide". J. Am. Chem. Soc. 39 (4): 633–635. doi:10.1021/ja02249a011. 
6. ^ G. F. Smith, J. L. Gring (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. 
7. ^ George B. Kauffman; Thurner, Joseph J.; Zatko, David A. (1967). "Ammonium Hexachloroplatinate(IV)". Inorganic Syntheses 9: 182–185. doi:10.1002/9780470132401.ch51. 
8. ^ Cotton, S. A. Chemistry of Precious Metals, Chapman and Hall (London): 1997. ISBN 0-7514-0413-6.
9. ^ J. L. Speier, J. A. Webster, G. H. Barnes (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. ^ John C. Saam, John L. Speier (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. ^ L. N. Lewis, K. G. Sy, G. L. Bryant and P. E. Donahue (1991). "Platinum-catalyzed hydrosilylation of alkynes". Organometallics 10 (10): 3750–3759. doi:10.1021/om00056a055. 
12. ^ R. T. Moravek, G. B. Kauffman and T. Mahmood (1967). "Nitrosyl Hexachloroplatinate(IV)". Inorganic Syntheses 9: 217–220. doi:10.1002/9780470132555.ch63.