Chloroplatinic acid (also known as hexachloroplatinic acid) is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...
with the formula
3O">3Osub>2
6">tCl6H
2O)
''x'' (0 ≤ ''x'' ≤ 6). A red solid, it is an important commercial source of
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Pla ...
, usually as an aqueous solution. Although often written in shorthand as H
2PtCl
6, it is the
hydronium
In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid ...
(H
3O
+) salt of the hexachloroplatinate anion ().
[ Hexachloroplatinic acid is highly ]hygroscopic
Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...
.
Production
Hexachloroplatinic acid may be produced via a variety of methods. The most common of these methods involves dissolution of platinum in aqua regia. Other methods include exposing an aqueous suspension of platinum particles to chlorine gas, or via electrolysis.
When produced by the aqua regia route, hexachloroplatinic acid is thought to arise by the following equation:
The resulting orange/red solution can be evaporated to produce brownish red crystals. Some authors suggest that hexachloroplatinic acid produced using this method is contaminated with nitrosonium hexachloroplatinate. Newer literature indicates that this is not the case, and that once the nitric acid has been driven off, samples prepared via this method contain no detectable nitrogen.
Alternative methods have been investigated and described, often motivated by the avoidance of nitrogen contamination.
Reactions
When heated, hexachloroplatinic acid decomposes to platinum(IV) chloride.
Applications
Potassium determination
Chloroplatinic acid was popularized for the quantitative analysis of potassium. The potassium is selectively precipitated from solution
Solution may refer to:
* Solution (chemistry), a mixture where one substance is dissolved in another
* Solution (equation), in mathematics
** Numerical solution, in numerical analysis, approximate solutions within specified error bounds
* Solutio ...
as potassium hexachloroplatinate. 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).
This method for determination of potassium was advantageous compared to the sodium cobaltinitrite method used previously, since it required a single precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
reaction. Gravimetric
Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest.
Units of measurement
G ...
analysis of precipitated products has been supplanted by modern instrumental analysis
Instrumental analysis is a field of analytical chemistry that investigates analytes using scientific instruments.
Spectroscopy
Spectroscopy measures the interaction of the molecules with electromagnetic radiation. Spectroscopy consists of many ...
methods such as ion selective electrodes, flame photometry, ICP-AES
Inductively coupled plasma atomic emission spectroscopy (ICP-AES), also referred to as inductively coupled plasma optical emission spectroscopy (ICP-OES), is an analytical technique used for the detection of chemical elements. It is a type of emiss ...
or ICP-MS
Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry that uses an inductively coupled plasma to ionize the sample. It atomizes the sample and creates atomic and small polyatomic ions, which are then detected. It is ...
.
Purification of platinum
Upon treatment with an ammonium salt, such as ammonium chloride, chloroplatinic acid converts to ammonium hexachloroplatinate
Ammonium hexachloroplatinate, also known as ammonium chloroplatinate, is the inorganic compound with the formula (NH4)2 tCl6 It is a rare example of a soluble platinum(IV) salt that is not hygroscopic. It forms intensely yellow solutions in water. ...
, which precipitates as a solid.[ Upon heating in an atmosphere of ]hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
, the ammonium salt converts to elemental platinum. Platinum is often isolated from ores or recycled from residues using this method.
Catalysis
Like many platinum compounds, chloroplatinic acid is a catalyst (or precatalyst) for hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
and related reactions. As first reported by John Speier and colleagues from Dow Corning
Dow Corning Corporation, was an American multinational corporation headquartered in Midland, Michigan, United States. Originally established as a joint venture between The Dow Chemical Company and Corning Incorporated, Dow bought out Corning and ...
, it catalyzes the addition of hydrosilanes to olefins, i.e. hydrosilylation Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds."Hydrosilylation A Comprehensive Review on Recent Advances" B. Marciniec (ed.), Advances in Silicon Science, Springer Science, 2009 ...
. Early demonstration reactions used isopropanol solutions of trichlorosilane
Trichlorosilane is an inorganic compound with the formula HCl3Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to pr ...
(SiHCl3) with pentene
Pentenes are alkenes with the chemical formula . Each contains one double bond within its molecular structure. Six different compounds are in this class, differing from each other by whether the carbon atoms are attached linearly or in a branched ...
s. Prior work on the addition of silanes to alkenes required radical reactions that were inefficient. As well as with Karstedt's catalyst
Karstedt's catalyst is an organoplatinum compound derived from divinyl-containing disiloxane. This coordination complex is widely used in hydrosilylation catalysis. It is a colorless solid that is generally assumed to be a mixture of related Pt( ...
, Speier's catalyst enjoys widespread use for hydrosilylation, the main drawback is the deliquescent properties of the catalyst.
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.
Related compounds
Chloroplatinic acid prepared from aqua regia is proposed to contain nitrosonium hexachloroplatinate, (NO)2PtCl6. Nitrosonium hexachloroplatinate is obtained by the reaction of nitrosyl chloride
Nitrosyl chloride is the chemical compound with the formula NOCl. It is a yellow gas that is commonly encountered as a component of aqua regia, a mixture of 3 parts concentrated hydrochloric acid and 1 part of concentrated nitric acid. It is a ...
(NOCl) and platinum metal. Nitrosonium hexachloroplatinate has been found to react vigorously with water and hydrochloric acid, making contamination of chloroplatinic acid prepared with aqua regia with nitrosonium hexachloroplatinate unlikely.
References
{{Hydrogen compounds
Hydrogen compounds
Coordination complexes
Platinum(IV) compounds
Chlorides
Inorganic compounds
Chloro complexes
Hexachloroplatinates