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Dihydrogen hexachloroplatinate (IV) hexahydrate
Additional recommended knowledge
Use in determination of potassium
Chloroplatinic acid was popularlized 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).
This method for determination of potassium was advantageous vs. the 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.
Chloroplatinic acid is produced by dissolving platinum metal sponge in a 1:4 (v:v) solution of nitric acid and hydrochloric acid called 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.
Alternative methods have been heavily investigated, but the older literature can be unreliable.
Like many platinum compounds, chloroplatinic acid is used in catalysis. This compound was first used by John Speier and his colleagues from Dow Corning Corporation to catalyze the reaction of silyl hydrides with olefins.(3) Typical of his reactions, Speier used isopropanol solutions containing trichlorosilane (SiHCl3), and methyldichlorosilane (CH3HSiCl2), with pentenes. Speier found that chloroplatinic acid avoided polymerization, a problem that plagued previous attempts at hydrosilylation.
Much speculation has surrounded the actual site of catalysis in chloroplatinic acid. Speier himself proposed that catalysis centered on the platinate ion, and possibly involved an oxidative addition reductive elimination process with the olefinic substrate. This process seems plausible since the chlorine ligands of the complex would be labile.
However, more recent evidence has suggested that catalysis with chloroplatinic acid involves low valent platinum. The II and IV oxidation states of platinum could not afford the highly catalytic nature of the reactions observed. Lewis and his coworkers have suggested a mechanism involving Pt(0) with olefins as ligands.
Chloroplatinic acid is occasionally contaminated with (NO)2PtCl6, and this problem has been the source of considerable discussion. This species is obtained by the reaction of nitrosyl chloride and Pt metal.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dihydrogen_hexachloroplatinate_(IV)_hexahydrate". A list of authors is available in Wikipedia.