Chloroplatinic Acid
Properties
| State | Solid (usually as red-orange hexahydrate); very hygroscopic |
| Color | Red to red-orange |
| Solubility | Very soluble in water; soluble in alcohols and ethers |
| Melting Point | 60 °C (hexahydrate decomposes) |
About Chloroplatinic Acid
H2PtCl6 is what you get when you dissolve platinum metal in aqua regia and crystallize the resulting deep-red solution — a strong acid (both protons fully dissociate in water) whose anion is the octahedral [PtCl6]^2- complex. Pt(IV) is a d6 ion with a strong octahedral preference and a very large crystal field stabilization, which is why this complex is kinetically inert in aqueous solution: chloride substitution by water is slow at room temperature, and you can leave H2PtCl6 dissolved in dilute HCl for months without significant hydrolysis. That kinetic inertness is also the engineering convenience that makes chloroplatinic acid the universal entry point to platinum chemistry — essentially every soluble platinum compound and every supported platinum catalyst starts as a solution of H2PtCl6 in HCl. To make Pt/Al2O3 for a refinery reformer, you impregnate gamma-alumina extrudates with H2PtCl6, dry, and reduce under H2 at 400 °C — the chloride leaves as HCl, the platinum reduces to nanoparticles 1-3 nm in diameter, and you've got a working catalyst loaded at 0.3-0.6 wt% Pt. To make cisplatin you reduce H2PtCl6 to K2PtCl4 with K2C2O4, then displace two cis chlorides with ammonia. To make Karstedt's catalyst for silicone curing you reduce H2PtCl6 with vinyl-terminated siloxane in isopropanol. The compound itself is sold and shipped as the red-orange hexahydrate H2PtCl6.6H2O at 517.90 g/mol because the anhydrous form is too hygroscopic to handle.
Where you'll encounter it
If you've toured a precious-metals refinery, the dark-red solution being pumped between extraction columns is most likely chloroplatinic acid going through purification by solvent extraction (typically with tributyl phosphate or methyl isobutyl ketone) to separate Pt from Pd, Rh, Ir, and Ru — those metals all have different distribution coefficients between aqueous HCl and the organic phase, so a counter-current extraction train can purify each one. In a heterogeneous catalysis lab, the bright red 'platinum stock solution' that gets aliquoted out for impregnation experiments is dilute H2PtCl6 in HCl, usually 8-10 wt% Pt by mass. In medicinal chemistry, a kilogram of cisplatin starts as roughly 1.7 kg of chloroplatinic acid hexahydrate going through the Dhara synthesis.
Common Uses
- Universal precursor for impregnation of Pt/Al2O3 reforming catalysts and three-way automotive converters
- Starting material for cisplatin, carboplatin, and oxaliplatin antineoplastic synthesis routes
- Reduction precursor for Karstedt catalyst used in silicone hydrosilylation curing reactions
- Source of platinum for electroplating baths in jewelry, electrical contacts, and corrosion coatings
- Hot-injection precursor for shape-controlled platinum nanoparticles used in fuel cell electrocatalysts
- Spot-test reagent for alkali-metal identification by precipitation as M2PtCl6 in classical qualitative analysis
- Raw material for purifying platinum group metals via solvent extraction in refinery operations
- Reference standard for platinum quantification in ICP-OES and ICP-MS calibration curves
Safety Information
Chloroplatinic acid is the textbook respiratory sensitizer — GHS H334 (Category 1) — and chronic inhalation exposure causes platinosis, an asthma-like syndrome that develops in 30-50% of refinery workers handling soluble platinum salts within their first few years on the job. Once sensitized, even trace exposure triggers severe bronchospasm, and the sensitization is generally permanent. The OSHA PEL for soluble platinum compounds is 2 micrograms per cubic meter (note: micrograms, not milligrams) — among the lowest workplace exposure limits for any metal. It's also Skin Corrosion 1B and Acute Toxicity 4 (oral). Practical handling: never weigh out H2PtCl6 powder on the open bench. Use a glovebox or fume hood with HEPA filtration, double gloves, and a P100 or supplied-air respirator. Even residue on glassware can sensitize a worker; lab equipment that has touched platinum salts should be cleaned and segregated.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.