What Is Phosphotungstic Acid?
Phosphotungstic acid, an inorganic heteropoly acid of tungsten, is known for its various aliases including tungstophosphoric acid and 12-tungstophosphoric acid, with abbreviations TPA and PTA. A notable example is H3PW12O40.
Uses of Phosphotungstic Acid
1. Synthetic Reaction Catalysts
As a catalyst, phosphotungstic acid facilitates numerous organic synthetic reactions, demonstrating thermal stability up to 400°C. It is applicable both as a homogeneous catalyst in solution for hydration, ester exchange, and polymerization, and as a heterogeneous catalyst on substrates like alumina or silica.
- Homogeneous catalysis in 2-propanol hydrolysis and the Prins reaction.
- Heterogeneous catalysis in converting 2-propanol to propene and methanol to hydrocarbons.
The Prins reaction exemplifies its role as an acid catalyst, producing homoallylic alcohols from aldehydes and allyl compounds.
2. Staining Agent
It is employed as a staining agent for phosphoric acid colorimetric determination and for cell negative staining in transmission electron microscopy.
3. Protein Precipitant
Phosphotungstic acid effectively precipitates polar proteins, targeting guanidino, epsilon-amino, and imidazole groups.
Properties of Phosphotungstic Acid
Its chemical formula, molecular weight, and CAS number are H3O40PW12, 2880.2, and 1343-93-7, respectively. The 24-hydrate form melts at 89°C, appearing as a white or yellow-green crystalline powder, soluble in water, ethanol, and diethyl ether, exhibiting high acid strength in concentrated solutions.
The anion structure exhibits tetrahedral symmetry, with 12 tungsten atoms forming a cage around a centrally placed phosphorus atom.
Types of Phosphotungstic Acid
Typically sold as a hydrate, its formula is H3O40PW12・nH2O, with the CAS number 12501-23-4, predominantly isolated as 24-hydrate but also available in 6-hydrate.
Other Information on Phosphotungstic Acid
1. Production Process of Phosphotungstic Acid
It is synthesized by reacting sodium tungstate dihydrate with phosphoric acid, acidified using hydrochloric acid.
2. Regulatory Information
- Identified in Industrial Safety and Health Law as hazardous, with specific regulations for transport and storage.
- Classified as a corrosive substance under maritime and aviation regulations.
3. Precautions for Handling and Storage
Handling requires protective gear, with fire safety precautions due to potential toxic gas release. Store as a hydrate in sealed containers, refrigerated, away from sunlight, in a locked area.