Silicotungstic acid

Silicotungstic acid

Names
Other names Tungstosilicic acid
Identifiers
CAS Number	12027-38-2 Y 12027-43-9 (hydrate) N
Properties
Chemical formula	H4[W12SiO40]
Molar mass	2878.2 g/mol
Melting point	53 °C (127 °F; 326 K)
Structure
Dipole moment	zero
Vapor pressure	{{{value}}}
Related compounds
Related heteropoly acids	Phosphotungstic acid
Related compounds	Tungsten trioxide Tungstic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Silicotungstic acid (also known as tungstosilicic acid) is the most commonly encountered heteropoly acid. It is a pale yellow solid with the chemical formula H₄[W₁₂SiO₄₀]. It is used as a catalyst in the chemical industry.

Applications

Silicotungstic acid is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene:

C₂H₄ + CH₃CO₂H → CH₃CO₂C₂H₅

It has also been commercialized for the oxidation of ethylene to acetic acid:

C₂H₄ + O₂ → CH₃CO₂H

This route is claimed as a "greener" than methanol carbonylation. The heteropoly acid is dispersed on silica gel at 20-30 wt% to maximize catalytic ability.

It has also recently been proposed as a mediator in production of hydrogen through electrolysis of water by a process that would reduce the danger of explosion while allowing efficient hydrogen production at low current densities, conducive to hydrogen production using renewable energy.

Synthesis and structure

The free acid is produced by combining sodium silicate and tungsten trioxide followed treatment of the mixture with hydrochloric acid. The polyoxo cluster adopts a Keggin structure, with T_d point group symmetry.