Silicotungstic acid

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Silicotungstic acid
CAS number 12027-38-2 YesY
12027-43-9 (hydrate)
Molecular formula H4[W12SiO40]
Molar mass 2878.2 g/mol
Melting point 53°C
Dipole moment zero
EU Index Not listed
Flash point Non-flammable
Related compounds
Related heteropoly acids Phosphotungstic acid
Related compounds Tungsten trioxide
Tungstic acid
Except where noted otherwise, 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.[1]


Silicotungstic acid is used to manufacture ethyla 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:[1]

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.

Synthesis and structure[edit]

The free acid is produced by combining sodium silicate and tungsten trioxide followed treatment of the mixture with hydrochloric acid.[2] The polyoxo cluster adopts a Keggin structure, with Td point group symmetry.


  1. ^ a b Misono, Makoto "Recent progress in the practical applications of heteropolyacid and perovskite catalysts: Catalytic technology for the sustainable society" Catalysis Today 2009, vol. 144, pp. 285-291.
  2. ^ Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY.