Silicotungstic acid

Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula H4[SiW12O40]. It forms hydrates H4[SiW12O40]·nH2O. In freshly prepared samples, n is approximately 29, but after prolonged desiccation, n = 6.[1] It is a white solid although impure samples appear yellow. It is used as a catalyst in the chemical industry.[2]

Silicotungstic acid
Names
Other names
Tungstosilicic acid
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.206.333
UNII
  • InChI=1S/H4O4Si.36O.12W/c1-5(2,3)4;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;/h1-4H;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    Key: CGFYHILWFSGVJS-UHFFFAOYSA-N
  • (hydrate): InChI=1S/H4O4Si.H2O.36O.12W/c1-5(2,3)4;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;/h1-4H;1H2;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    Key: ACTPFSYIGLFGLY-UHFFFAOYSA-N
  • (anhydrous): [W]18%21%24(O[W]%16%18%23(O[W]56(O1)(O[W]247(O[W]9%22(O[W]%12%13(O2)(O[W]3%11%14(O[W]%17%19(O[W](O3)(O4)(O5)([O++]67[Si]%15%20[O++]89[W]%10(O[W](O[W](O%10)(O%11)(O%12)([O++]%13%14%15)[O-])(O%16)(O%17)([O++]%18%19%20)[O-])(O%21)(O%22)[O-])O)(O%23)[O-])[O-])[O-])(O%24)O)[O-])O)[O-])O
Properties
H4[SiW12O40]
Molar mass 2878.2 g/mol
Appearance White solid
Melting point 53 °C (127 °F; 326 K)
Structure
zero
Hazards
GHS labelling:
GHS05: CorrosiveGHS07: Exclamation mark
Danger
H314, H315, H319, H335, H412
P260, P261, P264, P271, P273, P280, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P332+P313, P337+P313, P362, P363, P403+P233, P405, P501
Flash point Non-flammable
Related compounds
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

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:[2]

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.[3]

Synthesis and structure

The free acid is produced by combining sodium silicate and tungsten trioxide followed treatment of the mixture with hydrochloric acid.[1][4] The polyoxo cluster adopts a Keggin structure, with Td point group symmetry.

Hazards

Silicotungstic acid is an irritating and odorless substance.

References
  1. Dias, J. A.; Dias, S. C. L.; Caliman, E. (2014). "Keggin Structure Polyoxometalates". Keggin Structure Polyoxoometalates. Inorganic Syntheses. Vol. 36. p. 210-217. doi:10.1002/9781118744994.ch39. ISBN 9781118744994.
  2. Misono, Makoto (2009). "Recent progress in the practical applications of heteropolyacid and perovskite catalysts: Catalytic technology for the sustainable society". Catalysis Today. 144 (3–4): 285–291. doi:10.1016/j.cattod.2008.10.054.
  3. Rausch, Benjamin; Symes, Mark D.; Chisholm, Greig; Cronin, Leroy (September 12, 2014). "Decoupled catalytic hydrogen evolution from a molecular metal oxide redox mediator in water splitting". Science. American Association for the Advancement of Science. 345 (6202): 1326–1330. Bibcode:2014Sci...345.1326R. doi:10.1126/science.1257443. PMID 25214625. S2CID 20572410.
  4. Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY.


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