Silicotungstic acid

Silicotungstic acid
Names
	Other names Tungstosilicic acid
Identifiers
CAS Number	(anhydrous): 12027-38-2 ; (hydrate): 12027-43-9 ;
3D model (JSmol)	(anhydrous): Interactive image;
ChemSpider	(anhydrous): 21241680; (hydrate): 30782693;
ECHA InfoCard	100.206.333
PubChem CID	(anhydrous): 90478850; (hydrate): 71307034;
UNII	(anhydrous): HC56ET3NXY ; (hydrate): 26XKI06R59 ;
CompTox Dashboard (EPA)	(anhydrous): DTXSID50923295 ;
	show InChI
	show SMILES
Properties
Chemical formula	H4[W12SiO40]
Molar mass	2878.2 g/mol
Melting point	53 °C (127 °F; 326 K)
Structure
Dipole moment	zero
Hazards
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H314, H315, H319, H335, H412
GHS precautionary statements	P260, P261, P264, P271, P273, P280, P301+330+331, P302+352, P303+361+353, P304+340, P305+351+338, P310, P312, P321, P332+313, P337+313, P362, P363, P403+233, P405, P501
Flash point	Non-flammable
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).
	(what is ?)
	Infobox references

Silicotungstic acid (also known as tungstosilicic acid) is a heteropoly acid with the formula H₄SiW₁₂O₄₀^.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]

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]

Silicotungstic acid is also used for detecting nicotine and measuring its concentration.^{[citation needed]}

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 T_d point group symmetry.

Hazards[]

The silicotungstic acid is an irritating and odorless substance.

References[]

^ Jump up to: ^a ^b Dias, J. A.; Dias, S. C. L.; Caliman, E. (2014). "Keggin Structure Polyoxoometalates". Inorganic Syntheses. 36: 210-217. doi:10.1002/9781118744994.ch39.
^ Jump up to: ^a ^b 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.
^ 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.
^ Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY.

This inorganic compound–related article is a stub. You can help Wikipedia by .

[Dias-1] Jump up to: ^a ^b Dias, J. A.; Dias, S. C. L.; Caliman, E. (2014). "Keggin Structure Polyoxoometalates". Inorganic Syntheses. 36: 210-217. doi:10.1002/9781118744994.ch39.

[Misono-2] Jump up to: ^a ^b 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.

[4] Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY.

[1]

[2]

[3]

[4]