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
CAS Number	(anhydrous): 12027-38-2 Y (hydrate): 12027-43-9 Y
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 Y (hydrate): 26XKI06R59 Y
CompTox Dashboard (EPA)	(anhydrous): DTXSID50923295
InChI 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
SMILES (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
Chemical formula	H4[SiW12O40]
Molar mass	2878.2 g/mol
Appearance	White solid
Melting point	53 °C (127 °F; 326 K)
Structure
Dipole moment	0 D
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H315, H319, H335, H412
Precautionary statements	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
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). N verify (what is YN ?) Infobox references

Applications

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

C₂H₄ + CH₃CO₂H → CH₃CO₂C₂H₅

It's 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 was recently 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 by the treatment of the mixture with hydrochloric acid.^[1][4] The polyoxo cluster adopts a Keggin structure, with T_d point group symmetry.

Hazards

Silicotungstic acid is an irritating and odorless substance.