Telluric acid

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Telluric acid
Skeletal formula of ortho-telluric acid
Ball-and-stick model of ortho-telluric acid
Names
IUPAC name
Hexahydroxidotellurium
Other names
  • Orthotelluric acid
  • Hexahydroxytellurium
  • Hexahydroxy-λ6-tellane
  • Tellurium hexahydroxide
  • Tellurium(VI) hydroxide
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
ECHA InfoCard
 100.029.334 Edit this at Wikidata
UNII
  • InChI=1S/H2O4Te/c1-5(2,3)4/h(H2,1,2,3,4) checkY
    Key: XHGGEBRKUWZHEK-UHFFFAOYSA-N checkY
  • InChI=1/H2O4Te/c1-5(2,3)4/h(H2,1,2,3,4)
    Key: XHGGEBRKUWZHEK-UHFFFAOYAT
  • O[Te](O)(O)(O)(O)O
Properties
Te(OH)6
Molar mass 229.64 g·mol−1
Appearance White
monoclinic
crystals
Density 3.07 g/cm3
Melting point 136 °C (277 °F; 409 K)
50.1 g/(100 ml) at 30 °C[1]
Acidity (pKa) 7.68, 11.0 at 18 °C[1]
Conjugate base
 Tellurate
Structure
octahedral
0 D
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 corrosive
Related compounds
Other anions
Hydrotelluric acid
Tellurous acid
Hydrogen telluride
Related compounds
 Teflic acid
Sulfuric acid
Selenic 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 checkY☒N ?)

Telluric acid, or more accurately

hydroxyl
(–OH) groups, thus, it can be called tellurium(VI) hydroxide. Telluric acid is a
strong bases and hydrogen tellurate salts with weaker bases or upon hydrolysis of tellurates in water.[3][4]
It is used as tellurium-source in the synthesis of oxidation catalysts.

Preparation

Telluric acid is formed by the

oxidising agent such as hydrogen peroxide, chromium trioxide or sodium peroxide.[3]

TeO2 + H2O2 + 2 H2O → Te(OH)6

Crystallization of telluric acid solutions below 10 °C gives telluric acid tetrahydrate Te(OH)6·4H2O.[2] It is an oxidising agent, as shown by the electrode potential for the reaction below, although it is kinetically slow in its oxidations.[3]

Te(OH)6 + 2 H+ + 2 e− ⇌ TeO2 + 4 H2O, Eo = +1.02 V

Chlorine, by comparison, is +1.36 V and selenous acid is +0.74 V in oxidizing conditions.

Properties and reactions

The anhydrous acid is stable in air at 100 °C but above this it dehydrates to form polymetatelluric acid, a white hygroscopic powder (approximate composition (H2TeO4)10), and allotelluric acid, an acid syrup of unknown structure (approximate composition 3·H2TeO4·4H2O).[5][2]

Typical salts of the acid contains the anions [Te(O)(OH)5]− and [Te(O)2(OH)4]2−. The presence of the tellurate ion TeO2−4 has been confirmed in the solid state structure of Rb6[TeO5][TeO4].[6] Strong heating at over 300 °C produces the α crystalline modification of tellurium trioxide, α-TeO3. [4] Reaction with diazomethane gives the hexamethyl ester, Te(OCH3)6.[2]

Telluric acid and its salts mostly contain hexacoordinate tellurium.[3] This is true even for salts such as magnesium tellurate, MgTeO4, which is isostructural with magnesium molybdate and contains TeO6 octahedra.[3]

Other forms of telluric acid

Metatelluric acid, H2TeO4, the tellurium analogue of sulfuric acid, H2SO4, is unknown. Allotelluric acid of approximate composition 3·H2TeO4·4H2O, is not well characterised and may be a mixture of Te(OH)6 and (H2TeO4)n.[2]

Other tellurium acids

Tellurous acid H2TeO3, containing tellurium in its +4 oxidation state, is known but not well characterised.

hydrotelluric acid
upon addition to water.

References

  1. ^ a b Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, Florida: CRC Press,
    ISBN 0-8493-0594-2
  2. ^
    ISBN 978-0-08-037941-8
    .
  3. ^
    ISBN 0-471-19957-5
  4. ^
    ISBN 0-12-352651-5
    .
  5. doi:10.1107/S0567740879011286
    .
  6. ISBN 978-0-13-175553-6
    .
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