TELLURIC ACID

Chemical Properties

Formula weight 229.66. Colorless crystals, stable in air. May occur in a monoclinic modification (space group C⁵₂h) and a cubic modification (space group O^3 ); the large crystals are generally monoclinic while the microcrystalline powder frequently consists of a mixture of both forms.
Heating H6TeO6 between 100 and 220°C converts it to solid, water-insoluble polymetatelluric acid; the latter decomposes above 220°C into TeO3, and at 400°C or higher into TeO2 and O2. Melts in a sealed tube at about 136°C, forming a concentrated aqueous solution of polymetatelluric acid and some polyorthotelluric acid, d (monoclinic) 3.071; d (cubic) 3.17.

Definition

ChEBI: Telluric acid is a tellurium oxoacid. It is a conjugate acid of a hydrogentellurate.

Synthesis

(1) The starting materials are very fine Te powder and aqueous HClO3 solution. The acid required for the oxidation of 0.1 mole (that is, 12.75 g.) of Te is prepared by adding a lukewarm mixture of 40 ml. of H2O and 7.2 ml. of concentrated H2SO4 to a solution of 24 g. of Ba(ClO3)2·H2O in 100 ml. of H2O. After about five hours, the solution is decanted from the precipitated BaSO4 through a filter, and if desired the residue is extracted once with H2O. To oxidize the Te, it is added to a 500-ml., round-bottom flask placed under the hood. It is then moistened with 5 ml. of 50% HNO3 and about one fourth of the HClO3 solution. With thorough agitation (by swirling) the flask contents soon boil and the reaction proceeds at boiling with strong Cl2 evolution to form H6TeO6 .

(2) The process is somewhat more cumbersome than method I since it requires, among other things, separate preparation of TeO2 as well as repeated recrystallization of the acid to quantitatively re - move the simultaneously formed salts. The yield is 75-85%. For detailed description of the procedure, see the literature below.

(3) Reaction of Te or TeO2 with 30% H2O2 in sulfuric acid or alkaline solution and subsequent precipitation of H6TeO6 with concentrated nitric acid.
(4) Oxidation of Te with HNO3 and CrO3. The product must be re - crystallized several times in order to remove the Cr(NO3)3 byproduct.

Solubility in water

Readily soluble in water; very slightly soluble in concentrated nitric acid.

Raw materials

Preparation Products