Tellurium-Sulphur Sesquioxide, TeSO₃

As mentioned, tellurium dissolves in sulphuric acid giving a red solution which probably contains a Tellurium-Sulphur Sesquioxide or Tellurium Sulphoxide, TeSO₃.

The compound is obtainable in the solid state by the addition of powdered tellurium to sulphur trioxide, when combination occurs with evolution of heat. Any excess of sulphur trioxide can be removed mechanically or by evaporation under reduced pressure.

The substance, which is of a type general to the sulphur group, is a red solid which softens at 30° C. without melting. It is decomposed by water mainly into tellurium and sulphuric acid, whilst in solution in sulphuric acid it undergoes oxidation into basic tellurium sulphate on warming. Between 35° and 90° C. it is stated that the red compound is converted into an isomeric form having a reddish-brown colour.