tellurites

Tellurites are inorganic compounds containing the tellurite anion TeO3^2-, in which tellurium is in the +4 oxidation state. They are the salts of tellurous acid (H2TeO3) and include alkali and alkaline earth tellurites such as Na2TeO3, K2TeO3, CaTeO3, as well as ammonium tellurite (NH4)2TeO3. The TeO3^2- anion features a trigonal pyramidal geometry around tellurium due to a lone pair.

Preparation and structure: Tellurite salts are commonly prepared by reacting TeO2 with base, for example TeO2 + 2 NaOH → Na2TeO3 + H2O. Solutions of tellurites can be oxidized to tellurates (TeO4^2-) by strong oxidants, and under certain conditions they may hydrolyze or transform in acid to tellurous acid.

Properties: Tellurite salts are typically white or colorless crystalline solids and are generally soluble to varying degrees in water depending on the cation. They act as reducing agents and can be oxidized to tellurate (TeO4^2-). In acidic conditions, tellurites may convert to tellurous acid and can undergo further transformations depending on the redox environment.

Applications and occurrence: Tellurites have uses in laboratory chemistry and microbiology. Potassium tellurite, for example, is used as a selective agent in culture media to isolate certain bacteria such as Corynebacterium diphtheriae due to its toxicity to many competing microbes. Tellurite reagents also appear in qualitative analyses and some gravimetric procedures, though their use is largely specialized and increasingly limited by toxicity.

Safety: Tellurites are toxic and potentially irritants. Appropriate protective equipment and disposal procedures are required in handling and experimentation.