Tellurium Dicyanide, Te(CN)₂

Tellurium tetrabromide and silver cyanide in a suitable organic solvent such as benzene react according to the equation

TeBr₄ + 3AgCN = Te(CN)₂ + 3AgBr + CNBr.

The tellurium cyanide may be obtained as a colourless solution on extraction with ether. On evaporation and crystallisation of this solution a double compound of cyanide and ether is obtained, from which the pure cyanide may be prepared by distillation in vacuo.

Tellurium dicyanide after a few minutes' exposure to air assumes a graphite-like appearance due to the deposition of tellurium. Water and alkalis hydrolyse it with precipitation of tellurium:

2Te(CN)₂ + 3H₂O = Te + TeO(OH)₂ + 4HCN.

When heated in air the cyanide burns with a pale blue flame. It is soluble to a slight extent in chloroform and carbon tetrachloride. It is also soluble in cold methyl alcohol without change, but when the solution is warmed hydrolysis occurs.

Tellurium dicyanide decomposes into tellurium and cyanogen to a slight extent at 100° C. The decomposition increases more rapidly above this temperature. At about 190° C. there is a sudden increase in the rate of evolution of the gas.