Potassium Selenocyanate, KCNSe

Berzelius prepared Potassium Selenocyanate, KCNSe, by the action of selenium on potassium ferrocyanide:

K₄Fe(CN)₆ + 4Se = 4KCNSe + FeC₂ + N₂.

By fusing pure potassium cyanide with selenium, Muthmann and Schroder obtained potassium selenocyanate satisfactorily.

The salt crystallises in very deliquescent needles. The action of chlorine on its solution is complex, intermediate compounds being formed; the solution becomes dark red, some selenium is precipitated, and cyanogen triselenide is finally formed. The main reaction may probably be expressed by the equation:

16KCNSe + 7Cl₂ + 3H₂O = 5Se₃(CN)₂ + K₂SeO₃ + 6HCN + 14KCl.

Iodine reacts with potassium selenocyanate in solution in the presence of much sodium bicarbonate according to the following equation:

KCNSe + 6I + 3H₂O = H₂SeO₃ + KI + 4HI + ICN.

By using excess of iodine and titrating after one hour with sodium thiosulphate in the presence of a little carbon disulphide, the reaction may be used for the determination of the selenocyanate.

A double selenocyanate of potassium and platinum may be obtained by mixing alcohol solutions of potassium selenocyanate and either platinum tetrachloride or chloroplatinic acid. The double salt, potassium platiselenocyanate, K₂Pt(CNSe)₆, consists of hexagonal plates, density 3.377 at 10.2° C., dark red by transmitted light and black by reflected light. The gold salt, KAu(CNSe)₂, is obtained in a similar manner and consists of very easily decomposable dark red prisms.