Thiocyanogen

Thiocyanogen, (SCN)2, is a pseudohalogen derived from the pseudohalide thiocyanate, [SCN]−. This hexatomic compound exhibits C2 point group symmetry and has the connectivity NCS-SCN. It is attacked by water and apparently has only been obtained as a solution.

Thiocyanogen was originally prepared by the reaction of iodine with a suspension of silver thiocyanate in diethyl ether, but this reaction suffers from competing equilibria attributed to the weak oxidizing power of iodine. An improved method for generating thiocyanogen entails oxidation of plumbous thiocyanate, which precipitates when aqueous solutions of lead(II) nitrate and sodium thiocyanate are combined. A suspension of anhydrous Pb(SCN)2 is treated with bromine in glacial acetic acid to afford a 0.1M solution of thiocyanogen that is stable for days.


 * Pb(SCN)2 +  Br2   →   (SCN)2  +  PbBr2

Thiocyanogen adds to alkenes to give 1,2-bis(thiocyanato) compounds.