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Thiocyanogen, (SCN)2, is a pseudohalogen derived from the pseudohalide
thiocyanate Thiocyanate (also known as rhodanide) is the anion . It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Mercury(II) thiocyanate was formerly used in pyr ...
, CNsup>−. This hexatomic compound exhibits C2 point group symmetry and has the connectivity NCS-SCN. The oxidation ability is greater than bromine. It reacts with water: :3(SCN)2 + 4H2O → H2SO4 + HCN + 5SCN− + 5H+ Thiocyanogen was originally prepared by the reaction of iodine with a suspension of silver thiocyanate in
diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...
, but this reaction suffers from competing equilibria attributed to the weak oxidizing power of iodine. These same investigations led Söderbäck to the isolation of sulfur dicyanide. An improved method for generating thiocyanogen entails
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
of plumbous thiocyanate, which precipitates when aqueous solutions of
lead(II) nitrate Lead(II) nitrate is an inorganic compound with the chemical formula Pb( NO3)2. It commonly occurs as a colourless crystal or white powder and, unlike most other lead(II) salts, is soluble in water. Known since the Middle Ages by the name plumbu ...
and sodium thiocyanate are combined. A suspension of anhydrous Pb(SCN)2 is treated with
bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
in
glacial acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
to afford a 0.1M solution of thiocyanogen that is stable for days. Alternatively, a solution of bromine in methylene chloride is added to a suspension of Pb(SCN)2 in methylene chloride at 0 °C. :Pb(SCN)2 + Br2 → (SCN)2 + PbBr2 Thiocyanogen adds to alkenes to give 1,2-bis(thiocyanato) compounds and reacts with titanacyclopentadienes giving (''Z'',''Z'')-1,4-bis(thiocyanato)-1,3-butadienes, which in turn can be converted to 1,2-dithiins. Selenocyanogen, (SeCN)2, prepared from reaction of silver selenocyanate with iodine in
tetrahydrofuran Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
at 0 °C, reacts in a similar manner to thiocyanogen.


References

Inorganic carbon compounds Inorganic sulfur compounds Inorganic nitrogen compounds Thiocyanates Pseudohalogens {{Inorganic-compound-stub