Chemical elements
    Amorphous Sulphur
    Colloidal Sulphur
    Physical Properties
    Chemical Properties
      Hydrogen Sulphide
      Metal Polysulphides
      Hydrogen Polysulphides
      Hydrogen Pentasulphide
      Hydrogen Trisulphide
      Hydrogen Disulphide
      Sulphur Monofluoride
      Sulphur Tetrafluoride
      Sulphur Hexafluoride
      Sulphur Monochloride
      Sulphur Dichloride
      Sulphur Tetrachloride
      Sulphur Monobromide
      Thionyl Fluoride
      Sulphuryl Fluoride
      Fluorosulphonic Acid
      Thionyl Chloride
      Sulphuryl Chloride
      Sulphur Oxytetrachloride
      Pyrosulphuryl Chloride
      Chlorosulphonic Acid
      Thionyl Bromide
      Sodium Sulphoxylate
      Sulphur Dioxide
      Sulphurous Acid
      Sulphur Trioxide
      Pyrosulphuric Acid
      Sulphuric Acid
      Persulphuric Anhydride
      Persulphuric Acid or Perdisulphuric Acid
      Permonosulphuric Acid
      Amidopermonosulphuric Acid
      Thiosulphuric Acid
      Polythionic Acids
      Dithionic Acid
      Trithionic Acid
      Tetrathionic Acid
      Pentathionic Acid
      Wackenroders Solution
      Hexathionic Acid
      Polythionic Acids
      Sulphur Sesquioxide
      Hydrosulphurous Acid
      Nitrogen Sulphide
      Nitrogen Persulphide
      Nitrogen Pentasulphide
      Nitrogen Chlorosulphide
      Trithiazyl Chloride
      Thiotrithiazyl Chloride
      Dithiotetrathiazyl Chloride
      Nitrogen Bromosulphide
      Thiotrithiazyl Bromide
      Thiotrithiazyl Iodide
      Thiotrithiazyl Nitrate
      Thiotrithiazyl Hydrogen Sulphate
      Thiotrithiazyl Thiocyanate
      Sulphonic Acids
      Amidosulphonic Acid
      Imidosulphonic Acid
      Nitrilosulphonic Acid
      Hydroxylamine-monosulphonic Acid
      Nitrososulphonic Acid
      Hydroxylamine-disulphonic Acid
      Hydroxylamine-isodisulphonic Acid
      Hydroxylamine-trisulphonic Acid
      Dihydroxylamidosulphonic Acid
      Sulphazinic Acid
      Sulphazotinic Acid
      Dehydrosulphazotinic Acid
      Nitrosulphonic Acid
      Nitrosulphonyl Chloride
      Nitrosulphonic Anhydride
      Nitrosulphuric Acid
      Nitrosodisulphonic Acid
      Sulphonitronic Acid
      Sulphates of Hydroxylamine
      Hydroxylamine Dithionate
      Hydrazine Dithionate
      Hydrazine Amidosulphonate
      Carbon Subsulphide
      Carbon Monosulphide
      Carbon Disulphide
      Thiocarbonic Acid
      Ammonium thiocarbonate
      Thiolcarbonic Acid
      Xanthic Acid
      Perthiocarbonic Acid
      Sodium perthiocarbonate
      Carbonyl Sulphide
      Thiocarbonyl Chloride
      Thiocarbonyl Tetrachloride or
      Carbon Hexachlorosulphide
      Trichloromethyl Disulphide
      Thiocarbonyl Sulphochloride
      Carbon Bromosulphide
      Amino-derivatives of Thiocarbonic Acid
      Dithiocarbamic Acid
      Azidodithiocarbonic Acid
      Cyanogen Monosulphide
      Cyanogen Trisulphide
      Sulphur Thiocyanate
      Disulphur Dithiocyanate
      Thiocyanic Acid
      Dithiocyanic Acid
      Trithiocyanuric Acid
      Perthiocyanic Acid

Thiocyanogen, (CNS)2

Thiocyanogen, (CNS)2, was first obtained by Soderback by the action of bromine or iodine on a suspension of the thiocyanate of silver, lead, cadmium, mercury, zinc, thallium or copper in carbon disulphide:

2MSCN + Br2 = 2MBr + (CNS)2.

It may also be prepared by electrolysis of the alkali thiocyanates in aqueous or alcoholic solution, using a platinum gauze anode and a silver cathode. On evaporation under reduced pressure, thiocyanogen is obtained as a viscous oil, solidifying at -70° C.

A usual method for the preparation of a solution of thiocyanogen is to treat lead thiocyanate with a dry ethereal solution of bromine cooled in ice.

When a solution of thiocyanogen in carbon disulphide is cooled to -70° C., the thiocyanogen is obtained in cruciform aggregates of almost colourless crystals, melting at -2° to -3° C. On warming to ordinary temperatures the thiocyanogen becomes reddish-brown in colour and more viscous; finally a brick-red amorphous solid is obtained. Thiocyanogen is very readily soluble in ethyl alcohol and ether, slowly soluble in carbon disulphide and carbon tetrachloride.

In many of its reactions, and in its molecular formula, thiocyanogen shows a close analogy with the halogens. Its molecular weight has been determined by the cryoscopic method, allowing a known weight of bromine to react with lead thiocyanate in the presence of bromoform,

Pb(CNS)2 + Br2 = PbBr2 + (CNS)2,

and measuring the depression of the freezing-point thus obtained. The result obtained is in agreement with that required by the molecular formula (CNS)2.

When thiocyanogen is treated with chlorides or bromides no appreciable effect is produced. It liberates iodine from aqueous or alcoholic solutions of the iodides of cadmium, lead, silver and mercury. When treated with iron powder, or mercury, the corresponding thiocyanates are formed. Water interacts with thiocyanogen to form thiocyanic acid, hydrogen cyanide and sulphuric acid.

The reactions of thiocyanogen may roughly be divided into two types: . (1) Reactions in which the radical combines directly with metals to form the corresponding thiocyanates, and with cuprous thiocyanate to form the cupric salt. (2) Reactions in which a substitution is effected; for example, with aniline, dimethylaniline and phenol, the corresponding p-thioeyano-derivatives and thiocyanic acid are formed.

According to Kerstein and Hoffmann a further analogy between thiocyanogen and iodine lies in the formation of trithiocyanates by the union of thiocyanogen with thiocyanates. These trithiocyanates behave like free thiocyanogen, except for their lesser sensitiveness towards water.

Thiocyanogen in solution in chloroform may react with chlorine in three distinct ways yielding (1) thiocyanogen monochloride, SCNCl, (2) sulphur chloride and cyanuric chloride, and (3) thiocyanogen trichloride, SCNCl3.

Estimation of Thiocyanogen

Solutions of thiocyanogen in organic solvents can be titrated accurately by agitation with at least twice the equivalent quantity of potassium iodide and determination of the liberated iodine.

The application of thiocyanogen in volumetric analysis is restricted by the necessity of using anhydrous solvents and dry vessels, to avoid hydrolysis. With a sufficient excess of sodium thiosulphate or hydrogen sulphide, respectively, thiocyanogen reacts quantitatively according to the equations:

(CNS)2 + 2Na2S2O3 = 2NaSCN + Na2S4O6
(CNS)2 + S' = 2SCN' + S.
© Copyright 2008-2012 by