Chemical elements
  Selenium
    Isotopes
    Energy
    Production
    Application
    Allotropy
    Colloidal
    Physical Properties
    Chemical Properties
      Hydrogen Selenide
      Selenium Fluorides
      Selenium Monochloride
      Selenium Tetrachloride
      Selenium Monobromide
      Selenium Tetrabromide
      Selenium Chlorobromides
      Selenium Oxyfluoride
      Selenium Oxychloride
      Sulphur Selenium Oxytetrachloride
      Selenium Oxybromide
      Chloroselenic Acid
      Selenium Dioxide
      Selenious Acid
      Selenium Trioxide
      Selenic Acid
      Selenates
      Perselenic Acid
      Selenium Sulphoxide
      Selenotrithionic Acid
      Diselenotrithionic Acid
      Selenopentathionic Acid
      Selenium Nitride
      Nitrosylselenic Acid
      Phosphorus Subselenide
      Phosphorus Monoselenide
      Tetraphosphorus Triselenide
      Phosphorus Triselenide
      Phosphorus Pentaselenide
      Phosphorus Chloroselenide
      Selenophosphates and Oxyselenophosphates
      Carbon Diselenide
      Carbon Subselenides
      Carbon Oxyselenide
      Carbon Sulphidoselenide
      Cyanogen Monoselenide
      Cyanogen Diselenide or Selenocyanogen
      Cyanogen Triselenide
      Selenocyanic Acid
      Ammonium Selenocyanate
      Caesium Triselenocyanate
      Copper Selenocyanate
      Lead Selenocyanate
      Magnesium Selenocyanate
      Mercurous Selenocyanate
      Mercuric Selenocyanate
      Potassium Selenocyanate
      Silver Selenocyanate
      Sodium Selenocyanate
      Zinc Selenocyanate
      Silicon Selenide
    Detection and Estimation

Cyanogen Diselenide or Selenocyanogen, Se2(CN)2






By heating together selenious anhydride, anhydrous hydrocyanic acid and acetic anhydride to 100° C. under pressure in a sealed tube until solution is complete, there are formed on evaporation of the product, yellowish crystals which have been regarded as impure cyanogen diselenide, Se2(CN)2. On examination under the microscope these yellowish crystals appear as a mixture of brownish plates and needle-shaped crystals.

The action of iodine on silver selenocyanate yields selenocyanogen. When potassium selenocyanate dissolved in anhydrous acetone reacts with a solution of lead tetra-acetate in chloroform, lead selenocyanate and selenocyanogen result.

The diselenide has an intensely disagreeable smell and its vapours are very poisonous. It is hydrolysed by water thus:

2Se2(CN)2 + 3H2O = H2SeO3 + HCN + 3HCNSe;

the selenocyanic acid is only stable in neutral or alkaline solution. The diselenide is also readily decomposed by warm alcohol, and by dilute acids or alkalis. It undergoes polymerisation when heated in carbon disulphide solution, forming cyanogen mono- and tri-selenides:

2Se2(CN)2 = Se(CN)2 + Se3(CN)2.

Selenocyanogen may be identified by conversion into diantipyryl selenide, C22H22O2N4Se, m.pt. 236° C.


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