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

Selenium Monochloride, Se2Cl2






Selenium Monochloride, Se2Cl2 is most easily obtained by the action of chlorine on heated selenium, but it is always accompanied by a certain quantity of the more stable tetrachloride which, however, is less volatile. It may be prepared by saturating with chlorine a suspension of selenium or a selenium mineral in carbon tetrachloride. The selenium monochloride is soluble in carbon tetrachloride, whilst the chlorides of other elements present are insoluble. The monochloride is therefore obtained by evaporation of the solvent after filtration.

The chlorides of certain non-metals such as phosphorus have a similar action on selenium, possibly on account of previous dissociation with formation of chlorine.

In some commercial acids selenium is present in the form of the monochloride, produced when seleniferous sulphuric acid is heated with salt. On the addition of ferric chloride, the monochloride gradually separates.

A solution of selenium in fuming sulphuric acid gives a gradual separation of the monochloride on the addition of hydrogen chloride.

Selenium monochloride is a clear reddish-brown liquid of density (D25°) 2.7741, and can be condensed to a solid of melting-point -85° C. Its odour somewhat resembles that of sulphur monochloride. The liquid has a refractive index of 1.59617 at 25° C., and its specific conductance is 5.12×10-6 mho. On vaporisation it undergoes partial dissociation. Boiling commences at 145° C., the yellowish-brown vapour containing the tetrachloride and a residue of selenium being obtained in the retort:

2Se2Cl2 SeCl4 + 3Se.

The monoehloride is soluble in various inert organic liquids, more particularly in benzene, chloroform, carbon tetrachloride and carbon disulphide, without undergoing chemical change. It is an exothermic compound, its heat of formation from gaseous chlorine and the amorphous modification of selenium being 22.1 Cals. Water causes a gradual decomposition of the chloride, selenium dioxide and selenium being formed:

2Se2Cl2 + 2H2O = SeO2 + 3Se + 4HCl.

Selenium monochloride behaves as a strong chlorinating agent towards metals, metallic selenides and hydrocarbons. Phosphorus displaces selenium from the chloride with formation of phosphorus trichloride. Chlorine converts it into the tetrachloride.

The action of liquid ammonia on selenium monochloride is exceedingly vigorous and results in the deposition of red selenium. The monochloride in ether solution, however, yields with liquid ammonia a pale brown amorphous compound of formula Se2NCl.

The constitution of selenium monochloride is uncertain; it may be represented by

or Cl-Se-Se-Cl; that the molecular weight is in accordance with this formula has been demonstrated by cryoscopic investigation in solution in ethylene dibromide.


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