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 Tetrabromide, SeBr4






Selenium Tetrabromide, SeBr4, is formed by the action of excess of bromine on selenium or on selenium monobromide, the latter preferably being in solution in carbon disulphide, in order to moderate the vigour of the process.

When selenium dioxide is dissolved in aqueous hydrobromic acid, selenium tetrabromide is also formed:

SeO2 + 4HBr SeBr4 + 2H2O.

Its presence may be shown by the separation of potassium selenibromide, K2SeBr6, on addition of concentrated potassium bromide solution.

Selenium tetrabromide is a reddish-brown crystalline powder which decomposes to some extent on warming, giving bromine and the monobromide, but much sublimes unchanged.

With sufficient water the tetrabromide is decomposed into the dioxide and hydrobromic acid. Carbon disulphide and chloroform dissolve it to a slight extent.

With the alkali bromides and alkyl ammonium bromides selenium tetrabromide can form crystalline additive compounds of the type M2SeBr6, termed selenibromides. Indeed, by the action of bromine on finely divided selenium in the presence of concentrated hydrobromic acid, a solution is obtained which gradually deposits deep red crystals of hydrogen selenibromide, H2SeBr6. The solution of this body in hydrobromic acid on dilution with water undergoes decomposition with liberation of colloidal selenium. Two reactions probably occur concurrently:

(1) H2SeBr6 + 3H2O = H2SeO3 + 6HBr,
and
(2) H2SeBr6 + H2O = Se + Br2 + 3HBr + HBrO.

The potassium and ammonium selenibromides have been prepared by dissolving selenium dioxide in hydrobromic acid and adding either potassium or ammonium bromide. The selenibromides are orange-red in colour and are decomposed by water into selenious acid, hydrogen bromide and the alkali bromide, yielding colourless solutions.

Selenium tetrabromide and sulphur trioxide yield the additive compound SeBr4.2SO3 in the form of bright yellow needles which at 170° C. form the yellow compound SeOBr2.SO3.


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