Chemical elements
    Physical properties
    Chemical properties
      Boron Hydrides
      Boron trihydride
      Boron halogen
      Boron trifluoride
      Hydrofluoboric acid
      Potassium borofluoride
      Fluoboric acid
      Perfluoboric acid
      Boron subchloride
      Boron trichloride
      Boron tribromide
      Boron tri-iodide
      Oxides of Boron
      Tetraboron trioxide
      Boron dioxide
      Tetraboron pentoxide
      Boron sesqui-oxide
      Boron trioxide
      Boric anhydride
      Boric Acids
      Orthoboric acid
      Boric acid
      Boracic acid
      Complex Boric Acids
      Perboric Acid and Perborates
      Sodium perborate
      Sodium hyperborate
      Potassium perborate
      Rubidium perborate
      Ammonium perborate
      Barium perborate
      Boron sesquisulphide
      Boron trisulphide
      Boron pentasulphide
      Boron selenide
      Boron nitride
      Boron amide
      Boron imide
      Boron phosphide
      Boron phospho-iodides
      Boron carbide
      Boron thiocyanate
      Boron Alkyls
      Boron trimethyl
      Boron Silicides and

Boron trifluoride, BF3

Boron trifluoride, BF3, was originally prepared by heating a mixture of boron oxide and calcium fluoride to a white heat in an iron tube. It may be prepared by heating a mixture of boron trioxide (1 pt.) and calcium fluoride (2 pts.) with concentrated sulphuric acid, or better, by mixing 100 parts of potassium borofluoride with 15 to 20 parts of powdered boron sesqui-oxide and heating with concentrated sulphuric acid. The gas may be collected over mercury.

Boron trifluoride is a very stable, colourless gas of suffocating odour. Its density corresponds to that required for the simple formula BF3. When purified from hydrogen fluoride by passage over sodium fluoride, it melts at -127° and boils at -101°. The liquefaction of the fluoride was first effected by Faraday. Boron trifluoride combines with its own volume of ammonia, producing a white, opaque solid, BF3.NH3, which can be sublimed without decomposition. Liquids of the composition BF3.2NH3 and BF3.3NH3 may be obtained if more ammonia is employed (J. Davy), but their individuality is doubtful. With dry phosphine at -50°, boron fluoride unites to form a white, unstable solid of the formula 2BF3.PH3. It also combines with the oxides of nitrogen.

Boron trifluoride is rapidly absorbed by water, 1057 volumes being absorbed at 0° C. The products of the reaction are boric acid and hydro-fluoboric acid: -

4(BF3) + 3H2O + Aq. = 3HBF4Aq. + H3BO3Aq. + 98.04 Cals.

Owing to the readiness with which boron trifluoride reacts with water, it has been proposed as a dehydrating agent in organic chemistry.

Boron trifluoride appears to combine with hydrogen fluoride in two proportions, giving rise to BF3.HF or HBF4 and BF3.3HF. Little or nothing is known of the latter beyond the fact that it is a colourless liquid of normal vapour density. The former is a well-known acid, hydrofluoboric acid.

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