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 trichloride, BCl3

For the synthesis, impure boron (prepared by heating the oxide with magnesium and boiling the resulting mass with hydrochloric acid) is employed. It is heated to dull redness in a stream of dry hydrogen, allowed to cool in the gas, and, after displacing the hydrogen with chlorine, heated in chlorine to redness. The product is strongly cooled and protected from moisture, shaken with mercury or silver powder to remove chlorine, and fractionally distilled to eliminate hydrogen chloride and silicon chloride. Boron trichloride is also produced when boron sesqui-oxide is heated for some days at 150° with phosphorus pentachloride.

Boron trichloride is a colourless liquid of high refractive index and normal vapour density (Wohler and Deville). At 0° C. its density is 1.43386; its coefficient of expansion is large. It melts at -107° C. and boils at 12.5° C.; its vapour pressure is as follows: -


One gram-molecule of the trichloride, when decomposed by water, produces 79.2 Cals. Boron trichloride is without action on sodium below 150°, zinc below 200°, and sulphur below 250°, but it reacts with sulphur trioxide at 120°, producing sulphuryl chloride and boron sesqui-oxide (Gustavson).

When boron trichloride vapour is passed into liquid ammonia, excess of which is then removed at -23°, 15 molecules of ammonia are fixed for each molecule of the chloride used. The products are boron araide and an ammonia addition-product of ammonium chloride: -

BCl3 + 15NH3 = B(NH2)3 + 3NH4Cl.3NH3.

If the ammonia be removed at 0°, only 6 molecules are fixed, since the dissociation pressure of NH4Cl.3NH3 exceeds 760 mm. at 0°. When the reaction takes place above 0° C., boron imide, B2(NH)3, is produced: -

2B(NH2)3 = B2(NH)3 + 3NH3.

According to Besson, boron trichloride forms a white, solid compound, BCl3.PH3, with phosphine. The following double compounds have also been described, besides various addition-compounds with organic substances: BCl3.NOCl, BCl3.POCl3, BCl3.CNCl, and BCl3.HCN.

When boron trichloride is introduced into the afterglow of active nitrogen, a pale bluish-green glow is developed, easily distinguished from the green colour of the boric acid flame, and a white, amorphous solid that contains both boron and nitrogen (probably boron nitride) is deposited.

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