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


Stock and Kuss have shown that when either of the hydrides B2H6 or B4H10 dissolves in aqueous alkali hydroxide, the initial product is an alkali compound of the type MO.BH3, which they term an alkali hypoborate; e.g.: -

B2H6 + 2KOH = 2KOBH3 + H2 B4H10 + 4KOH = 4KOBH3 + H2.

Solutions of the alkali hypoborates are fairly stable at 0°, particularly when excess of alkali is present, and may be exposed to air. When boiled, however, decomposition takes place rapidly: -

2KOBH3 + 2H2O = 2KBO2 + 5H2.

Potassium hypoborate, KOBH3

Potassium hypoborate, KOBH3, may be isolated by dissolving potassium hydroxide in one and a half times its weight of water and treating it with an excess of B4H10 at 0°; the solid hypoborate is then obtained in colourless, glistening, octahedral crystals which may be dried in a high vacuum.

The compound is stable when dry. It is deliquescent, and its aqueous solution slowly decomposes at the ordinary temperature. Acids, even acetic acid, immediately decompose it. The aqueous solution is a powerful reducing agent, and gives precipitates with solutions of most salts, but insoluble hypoborates are never obtained. With copper sulphate, a precipitate of copper hydride, CuH2, is obtained; with nickel sulphate a very remarkable change takes place, nickel boride, Ni2B, being precipitated.

When potassium hypoborate is heated to 500°, potassium, hydrogen, and water are expelled. The water is evolved first, and is completely expelled at 200°; potassium begins to distil from the residue at 400°. The reaction may be expressed thus: -

5KOBH3 = K3B5O3 + 2K + 2H2O + 11H.

The residue, K3B5O3, is soluble in water, giving an alkaline solution the properties of which resemble those of a solution obtained by heating boric oxide with magnesium and extracting the product with water.

Sodium hypoborate, NaOBH3

Sodium hypoborate, NaOBH3, resembles the potassium compound. The barium and magnesium hypoborates are only known in aqueous solution.
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