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 sesquisulphide, B2S3

Boron sesquisulphide (boron trisulphide), B2S3, is produced when boron is heated to bright redness in sulphur vapour, or when boron is heated to redness in a current of hydrogen sulphide. It may also be prepared by heating to redness in a current of carbon disulphide vapour an intimate mixture of boron sesqui-oxide and carbon. Other reactions which lead to the formation of the sulphide are the action of sulphur upon boron tri-iodide and the action of carbon disulphide and various other sulphides on boron (Moissan). The pure sesquisulphide is best prepared by heating pure boron in a stream of hydrogen sulphide largely diluted with hydrogen, and a cheap method for its preparation consists in heating commercial iron boride or manganese boride to 300°-400° in hydrogen sulphide and washing away admixed sulphur from the product with carbon disulphide. Only part of the boron in these borides can be removed as the sulphide.

The properties of boron sesquisulphide have been studied mainly by Moissan. It forms fine, white needles, of density 1.55, which melt at 310° and volatilise without decomposition when heated in a current of hydrogen. It is unacted upon at a red heat by hydrogen, nitrogen, phosphorus, carbon, and silicon. It inflames in chlorine in the cold, in bromine vapour when warmed, and in oxygen when heated to dull redness; in each case both the boron and sulphur are converted into chloride, bromide, or oxide. At a dull red heat, boron sesquisulphide is violently decomposed by potassium, sodium, magnesium, and aluminium, but iron, zinc, copper, mercury, and silver are without action upon it. It is decomposed by carbon dioxide above 300° as follows

B2S3 + 3CO2 = B2O3 + 3CO + 3S.

It is violently decomposed by water at ordinary temperatures, boric acid and hydrogen sulphide being produced and much heat evolved: -

[B2S3] + 6H2O + aq. = 2H3BO3aq. + 3(H2S) + 57.8 Cals.

Boron sesquisulphide is slightly soluble in phosphorus trichloride, from which it crystallises in needles. It forms the addition-compounds B2S3.BCl3 and B2S3.BBr3, and according to Moissan, combines with the chlorides of phosphorus, arsenic, and antimony. When dissolved in hot carbon disulphide, saturated with hydrogen sulphide, the solvent evaporated in vacuo and the residue recrystallised from either carbon disulphide or benzene, white crystals of B2S3.H2S or thiometaboric acid are obtained. This substance, which smells of hydrogen sulphide and is rapidly decomposed by water, has a molecular weight corresponding to the formula H2B2S4 in benzene solutions; unlike boron sesquisulphide, it is extremely soluble in both benzene and carbon disulphide. Heated in a sealed tube, it begins to melt at 120° and forms a clear, transparent liquid at 140°; when heated in air, it readily dissociates into boron sesquisulphide and hydrogen sulphide. Thiometaboric acid dissolves in liquid ammonia; when excess of solvent is removed at ordinary temperatures, yellow crystals of B2S3.6NH3 separate out.

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