Ruthenium Trichloride, RuCl₃

Ruthenium Trichloride, RuCl₃, is conveniently prepared by warming the tetroxide with concentrated hydrochloric acid on the water-bath. Chlorine is vigorously evolved, the reaction proceeding according to the equation:

2RuO₄ + 16HCl = 2RuCl₃ + 5Cl₂ + 8H₂O.

The reaction, if slow to begin, may be started by the addition of a few drops of alcohol. Gut bier prepared the salt by treating the tetroxide, RuO₄, with 20 per cent, hydrogen chloride solution and allowing it to stand under reduced pressure for two hours. The solution thus obtained was freed from chlorine and unaltered oxide and concentrated to a syrup by passage of air over the warmed liquid. Exposure over concentrated sulphuric acid in a vacuum desiccator left the crystalline salt as a black mass.1 The trichloride is also formed by dissolving the tetroxide in chlorine water. On evaporation a lustrous, somewhat hygroscopic mass of trichloride remains behind which is readily soluble in water and in alcohol, yielding an orange-yellow solution. The aqueous solution is very sensitive to rise in temperature, and decomposes even at 50° C. into a black hydrated oxide or oxychloride and free hydrochloric acid. The colour of the precipitate is so intense that one part of the metal distinctly darkens 100,000 parts of water.

Ruthenium trichloride begins to be reduced by hydrogen at 190° C., it readily absorbs dry ammonia gas, yielding a black-violet addition compound, 2RuCl₃.7NH₃, which dissolves in water to a bright red solution. Heat is set free during the absorption of ammonia, but if the temperature is maintained at 0° C. the reaction is complete.