GB832049A - Improvements in or relating to the production of boron hydrides - Google Patents

Abstract

Boron hydrides, e.g. B2H6 and B5H9, are prepared by reacting boric oxide and hydrogen at 100-800 DEG C. in the presence of an electro-positive metal (i.e. a metal above H2 in the electromotive series), having an atomic number of 11-26 and of a metal halide or mixture of metal halides which is inert to diborane, and is molten at the reaction temperature, as a flux. Metal borates which decompose to boric oxide under the reaction conditions, e.g. metaborates of Li, Na, K, Ca, Mg, or Ba, or tetraborates of Na, or K, may be used alternatively. The electro-positive metal may be Na, Mg, Al, K, Ca or Fe. The flux may be mixtures of alkali or alkaline earth metal chlorides, bromides, or iodides, mixtures of aluminium chloride, bromide, or iodide, with Li, Na, K, Rb, or Cs, chloride, bromide, or iodide, preferably containing at least 50 mol. per cent of AlCl3, mixtures of sodium and magnesium chlorides, zinc chloride or mixtures of zinc chloride and alkali metal chloride, bromide or iodide. Up to 2% of iodine, methyl iodide, or mixtures thereof may be added as catalyst. Pressures of 0.5-1000 atmos., and excess O2-free H2 and metal over equimolar proportions of metal and boric oxide may be used. At reaction temperatures of 100-250 DEG C. 1/2 -5 hours reaction time are sufficient, but at above 300 DEG C. the reaction products should be cooled below 300 DEG C. in less than 1 min., preferably less than 30 secs. The reaction products may be led through liquid N2-cooled traps and the hydrides isolated by fractional distillation.