New and Known Complex Borohydrides and some of their Applications in Organic Syntheses

Abstract

WE have found that alcoholic solutions of lithium borohydride can be obtained by a new and very simple method: solutions of sodium borohydride and lithium chloride in absolute ethanol give, on mixing at − 10° C.—in metathetical reaction—a nearly pure solution of lithium borohydride: NaBH₄ + LiCl = LiBH₄ + NaCl. 85–90 per cent of the calculated amount of sodium chloride can be filtered off; thus we obtain a solution which contains 85–90 per cent of the theoretical amount of lithium borohydride and 10–15 per cent of sodium borohydride. We have investigated the stability of these solutions; very surprisingly, these alcoholic solutions of lithium borohydride showed no appreciable decomposition in 2–4 hr., provided that the temperature remained at about 0°. This observation is in sharp contrast with the results of others¹, according to which this substance decomposes with alcohols very rapidly, evolving hydrogen. (Schlesinger, Brown and Hyde have recently described² the preparation of lithium borohydride by the reaction of lithium chloride and sodium borohydride in iso-propylamine; for preparation in quantity their method is better than ours.)