摘要：

In the presence of diethyl ether, lithium hydride reacts readily with diborane to form lithium borohydride: LiH + 1/2-B2H6 → LiBH4. The latter is also formed by reaction of diborane with either lithium ethoxide or lithium tetramethoxyboro-hydride: 2B2H6 + 3LiOC2H5 → 3LiBH4 + B(CC2H5)3, and 2B2H5 + 3LiB(OCH3)4 → 3LiBH4 + 4B(OCH3)3. Lithium borohydride is readily purified by recrystallization from ethyl ether; the etherate, LiBH4·(C2H5)2O, is obtained, but the ether is removed easily. Attempts to bring about a direct reaction between sodium hydride and diborane have not succeeded. However, diborane is rapidly and quantitatively absorbed by sodium trimethoxyborohydride in accordance with the equation: 1/2B2H6 + NaBH(OCH3)3 → NaBH4 + B(OCH3)3. Dimethoxyborine reacts in similar fashion with the trimethoxyborohydride. The new product, sodium borohydride, may also be prepared by the reaction of diborane with either sodium methoxide or sodium tetramethoxyborohydride. Potassium borohydride, also prepared for the first time, is obtained by the interaction of potassium tetramethoxyborohydride with diborane. These new methods, together with others described in other papers of this series, make the alkali metal borohydrides readily available. Sodium borohydride is a white crystalline solid of remarkable stability. It has been heated in air to 300° and in vacuum to 400° without apparent change. It dissolves in cold water without extensive reaction. From its aqueous solutions it may be recovered as the dihydrate. At 100° it reacts rapidly with water to liberate 4 moles of hydrogen, a reaction which also occurs rapidly at room temperature in the presence of acids or of certain catalysts. Boron fluoride liberates diborane quantitatively. The borohydride is a strong reducing agent both for organic and inorganic compounds. Potassium borohydride has properties similar to those of the sodium salt, but has not yet been investigated as thoroughly.

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