Regeneration of sodium borohydride from sodium metaborate, and isolation of intermediate compounds

A method for the regeneration of sodium borohydride from its hydrolysis product, sodium borate, is described. The dried borate salt was converted to a series of sodium tetraalkoxyborates prior to reaction with NaAlH4 in refluxing diglyme to regenerate sodium borohydride. At room temperature in tetrahydrofuran, the same reactants formed the partial hydrides NaBH3(OR) (R = C1-4 alkyl). Products were characterised by multinuclear 1H, 13C, 11B and 27Al NMR studies. The intermediate alkoxyborate products were confirmed by single crystal X-ray structural studies.