Ammonia borane (AB) has been synthesized in very high purity (>99%) from sodium borohydride and ammonium sulfate under ambient conditions in tetrahydrofuran (THF) at 1 M concentration using water as the promoter. Less than quantitative yields of AB are obtained due to a competing hydrolysis of the primary metathesis product ammonium borohydride. The solvent THF can be substituted with a greener alternative, 2-methylTHF, with no loss in yield or purity and complete recyclability. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.