Reactive and non-reactive species formed during the methanolysis of NaBH4: A theoretical and experimental approach

Abstract

The formation, stability, and reactivity of the species generated by the reduction reactionof solid NaBH4 with methanol in the liquid phase were investigated by experimental FTIRstudies and Density Functional Theory (DFT) calculations. A complete reaction systemof NaBH4 methanolysis considering solid-liquid-gas interfaces was outlined. The main,species identified and differentiated through FTIR analysis of experimental testscorrespond to the [BH4]-, alkoxyborohydride [BH4-n(OCH3)n]- (n= 1, 2, and 3), andtetramethoxyborate [B(OCH3)4]-. In correlation with the experimental results, theexistence of reducing species, which are present in the liquid phase and in the equilibriumassociated with Na+ in the solid phase are elucidated by DFT. The molecular modeling ofthe experimental results allows to establish the reaction mechanism involved in thegeneration of all the species and molecular hydrogen. The mechanism consists of foursteps where the [BH4]- species initially interacts with methanol to generate hydrogen andthe monosubstituted [BH3(OCH3)]- species. Subsequently, this species reactsconsecutively with methanol until generating the fully substituted species [B(OCH3)4]-.