Unraveling the Crystal Structure of Sodium Tetrabenzylborate: Synthesis through the Sodium Borohydride Reduction of Benzaldehyde in the Solid State

Abstract

We present the synthesis, characterization, and crystal structure of sodium tetrabenzylborate, a novel tetraalkoxyborate obtained via a direct mechanochemical reaction between benzaldehyde and sodium borohydride at room temperature. The molecular and crystal structures of this borate were investigated using 11B MAS NMR, IR spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses. Crystalline sodium tetrabenzylborate exists in two different crystal structures, which were elucidated using powder- and single-crystal-XRD analyses. At a low temperature (e.g., −100 °C), sodium tetrabenzylborate crystallizes in the monoclinic system with the space group P21 (No. 4), but at room temperature, it displays a crystallization in the tetragonal system with the space group I4¯ (No. 82). According to the DSC analysis, the phase transition occurs at −45 °C. Upon hydrolysis, sodium tetrabenzylborate undergoes direct transformation into benzyl alcohol, thereby confirming the ability of sodium borohydride to convert an aldehyde into its primary alcohol analog. The key findings from our analyses are presented herein.