Reductive Amination of Oligoxylans with Fatty Amide-Amines: Comparison of Picoline-Borane and Sodium Cyanoborohydride as Reductive Agents and Influence of the Synthetic Route on Surface Activity and Self-Assembly

Xylans extracted from corn cobs, primarily composed of xylobiose and xylotriose, were valorized as the hydrophilic moiety of biobased surfactants. These oligosaccharides were coupled either to oleic acid (C18:1), previously modified by transamidation with a diamine (NH2-C4-NH2), or to oleylamine (NH2-C18:1). The resulting surfactants were synthesized through reductive amination between the aldehyde function at the xylan reducing end and the primary amine function. Initially, sodium cyanoborohydride (NaBH3CN) was used as the reducing agent and then replaced by picoline-borane (Pic-BH3), a less toxic alternative. The effect of different acidic catalysts (acetic acid and hydrochloric acid) was investigated in the presence of Pic-BH3, conditions that appeared to affect the physicochemical properties of the resulting surfactants. The surface activity and self-assembly behavior of the surfactants XOS2.7-NH-C18:1 and XOS2.7-NH-C4-CONH-C18:1 were evaluated via surface tension measurements at the water/air interface (pendant drop), static light scattering, and electron microscopy. Structure–property relationships were established, revealing that not only the molecular structure but also environmental factors introduced by different synthetic protocols─such as residual acidity─significantly influenced the behavior of the surfactants. These surfactants were also tested for oil-in-water emulsion stabilization, where they demonstrated promising performance, highlighting their potential in green formulation applications.