The acetobromination of alkali-lignin through a flow chemistry approach

Utilizing a continuous-flow chemistry platform, we demonstrate the in-situ generation of acetyl bromide and acetyl hypobromite from acetic anhydride and bromine, enabling simultaneous benzylic and aromatic bromination alongside acetylation of alkali-lignin in a single, integrated process. Compared to conventional batch acetobromination, which affords only side-chain modification and yields just 0.24 at.% surface bromine, our flow method delivers up to 5.67 at.% surface bromine and clear evidence of aromatic CBr formation, as confirmed by X-ray photoelectron spectroscopy (XPS) and Heteronuclear single quantum coherence-Nuclear magnetic resonance (HSQC-NMR) spectroscopic analyses. The continuous-flow setup affords precise control over reagent stoichiometry, temperature, and residence time, markedly improving safety and reproducibility when handling corrosive bromine reagents, and offering straightforward scalability for larger-scale production. Additional analytical techniques, including Fourier transform mid- and near-infrared spectroscopy (FT-MIR-NIR), Field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Dilute solution viscometry (DSV) and Thermogravimetry (TG) were employed to evaluate the molecular properties. The resulting acetobrominated lignins show enhanced solubility in common organic solvents (e.g., tetrahydrofuran, dimethylsulfoxide, acetone, etc.), characteristic thermal degradation profile and significant char formation, and tunable structure-property relationships, underscoring their promise as advanced, customizable intermediates for next-generation polybrominated flame retardants and other high-performance applications.