Boron Tribromide

Selective demethylation reactions of biomass-derived aromatic ether polymers for bio-based lignin chemicals

“…16). [148][149][150] The technique of phosphitylation followed by 31 P NMR spectroscopy extends straightforward advantages in measuring lignin hydroxyl (OH) groups at high single-spectrum resolution. Meng et al published a well-defined protocol to ensure the scientific accuracy and uniform application of this methodology.…”

“…14,15 While the use of BBr 3 enables the successful demethylation of guaiacol-type compounds under mild conditions it has to be noted that BBr 3 is highly hazardous, it is toxic and it reacts violently with water and alcohols forming HBr, which also makes handling difficult. 31 In addition, the reaction is currently tied to the use of DCM as solvent, which is considered a hazardous solvent. 32 In sum, however, the BBr 3 -based approach, while highly efficient from a conventional perspective, is highly problematic from a green chemistry standpoint and should thus be avoided if suitable alternatives exist for the application in question.…”

“…Significant progress has been made in evaluating lignin's structural features by nuclear magnetic resonance (NMR) methodologies. A variety of lignin functional groups and structural insights have been identified by quantitative 31 P NMR and semiquantitative two-dimensional heteronuclear (2D 1 H- 13 C HSQC) NMR spectroscopy (Fig. 16).…”

“…Meng et al published a well-defined protocol to ensure the scientific accuracy and uniform application of this methodology. 149 With an appropriate phosphorus reagent, different lignin OH groups, which also depend on the biomass source, can be quantified by 31 P NMR. Among the aliphatic, phenolic and carboxylic OH groups, the content of phenolic OH is the key lignin structural feature that affects its chemical properties and reactivity.…”

α-Diimine-Niobium Complex-Catalyzed Deoxychlorination of Benzyl Ethers with Silicon Tetrachloride

“…In sharp contrast, the reverse reaction is considered to be significantly more difficult, since deoxygenation of ethers back to alkyl halides is generally thermodynamically unfavorable due to the strength of the C–O bond and relative weakness of the C–X bond formed in the alkyl halide products, as shown in selected examples in Figure . , One notable application of such ether cleavage reactions has been the deprotection of phenol derivatives; boron tribromide is a classic reagent for the cleavage of methyl ethers of phenols as well as certain other ethers. , Other reactions with milder reagents or conditions for the cleavage of dimethyl ether and similar ethers have also been developed that tolerate a wider range of functional groups. , In addition to deprotection reactions, ether cleavage can be used in its own right in synthesis and semisynthesis from ether natural products and substrates, such as in the depolymerization of lignin, which is a critical step in biomass conversion to liquid fuels. − In a similar manner, the treatment and recycling of ethereal solvents, including benzyl ether, by deoxygenation reactions are used to produce useful chemical products from what would otherwise be waste material. , …”