Understanding interactions between lignin and ionic liquids with experimental and theoretical studies during catalytic depolymerisation

Experimental and theoretical investigation of synergistic effects in a binary ionic liquid system for the selective production of benzaldehyde from lignin model compound

Lignin is an abundant and cost-effective aromatic polymer, which makes the production of high-value aromatic aldehydes from it highly significant. However, a challenge is that these aldehydes can easily over-oxidation into aromatic acids during aerobic oxidation. Therefore, preventing over-oxidation is crucial. In this study, a binary ionic liquid system ([Emim][Ac] and [Bmim][FeCl4]) was employed for synergistic catalysis to mitigate this issue. Notably, density functional theory analyses have revealed that [Ac]- and [FeCl4]- can engage in hydrogen bonding and van der Waals interactions with the β-O-4 linkages in lignin. These interactions can effectively reduce the bond energy of the Cβ-H bonds, facilitating its homolysis to generate free radicals. Furthermore, under mild conditions, these free radicals can readily break CC bonds, producing aromatic aldehydes while minimizing over-oxidation. In this system, the lignin model compound 2-Phenoxy-1-phenylethanone (PP) was cleaved to produce benzaldehyde (46.4 %) and phenol (73.4 %), enzymatic lignin was degraded to yield aromatic products like vanillic aldehyde, all without over-oxidation. To meet the growing demand for biomass upgrading, this work introduces a green and controlled conversion technology capable of cleaving inert CC bonds under mild conditions, establishing a foundation for future advancements in renewable energy production.

Chloromethylation of Lignin as a Route to Functional Material with Catalytic Properties in Cross-Coupling and Click Reactions

We present a novel, greener chloromethylation procedure for organosolv aspen lignin under mild reaction conditions without Lewis acid as a catalyst and in acetic acid as a solvent. This synthetic protocol provides a reliable approach to chloromethylated lignin (CML) and means to obtain valuable lignin derivatives. The resulted CML was subsequently transformed into 1-methylimidazolium lignin (ImL), which effectively serves as a stabilizing agent for Pd/CuO nanoparticles (Pd/CuO-NPs). To evaluate the versatility of developed lignin-based catalyst, we investigate its performance in a series of carbon-carbon bond formation reactions, including Suzuki-Miyaura, Sonogashira, Heck reactions, and azide-alkyne cycloaddition (click) reaction. Remarkably, this catalyst exhibited a high degree of catalytic efficiency, resulting in reactions with yields ranging from average to excellent. The heterogeneous catalyst demonstrated outstanding recyclability, enabling its reuse for at least 10 consecutive reaction cycles, with yields consistently falling within the range of 42 % to 84 %. A continuous flow reactor cartridge prototype employing Lignin@Pd/CuO-NPs was developed, yielding results comparable to those achieved in batch reactions. The utilization of Lignin@Pd/CuO-NPs as a catalyst showcases its potential to facilitate diverse carbon-carbon bond formation reactions and underscores its promising recyclability, aligning with the green chemistry metrics and principles of sustainability in chemical processes.

Experimental and in silico insights: interaction of dimethyl sulphoxide with 1-hexyl-2-methyl imidazolium bromide/1-octyl-2-methyl imidazolium bromide at different temperatures

Ionic liquids have gained attention as 'designer solvents' since they offer a broad spectrum of properties that can be tuned by altering the constituent ions. In this work, 1-alkyl-2-methyl imidazolium-based ionic liquids with two different alkyl chains (alkyl = hexyl and octyl) have been synthesized and characterized. Since the binary mixture of ionic liquids with molecular solvents can give rise to striking physicochemical properties, the interaction of the synthesized room temperature ionic liquids, 1-hexyl-2-methyl imidazolium bromide [HMIM][Br]/1-octyl-2-methyl imidazolium bromide [OMIM][Br] with DMSO has been examined through density and specific conductance at T = (303.15, 308.15, 313.15 and 318.15) K under atmospheric pressure. The obtained molar volume and excess molar volume are fitted to the Redlich-Kister polynomial equation, and the standard deviation is noted. The positive excess molar volume at elevated temperatures indicates volume expansion due to the mutual loss of dipolar association and differences in the sizes and shapes of the constituent molecules. To have a better understanding of the reactivity and efficacy of 1-hexyl-2-methyl imidazolium bromide and 1-octyl-2-methyl imidazolium bromide with DMSO, the Becke, 3-parameter, Lee-Yang-Parr (B3LYP) correlation function of density functional theory (DFT) has been used. The ORCA Program version 4.0 calculates the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy. The effective reactivities of both the compounds that showed an energy band gap (ΔE), i.e., the difference between ELUMO and EHOMO, are 7.147 and 8.037 kcal mol-1.

Bioinspired carbon dots: from rose petals to tunable emissive nanodots

Engineering biomass into functional nanomaterials is captivating. The limitation of versatility in green precursors is pursued by exploring the formation of carbon dots with respect to the contents of the green precursor, i.e. Rosa indica. The intermediates formed at different intervals are analyzed. Moreover, the mechanism of heteroatom-doped Rosa indica derived carbon-dot is proposed.

Degradation of lignin with aqueous ammonium-based ionic liquid solutions under milder conditions

Ammonium-based ionic liquids can serve as solvents and promoters for lignin depolymerization.