Structural Analysis of Lignin-Based Furan Resin

The global “carbon emission peak” and “carbon neutrality” strategic goals promote us to replace current petroleum-based resin products with biomass-based resins. The use of technical lignins and hemicellulose-derived furfuryl alcohol in the production of biomass-based resins are among the most promising ways. Deep understanding of the resulting resin structure is a prerequisite for the optimization of biomass-based resins. Herein, a semiquantitative 2D HSQC NMR technique supplemented by the quantitative 31P NMR and methoxyl group wet chemistry analysis were employed for the structural elucidation of softwood kraft lignin-based furfuryl alcohol resin (LFA). The LFA was fractionated into water-insoluble (LFA-I) and soluble (LFA-S) parts. The analysis of methoxyl groups showed that the amount of lignin was 85 wt% and 44 wt% in LFA-I and LFA-S fractions, respectively. The HSQC spectra revealed the high diversity of linkages formed between lignin and poly FA (pFA). The HSQC and 31P results indicated the formation of new condensed structures, particularly at the 5-position of the aromatic ring. Esterification reactions between carboxyl groups of lignin and hydroxyl groups of pFA could also occur. Furthermore, it was suggested that lignin phenolic hydroxyl oxygen could attack an opened furan ring to form several aryl ethers structures. Therefore, the LFA resin was produced through crosslinking between lignin fragments and pFA chains.

Radical and Ionic Mechanisms in Rearrangements of o-Tolyl Aryl Ethers and Amines Initiated by the Grubbs–Stoltz Reagent, Et3SiH/KOtBu

Rearrangements of o-tolyl aryl ethers, amines, and sulfides with the Grubbs–Stoltz reagent (Et3SiH + KOtBu) were recently announced, in which the ethers were converted to o-hydroxydiarylmethanes, while the (o-tol)(Ar)NH amines were transformed into dihydroacridines. Radical mechanisms were proposed, based on prior evidence for triethylsilyl radicals in this reagent system. A detailed computational investigation of the rearrangements of the aryl tolyl ethers now instead supports an anionic Truce–Smiles rearrangement, where the initial benzyl anion can be formed by either of two pathways: (i) direct deprotonation of the tolyl methyl group under basic conditions or (ii) electron transfer to an initially formed benzyl radical. By contrast, the rearrangements of o-tolyl aryl amines depend on the nature of the amine. Secondary amines undergo deprotonation of the N-H followed by a radical rearrangement, to form dihydroacridines, while tertiary amines form both dihydroacridines and diarylmethanes through radical and/or anionic pathways. Overall, this study highlights the competition between the reactive intermediates formed by the Et3SiH/KOtBu system.

Monitoring transformation of two tropical lignocellulosics and their lignins after residence in Benin soils

Thermally assisted Hydrolysis and Methylation (THM), and 2D-heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy were used to monitor the transformation of ramial chipped wood (RCW) from Gmelina arborea and Sarcocephalus latifolius, together with their organosolv lignins, following soil incubation in Benin (West Africa). Mesh litterbags containing RCW were buried in soils (10 cm depth) and were retrieved after 0, 6, 12 and 18 months of field incubation. Chemical analysis showed that total carbohydrate content decreased, while total lignin content increased as RCW decomposition progressed. Ash and mineral content of RCW increased significantly after 18 months of decomposition in soil. Significant N-enrichment of the RCW was determined following 18 months incubation in soils, reaching 2.6 and 1.9 times the initial N-content for G. arborea and S. latifolius. Results of THM showed that the S + G sum, corresponding to lignins, increased with RCW residence time in the soils, in contrast to the response of compounds derived from carbohydrates, the sum of which decreased. Remarkably, lignin interunit linkages, most notably β-O-4′ aryl ethers, β-β′ resinol, β-5′ phenylcoumaran and p-PCA p-coumarate, survived after 18 months in the soil, despite their gradual decrease over the duration of the experiment.

Synthesis and antiprotozoal activity of 2-phenoxy derivatives of pyridine

The aim of the present work is to synthesize phenoxypyridine derivatives and to screen substances with a high level of biological activity within the series of synthesized compounds, which is essential for solving the problem of overcoming the growing drug resistance of bacteria and protozoa. The interaction of 2-chloro-5-nitro- and 2-chloro-3-nitro-pyridine with aromatic aldehydes containing phenolic hydroxyl gave 15 pyridine series aryl ethers in high yields when reacted in dimethylformamide (DMFA) or dimethyl sulfoxide (DMSO) in the presence of bases. In the reaction we used phenolic derivative of kojic acid (compound 1 of Table 1), a number of benzene series aldehydes with different substituents: 3-methoxy-4-hydroxybenzaldehyde (compound 2 of Table 1), 4-hydroxybenzaldehyde (compound 3 of Table 1), 2,4-dihydroxybenzaldehyde (compound 5 of Table 1), 3-methoxy-4-hydroxybenzaldehyde (compound 7 of Table 1 ), salicylic aldehyde (compound 11 of Table 1), 3,4-dihydroxybenzaldehyde (compound 12 of Table 1), vanillin (compound 13 of Table 1), and compound 15 (Table 1) of the benzene series with two hydroxyl and aldehyde groups. As well as benzene-type aldehydes, the methyl ester of salicylic acid (compound 4 of Table 1), 4-hydroxymethylphenol (compound 6 of Table 1), 4-acetylphenol (compound 8 of Table 1), and 3-hydroxy benzoic acid (compound 14 of Table 1) were used. In the reaction, in addition to the above compounds, 7-hydroxycoumarin (compound 9 of Table 1) and semicarbazide-4-hydroxybenzaldehyde (compound 10 of Table 1) were also used. Their purification was performed by recrystallization from organic solvents (ethyl acetate, benzene, ethanol, and isopropanol). The obtained compounds were studied as part of the institute's search for compounds to expand the range of active substances with protistoсid and antibacterial activity with low toxicity. Synthesized compounds have pronounced antiprotozoal activity against Colpoda steinii. the most active compound contains a nitro group in the 3rd position of the pyridine ring as well as an aldehyde and hydroxyl group in the benzene ring. The minimum protistocidal concentration of this compound is 0.9 µg/ml, which is 60 fold more active than toltrazuril and 8 fold more active than chloroquine. This compound is recommended for extended toxicological and pharmacological studies.

Weak arene/nickel interaction lights on monoarylation of alcohols

Despite a growing body of work in nickel catalysis, the potential of organo-photocatalyst serving both as an arene ligand and a sensitizer remains underexplored. Here, we describe such an organo-photocatalyst to promote arylation of alcohols. Mechanistic studies suggest that the formation of sandwich complex via weak arene/nickel interaction and the resulting dexter energy transfer be responsible for this activity. This interaction provides a mechanistically alternative strategy for challenging carbon-oxygen bond assembly, where the elementary steps in transition metal catalysis previously facilitated by intermolecular photoevents replaced by more efficient intramolecular ones. With only 0.05 mol% photocatalyst loading and 8 mol% nickel bromide, a series of alcohols, diols and triols were (mono)arylated with (hetero)aryl bromides and chlorides. Importantly, many bioactive molecules and active pharmaceutical ingredients containing multiple hydroxyl groups could be efficiently monoarylated, too. This work provides a new approach to access bioactive aryl ethers, but also lights on a highly desirable direction to manipulate the catalytic reactivity of earth abundant nickel.

Nickel-catalyzed Homo-coupling of Aryl Ethers with Magnesium Anthracene Reductant

Nickel-catalyzed reductive homo-coupling of aryl ethers has been achieved with Mg(anthracene)(thf)3 as a readily available low-cost reductant. DFT calculations provided a rationale for the specific efficiency of the diorganomagnesium-type two-electron reducing agent. The calculations showed that the dianionic anthracene-9,10-diyl ligand reduces the two aryl ether substrates resulting in the homo-coupling reaction through supplying the electrons to the Ni-Mg bimetallic system to form organomagnesium nickel(0)-ate complexes, which cause two sequential C–O bond cleavage reactions. The calculations also showed cooperative actions of Lewis-acidic magnesium atoms and electron-rich nickel atoms in the C–O cleavage reactions.