65076-90-6

Upstream product

• 56122-34-0 3-(4-hydroxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol 
• 7382-59-4 guaiacylglycerol-β-guaiacyl ether 
• 92409-34-2 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(2'-methoxyphenoxy)-1,3-propanediol 

Relevant academic research and scientific papers

Photocatalytic Chemoselective C-C Bond Cleavage at Room Temperature in Dye-Sensitized Photoelectrochemical Cells

Selective cleavage of C-C bonds can be a valuable tool for various applications including polymer degradation and biomass utilization. Performing chemical transformations involving C-C bond cleavage steps under mild conditions and ambient temperature remains challenging due to the high dissociation energies of the C-C bond. This fundamental challenge can be solved by coupling a dye-sensitized photoelectrochemical cell (DSPEC) system, that generally targets the water splitting reaction, with a hydrogen atom transfer (HAT) mediator (HAT-DSPEC). Here, we report the solar-driven selective cleavage of the C(aryl)-C(alkyl) σ-bond in lignin at ambient temperature using an HAT-DSPEC under redox-neutral conditions. The photocatalyst (bis-2,2′-bipyridine)(2,2′-bipyridine-4,4′-dicarboxylic acid)Ru(II) (RuC) adsorbed onto a TiO2 nanorod array with the length of ～1.6 μm and a rod diameter of 100 nm atop fluorine-doped tin oxide (FTO|TiO2 NRAs|RuC) film was prepared and investigated with an HAT mediator, 4-acetamido 2,2,6,6-tetramethylpiperidine-1-oxyl (ACT), in solution. Photophysical and electrochemical studies of RuC and ACT with a lignin model compound, 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(2-methoxyphenoxy) propane-1,3-diol (LMC) reveal that the metal-to-ligand charge transfer (MLCT) excited states from the RuC are efficiently quenched in the presence of ACT with LMC. The HAT-DSPEC photoanode, containing the surface-bound photocatalyst RuC at the photoanode with ACT and LMC in solution, sustained an excellent photocurrent density, significantly outperforming that with the photocatalyst RuC alone. Moreover, the chemoselective cleavage of the C(aryl)-C(alkyl) bond in the LMC at the ambient temperature was demonstrated in the HAT-DSPEC system with a remarkable photocatalytic turnover number (>3000) leading to excellent selectivity (>90%) of C-C bond cleavage under AM1.5G irradiation (1 sun, 100 mW cm-2). These results were obtained over short reaction times and mild, redox-neutral reaction conditions without the need for extended reaction time (e.g., >24 h) or high temperature that is typical of homogeneous catalytic systems. This is the first report to demonstrate that an HAT-DSPEC can serve as a viable method for performing visible-light-driven selective C-C bond cleavage at ambient temperature.

Copper catalysts for selective C-C bond cleavage of β-O-4 lignin model compounds

The reactivity of homogeneous copper catalysts towards the selective C-C bond cleavage of both phenolic and non-phenolic arylglycerol β-aryl ether lignin model compounds has been explored. Several copper precursors, nitrogen ligands, and solvents were evaluated in order to optimize the catalyst system. Using the optimized catalyst system, copper(I) trifluoromethanesulfonate [CuACHTUNGTRENUNG(OTf)]/L/ TEMPO (L=2,6-lutidine, TEMPO=2,2,6,6-tetramethyl- piperidin-1-yl-oxyl), aerobic oxidation of the non-phenolic β-O-4 lignin model compound proceeded with good selectivity for Cα-Cβ bond cleavage, affording 3,5-dimethoxybenzaldehyde as the major product. Aerobic oxidation of the corresponding phenolic β-O-4 lignin model proceeded with different selectivity, affording 2,6-dimethoxybenzoquinone and a,β-unsaturated aldehyde products resulting from cleavage of the Ca-Caryl bond. At low catalyst concentrations, however, a change in selectivity was observed as oxidation of the benzylic secondary alcohol predominated with both substrates.

Copper catalysts for selective c-c bond cleavage of b-o-4 lignin model compounds

The reactivity of homogeneous copper catalysts towards the selective C-C bond cleavage of both phenolic and non-phenolic arylglycerol b-aryl ether lignin model compounds has been explored. Several copper precursors, nitrogen ligands, and solvents were evaluated in order to optimize the catalyst system. Using the optimized catalyst system, copper(I) trifluoromethanesulfonate [CuACHTUNGTRENUNG(OTf)]/L/TEMPO (L=2,6-lutidine, TEMPO=2,2,6,6-tetramethyl-piperidin-1-yl-oxyl), aerobic oxidation of the non-phenolic b-O-4 lignin model compound proceeded with good selectivity for Ca-Cb bond cleavage, affording 3,5-dimethoxybenzaldehyde as the major product. Aerobic oxidation of the corresponding phenolic b-O-4 lignin model proceeded with different selectivity, affording 2,6-dimethoxybenzoquinone and a,b-unsaturated aldehyde products resulting from cleavage of the CaCaryl bond. At low catalyst concentrations, however, a change in selectivity was observed as oxidation of the benzylic secondary alcohol predominated with both substrates.

Oxidative degradation of monomeric and dimeric phenylpropanoids: Reactivity and mechanistic investigation

The oxidative degradation of lignin related model compounds catalysed by [N,N'-bis(salicylidene)ethane-1,2-diaminato]cobalt(II), [Co(salen)], have been studied in chloroform. Arylglycerol β-aryl ethers, phenylcoumarans and apocynol showed very high conversion values within 30 minutes of the start of the reaction and their conversion rates were higher than those reported for phenylpropenoidic compounds, methyl (E)-ferulate and methyl (E)-4-hydroxycinnamate. The results of the CW electron paramagnetic resonance (EPR) investigation using the X-band, performed at the reaction temperature (298 K) showed that two phenoxy cobalt radicals ([CoIII(salen)(ROH)(RO·)] and [CoIII(salen)(RO-)(RO·)]) are involved in the oxidation mechanism of all the phenol compounds ROH. In a frozen solution the [CoIII(salen)(ROH))(RO·)] radical prevailed and its axial magnetic anisotropy was determined using high frequency, 190 GHz, CW EPR spectra. The X-band EPR monitoring of the phenoxy cobalt radicals during the reaction showed a faster decrease in the amounts of radical in the oxidation of propanoidic phenols compared with that of propenoidic phenols. The lifetime of the radicals formed from substrates having a methoxy group ortho to the aromatic hydroxy was also shorter than from substrates lacking this functionality. Both reactivity and spectroscopic data suggest that the lifetime of the phenoxy cobalt radicals correlates with the conversion rates of the substrates.