488-17-5Relevant academic research and scientific papers
Role of Catalyst Support's Physicochemical Properties on Catalytic Transfer Hydrogenation over Palladium Catalysts
Batalha, Nuno,Fraga, Gabriel,Hasan, M. D.,Konarova, Muxina,Laycock, Bronwyn,Pratt, Steven,Santos, Mirella S.
, p. 5191 - 5202 (2021/10/29)
Catalytic transfer hydrogenation (CTH) is a promising reaction for valorisation of bio-based feedstocks via hydrogenation without needing to use H2. Unlike standard hydrogenation, CTH occurs via dehydrogenation (DHD) of a hydrogen donor (H-donor) and hydrogenation (HYD) of a substrate. Therefore, the “ideal” CTH catalyst must balance the catalysis of both reactions to maximize the hydrogen transfer between H-donor and substrate with minimal H2 loss to gas (high atom efficiency). Additionally, the H-donor must be highly stable to prevent secondary reactions with the substrate. Herein we study the impact of the catalyst's properties on CTH of guaiacol using bicyclohexyl, a liquid organic hydrogen carrier, as a H-donor. The reaction was promoted by palladium dispersed on three typical support materials (γ-Al2O3, MgO, and SiO2). The performance of these catalysts in the conversion of bicyclohexyl and guaiacol was evaluated, allowing to estimate the H-transfer efficiency, as well as the potential for recycling the spent H-donor (bicyclohexyl). The apparent activation energies for DHD of bicyclohexyl and HYD of guaiacol revealed that slow DHD combined with fast HYD, as is the case with Pd/MgO, favours hydrogen transfer efficiency and selectivity towards hydrogenated products. In addition, an investigation of the DHD of bicyclohexyl and HYD of guaiacol independently showed that the affinity between the organic molecules and the support significantly impacts CTH. Indeed, Pd/SiO2 was highly active for both reactions individually and almost inactive for CTH. Consequently, these findings highlight the importance of the interaction between solvent-substrate-support in designing catalysts for transfer hydrogenation.
Structural features and antioxidant activities of Chinese quince (Chaenomeles sinensis) fruits lignin during auto-catalyzed ethanol organosolv pretreatment
Cheng, Xi-Chuang,Guo, Xin-Ran,Liu, Hua-Min,Liu, Yu-Lan,Qin, Zhao,Wang, Xue-De
, p. 4348 - 4358 (2020/09/22)
Chinese quince fruits (Chaenomeles sinensis) have an abundance of lignins with antioxidant activities. To facilitate the utilization of Chinese quince fruits, lignin was isolated from it by auto-catalyzed ethanol organosolv pretreatment. The effects of three processing conditions (temperature, time, and ethanol concentration) on yield, structural features and antioxidant activities of the auto-catalyzed ethanol organosolv lignin samples were assessed individually. Results showed the pretreatment temperature was the most significant factor; it affected the molecular weight, S/G ratio, number of β-O-4′ linkages, thermal stability, and antioxidant activities of lignin samples. According to the GPC analyses, the molecular weight of lignin samples had a negative correlation with pretreatment temperature. 2D-HSQC NMR and Py-GC/MS results revealed that the S/G ratios of lignin samples increased with temperature, while total phenolic hydroxyl content of lignin samples decreased. The structural characterization clearly indicated that the various pretreatment conditions affected the structures of organosolv lignin, which further resulted in differences in the antioxidant activities of the lignin samples. These results can be helpful for controlling and optimizing delignification during auto-catalyzed ethanol organosolv pretreatment, and they provide theoretical support for the potential applications of Chinese quince fruits lignin as a natural antioxidant in the food industry.
The multifunctional globin dehaloperoxidase strikes again: Simultaneous peroxidase and peroxygenase mechanisms in the oxidation of EPA pollutants
Ghiladi, Reza A.,Malewschik, Talita,McGuire, Ashlyn H.,de Serrano, Vesna
, (2019/08/30)
The multifunctional catalytic hemoglobin dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata was found to catalyze the H2O2-dependent oxidation of EPA Priority Pollutants (4-Me-o-cresol, 4-Cl-m-cresol and pentachlorophenol) and EPA Toxic Substances Control Act compounds (o-, m-, p-cresol and 4-Cl-o-cresol). Biochemical assays (HPLC/LC-MS) indicated formation of multiple oxidation products, including the corresponding catechol, 2-methylbenzoquinone (2-MeBq), and oligomers with varying degrees of oxidation and/or dehalogenation. Using 4-Br-o-cresol as a representative substrate, labeling studies with 18O confirmed that the O-atom incorporated into the catechol was derived exclusively from H2O2, whereas the O-atom incorporated into 2-MeBq was from H2O, consistent with this single substrate being oxidized by both peroxygenase and peroxidase mechanisms, respectively. Stopped-flow UV–visible spectroscopic studies strongly implicate a role for Compound I in the peroxygenase mechanism leading to catechol formation, and for Compounds I and ES in the peroxidase mechanism that yields the 2-MeBq product. The X-ray crystal structures of DHP bound with 4-F-o-cresol (1.42 ?; PDB 6ONG), 4-Cl-o-cresol (1.50 ?; PDB 6ONK), 4-Br-o-cresol (1.70 ?; PDB 6ONX), 4-NO2-o-cresol (1.80 ?; PDB 6ONZ), o-cresol (1.60 ?; PDB 6OO1), p-cresol (2.10 ?; PDB 6OO6), 4-Me-o-cresol (1.35 ?; PDB 6ONR) and pentachlorophenol (1.80 ?; PDB 6OO8) revealed substrate binding sites in the distal pocket in close proximity to the heme cofactor, consistent with both oxidation mechanisms. The findings establish cresols as a new class of substrate for DHP, demonstrate that multiple oxidation mechanisms may exist for a given substrate, and provide further evidence that different substituents can serve as functional switches between the different activities performed by dehaloperoxidase. More broadly, the results demonstrate the complexities of marine pollution where both microbial and non-microbial systems may play significant roles in the biotransformations of EPA-classified pollutants, and further reinforces that heterocyclic compounds of anthropogenic origin should be considered as environmental stressors of infaunal organisms.
Formation of Phenolic Compounds from d -Galacturonic Acid
Urbisch, Alexandra,Einhorn-Stoll, Ulrike,Kastner, Hanna,Drusch, Stephan,Kroh, Lothar W.
, (2018/10/31)
Aqueous d-galacturonic acid (d-GalA) model systems treated at 130 °C at different pH values show an intense color formation, whereas other reducing sugars, such as d-galactose (d-Gal), scarcely react. GC-MS measurements revealed the presence of several ph
Enzyme-Catalysed Synthesis of Cyclohex-2-en-1-one cis-Diols from Substituted Phenols, Anilines and Derived 4-Hydroxycyclohex-2-en-1-ones
Boyd, Derek R.,Sharma, Narain D.,McIntyre, Peter B. A.,Stevenson, Paul J.,McRoberts, W. Colin,Gohil, Amit,Hoering, Patrick,Allen, Christopher C. R.
, p. 4002 - 4014 (2017/11/22)
Toluene dioxygenase-catalysed cis-dihydroxylations of substituted aniline and phenol substrates, with a Pseudomonas putida UV4 mutant strain and an Escherichia coli pCL-4t recombinant strain, yielded identical arene cis-dihydrodiols, which were isolated as the preferred cyclohex-2-en-1-one cis-diol tautomers. These cis-diol metabolites were predicted by preliminary molecular docking studies, of anilines and phenols, at the active site of toluene dioxygenase. Further biotransformations of cyclohex-2-en-1-one cis-diol and hydroquinone metabolites, using Pseudomonas putida UV4 whole cells, were found to yield 4-hydroxycyclohex-2-en-1-ones as a new type of phenol bioproduct. Multistep pathways, involving ene reductase- and carbonyl reductase-catalysed reactions, were proposed to account for the production of 4-hydroxycyclohex-2-en-1-one metabolites. Evidence for the phenol hydrate tautomers of 4-hydroxycyclohex-2-en-1-one metabolites was shown by formation of the corresponding trimethylsilyl ether derivatives. (Figure presented.).
A highly efficient metal-free approach to: Meta - And multiple-substituted phenols via a simple oxidation of cyclohexenones
Liang, Yu-Feng,Song, Song,Ai, Lingsheng,Li, Xinwei,Jiao, Ning
supporting information, p. 6462 - 6467 (2018/06/08)
A novel and efficient metal-free approach to substituted phenols has been disclosed from simple and readily available cyclohexenones and cyclohexenone equivalents. Dimethyl sulfoxide (DMSO), a simple and common organic reagent, was employed as a mild oxidant in this I2-catalysis, which significantly tolerates various substituents including some easily oxidizable or reducible functionalities. The challenging meta- and multiple-substituted phenols could be well prepared by this method. The metal-free and mild oxidation make this protocol very simple, practical, and easy to handle.
Conversion of Simple Cyclohexanones into Catechols
Liang, Yu-Feng,Li, Xinyao,Wang, Xiaoyang,Zou, Miancheng,Tang, Conghui,Liang, Yujie,Song, Song,Jiao, Ning
supporting information, p. 12271 - 12277 (2016/09/28)
A novel I2-catalyzed direct conversion of cyclohexanones to substituted catechols under mild and simple conditions has been described. This novel transformation is remarkable with the multiple oxygenation and dehydrogenative aromatization processes enabled just by using DMSO as the solvent, oxidant, and oxygen source. This metal-free and simple system demonstrates a versatile protocol for the synthesis of highly valuable substituted catechols and therefore streamlines the synthesis and modification of biologically important molecules for drug discovery.
H2O2 in WEB: a highly efficient catalyst system for the Dakin reaction
Saikia, Bishwajit,Borah, Parinita,Barua, Nabin Chandra
supporting information, p. 4533 - 4536 (2015/09/15)
Without using any transition metal catalyst, ligand, base, toxic or hazardous reagent, additives/promoters and organic solvent, green Dakin reactions have been successfully carried out by using H2O2 in a natural feedstock extract. The reaction proceeds in neat 'Water Extract of Banana' (WEB) at room temperature under aerobic conditions in very short reaction times and, therefore, it is an evergreen and environmentally sound alternative to the existing protocols for the Dakin reaction. In our system, the reaction was found to afford excellent yield for the desired product with different electron-withdrawing and electron-donating hydroxylated benzaldehydes.
A new avenue to the Dakin reaction in H2O2-WERSA
Saikia, Bishwajit,Borah, Parinita
, p. 105583 - 105586 (2015/12/30)
We have developed a novel protocol to realize the Dakin reaction in a more greener way. In fact, by the use of H2O2-WERSA, we can oxidize aromatic arylaldehydes to phenols at room temperature. It is remarkable that the catalytic system does not require activation or any toxic ligand, additive/promoter, transition metal catalyst, base, organic solvent and so on. A range of substituted hydroxylated benzaldehydes were screened to investigate the scope of this protocol.
Ruthenium(II)-Catalyzed CH acyloxylation of phenols with removable auxiliary
Raghuvanshi, Keshav,Rauch, Karsten,Ackermann, Lutz
supporting information, p. 1790 - 1794 (2015/01/30)
Intermolecular CH acyloxylations of phenols with removable directing groups were accomplished with a versatile ruthenium catalyst. Specifically, a cationic ruthenium(II) complex, formed in situ, enabled the chemoselective CH oxygenations of a broad range of substrates. The catalyst proved tolerant of synthetically valuable functional groups, and the substrate scope included both (hetero)aromatic, the more challenging, aliphatic carboxylic acids. The proposed reaction mechanism involves a reversible CH ruthenation and an oxidatively induced CO-bond-forming reductive elimination.
