645-62-5Relevant articles and documents
Two sides of the same amino acid - Development of a tandem aldol condensation/epoxidation by using the synergy of different catalytic centres in amino acids
Ostrowski, Karoline A.,Lichte, Dominik,Terhorst, Michael,Vorholt, Andreas J.
, p. 1 - 7 (2016)
A new tandem catalysis was set up after intensive investigations regarding the amino catalysed aldol condensation and epoxidation. 20 proteinogenic amino acids were investigated as organocatalysts in the epoxidation of an α-branched α,β-unsaturated aldehyde. The most active amino acids were chosen for the optimization of the reaction conditions obtaining excellent yields in the epoxidation. With these insights the first tandem aldol condensation/epoxidation was developed gaining very good yields of the epoxy aldehyde, which was obtained directly from butanal without any purification or isolation of the intermediate. Applying butanal as substrate, which is produced on a large industrial scale, opens up new horizons for novel useful and reactive products. Furthermore, the beneficial influence of lysine and arginine was proven and it was revealed that these amino acids bear two different catalytic centres, which have impact on the synergy in this new tandem catalysis being active within two different reaction mechanisms. The α-amino function catalyses the aldol condensation and the corresponding side chain group is responsible for the catalytically conversion in the epoxidation.
Tailoring the cooperative acid-base effects in silica-supported amine catalysts: Applications in the continuous gas-phase self-condensation of n-butanal
Shylesh, Sankaranarayanapillai,Hanna, David,Gomes, Joseph,Krishna, Siddarth,Canlas, Christian G.,Head-Gordon, Martin,Bell, Alexis T.
, p. 1283 - 1290 (2014)
A highly efficient solid-base organocatalyst for the gas-phase aldol self-condensation of n-butanal to 2-ethylhexenal was developed by grafting site-isolated amines on tailored silica surfaces. The catalytic activity depends largely on the nature of amine species, the surface concentration of amine and silanol groups, and the spatial separation between the silanol and amine groups. In situ FTIR measurements demonstrated that the formation of nucleophilic enamines leads to the enhanced catalytic activity of secondary amine catalysts, whereas the formation of imines (stable up to 473 K) leads to the low activity observed for silica-supported primary amines. Blocking the silanol groups on the silica support by silylation or cofeeding water into the reaction stream drastically decreased the reaction rates, demonstrating that weaker acidic silanol groups participate cooperatively with the amine groups to catalyze the condensation reaction. This work demonstrates that the spatial separation of the weakly acidic silanols and amines can be tuned by the controlled dehydration of the supporting silica and by varying the linker length of the amine organosilane precursor used to graft the amine to the support surface. A mechanism for aldol condensation was proposed and then analyzed by DFT calculations. DFT analysis of the reaction pathway suggested that the rate-limiting step in aldol condensation is carbon-carbon bond formation, which is consistent with the observed kinetics. The calculated apparent activation barrier agrees reasonably with that measured experimentally. Secondary amines come first: A solid-base organocatalyst achieved by grafting amines onto silica surfaces is applied to the gas-phase aldol self-condensation of n-butanal to 2-ethylhexenal. Silica-supported secondary amine catalysts demonstrate a much higher catalytic activity than the primary amine analogues, owing to the respective formation of enamines as shown by in situ FTIR analysis. The reaction pathway is analyzed by DFT calculations.
Vapor-phase self-aldol condensation of butanal over Ag-modified TiO2
Sun, Daolai,Moriya, Shizuka,Yamada, Yasuhiro,Sato, Satoshi
, p. 8 - 16 (2016)
Vapor-phase self-aldol condensation of butanal was performed over various solid catalysts. Among the tested catalysts, SiO2-Al2O3, Nb2O5 and TiO2 showed relatively high catalytic activity for the formation of aldol condensation product, 2-ethyl-2-hexenal, whereas all the catalysts deactivated rapidly. In order to stabilize the catalytic activity, metal-modified catalysts were investigated in hydrogen flow, and it was found that Ag-modified TiO2 showed the best catalytic performance. Characterizations such as XRD, TPD, TPR, TG-DTA, and DRIFT were performed for investigating the effect of the additive Ag and analyzing the coke component. The loaded Ag metal inhibited the formation of carbon accumulated on catalyst surface, and H2 carrier gas was indispensable in the inhibition. Ag would work as a remover of the products on the catalyst surface together with H2 to prevent dehydrogenation followed by coke formation. Self-aldol condensation of butanal was stabilized over Ag-modified TiO2 at Ag2O loadings higher than 3 wt.% at 220 °C in H2 flow. TiO2 with Ag2O of 5 wt.% showed the best catalytic performance and gave a 72.2% selectivity to 2-ethyl-2-hexenal at 72.1% conversion in H2 flow at 220 °C.
Hierarchical Beta zeolites as catalysts in a one-pot three-component cascade Prins-Friedel-Crafts reaction
?ejka, Ji?í,Barakov, Roman,Bezverkhyy, Igor,Opanasenko, Maksym,Shcherban, Nataliya,Yaremov, Pavel
, p. 6992 - 7002 (2020)
Hierarchical Beta zeolites obtained from concentrated reaction mixtures (H2O/Si = 2.5-7.0) in the presence of CTAB and their conventional and nanosponge analogues were investigated in a one-pot cascade environmentally friendly Prins-Friedel-Crafts reaction of butyraldehyde with 3-buten-1-ol and anisole under mild conditions (60 °C). The highest yields of the desired products with 4-aryltetrahydropyran structure were achieved when using hierarchical zeolites characterised by well-developed mesoporosity (facilitating the formation of bulky intermediates and products) and by an increased fraction of highly accessible (evaluated by TTBPy method) medium-strength Br?nsted acid sites. Acid sites with higher strength promote strong adsorption of bulk O-containing intermediates or products and the formation of byproducts (tetrahydropyranyl ether and 2-propyloxan-4-ol). Therefore, this is an inexpensive and simple synthesis method for preparing hierarchical zeolites with catalytic activity comparable to that of nanosponge Beta, which is however prepared using complex and expensive multi-quaternary ammonium surfactants. Moreover, this synthetic protocol for 4-aryltetrahydropyrans replaces the carcinogenic and toxic chemicals, which have been previously used for Prins-Friedel-Crafts reactions, with green and non-toxic substances. This journal is
Preparation and catalytic performance of NiO-MnO2/Nb2O5-TiO2 for one-step synthesis of 2-ethylhexanol from n-butyraldehyde
An, Hualiang,Li, Sibo,Wang, Yanji,Zhang, Jiaxun,Zhao, Xinqiang
, (2020/12/02)
One-pot synthesis of 2-ethylhexanol(2EHO) from n-butyraldehyde is of commercialimportance. The promotion of 2EHO selectivity requires suppressing direct hydrogenation of n-butyraldehyde. In this work, a series of NiO-MOx/Nb2O5-TiO2 catalysts were prepared and utilized by means of reduction-in-reaction technique, aiming at delaying the formation of metal sites and suppressing the direct hydrogenation. NiO-MnO2/Nb2O5-TiO2 with a Ni/Mn mass ratio of 10 and NiO-MnO2 loading of 14.3 wt% shows the best catalytic performance; 2-EHO selectivity could reach 90.0% at a complete conversion of n-butyraldehyde. Furthermore the catalyst could be used for four times without a substantial change in its catalytic performance.
Electronic and steric factors for enhanced selective synthesis of 2-ethyl-1-hexanol in the Ir-complex-catalyzed Guerbet reaction of 1-butanol
Xu, Zhanwei,Yan, Peifang,Liang, Changhui,Jia, Songyan,Liu, Xiumei,Zhang, Z. Conrad
, p. 1586 - 1592 (2021/05/10)
1-Butanol is a potential bio-based fermentation product obtained from cellulosic biomass. As a value-added chemical, 2-ethyl-1-hexanol (2-EH) can be produced by Guerbet conversion from 1-butanol. This work reports the enhanced catalytic Guerbet reaction of 1-butanol to 2-EH by a series of Cp*Ir complexes (Cp*: 1,2,3,4,5-pentamethylcyclopenta-1,3-diene) coordinated to bipyridine-type ligands bearing an ortho-hydroxypyridine group with an electron-donating group and a Cl? anion. The catalytic activity of the Cp*Ir complex increased by increasing the electron density of the bipyridine ligand when functionalized with the para-NMe2 and ortho-hydroxypyridine groups. A record turnover number of 14047 was attained. A mechanistic study indicated that the steric effect of the ethyl group on the α-C of 2-ethylhexanal (2-EHA) and the conjugation effect of C=C–C=O in 2-ethylhex-2-enal (2-EEA) benefits the high selectivity of 2-EH from 1-butanol by inhibiting the cross-aldol reaction of 2-EHA and 2-EEA with butyraldehyde. Nuclear magnetic resonance study revealed the formation of a carbonyl group in the bipyridine-type ligand via the reaction of the Cp*Ir complex with KOH.
