18240-50-1Relevant articles and documents
gem-dialkyl effect in the intramolecular Diels-Alder reaction of 2-furfuryl methyl fumarates: The reactive rotamer effect, enthalpic basis for acceleration, and evidence for a polar transition state
Jung, Michael E.,Gervay, Jacquelyn
, p. 224 - 232 (1991)
Investigation of the rates of cyclization of a series of substituted 2-furfuryl methyl fumarates 1a-h has allowed us to determine which of the two explanations for the gem-dialkyl effect is more important. Studies with compounds substituted with small-membered rings showed that the rate acceleration is due primarily to the reactive rotamer effect and not to angle compression ("Thorpe-lngold effect"). For example, the cyclobutyl-substituted compound 1d would experience a reactive rotamer effect similar to that of the dimethyl compound 1e and thus should cyclize relatively rapidly if this effect were dominant. However, due to the small ring, 1d would have a larger "internal" angle than other disubstituted derivatives and thus should cyclize even more slowly than the dihydrido compound 1a if the angle compression effect were dominant. Since the cyclobutyl-substituted compound 1d cyclizes in CD3CN at 25 °C 208 times faster than the dihydrido compound 1a, we have concluded that the reactive rotamer effect outweighs angle compression in determining the rate of cyclization in this system. The activation parameters for the cyclization of 1a-f in CD3CN have been calculated. These data show that the large rate acceleration seen in this system, namely the significant lowering of the ΔG?, is due almost entirely to a lowering of the enthalpy of activation (ΔH?) and not to a difference in the entropy of activation. For example, on going from the dihydrido 1a to the monomethyl compound 1b, the 1.3 kcal/mol decrease in the ΔG? is almost entirely due to the 1.4 kcal/mol decrease in the ΔH?. Likewise, comparison of the dihydrido and dimethyl cases shows that the ΔΔG? of 4.5 kcal/mol is due very largely to the 4.9 kcal/mol difference in the ΔH? with little contribution from the entropy of activation (ΔS?). In fact, the entropy of activation is more negative for the more substituted cases (1b vs 1a and 1e vs 1a or 1b) and would, therefore, retard the rate rather than accelerate it, if it were not for the enthalpy change (an isokinetic relationship). The rate enhancements due to the gem-dialkyl effect in this system are much higher than those generally seen in other systems (normally no larger than a factor of 10 for the dimethyl case vs the dihydrido one, but here a ratio of 2100). This discrepancy in rate effects is almost certainly due to the presence of an oxygen atom in the tether of our system next to the affected carbon compared to the all carbon tethers in the other cases. Finally, examination of the effect of solvents on this reaction reveals a strong acceleration of the cycloaddition in polar solvents, with the reaction being slowest in toluene, faster in acetonitrile, and faster again in DMSO. The solvent effect can be quite large in certain cases, with Arel being as large as 3200. The results for the monomethyl compound 1b in a wide variety of solvents indicate a better agreement with the dielectric constant of the solvent rather than other solvent polarity parameters, such as ET. This solvent effect is explained by the rotation of the most stable conformation of the starting material, the s-trans ester conformation 5, about the C-O bond to give the higher energy s-cis conformation 6, which can then cyclize via the transition state 7 to the observed products, the lactones 2. Since the s-cis conformation and the transition state derived from it have a net dipole due to the overlap of the dipoles of the ester, it is more polar than the starting material and thus would be expected to be stabilized by polar solvents. This is not the case for the intermolecular cycloaddition because the s-cis ester conformation is not required in the transition state. As additional evidence for this mechanistic rationale, the analogous tertiary amide 8, which would not have this more polar transition state (relative to the starting material), shows essentially no solvent effect in several solvents under similar conditions.
Selective Synthesis of Furfurylamine by Reductive Amination of Furfural over Raney Cobalt
Zhou, Kuo,Chen, Bixian,Zhou, Xiaoting,Kang, Shimin,Xu, Yongjun,Wei, Jinjia
, p. 5562 - 5569 (2019)
Effect of metal nature on reductive amination was investigated with biomass-based furfural as a typical substrate. Among the tested heterogeneous metal catalysts, cobalt proved to be the most effective metal for the synthesis of the corresponding primary amine. Under a relatively mild reaction condition, 98.9 % yield of furfurylamine was obtained over Raney Co and it can be reused more than eight times without a significant decrease in the catalytic performance. By extensively studying the catalytic pathways and reaction mechanism, it is found that the selectivity to primary amine and secondary amine was governed by the relative rate of hydrogenolysis and hydrogenation of the Schiff base intermediate. The superiority of Raney Co in furfurylamine synthesis can be ascribed to its high efficiency on hydrogenolysis of the Schiff base intermediate and its low performance in the hydrogenation of the Schiff base, carbonyl group and furan ring. Furthermore, ammonia greatly promoted the catalytic hydrogenolysis of the Schiff base intermediate over Raney Co without clear deactivation of the metal active sites.
Ru/HZSM-5 as an efficient and recyclable catalyst for reductive amination of furfural to furfurylamine
Dong, Chenglong,Wang, Hongtao,Du, Haochen,Peng, Jiebang,Cai, Yang,Guo, Shuai,Zhang, Jianli,Samart, Chanatip,Ding, Mingyue
, (2020)
Furfurylamine converted from biomass-based platform molecules furfural was proven a significant intermediate in the synthesis of different valuable compounds. The combination of Ruthenium with HZSM-5 was acted as an excellent selective and reusable catalyst for the reduction amination of furfural with environmentally friendly ammonia and hydrogen. Incorporation of Ru species into HZSM-5 had a significant enhancement to the acid sites of Ru/HZSM-5. The Ru/HZSM-5(46) catalyst with optimized acid sites and interaction of the Ru-O-Al bond displayed an excellent catalytic performance, producing 76 % yield of furfurylamine at only 15 min, and could be recycled five times without loss of performance. Synergistic effect between RuO2 and metallic Ru in the Ru/HZSM-5 catalyst facilitated the reduction amination of furfural.
Selective catalysis for the reductive amination of furfural toward furfurylamine by graphene-co-shelled cobalt nanoparticles
Liu, Jianguo,Ma, Longlong,Zhong, Shurong,Zhuang, Xiuzheng
, p. 271 - 284 (2022/01/19)
Amines with functional groups are widely used in the manufacture of pharmaceuticals, agricultural chemicals, and polymers but most of them are still prepared through petrochemical routes. The sustainable production of amines from renewable resources, such as biomass, is thus necessary. For this reason, we developed an eco-friendly, simplified, and highly effective procedure for the preparation of a non-toxic heterogeneous catalyst based on earth-abundant metals, whose catalytic activity on the reductive amination of furfural or other derivatives (more than 24 examples) proved to be broadly available. More surprisingly, the cobalt-supported catalyst was found to be magnetically recoverable and reusable up to eight times with an excellent catalytic activity; on the other hand, the gram-scale tests catalyzed by the same catalyst exhibited the similar yield of the target products in comparison to its smaller scale, which was comparable to the commercial noble-based catalysts. Further results from a series of analytical technologies involving XRD, XPS, TEM/mapping, and in situ FTIR revealed that the structural features of the catalyst are closely in relation to its catalytic mechanisms. In simple terms, the outer graphitic shell is activated by the electronic interaction as well as the induced charge redistribution, enabling the easy substitution of the –NH2 moiety toward functionalized and structurally diverse molecules, even under very mild industrially viable and scalable conditions. Overall, this newly developed catalyst introduces the synthesis of amines from biomass-derived platforms with satisfactory selectivity and carbon balance, providing cost-effective and sustainable access to the wide applications of reductive amination.
Hydrosilylative reduction of primary amides to primary amines catalyzed by a terminal [Ni-OH] complex
Pandey, Pragati,Bera, Jitendra K.
supporting information, p. 9204 - 9207 (2021/09/20)
A terminal [Ni-OH] complex1, supported by triflamide-functionalized NHC ligands, catalyzes the hydrosilylative reduction of a range of primary amides into primary amines in good to excellent yields under base-free conditions with key functional group tolerance. Catalyst1is also effective for the reduction of a variety of tertiary and secondary amides. In contrast to literature reports, the reactivity of1towards amide reduction follows an inverse trend,i.e., 1° amide > 3° amide > 2° amide. The reaction does not follow a usual dehydration pathway.
