Xiang Hui,Jianhui Shi,Jiajun Zhang,Yan Cao,Huiquan Li,Peng He,Liguo Wang
The carbonylation of amines offers a promising route for synthesizing N-substituted carbamates with high atom economy. However, conventional catalysts exhibit limited catalytic efficiency, and the underlying proton transfer mechanism remains elusive. Herein, we reported a metal-free, room-temperature strategy utilizing 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a dual hydrogen bond catalyst to synergistically activate propylamine (PA) and dimethyl carbonate (DMC). This green catalytic system achieves a 10-fold acceleration in reaction rate compared to other hydrogen bonding catalysts under mild conditions. This is enabled by dual hydrogen bonding of TBD with PA and DMC, which facilitates rapid proton transfer and stabilizes tetrahedral intermediates. Theoretical calculations confirm that the dual hydrogen bond system significantly lowers activation energy compared to single hydrogen bond analogs. Furthermore, it was revealed that the hydrogen bonding network within the product is the primary factor responsible for the sluggish reaction rate. This study demonstrates the effectiveness of a dual hydrogen bond system in accelerating the carbonylation of amines and provides a green route to access carbamates.
Xiaoqian Chang,Yuepeng Wang,Yanfei Zhao,Ying Wang,Rongxiang Li,Zhengang Ke,Penglei Chen,Zhimin Liu
1,4-Dioxane and its derivatives are a class of important chemicals, which can be produced via dehydrative cyclization of vicinal diols catalyzed by acid or Lewis acid catalysts, but generally suffer from their inherent shortcomings. Herein, we report a hydrogen-bonding catalyzed approach for the synthesis of 1,4-dioxanes from vicinal diols in ionic liquids under metal-free conditions. The ILs possessing a cation hydrogen-bond donor and an anion hydrogen-bond acceptor (e.g., 1-hydroxyethyl-3-methyl imidazolium trifluoromethanesulfonate, [HO-EtMIm][OTf]) were found to be effective for the reaction. In particular, [HO-EtMIm][OTf] showed the best performance among the tested ILs, even better than H2SO4, affording a series of 1,4-dioxanes in high yields and excellent selectivity under mild conditions (e.g., 120 °C). The mechanism investigation indicates that the IL cation and anion as the hydrogen-bond donor and acceptor, respectively, can activate the C–O and O–H bonds of diols via hydrogen-bonding, which synergistically realizes the dehydrative cyclization of vicinal diols to generate 1,4-dioxanes. In addition, this IL could be reused 5 times without activity loss. This work provides a simple, green route to produce 1,4-dioxanes, which may have promising applications.
5,5′(oxy-bis(methylene)) bis-2-furfural (OBMF) is an important biobased chemical that can be synthesized through the self-etherification of 5-hydroxymethylfurfural (HMF) in the presence of either homogeneous acid or solid acid catalysts, such as p-toluenesulfonic acid (PTSA) and molecular sieves. In previous studies, all authors believed that this process follows an acid-catalyzed mechanism, even though some argued that acid strength is not the key factor in the formation of OBMF. In this work, we present a new route for the synthesis of OBMF from HMF, utilizing hydrogen-bonding catalysis with protonated ionic liquids under metal-free conditions. [NMPH][OTf] featuring a cationic hydrogen bond donor and an anionic hydrogen bond acceptor, is effective for the self-etherification of HMF. Under the optimal conditions, the yield of OBMF reached approximately 92.4 %. Based on the results of Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR), Nuclear Magnetic Resonance (NMR) and Density Functional Theory (DFT) calculation, it is determined that the cations and anions of ILs could activate the C O and O H bonds of HMF via hydrogen bonds respectively. This synergistically facilitates the self-etherification of two HMF molecules to form OBMF. After recycling the catalyst four times, the yield of OBMF did not decrease significantly. According to the Arrhenius law, the apparent activation energy and reaction order for [NMPH][OTf] in the self-etherification of HMF to OBMF are determined 40.7 kJ/mol and 1.0, respectively. The results suggested that [NMPH][OTf] is an excellent catalyst for the generation of OBMF from HMF. Therefore, this study offers a simple and environmentally friendly method for the production of OBMF, which holds promising potential for broad application prospect in the future.
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