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Transesterification of Dimethyl Carbonate with Ethanol Catalyzed by Guanidine: A Theoretical Analysis
The Journal of Organic Chemistry ( IF 3.6 ) Pub Date : 2024-05-02 , DOI: 10.1021/acs.joc.4c00382
Sina Gilassi 1 , Serge Kaliaguine 1
Affiliation  

Density-functional theory (DFT) was performed to investigate the mechanistic features of different guanidine-based catalysts, namely, 1,1,3,3-tetramethyl guanidine (TMG) and 1,5,7-triaza-bicyclo-[4.4.0]dec-5-ene (TBD), for the transesterification reaction of dimethyl carbonate (DMC) with ethanol (EtOH). Different possible pathways were suggested in which these catalysts act as either nucleophile or base within a homogeneous system. The DFT results allowed not only the study of the thermochemistry aspects of all elementary reactions featured in the two different activation modes but also the accurate calculation of the free energy barriers for each case. Our findings showed that the catalyzed reaction proceeded through simultaneous activation of DMC and EtOH, facilitated by hydrogen bonding for both catalysts. This feature led to the formation of a stable intermediate with a relatively low free energy barrier. TBD exhibited a potentially more efficient mechanism, owing to its planar structure and dual-activation mode. The free energy barrier of the rate-limiting step, identified as the formation of a zwitterionic complex, then declined by approximately 50% when compared with the reaction without catalysts. Overall, the DFT approach provides good insight into the reactivity of both catalysts and helps to find possibilities for further enhancing the mechanistic features of both catalysts for this type of transesterification reaction.

中文翻译:

胍催化碳酸二甲酯与乙醇酯交换反应的理论分析

采用密度泛函理论(DFT)研究了不同胍基催化剂的机理特征,即1,1,3,3-四甲基胍(TMG)和1,5,7-三氮杂-双环-[4.4。 0]dec-5-ene (TBD),用于碳酸二甲酯 (DMC) 与乙醇 (EtOH) 的酯交换反应。提出了不同的可能途径,其中这些催化剂在均相系统中充当亲核试剂或碱。 DFT 结果不仅可以研究两种不同激活模式下所有基元反应的热化学方面,还可以准确计算每种情况的自由能垒。我们的研究结果表明,催化反应是通过 DMC 和 EtOH 的同时活化进行的,两种催化剂的氢键促进了催化反应。这一特征导致形成具有相对较低自由能垒的稳定中间体。由于其平面结构和双激活模式,TBD 表现出潜在的更有效的机制。与没有催化剂的反应相比,限速步骤的自由能垒(被确定为两性离子络合物的形成)下降了约 50%。总体而言,DFT 方法可以很好地了解两种催化剂的反应性,并有助于找到进一步增强两种催化剂用于此类酯交换反应的机械特征的可能性。
更新日期:2024-05-02
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