Romero Maria, Kushnir Jamie S, Mochi Bruno, Velez Caroline, Acevedo Orlando
Department of Chemistry, University of Miami, Coral Gables, Florida 33146, USA.
J Chem Phys. 2024 Aug 28;161(8). doi: 10.1063/5.0222092.
The conversion of biomass to 5-hydroxymethylfurfural (HMF) holds substantial promise as a renewable energy source. Notably, HMF can be transformed into 2,5-bis(hydroxymethyl)furan (BHMF), a crucial reactant in biofuel production, but requires harsh operating conditions, H2, and precious metal catalysts. A recently reported Cannizzaro reaction of HMF to BHMF, characterized by its efficiency, mild conditions, and eco-friendliness, instead employed ionic liquids (ILs) to achieve high yields. In this study, combined quantum mechanical and molecular mechanical (QM/MM) simulations in conjunction with Metropolis Monte Carlo statistical mechanics and free-energy perturbation theory utilized M06-2X/6-31+G(d), PDDG/PM3, and the OPLS-VSIL force field to uncover important solute-solvent interactions present in the HMF to BHMF reaction pathway. The Cannizzaro reaction was examined in water and in five ILs composed of the 1-butyl-3-methylimidazolium [BMIM] cation coupled to hexafluorophosphate, tetrafluoroborate, thiocyanate, chloride, and bromide. Energetic and structural analysis of the rate-determining hydride transfer between HMF and the hydride-donor anion HMFOH- attributed the enhanced reactivity to highly organized solvent interactions featuring (1) hydrogen bonding between the ring protons of [BMIM] and the negatively charged carbonyl oxygen atoms on the transition structure, (2) favorable electrostatic interactions between the IL anions and solute hydroxyl groups, and (3) beneficial π-π stacking interactions between [BMIM] and the two aromatic rings present in HMF and HMFOH-.
将生物质转化为5-羟甲基糠醛（HMF）作为一种可再生能源具有巨大的潜力。值得注意的是，HMF可以转化为2,5-双（羟甲基）呋喃（BHMF），这是生物燃料生产中的一种关键反应物，但需要苛刻的操作条件、氢气和贵金属催化剂。最近报道的HMF到BHMF的坎尼扎罗反应，以其效率、温和条件和环境友好性为特征，取而代之的是使用离子液体（ILs）来实现高产率。在本研究中，结合量子力学和分子力学（QM/MM）模拟，以及大都会蒙特卡罗统计力学和自由能微扰理论，利用M06-2X/6-31+G(d)、PDDG/PM3和OPLS-VSIL力场，揭示了HMF到BHMF反应途径中存在的重要溶质-溶剂相互作用。在水中以及由1-丁基-3-甲基咪唑鎓[BMIM]阳离子与六氟磷酸盐、四氟硼酸盐、硫氰酸盐、氯化物和溴化物组成的五种离子液体中对坎尼扎罗反应进行了研究。对HMF与氢化物供体阴离子HMFOH-之间的速率决定氢化物转移进行的能量和结构分析，将反应活性的提高归因于高度有序的溶剂相互作用，其特征包括：（1）[BMIM]的环质子与过渡结构上带负电荷的羰基氧原子之间的氢键；（2）离子液体阴离子与溶质羟基之间有利的静电相互作用；（3）[BMIM]与HMF和HMFOH-中存在的两个芳香环之间有益的π-π堆积相互作用。
