“溶剂剪刀”克服惰性氢键促进常压氧气下高效催化氧化芳香烃  

Solvent-scissors overcoming inert hydrogen bonding enable efficient oxidation of aromatic hydrocarbons under atmospheric oxygen

作　　者：金魁 张美云 车鹏华[2] 孙冬茹 王永 马红[2] 张巧红 陈晨 徐杰[2] Kui Jin;Meiyun Zhang;Penghua Che;Dongru Sun;Yong Wang;Hong Ma;Qiaohong Zhang;Chen Chen;Jie Xu(School of Materials Science&Chemical Engineering,Ningbo University,Ningbo 315211,Zhejiang,China;State Key Laboratory of Catalysis,Dalian National Laboratory for Clean Energy,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning,China;University of Chinese Academy of Sciences,Beijing 100049,China;Institute of Drug Discovery Technology,Ningbo University,Ningbo 315211,Zhejiang,China)

机构地区：[1]宁波大学材料科学与化学工程学院,浙江宁波315211 [2]中国科学院大连化学物理研究所,辽宁大连116023 [3]中国科学院大学,北京100049 [4]宁波大学新药技术研究院,浙江宁波315211

出　　处：《Chinese Journal of Catalysis》2024年第6期322-330,共9页催化学报（英文）

基　　金：国家重点研发计划(2022YFA1504902);国家自然科学基金(21872075,22272172,22072149).

摘　　要：氢键是调节各类催化反应体系中分子行为的重要作用力,能够有效活化分子、改变作用位置及控制反应途径,具有重要的科学意义和应用潜力.然而,氢键的利用过程存在着惰性效应难题,严重阻碍反应的顺利进行.如何有针对性地打破惰性的氢键作用力,探索氢键的构建与破坏机制,成为提高反应转化效率和选择性的重要途径,有利于实现高原子经济性并减少碳足迹.芳香烃氧化制羧酸是工业上重要的催化氧化过程,但存在高能耗、副产物多以及二氧化碳排放等问题.本文以甲苯液相氧气氧化制苯甲酸为模型反应,提出了旨在克服惰性氢键的"溶剂剪刀"策略.通过利用氢键受体溶剂(如醋酸、醋酸乙酯、氯乙酸乙酯或氯乙酸甲酯)作为破坏试剂,与强氢键供体溶剂六氟异丙醇(HFIP)形成氢键,从而将关键中间体苯甲醛从惰性的氢键结合状态中释放出来,将甲苯在温和条件下高效氧化为苯甲酸.使用NHPI/金属醋酸盐/HFIP-HOAc作为催化体系,在温和的反应条件(45°C,0.1 MPa O_(2))下反应4 h,甲苯转化率达到96.8%,苯甲酸选择性达98.7%.该方法不仅成功实现了甲苯到苯甲酸的高效转化,还可进一步拓展至邻(间,对)甲基甲苯等甲基芳烃,在25‒45°C和常压氧气条件下高效氧化制备芳香羧酸.利用变浓度核磁共振实验,定量测定了氢键供体HFIP与不同“剪刀溶剂”形成氢键的标准吉布斯自由能变化(ΔG^(0)).结果显示,‒ΔG^(0)顺序为醋酸>醋酸乙酯>氯乙酸乙酯>氯乙酸甲酯,其中醋酸的ΔG^(0)达到‒4.319 kJ/mol,具有最强的氢键裁剪能力.实验显示,‒ΔG^(0)与周转次数(TON)值(促进苯甲醛氧化的能力)的顺序一致,表明氢键裁剪能力越强的“溶剂-剪刀”越有利于促进苯甲醛的氧化.综上,本文利用“溶剂-剪刀”重建了甲基芳烃氧化反应中的氢键平衡体系,切断了使苯甲醛惰性化的氢键,促进游离苯甲醛的释放,使�Hydrogen bonding is a fascinating interaction that controls the outcomes of chemical reactions.However,overcoming the strong deactivation arising from alterations in the polarity and electronic properties of the reactants and intermediates remains a challenge.Herein,we proposed a“solvent-scissors”strategy for overcoming the inert hydrogen bonding,enabling the efficient aerobic oxidation of methyl aromatics into aromatic acids under atmospheric oxygen at 25‒45°C.The hydrogen bonds between the key intermediate,benzaldehyde(PhCHO),and hexafluoroisopropanol(HFIP)were reconstructed using solvent-scissors(acetic acid(HOAc),ethyl acetate,ethyl chloroacetate,and methyl chloroacetate),which promoted the release of free PhCHO from its inert hydrogen-bonded state and enabled the one-step oxidation of toluene to benzoic acid under mild conditions.The standard Gibbs free energy changes(ΔG^(0))representing the proton acceptance capability of the solvent were of the same order of magnitude as the turnover number(TON)(capacity for promoting benzaldehyde oxidation).This approach affords remarkable benzoic acid selectivity(98.7%)with high toluene conversion(96.8%)at 45°C within 4 h under 0.1 MPa O_(2)using NHPI/metal acetate/HFIP-HOAc.This strategy opens up a new avenue for regulating hydrogen bonding in a wider range of applications for the planning and development of synthesis protocols.

关 键 词：氢键 芳香烃 选择氧化 溶剂剪刀 六氟异丙醇 

分 类 号：O621.251[理学—有机化学] O641.3[理学—化学]