木质素二聚体模型化合物热解机理的量子化学研究

β-O-4连接是木质素主体结构单元之间的主要联结方式。采用密度泛函理论方法B3LYP,在6-31G (d, p)基组水平上,对β-O-4型木质素二聚体模型化合物(1-愈创木基-2-(2-甲氧基苯氧基)-1,3丙二醇)的热解反应机理进行了研究。提出了三种热解反应途径:C_β-O键均裂的后续反应、C_α-C_β键均裂的后续反应以及协同反应。对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了各热解反应途径的标准动力学参数。分析了各种主要热解产物的形成演化机理以及热解过程中温度对热解机理的影响。计算结果表明,C_β-O键的均裂反应和协同反应路径(1)和(3)是木质素二聚体热解过程中主要的反应路径,而C_α-C_β键的均裂反应和协同反应路径(2)和(5)是主要的竞争反应路径;热解的主要产物是酚类化合物如愈创木酚、1-愈创木基-3-羟基丙酮、3-愈创木基-3-羟基丙醛、愈创木基甲醛和乙烯等。在热解低温阶段协同反应是热解过程中的主要反应形式,而在高温阶段自由基均裂反应是热解过程的主要反应形式。     

吡喃葡萄糖热解机理的量子化学理论研究

采用密度泛函理论方法 B3LYP/6-31G++(d,p),对纤维素的一个循环单体β-D-吡喃葡萄糖的热解反应机理进行了量子化学理论研究。设计了四种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了各热解反应途径的标准动力学参数。计算结果表明,反应路径1中速控步的活化能为297.02 kJ.mol,反应路径2中速控步的活化能为284.49 kJ.mol,与反应路径3,4相比,反应路径1,2的反应能垒更低,是主要的热解反应通道,乙醇醛、1-羟基-2-丙酮、5-羟甲基糠醛、CO等小分子产物是热解的主要产物。这与相关实验结果分析是一致的。     

O-乙酰基-吡喃木糖热解反应机理的理论研究

为了从微观上理解半纤维素热解过程及其主要产物的形成演变机理,采用密度泛函理论方法B3LYP/6-31G++(d,p),对O-乙酰基-吡喃木糖的热解反应机理进行了量子化学理论研究。在热解过程中,O-乙酰基-吡喃木糖中的O-乙酰基首先脱出,形成乙酸和中间体IM₁,该步反应能垒为269.4 kJ/mol。IM₁进一步发生开环反应形成IM₂,开环反应能垒较低,为181.8 kJ/mol。对中间体IM₂设计了四种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了各热解反应途径的热力学和动力学参数。计算结果表明,反应路径(4)和反应路径(2)是O-乙酰基-吡喃木糖热解的主要反应通道,乙酸、乙醛、乙醇醛、丙酮、CO、CO₂、CH₄等小分子产物是热解的主要产物。这与相关实验结果分析是一致的。     

纤维素单体热解机理的热力学研究

为了了解纤维素热解机理, 结合相关实验结果对纤维素单体(β-D-吡喃葡萄糖)的热解设计了四种热解反应途径. 利用Gaussian 03程序, 采用密度泛函理论(DFT), 在UB3LYP/6-31G(d)水平上, 对各反应物和产物的几何结构进行了能量梯度法全优化, 计算了不同温度下各反应路径的热力学参数. 计算结果表明: 所有反应均为吸热反应; 当温度在550 K以上时, 所有反应都能自发进行. 从热力学的角度分析, 热解更有利于发生开环反应而形成乙醇醛、1-羟基-2-丙酮、CO等小分子产物.     

2,2,6,6-四甲基哌啶氧自由基/Ca(ClO)2催化氧化甲基葡糖苷制备葡醛酸

采用2,2,6,6-四甲基哌啶氧自由基/Ca(ClO)2体系选择氧化甲基葡萄糖苷(简称甲苷)合成了葡萄糖甲苷酸盐,再用硫酸酸解葡萄糖甲苷酸盐,得到葡萄糖醛酸和副产物硫酸钙。考察了氧化工艺条件对葡萄糖醛酸收率的影响;用pH计监控反应过程,反应中间体和终产物用UV和HPLC检测。结果表明,该体系对甲苷伯羟基的氧化具有较好的催化活性和反应选择性,葡萄糖醛酸收率达到92%,且金属离子易于去除。和传统的淀粉HNO3氧化法工艺相比,该方法具有资源节约、环境友好的特点。     

木质素模化物紫丁香酚热解机理的量子化学研究

采用密度泛函理论方法B3LYP/6-31G++(d,p),对木质素模化物紫丁香酚的热解反应机理进行了量子化学理论研究。提出了三种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化。计算了各热解反应途径的标准动力学参数,分析了各种主要热解产物的形成演化机理。键离解能计算结果表明,紫丁香酚中CH₃-O键的键离解能最小,各种键离解能的大小顺序为CH₃-O < O-H < CH₃O-C_aromatic < CH₂-H < HO-C_aromatic < C_aromatic-H。在反应路径(1)中,主要热解产物是3-甲氧基邻苯二酚,其形成反应的总能垒为366.6 kJ/mol;在反应路径(2)中主要热解产物是2-甲氧基-6-甲基苯酚,其形成反应的总能垒为474.8 kJ/mol;在反应路径(3)中形成邻甲氧基苯酚的总能垒很低,为21.4 kJ/mol,这表明,在连接甲氧基的碳原子上加氢后能够有效地降低木质素芳环模化物紫丁香酚去甲氧基反应的反应能垒。     

1-甲基-2-苯基吲哚的琥红敏化单重态氧反应

1-甲基-2-苯基吲哚(1)在甲醇中的琥红(RB)敏化单重态氧反应生成1-甲基-2-甲基氧-2-苯基-1, 2-二氢-3H-吲哚-3-酮(4)和1-甲基-2-羟基-2-苯基-1, 2-二氢-3H-吲哚-3-酮(6), 后者在强碱性介质下发生苯乙醇酸型重排生成1-甲基-3-羟基-3-苯基氧化吲哚(14)。研究了6的溶剂分解反应以及外加碱对光氧化反应的影响。探讨了光氧化产物的形成途径。结果表明: 4系两性离子中间体2的溶剂捕获、脱水产物, 而6则系二氧杂环丁烷中间体7的裂解、抽氢产物。     

新型海参硫酸软骨素葡萄糖受体及葡萄糖醛酸受体的高效合成

以D-葡萄糖为起始原料,经9步反应合成了2-O-苄基-3-O-烯丙基-1-O-对甲氧基苯基α-D-葡萄糖(9);将9的6-位伯羟基经叔丁基二苯基硅烷基(TBDPS)保护,首次合成了正交保护的新型葡萄糖受体2-O-苄基-3-O-烯丙基6-O-叔丁基二苯基硅烷基1-O-对甲氧基苯基α-D-葡萄糖(Ⅱ),总收率28.2%;将9的6-位伯羟基氧化糖醛酸化后,再经甲酯化,以25.0%的总收率首次合成了新型葡萄糖醛酸受体2-O-苄基-3-O-烯丙基-1-O-对甲氧基苯基α-D-葡萄糖醛酸甲酯(Ⅲ),化合物结构经¹H NMR,¹³C NMR, IR和HR-MS(ESI)表征。     

N-丁基-1-脱氧野尻霉素的合成新方法

以2,3,4,6-四-O-苄基-α-D-葡萄糖为原料,经4步反应制得中间体2,3,4,6-四-O-苄基-D-葡萄糖酸-δ-内酰胺(6);在碱性条件下6与正溴丁烷进行氮原子上的烃基化反应得N-丁基-2,3,4,6-四-O-苄基-D-葡萄糖酸-δ-内酰胺(7);用氢化铝锂将7的羰基还原为亚甲基得N-丁基-2,3,4,6-四-O-苄基-1-脱氧野尻霉素(8);8经催化氢解脱去苄基合成了N-丁基-1-脱氧野尻霉素,其结构经1H NMR,13C NMR和MS确证。     

达格列净的合成

以5-溴-2-氯苯甲酸为原料,经酰氯化、傅克酰化反应、还原得中间体5-溴-2-氯-4'-乙氧基二苯甲烷,该中间体与2,3,4,6-四-O-三甲基硅基-D-葡萄糖酸内酯经缩合、醚化、脱甲氧基、酯化、脱保护得目标化合物,总收率45%,纯度99.1%,其结构经1H NMR及MS确证。     

磷酸钾中和法邻甲酚羧化反应的绿色合成

以邻甲酚和二氧化碳为原料,以磷酸钾为中和剂一步羧化合成邻甲基水杨酸及相关产物。探讨了反应条件对产率的影响。实验结果表明,当磷酸钾与邻甲酚物料比为2.5∶1,反应温度150 ℃,反应压力3.0 MPa时,羧化反应产物总收率达到95.4%,同时邻甲基水杨酸收率也达到最大。与传统碳酸钾中和法相比,磷酸钾中和法产物在后处理过程中无二氧化碳放出,后处理过程中的磷酸根可制备为磷酸钾使用,新工艺是一条绿色化工路线。     

Mechanism of Xylan Pyrolysis by Py-GC/MS

In order to investigate the decomposition behavior of hemicellulose, xylan was chosen as the representative of hemicellulose to study the fast pyrolysis on the combination system of analytical pyrolyzer and gas chromatograph coupled with mass spectrometer(Py-GC/MS). The main condensable products of xylan pyrolysis consisted of acids, aldehydes, and ketones; while gas products contained CO₂, CO, CH₄ and H₂. Acetic acid and furfural were the most abundant products with the highest contents of 20.11% and 20.24% respectively. While furfural and acetic acid were formed competitively with residence time and temperature increases, the distribution of xylan pyrolysis products did not vary with the residence time and temperature, while the total content of several kinds of products changed a lot. According to the analysis of experimental data, a reaction pathway of xylan decomposition was deduced so as to illustrate the formation mechanism of main products.     

CL-20热分解反应机理的ReaxFF分子动力学模拟

为探究固相CL-20热分解反应机理,本文采用反应分子动力学ReaxFF MD模拟研究了含有128个CL-20分子的超胞模型在800–3000 K温度下的热分解过程。借助作者所在课题组研发的反应分析及可视化工具VARxMD得到了热分解过程中多种反应中间物和较为全面的反应路径。氮氧化物是CL-20初始分解的主要中间产物,其中NO₂是数量最多的初始分解产物,观察到的中间物NO₃的生成量仅次于NO₂。统计CL-20初始分解的所有反应后发现,在所有考察温度下CL-20初始分解路径主要是N―NO₂断裂反应和C―N键断裂引起开环的单分子反应路径。N―NO₂断裂反应数量在高温下显著增多,而C―N键断裂引起的开环反应数量随温度升高变化不大。在低温热分解模拟中还观察到CL-20初始分解阶段生成的NO₂会发生双分子反应—从CL-20分子中夺氧生成NO₃。对CL-20热分解过程中环结构演化进行分析后发现,CL-20分解的早期反应中间物主要为具有3元或2元稠环结构的吡嗪衍生物,随后它们会分解形成单环吡嗪。吡嗪六元环结构在热分解过程中非常稳定,这一模拟结果支持Py-GC/MS实验中提出吡嗪存在的结论。CL-20中的咪唑五元环结构相对不稳定,在热分解过程中会发生开环分解而较早消失。由ReaxFF MD模拟得到的3000 K高温热分解产物N₂,H₂O,CO₂和H₂的数量与爆轰实验的测量结果定量吻合。本文获得的对CL-20热分解机理的认识表明ReaxFF MD结合VARxMD有可能为深入了解热刺激下含能材料复杂化学过程提供一种有前景的方法。     

过渡金属催化CO2/H2参与的羰基化研究进展

Ever-increasing energy demands due to rapid industrialization and urban population growth have drastically reduced petroleum reserves and increased greenhouse-gas production, and the latter has consequently contributed to climate change and environmental damage. Therefore, it is highly desirable to produce fuels and chemicals from non-petroleum feedstocks and to reduce the atmospheric concentrations of greenhouse gases. One solution has involved using carbon dioxide (CO₂), a main greenhouse gas, as a C1 feedstock for producing industrial fuels and chemicals. However, this requires high energy input from reductants or reactants with relatively high free energy (e.g., H₂ gas) because CO₂ is a highly oxidized, thermodynamically stable form of carbon. H₂ can be generated through water photolysis, making it an ideal reductant for hydrogenating CO₂ to CO. In situ generation of CO such as this has been developed for various carbonylation reactions that produce high value-added chemicals and avoid deriving CO from fossil fuels. This is beneficial because CO is toxic, and when extracted from fossil fuels it requires tedious separation and transportation. This combination of CO₂ and H₂ allows for functional molecules to be synthesized as entries into the chemical industry value chain and would generate a carbon footprint much lower than that of conventional petrochemical pathways. Based on this, CO₂/H₂ carbonylations using homogeneous transition metal-based catalysts have attracted increasing attention. Through this process, alkenes have been converted to alcohols, carboxylic acids, amines, and aldehydes. Heterogeneous catalysis has also provided an innovative approach for the carbonylation of alkenes with CO₂/H₂. Based on these alkene carbonylations, the scope of CO₂/H₂ carbonylations has been expanded to include aryl halides, methanol, and methanol derivatives, which give the corresponding aryl aldehyde, acetic acid, and ethanol products. These carbonylations revealed indirect CO₂-HCOOH-CO pathways and direct CO₂ insertion pathways. The use of this process is ever-increasing and has expanded the scope of CO₂ utilization to produce novel, high value-added or bulk chemicals, and has promoted sustainable chemistry. This review summarizes the recent advances in transition-metal-catalyzed carbonylations with CO₂/H₂ and discusses the perspectives and challenges of further research.     

铜基串联催化剂电催化CO2还原的研究进展

化石燃料的燃烧和其他人类活动排放了大量的CO₂气体,引发了诸多环境问题。电催化CO₂还原反应(CO₂RR)可以储存间歇可再生能源,实现人为闭合碳循环,被认为是获得高附加值化学品和燃料的有效途径。电催化CO₂RR涉及多个电子-质子转移步骤,其中^*CO通常被认为是关键中间体。铜由于对^*CO具有合适的吸附能,已被广泛证明是唯一能够有效地将CO₂还原为碳氢化合物和含氧化合物的金属催化剂。然而,纯Cu稳定性差、产品选择性低、过电位高,阻碍了工业级多碳产品的生产。构筑Cu基串联催化剂是提高CO₂RR性能的一种有前途的策略。本文首先介绍电催化CO₂RR的反应路线和串联机理。然后,系统地总结铜基串联催化剂对电催化CO₂RR的最新研究进展。最后,提出合理设计和可控合成新型电催化CO₂RR串联催化剂面临的挑战和机遇。     

铜基串联催化剂电催化CO2还原的研究进展

Through the combustion of fossil fuels and other human activities, large amounts of CO₂ gas have been emitted into the atmosphere, causing many environmental problems, such as the greenhouse effect and global warming. Thus, developing and utilizing renewable clean energy is crucial to reduce CO₂ emission and achieve carbon neutrality. The electrochemical CO₂ reduction reaction (CO₂RR) has been considered as an effective approach to obtain high value-added chemicals and fuels, which can store intermittent renewable energy and achieve the artificial carbon cycle. In addition, due to its multiple advantages, such as mild reaction conditions, tunable products, and simple implementation, electrochemical CO₂RR has attracted extensive attention. Electrochemical CO₂RR involves multiple electron–proton transfer steps to obtain multitudinous products, such as C₁ products (CO, HCOOH, CH₄, etc.) and C₂ products (C₂H₄, C₂H₅OH, etc.). The intermediates, among which ^*CO is usually identified as the key intermediate, and reaction pathways of different products intersect, resulting in an extremely complex reaction mechanism. Currently, copper has been widely proven to be the only metal catalyst that can efficiently reduce CO₂ to hydrocarbons and oxygenates due to its suitable adsorption energy for ^*CO. However, the low product selectivity, poor stability, and high overpotential of pure Cu hinder its use for the production of industrial-grade multi-carbon products. Tandem catalysts with multiple types of active sites can sequentially reduce CO₂ molecules into desired products. When loaded onto a co-catalyst that can efficiently convert CO₂ to ^*CO (such as Au and Ag), Cu acts as an electron donor owing to its high electrochemical potential. ^*CO species generated from the substrate can spillover onto the surface of electron-poor Cu due to the stronger adsorption and be further reduced to C₂₊ products. The use of Cu-based tandem catalysts for electrochemical CO₂RR is a promising strategy for improving the performance of CO₂RR and thus, has become a research hotspot in recent years. In this review, we first introduce the reaction routes and tandem mechanisms of electrochemical CO₂RR. Then, we systematically summarize the recent research progress of Cu-based tandem catalysts for electrochemical CO₂RR, including Cu-based metallic materials (alloys, heterojunction, and core-shell structures) as well as Cu-based framework materials, carbon materials, and polymer-modified materials. Importantly, the preparation methods of various Cu-based tandem catalysts and their structure–activity relationship in CO₂RR are discussed and analyzed in detail. Finally, the challenges and opportunities of the rational design and controllable synthesis of advanced tandem catalysts for electrochemical CO₂RR are proposed.     

超临界二氧化碳中亚胺类共价有机骨架材料COF-LZU1的合成与表征

研究了超临界流体技术在共价有机骨架材料（COF）合成中的应用,以均苯三甲醛和对苯二胺为原料,N,N-二甲基甲酰胺为共溶剂,醋酸为催化剂,在超临界二氧化碳（scCO₂）中合成了亚胺类共价有机骨架材料COF-LZU1.考察了共溶剂、反应温度、反应压力、反应时间、醋酸含量和反应物摩尔比对COF-LZU1材料的晶体结构和微观形貌的影响.实验结果表明,反应温度的升高有利于提高scCO₂的传质速率及增加反应物在scCO₂中的溶解度,从而促进反应的进行;反应时间的延长有利于晶体的成熟和结晶度的提高;醋酸不仅是反应催化剂,还具有形貌导向剂的作用,通过改变醋酸用量分别获得了球状、块状和棒状形貌的COF-LZU1;反应物中对苯二胺含量过高会干扰反应过程中醛基与氨基的有序结合,导致结晶度的降低以及形貌规整程度的下降.在反应温度为60℃,反应压力为20 MPa,反应时间为6 h,均苯三甲醛与对苯二胺摩尔比为1：1.5,醋酸（3 mol/L）与N,N-二甲基甲酰胺体积比为1：1的条件下,制备的COF-LZU1呈现截面直径为80 nm的纳米棒形貌,具有良好的结晶度和优异的热稳定性,热分解温度高达550℃.本文首次在超临界环境中制备了COFs材料,为COFs的绿色合成提供了新途径.     

Pt电极上甲酸电催化氧化机理研究进展

本文综述了甲酸在铂电极上电催化氧化机理的实验和理论研究进展. 铂电极甲酸的电化学氧化主要有两种途径：1）间接途径,甲酸经由CO中间物氧化为最终产物CO₂,室温下该途径对总电流贡献不超过1%;2）直接途径,甲酸直接氧化生成CO₂. 作者课题组对文献中桥式吸附甲酸根是否是甲酸氧化反应直接途径的反应中间物的争论进行了详细的分析和探讨,认为桥式吸附的甲酸根不是间接途径中生成CO的前驱体,也不是甲酸直接氧化途径的中间物. 作者课题组还指出了支持甲酸根是甲酸直接氧化途径的反应中间物的推论的问题所在.