Emerging Bottom‐Up Strategies for the Synthesis of Graphene Nanoribbons and Related Structures

The solution‐phase synthesis is one of the most promising strategies for the preparation of well‐defined graphene nanoribbons (GNRs) in large scale. To prepare high quality, defect‐free GNRs, cycloaromatization reactions need to be very efficient, proceed without side reaction and mild enough to accommodate the presence of various functional groups. In this Minireview, we present the latest synthetic approaches for the synthesis of GNRs and related structures, including alkyne benzannulation, photochemical cyclodehydrohalogenation, Mallory and Pd‐ and Ni‐catalyzed reactions.     

Reductive Aromatization of Quinols with B2pin2 as Deoxidizing Agent

We have demonstrated B₂pin₂ as superior deoxidizing agent for the reductive deoxygenation of quinol derivatives under basic conditions. A wide range of highly functionalized phenols were obtained in good yields including a complex drug molecule, which revealed the high functional group tolerance of this protocol.     

金属氧化物和硅沉积改性 ZnO/SiO2/ZSM-5的甲醇择形芳构化反应催化研究

采用真空浸渍法对ZSM-5分子筛进行硅沉积和负载金属修饰,制备了复合改性的ZnO/SiO₂/ZSM-5催化剂,并将它应用于甲醇择形芳构化反应中。采用XRD、BET、NH₃-TPD、SEM、TEM等方法对制备的催化剂进行了物化表征。考察硅沉积次数和ZnO负载量对甲醇芳构化反应(MTA)中对二甲苯(PX)的选择性和收率的影响。结果表明,两次硅沉积改性并负载2.0%金属ZnO的ZSM-5分子筛具有较高的PX收率,在优化的反应温度420 ℃、反应压力0.2 MPa、甲醇空速WHSV为1.25 h^-1下,PX收率在28%以上。     

H-ZSM-5分子筛上环己烯芳构化反应历程的理论研究

基于76T簇模型,采用量子力学和分子力学联合的ONIOM2(B3LYP/6-31G(d,p):UFF)方法研究了H-ZSM-5分子筛上环己烯芳构化反应历程.结果表明,环己烯首先吸附在分子筛酸性位上,与酸性质子共同脱除一个H2分子后,在分子筛骨架氧上生成烷氧配合物中间体;然后再脱质子得到环己二烯,同时酸性位复原;再经历脱氢和脱质子历程,最后得到产物苯,并吸附在复原的分子筛酸性位上.计算得到脱氢的活化能依次为279.64和260.21kJ/mol,脱质子的活化能依次为74.64和59.14kJ/mol.所有脱氢反应都是吸热过程,生成表面烷氧活性中间体,随后的脱质子反应能垒较低,而且是放热过程.此外,比较了环己烯在分子筛酸性位上的三个竞争反应,即脱氢、质子化和氢交换反应的活化能垒,证明环己烯优先发生脱氢反应.     

正丁烷和异丁烷在改性纳米HZSM-5上的芳构化反应

用脉冲微反装置评价了正丁烷和异丁烷在氢型和锌改性的纳米ZSM-5催化剂上的反应活性和芳构化选择性.结果表明,在550℃下,异丁烷在氢型和不同锌负载量的纳米ZSM-5催化剂上的转化率都远高于正丁烷,但其芳构化选择性低于正丁烷.脱甲基活化是异丁烷和正丁烷的重要活化方式,也是影响其芳构化选择性的主要因素.锌改性在提高异丁烷和正丁烷转化率的同时,也促进了正丁烷和异丁烷的脱甲基活化.在混合丁烷进料反应的情况下,正丁烷和异丁烷的转化率与其单独进料时十分接近,这说明正丁烷和异丁烷共存时不会发生明显的竞争吸附和反应.纳米ZSM-5因晶粒度小,孔道短和微孔扩散阻力低而有利于异丁烷转化.     

Visible light mediated metal-free oxidative aromatization of 1,3,5-trisubstituted pyrazolines

The visible light mediated oxidation of 1,3,5-trisubstituted pyrazolines under metal-free conditions was developed. Various substituted pyrazolines were oxidized to pyrazoles by irradiation with visible light/sunlight. A plausible mechanism was proposed for the light mediated oxidation proceeding via formation of intermediates with electron rich C-3 positions and electron deficient C-5 positions. Correlation between the electronic effect induced by the aryl substituents and the rate of oxidation was studied by UV–vis spectroscopy. This correlation study supported the proposed mechanism. Electron withdrawing substituents at the 3-phenyl group and electron releasing substituents at the 5-phenyl group enhanced the rate of oxidation; whereas, electron donating substituents at the 3-phenyl group and electron withdrawing substituents at the 5-phenyl group reduced the rate.     

甲烷在Mo/HZRP-1催化剂上无氧脱氢芳构化反应Ⅰ.Mo/HZRP-1催化剂的催化性能和积炭行为

用高 硅含磷五 员环 沸 石 分子 筛（ 商 品 代号 Ｈ Ｚ Ｒ Ｐ１） 作 为 载体 ，制 备 了 Ｍｏ／ Ｈ Ｚ Ｒ Ｐ１ 催化剂． 与 Ｍｏ／ Ｈ Ｚ Ｓ Ｍ５ 相比， Ｍｏ／ Ｈ Ｚ Ｒ Ｐ１ 对 甲烷无 氧脱氢芳 构化反 应也表现 出较好的 催化 性能 ． 实验过程 中，在反 应气中添 加 Ｎ２ 作 为内标 物，给出包 括甲烷 在 Ｍｏ／ Ｈ Ｚ Ｒ Ｐ１ 上 的结焦量 、转化率 及各产物选 择性在内 的总碳 物料平衡 计算结果 ． 考 察了不同 Ｍｏ 担 载量对催 化剂性 能和 积炭 行为 的影响； 重点考察 了不同 温度焙烧 后２０ ％ Ｍｏ／ Ｈ Ｚ Ｒ Ｐ１ 催化剂 的性能和 积炭行 为． 在 反应的初 始阶段 ，６ ％ Ｍｏ／ Ｈ Ｚ Ｒ Ｐ１ 表 现出 很 高 的 活 性： 反 应 进 行 ３０ ｍｉｎ 时， 甲 烷 转 化 率 为 １１ ％ ， 芳 烃 选 择 性 达８１ ％ ， 而催化 剂的结焦 选择性 仅为１２ ％ ． Ｂ Ｅ Ｔ， Ｎ Ｈ３ Ｔ Ｐ Ｄ 和 催 化反 应等 表 征结 果表 明： Ｍｏ 物种的数量 和状态， 分子筛的 酸强度和 酸量以 及分子筛 的孔道 结构是 决定 甲烷 无氧 脱氢 芳构 化反 应性能和积 炭行为 的关键因 素．     

A novel biomimetic synthesis of (S)-(−)-zearalenone: via macrocyclization and transannular aromatization

On heating, a hydroxy-keto-dioxinone underwent retro-Diels-Alder fragmentation and the resultant α,γ-diketo-ketene was efficiently trapped intramolecularly by a secondary alcohol to provide a macrocyclic triketo-lactone. Following ketal hydrolysis, transannular aromatization gave the resorcylate natural product, (S)-(−)-zearalenone.     

Methane non-oxidative aromatization on Mo/ZSM-5: Effect of adding triethoxyphenylsilanes into the synthesis system of ZSM-5

A series of ZSM-5 zeolites were synthesized by adding triethoxyphenylsilane (PTEOS) into the initial sol of the synthesis system. The samples were studied by XRD, SEM, N₂ adsorption-desorption and acid assessment of d₃-acetonitrile adsorption. Characterization results showed that the crystal size of the ZSM-5 zeolites could be adjusted in a certain range by introducing different contents of PTEOS. Besides, the resultant materials possess hierarchical porosity in addition to those micropores generated by the MFI channels. Moreover, supported Mo/ZSM-5 catalysts were prepared, and their catalytic performances were investigated in the methane non-oxidative aromatization. It was found that the Mo/ZSM-5 catalyst, bearing suitable crystal size and mesoporous characteristic showed relatively high shape-selectivity to benzene and high stability for the reaction of methane aromatization.