碳水化合物转化为官能团化碳环化合物的研究进展

介绍利用碳水化合物合成官能团化碳环化合物的化学方法的最新进展

Recent advances in metal-free catalysts for the synthesis of cyclic carbonates from CO_2 and epoxides

The aim of ＂green chemistry＂ and ＂atom economy＂ is to utilize carbon dioxide and replace harmful reactants such as CO and phosgene for the production of cyclic carbonates. In this paper, metal-free catalysts including organic bases, ionic liquids, supported catalysts, organic copolymers and carbon materials for the synthesis of cyclic carbonates by the cycloaddition of carbon dioxide to epoxides are reviewed. Recent advances in the design of the catalysts and the understanding of the reaction mechanism are summarized and discussed. The synergistic effects of organic bases and hydrogen bond donors, organic bases and nucleophilic anions, hydrogen bond donors and nucleophilic anions and active components and supports are highlighted. The challenge is to develop metal-free catalysts suitable for carbon dioxide capture and fixation. The ultimate goal is to synthesize cyclic carbonates in a flow reactor directly using carbon dioxide from industrial flue gas at ambient temperature and atmospheric pressure. By using synergetic effects, a multi-functional approach can meet the design strategy of metal-free catalysts for carbon dioxide adsorption and activation as well as epoxide ring opening.

Synthesis of cyclic carbonates from epoxides and CO_2 in acetonitrile via the synergistic action of BMIMBr and electrogenerated magnesium

Using 1-butyl-3-methyl-imidazolium bromide （BM1MBr） as the supporting electrolyte and magne- sium as the sacrificial anode, a new and highly efficient electrochemically catalytic route was devel- oped for the synthesis of cyclic carbonates from epoxides and CO2. Based on the cooperative action of BMIMBr and an electrogenerated magnesium salt obtained under a N2 atmosphere, CO2 reacted with a wide range of epoxides to readily generate cyclic carbonates in moderate to excellent yields under mild conditions.

Self-reaction of initial active groups in coal

For further understanding of self-heating of coal, we tested the reactions of seven different ranks of coal under inert atmosphere. In the test, 50-gram of coal sample ranged from 0.18 mm to 0.38 mm was put into a special designed copper reaction vessel and let pure nitrogen to flow into the coal sample from the bottom at a rate of 100 mL/min. The programmed temperature enclosure was run at a programmed rate of 0.8 ~C/min. The concentration of the carbon oxides and the coal temperature were tested. The results show that the coal reactions under inert atmosphere can generate CO and C02. The reactions under inert atmosphere are affected by coal ranks, initial pore structure of coal and sulfur content. For low ranks of coal, the productions of carbon oxides are piecewise. The coal temperature is lower than the surrounding temperature throughout the reactions under inert atmosphere, but it rises quickly and reaches a crossing point temperature in the later stage under dry-air atmosphere. Based on the analysis, it indicates the self-reaction of initial active groups exists in the self-heating of coal besides the reactions in the two parallel reactions model. Spontaneous combustion of coal is due to both the oxidation heat accumulation and the chain reaction. A new reaction model of self-heating of coal was orooosed.

Silver-catalyzed carboxylative cyclization of alkynic hydrazones with carbon dioxide

The development of new catalytic methodologies to synthesize heterocyclic fine chemicals using carbon dioxide as a synthon has attracted considerable attention. Herein, we report the silver( I)-catalyzed carboxylative cyclization of a variety of alkynic hydrazones with carbon dioxide to produce the corresponding 1,3,4-oxadiazin-2-ones under mild reaction conditions. In this reaction, silver(I) salts play a π-Lewis acid role for the highly efficient activation of the alkyne moiety in the hydrazone substrates. Single-crystal X-ray analysis and NOE experiments confirm that the newly formed oxadiazinone products exhibit Z configuration. Based on control experiments and NMR studies, a mechanism including the formation of a reactive carbazate intermediate, electrophilic cyclization, and subsequent protonation is proposed. This study offers an efficient and atom- economical method for the synthesis of biologically important 1,3,4-oxadiazin-2-ones.

Molecular Simulation of Naphthenic Acid Removal on Acidic Catalyst(I) Mechanism of Catalytic Decarboxylation

In this paper, the charge distribution, the chemical bond order and the reactive performance of carboxylic acid model compounds on acidic catalyst were investigated by using molecular simulation technology. The simulation results showed that the bond order of C—O was higher than that of C—C, and C—C bond connected to the carbon atom in the carboxyl radical had the lowest bond order. The charge distributions of model naphthenic acids were similar in characteristics that the negative charges were concentrated on carboxyls. According to the simulation results, the mechanisms of catalytic decar- boxylation over acidic solid catalyst were proposed, and a new route was put forward regarding removal of the naphthenic acid from crude oil through catalytic decarboxylation.

Quantum Chemistry of PAHs Thermal Cracking with Different Hydrogenation Degree

In order to investigate the influence of hydrogenation degree and structural variety on reaction trend of polyaro- matic hydrocarbons (PAHs) in resins and asphaltenes portion of heavy oil, a series of PAHs with different hydrogenation degree were selected as model compounds to simulate their different hydrogenation stage, and the PAHs thermal cracking reaction was simulated based on free radical mechanism by the density functional theory (DFT) to search for reactions'transition state. By comparing the dynamic data obtained from reaction simulation, it is showed that processing difficulty could rise with increasing condensed aromatic ring number, and hydrogenation could promote ring cleavage reaction, but excessive hydrogenation would decrease the oil conversion rate to reduce light-end products. In conclusion, proper hydrogenation was quite critical in promoting light-end products conversion efficiency and saving the processing cost as well. Operational instructions were given based on both PAHs hydrogenation performance and conclusions were drawn up from reaction simulation results.

可见光驱动酚/芳胺联-1,6-烯炔与全卤代甲烷的Kharasch反应

1,n-烯炔合成子参与的涉及原子转移过程的自由基环化碳卤官能化是一类有效且实用的方法,它通过利用原子转移试剂中碳卤σ键的自由基龟裂及其在烯炔母核π键上的移位来实现卤代环系结构的有序构建,展现了完全原子经济性.近年来,该类反应成为研究热点之一.报道了一类通用可见光催化的酚/芳胺联-1,6-烯炔和全卤代甲烷(如三氯溴甲烷或四溴化碳)参与的环化碳卤官能团化反应,在温和且无氧化剂条件下原子经济且高效地合成了一系列作为主要立体异构体的(Z)-2,3-二氢苯并呋喃和(Z)-吲哚啉衍生物,收率优良,其中大部分产物仅以(Z)-构型被合成.该反应具有底物范围广、官能团耐受性高、高原子经济以及高立体选择性等优点,为2,3-二氢苯并呋喃和吲哚啉杂环的合成提供一类绿色、原子经济、高效的合成策略.

Wallichanol类天然产物ABC环系合成研究

Wallichanol是一类具有独特桥环结构的二萜天然产物.以2-甲基-1,3-环己二酮作为起始原料,通过高立体选择性的Diels-Alder反应和金催化的炔烃碳环化反应构建Wallichanol的ABC三环核心骨架,共七步路线,总收率为42%.该合成工作为Wallichanol类天然产物全合成奠定了研究基础.

Brexane骨架的快速合成策略

本文报道了三环[4,4,0,0^([3,7])]壬烷(Brexane)的快速合成策略。该方法以双功能路易斯酸介导的Diels-Alder/碳环化串联反应构建了目标环系,且核心反应具有高度立体选择性,该路线共五步反应,总产率为23%。本工作可为具有该骨架的萜类天然产物的全合成提供一可选的策略。