超临界(压缩)二氧化碳介质中的选择氧化*

由于超临界二氧化碳（SCCO₂）具有稳定、安全、不燃、清洁无毒、粘度小、扩散快、可压缩的特殊性质,所以使得超临界二氧化碳非常适合作为催化反应的绿色溶剂.除此之外,多种气体在超临界二氧化碳中的溶解度很高,这对于那些受传质阻碍和易引起安全隐患的气相反应来讲,使用SCCO₂作为替代的反应溶剂具有重要的价值。值得指出的是：如果选择超临界二氧化碳作为氧化反应的溶剂,其自身不会发生反应而产生副产物,从而容易得到清洁的产物。本文主要讨论了超临界二氧化碳作为反应介质对醇、烯烃和烷烃等选择氧化反应的影响,通过与传统溶剂比较可以看出超临界二氧化碳作为氧化反应溶剂的优势,对近几年来以分子氧为氧化剂,以超临界二氧化碳为介质的催化选择氧化的反应体系作了综述,并对未来的发展提出了展望。     

沉淀聚合制备聚(季戊四醇三丙烯酸酯-苯乙烯)单分散微球及其形成机理

以季戊四醇三丙烯酸酯(PETA)作交联剂,苯乙烯作共聚单体,偶氮二异丁腈作引发剂,在乙醇或其与水的混合溶剂中沉淀聚合制备了交联聚合物微球.研究了反应时间、交联剂用量以及溶剂中水含量对聚合过程及微球的影响.结果表明当PETA用量在单体质量的5%-35%之间且反应时间不低于6h时可制得单分散聚合物微球.当PETA用量低于20%时,所得微球的粒径随PETA用量的增加逐渐减小,粒径分布逐渐变窄;此后继续提高PETA用量,微球粒径又逐渐增大,粒径分布逐渐变宽.向反应介质中加入水,可明显提高微球产率及单体转化率,但其体积分数达30%时,所得微球分散性变宽.在此基础上对微球的形成机理也进行了讨论.     

超临界二氧化碳/聚乙二醇两相体系的性质及其在催化反应中的应用

非均相催化过程中常常出现产物的转化率低、选择性差的问题, 而均相催化过程往往具有优异的催化性能, 但是却受制于催化剂、产物难于分离而达到循环使用的缺点. 近年来两相催化体系的发展为这些问题的解决提供了一条新途径. 超临界二氧化碳/聚乙二醇参与的两相体系是使用超临界二氧化碳作流动相, 聚乙二醇作为另一溶剂之一, 用于固定和稳定催化剂, 进行有机催化反应. 其显著特点是: 可在反应的同时实现分离的操作, 可实现均相催化过程的连续化. 综述了超临界二氧化碳/聚乙二醇体系的相行为及其性质, 并介绍了其在催化合成反应中的应用.     

超临界二氧化碳中功能化聚乙二醇稳定的钯纳米粒子催化醇的选择氧化反应

 以超临界二氧化碳 (scCO2)/聚乙二醇 (PEG) 两相为反应介质, 双齿氮配体功能化聚乙二醇稳定的 Pd 纳米颗粒作为催化剂, 进行了醇的需氧氧化反应. 系统研究了催化剂制备条件和反应条件对苯甲醇需氧氧化反应的影响. 结果表明, 以氢气为还原剂制备的 Pd 纳米粒子的催化活性最高. 反应结束后, 可以利用 scCO2 直接进行原位萃取得到产物, 实现了催化剂与产物的有效分离和催化剂的循环使用. 反应中没有检测到钯的流失. 催化剂经过 5 次循环利用后转化率仍可达 98%.     

超临界二氧化碳中羰基钴催化的端基炔烃环三聚反应研究

原子经济性良好的炔烃[2+2+2]环加成反应与绿色溶剂超临界二氧化碳相结合,是一个符合绿色化学原则的环境友好反应过程.建立了一个纯超临界二氧化碳介质中八羰基二钴催化的端基炔烃环三聚反应体系,在优化的反应条件下,以较高产率选择性地制备1,2,4-三取代苯衍生物.优化了催化剂用量、二氧化碳压力、反应温度及时间等反应条件,讨论了反应物料及催化剂在超临界二氧化碳介质中的溶解性和相行为,提出了端基炔烃环三聚反应机理,并将反应底物从C≡C键拓展至C≡N键,对超临界二氧化碳介质中炔-腈环加成反应进行了初步探索.优化出的炔烃环三聚催化反应体系无需使用有机助溶剂和各类助剂,底物适应性好,产物选择性高,为合成1,2,4-三取代苯衍生物提供了一种绿色合成方法.     

超临界二氧化碳光聚合制备可交联含氟聚合物颗粒及应用

通过自由基无规共聚和酰化反应两步法制备了两类侧链含丙烯酸酯双键的含氟低聚物,并通过调节反应物种类、配比和链转移剂用量,制备出一系列不同双键含量、氟含量的多官能度低聚物。以制备的含氟低聚物为原料,进行超临界二氧化碳光聚合制粒。聚合得到的含氟颗粒作为增强相,加入TPGDA光固化配方中,可实现颗粒与树脂的化学交联,显著提高基材的交联密度,改善疏水性,降低吸水率,并增强热稳定性。     

光敏性双亲共聚物在水溶液中的胶束化行为

通过ε-己内酯改性丙烯酸酯(FAa，n=1～4)与肉桂酰氯间的酰化反应合成了一系列光敏性大单体(FAaC)，与甲基丙烯酸(MAA)在溶液中进行自由基聚合，制备了具有光敏性的双素无规共聚物(PMFAaC)。将PMFAaC在选择性溶剂中进行自组装，可以形成纳米结构的聚合物。用动态激光光散射(DLS)研究了聚合物胶束的溶液行为，同时考察了单体含量、聚合物终浓度、聚合物侧链长、pH值、离子强度及温度等因素对胶束粒径的影响。实验结果表明，PMFAaC在选择性溶剂中可自组装成胶束，其粒径及其分布对单体含量、聚合物终浓度、聚合物侧链长、pH值、离子强度等有一定的依赖性，而对温度无依赖性。进一步用紫外光使肉桂酰基发生交联反应。从而制备得到核交联且稳定的纳米胶束。用DIS表征发现交联后的胶束粒径较交联前的小。     

在超临界二氧化碳中制备超高分子量聚乙烯多孔微球

以超高分子量聚乙烯作为原料, 在超临界二氧化碳中通过热处理成功制备了聚合物微米球. 微球尺寸符合高斯分布, 并可以控制在较窄范围内, 微球表面多孔且内部中空. 微球的形成是恒温过程和超临界二氧化碳双重作用的结果. 降温过程导致聚合物溶解度降低, 超高分子量聚乙烯分子链析出结晶而形成微球, 内部包裹了少量二氧化碳; 温度进一步降低导致微球内外压力不平衡, 二氧化碳从空心球内部释放形成表面孔洞. 恒温结晶过程除了促使微球结晶度进一步提高外, 还可以使亚稳晶型单斜晶转化为稳定的正交晶.     

超临界CO_2萃取中草药活性成分溶剂特性研究

针对超临界二氧化碳流体的局限性和中草药中活性成分的特殊性,研究了超临界二氧二化碳流体、改性剂和混合溶液的溶解度参数,提出了改性剂的选择原则。结果表明:萃取温度和压力是影响超临界二氧化碳流体和混合溶剂溶解度参数的主要因素,改性剂的种类和浓度影响萃取体系的溶解特性。     

多重环境响应性蓝光共聚物的合成与表征

采用Suzuki偶联反应合成了一系列具有聚集诱导荧光增强特性的双亲性共聚物Pa,Pb和Pc,这些共聚物都有较高的分子量和可进一步支链化的羟基.聚合物Pa,Pb和Pc在四氢呋喃溶液中的紫外吸收峰在380 nm左右,荧光发射峰在470 nm左右,属于蓝光材料.对这些聚合物在四氢呋喃和水的混合溶剂中发光特性的研究发现,这类聚合物在一定比例混合溶剂中都有聚集诱导荧光增强现象,通过表征自组装得到胶束的粒径和形貌进一步验证了这一结果.3种共聚物在混合溶剂中的聚集诱导荧光增强特性与聚合物中聚集诱导荧光增强结构单元的含量有关,并且该特性只有在一定比例混合溶剂中才能体现.通过研究聚合物Pa在不同混合溶剂中荧光发射和自组装行为,发现聚合物Pa在四氢呋喃中处于高度分散状态,聚合物呈小的胶束;当减少混合溶剂中四氢呋喃的含量时,聚合物聚集形成了稳定的胶束并且粒径比较集中;当继续减小四氢呋喃的含量,聚合物部分析出.从动态光散射和透射电子显微镜结果中明显发现聚合物胶束的粒径有很大波动.聚合物Pb和Pc在不同溶剂中自组装得到的胶束的大小演变规律和聚合物Pa相似,说明共聚物中芴和聚集诱导荧光增强结构单元之间的比例只影响聚合物聚集时水的比例,并不对聚集形成胶束的演化过程产生明显影响.通过改变共聚物Pa,Pb和Pc自组装所用溶剂的比例和种类,可以得到尺寸在10到900 nm之间的胶束.聚合物Pa在不同溶剂中自组装形成胶束的尺寸分散性比较单一,而聚合物Pb和Pc在不同溶剂中自组装形成胶束的尺寸分布比较宽,形貌多样化.通过原子转移活性自由基聚合在聚合物Pb引入聚(N-异丙基丙烯酰胺)侧链,得到具有更高分子量、更窄分子量分布的水溶性和温度敏感性多重环境响应性蓝光聚合物P-N.在聚(N-异丙基丙烯酰胺)最低临界溶解温度附近,随着溶液温度的改变,该聚合物荧光发光峰的位置基本保持不变,但发射强度变化,聚合物P-N在混合溶剂中自组装形成胶束的大小和形貌也随之改变.     

Sol-Gel Route to Direct Formation of Silica Aerogel Microparticles Using Supercritical Solvents

A simple and versatile method to obtain silica aerogel particles based on the hydrolysis and subsequent condensation of silicon alkoxides in supercritical fluids is proposed. This microparticle production route reduces the number of steps of traditional microparticle sol-gel processing.A case example is explained in more detail. Spherical and fiber silica morphologies were obtained by a one step method using a sol-gel process with supercritical acetone as a solvent. Particle size was controlled by varying the relative amounts of alkoxysilane, water and acetone. The resulting materials are influenced by a large number of experimental parameters; it has been observed that a quite relevant one is the supercritical fluid venting rate. The morphology of the particles was characterized by electron microscopy (SEM and TEM) and Atomic Force Microscopy (AFM). Alternatively, a low temperature synthesis can be performed by using supercritical carbon dioxide as solvent and formic acid as condensation agent.     

Development of machine learning model and analysis study of drug solubility in supercritical solvent for green technology development

The current research is focused on development of machine learning model for estimation of pharmaceutical solubility in supercritical CO₂ as the green solvent. The main aim is to assess the suitability of supercritical processing for preparation of nanomedicine. Oxaprozin was taken as model drug for the solubility measurements, and its solubility was determined at different operational conditions by variation of temperature and pressure of the process. Artificial Neural Network (ANN) model was implemented for simulation of the drug solubility, and the best model was obtained with R² greater than 0.99 for the training and validation as well. The tested model was then exploited to understand the process, and it turned out that both pressure and temperature had major and considerable influence on the solubility of Oxaprozin in supercritical carbon dioxide as solvent. However, the effect of pressure was shown to be more significant on the solubility compared to the effect of pressure, which was attributed to the effect of pressure on the density of the supercritical solvent. The developed ANN model was indicated to be robust in estimating the values of drug solubility in wide range of conditions which can save time and cost of the measurements.     

CO2 utilization as gas antisolvent for the pharmaceutical micro and nanoparticle production: A review

A reduction in particle size improves the solubility and bioavailability of pharmaceuticals. The traditional methods utilized in this regard are associated with problems so the use of supercritical fluid has been highlighted in recent decades. To prepare nanoparticles by employing the gas antisolvent (GAS) technique, a specific amount of solution (solute dissolved in organic solvent) was loaded into a cell in the oven. The supercritical carbon dioxide was injected and dissolved into the organic solvent. Therefore, volume expansion occurred and the solute was precipitated with a new particle size distribution on the filter at the end of the cell. This technique exhibits advantages such as particle size control, solvent-free product, and low-temperature process. Many experimental and modeling research has been conducted to synthesize nano- and microparticles based on the GAS process. The present study seeks to review the effective factors and literature on the GAS technique. All parameters affecting the GAS process including pressure, temperature, antisolvent addition rate, initial soluble concentration, and solvent were investigated. Volume expansion, thermodynamic modeling, and kinetic modeling of the GAS process were reviewed. A comparison was conducted between the advantages and disadvantages of this method with other methods of producing nanoparticles with supercritical fluid.     

Solubility of disperse yellow 54 in supercritical carbon dioxide with or without cosolvent

Extraction of disperse yellow 54 with supercritical carbon dioxide was conducted at 393.2 K and 30 MPa over a wide range of contact times. Saturated solubilities of the disperse dyestuff in supercritical carbon dioxide with or without cosolvent were also measured over the temperature and pressure ranges of 353.2 K to 393.2 K and 15 MPa to 30 MPa. Either ethanol or dimethyl sulfoxide, up to 5 mol%, was used as a cosolvent. As evidenced from the experimental results, the magnitudes of equilibrium solubility can be effectively enhanced in the presence of both two cosolvents. Dimethyl sulfoxide was found to yield higher solubility enhancement. Cosolvent effects were discussed on the basis of the Kamlet-Taft solvatochromic solvent parameters of cosolvents. The saturated solubility data were correlated with the Chrastil and the Mendez-Santiago and Teja equations. The Chrastil model correlated the solubility data to about within the experimental uncertainty. The correlated results of the Mendez-Santiago–Teja model supported the consistency of the solubility data over the entire experimental conditions.     

Supercritical fluid solvents in organic chemistry

The solubility of complex organic molecules in supercritical solvents is well-established. Under isothermal conditions, slightly above the critical temperature, this phenomenon, as well as most other physical properties of the solvent, exhibits a substantial pressure dependence. This behavior makes supercritical solvents attractive as media for organic reactions, both from a synthetic and a physical organic perspective.

An apparatus has been constructed and techniques have been developed to investigate the effects of supercritical solvent interactions on organic reaction rates and equilibria. The construction and operation of a supercritical reactor is described. Finally the reactor is used to investigate the photoisomerization of trans-stilbene in supercritical carbon dioxide.     

New device for controlling the amount of methanol in carbon dioxide mobile phase for supercritical fluid chromatography

A new device to accurately deliver a small amount of methanol into supercritical carbon dioxide fluid is described. Carbon dioxide, the most widely used mobile phase in supercritical fluid chromatography, is a relatively non-polar fluid, and hence the addition of a small amount of methanol could change the solvent strength of the mobile phase. In this work, supercritical CO₂ and methanol are delivered from the pump to a 100-μl mixing chamber in which a small magnetic bar is rotating. After passing through the mixing chamber, supercritical CO₂ is changed to a new mobile phase with different polarity. The modified mobile phase was successfully used for the separations of polar compounds and polyaromatic hydrocarbons (PAHs).     

Efficient Fixation of Carbon Dioxide by Electrolysis Facile Synthesis of Useful Carboxylic Acids

Electrochemical fixation of atmospheric pressure of carbon dioxide to organic compounds is a useful and attractive method for synthesizing of various carboxylic acids. Electrochemical fixation of carbon dioxide, electrochemical carboxylation, organic halides, organic triflates, alkenes, aromatic compounds, and carbonyl compounds can readily occur in the presence of an atmospheric pressure of carbon dioxide to form the corresponding carboxylic acids with high yields, when a sacrificial anode such as magnesium or aluminum is used in the electrolysis. The electrochemical carboxylation of vinyl bromides was successfully applied for the synthesis of the precursor of nonsteroidal anti-inflammatory agents such as ibuprofen and naproxen. On the other hand, supercritical carbon dioxide （scCO2） has significant potential as an environmentally benign solvent in organic synthesis and it could be used both as a solvent and as a reagent in these electrochemical carboxylations by using a small amount of cosolvent.     

A Comparative Study of Naproxen – Beta Cyclodextrin Complexes Prepared by Conventional Methods and Using Supercritical Carbon Dioxide

Naproxen is a poorly soluble anti-inflammatorydrug, the solubility of which canbe enhanced by complexation withbeta-cyclodextrin. Besides that, the inclusioncomplex reduces the incidence of gastrointestinal side effects of the drug. The aim of this work was to compare the physicochemical characteristics of the solid complexes prepared by traditional methods (kneading, freeze-drying and spray-drying) and using a supercritical fluid technology. The unusual solvent properties of carbon dioxide above their critical temperature and pressure were exploited in order to prepare inclusion compounds. Complexes prepared using supercritical fluid technology showed similar properties to those of freeze-drying andspray-drying complexes as proved by DSC, FT-IRand UV.     

Stereoselective Aromatic Ring Hydrogenation over Supported Rhodium Catalysts in Supercritical Carbon Dioxide Solvent

The combination of supported rhodium metal catalysts and supercritical carbon dioxide solvent was effective for the stereoselective ring hydrogenations of aromatic compounds at low temperature. Higher solubility of hydrogen in supercritical carbon dioxide provides higher concentration of hydrogen on the rhodium surface, but lower that of the intermediate on rhodium surface, which suppresses the flipping of surface intermediate, leading to higher catalyst activities and cis selectivities to the corresponding ring‐hydrogenated products as compared with those in organic solvents.     

Applications of a Technique for the HPLC Analysis of Liquid Carbon Dioxide Solutions

Abstract

A novel technique has been developed whereby substrate and solvent quantitation can be effected by means of reversed-phase high performance liquid chromatography. Carbon dioxide is detected by a differential refractometer.

Applications of this technique include the analysis of liquefied carbon dioxide-based aerosol mixtures, solubility measurements and liquid carbon dioxide extraction studies. Preliminary experiments suggest that this technique may also find application to the direct analysis of supercritical carbon dioxide extraction systems.