Rhodium-tris(3,5-bis(trifluoromethyl)phenyl)phosphine catalyzed hydroformylation of dienes to dialdehydes in supercritical carbon dioxide with high activity

Rhodium-catalyzed hydroformylation of 1,5-hexadiene and 1,7-octadiene to corresponding dialdehydes was investigated in compressed CO₂ and in toluene using different fluorinated phosphine compounds as ligands. A rhodium complex using tris(3,5-bis(trifluoromethyl)phenyl)phosphine is highly effective in compressed CO₂ for double hydroformylation of 1,5-hexadiene, whose TOF value is much larger than those reported so far. It has been shown that this ligand is effective also for the hydroformylation of 1,7-octadiene and scCO₂ is a better solvent than a conventional organic solvent of toluene for the title reaction.     

The use of carboranylphosphite ligands in Rh-catalyzed hydroformylation of alkenes in supercritical carbon dioxide

Novel carborane-containing phosphites were synthesized. The efficiency of the ligands was tested in the Rh-catalyzed hydroformylation of styrene, hept-1-ene, and oct-1-ene in super-critical carbon dioxide (scCO₂) and toluene. The use of scCO₂ as the reaction medium allows one to attain higher conversions and regioselectivities compared to toluene.     

A new method of using supercritical carbon dioxide as a green solvent for synthesis and purification of 5,5‴-bis(tridecafluorohexyl)-2,2′:5′,2″:5″,2‴-quaterthiophene,which is one of n-type organic semiconducting materials

We have investigated synthesis as well as purification of 5,5?-bis(tridecafluorohexyl)-2,2′:5′,2″:5″,2?-quaterthiophene (BFH-4?T, n-type organic semiconducting material) using supercritical carbon dioxide (scCO₂) as a green solvent. BFH-4T was obtained in good selectivity and high yield by TDAE/PdCl₂-catalyzed reductive coupling reaction of 5-bromo-5′-(tridecafluorohexyl)-2,2′-bithiophene in scCO₂. We have also successfully established purification of the reaction mixture by passing scCO₂ in the reaction vessel. The product was yellow powder of BFH-4T with purity of more than 99% and Pd catalyst was not contained.     

Pyrazoles as ligands for the Rh-catalyzed hydroformylation of alkenes in supercritical carbon dioxide

Activity of pyrazole ligands in hydroformylation of a number of unsaturated terminal substrates in supercritical carbon dioxide (scCO₂) in the presence of Rh-catalyst was studied. The ligands without free NH group at position 1 of the pyrazole ring were found to be active. The use of scCO₂ as the reaction medium served to reach a higher conversion and regioselectivity of hydroformylation as compared to those in toluene.     

Synthesis and properties of conjugated fluoroalkyl ether-substituted polythiophenes prepared in organic solvent and supercritical carbon dioxide

A number of new fluoroalkyl ether-containing polythiophenes are synthesized via oxidative polymerization in supercritical CO₂ (scCO₂) and chloroform. In both cases, high-molecular-mass polymers with high yields are prepared. The properties of the polymers synthesized in scCO₂, such as molecular mass, polydispersity, conjugation, and UV absorption, are similar to the properties of the polymers obtained in chloroform. All poly(fluoroalkyl ether thiophenes) show solubility in DMF, toluene, THF, chloroform, and acetone. The glass-transition temperatures of the polymers are in the range 58–82°C, and the temperatures corresponding to 10% loss in their weight are in the ranges 248–294 and 260–303°C for poly(fluoroalkyl ether thiophenes) synthesized in scCO₂ and chloroform, respectively. All polymers fluoresce in the blue region with emission maxima at 506 to 526 nm. Because of the unique combination of fluoroalkyl and carbonyl groups, poly(fluoroalkyl ether thiophenes) feature good solubility in scCO₂, which is a promising alternative solvent for the oxidative polymerization of fluoroalkyl ether thiophenes.     

Supercritical fluid extraction of microbial phospholipid fatty acids from activated sludge

Supercritical carbon dioxide (scCO₂) extraction was applied for the determination of microbial phospholipid fatty acids (PLFA) in activated sludge. Quantification was performed by using gas chromatography–mass spectrometry (GC–MS). The highest extraction yields of PLFA, at a concentration of 7.28 nmol/mg-dry activated sludge, was obtained at a temperature of 80 °C, pressure of 25 MPa and 10% (v/v) methanol for a 15-min extraction time. ScCO₂ extraction results obtained in these conditions were comparable with those obtained by liquid organic solvent extraction (LSE) based on diversity and equalibility indices. The repeatability test showed that the relative standard deviation values were less than 13%. The experimental results show that the scCO₂ extraction saves time and uses much less organic solvent. In addition, scCO₂ extraction is a promising and alternative method for the analysis of microbial community structure in environmental assessment using the PLFA profile.     

Chemische Synthese in überkritischem Kohlendioxid: Die „bessere Lösung”︁?

Supercritical carbon dioxide (scCO₂)is receiving considerable attention recently as a reaction medium for catalytic chemical synthesis. Its lack of toxicity and ecological hazards make scCO₂ a very attractive alternative to conventional organic solvents. It is readily available and can be handled safely on a laboratory and industrial scale, as nicely illustrated by large scale applications in the extraction of natural products like coffee or hops. For chemical reactions, the unique combination of gas-and liquid-like properties can lead to additional benefits. The tuneable solvent properties of scCO₂ open a wide range of fascinating applications in heterogeneous, organometallic and enzymatic catalysis.     

Colloidal Noble‐Metal and Bimetallic Alloy Nanocrystals: A General Synthetic Method and Their Catalytic Hydrogenation Properties

A general single‐step strategy has been developed for the direct thermal decomposition of noble‐metal salts in octadecylamine to synthesize octahedron‐ and rod‐shaped noble‐metal aggregates and monodisperse noble‐metal or bimetallic alloy nanocrystals without introducing any additive into the system. It has presented a facile and economic way to fabricate these nanocrystals, especially alloy nanocrystals, which does not require a post‐synthesis solid‐state annealing process. The morphology of the nanocrystals can be easily controlled by tuning the synthetic temperature. Their ability to catalyze heterogeneous Suzuki coupling reactions has been investigated and showed satisfactory catalytic activity. The catalytic performance of the monometallic and bimetallic alloy nanocrystals were also evaluated in the selective hydrogenation of citral in a conventional organic solvent (toluene) and a green solvent (supercritical carbon dioxide, scCO₂). Interestingly, the catalysts performed differently to each other when they were in scCO₂ owing to the different morphology, which should be readily optimized for further use.     

Synthesis of short straight-chain alkylamine based hyperbranched nickel complexes and their catalytic performance of ethylene oligomerization

Short straight-chain alkylamine based hyperbranched molecules and their corresponding salicylaldimine nickel complexes have been synthesized in high yield and characterized by FTIR, ¹H-NMR and mass spectrometry. The optimal reaction parameters were determined under the catalytic system of methylaluminoxane (MAO) as co-catalyst and toluene as solvent. Under these conditions, the effect of catalyst structure, solvent and co-catalyst were determined. Upon activation of MAO in toluene, ethylene oligomerization products were homogeneous distribution of butene, hexene and octene with trace higher olefin. The same catalytic system under cyclohexane and methyl cyclohexane as solvent, however, produced majority of butene. Under the activation of EtAlCl₂, Et₂AlCl and EASC as co-catalyst in toluene, ethylene oligomerization reaction was tandem with Friedel-Crafts reaction in catalytic system.     

L-Proline catalyzed aldol reactions between acetone and aldehydes in supercritical fluids: An environmentally friendly reaction procedure

The direct asymmetric aldol reaction between various aldehydes and acetone catalyzed by l-proline catalyst was successfully carried out in supercritical CO₂ (scCO₂) and 1,1,1,2-tetrafluoroethane (R-134a) fluids. The enantioselectivity of 84% ee to the targeted product was achieved under 20 MPa, 40 °C, and 15 mol% of the catalyst in supercritical CO₂ (scCO₂) fluid. The effects of reaction parameters, such as temperature, pressure, catalyst loading and different substituted aldehydes on both enantioselectivity and aldol yield were discussed. The titled reaction was also performed in 1,1,1,2-tetrafluoroethane, and the obtained results were compared with those in scCO₂. This new reaction procedure provides an environmental asymmetric aldol reaction system as compared with that in organic solvents.     

Übergangsmetall-Organoverbindungen in superkritischem Kohlendioxid: Löslichkeiten,Reaktionen, Katalysen

Organometallics of Transition Metals in Supercritical Carbon Dioxide: Solubilities, Reactions, Catalysis Monomeric compounds of the type Cp₂M (p. e. M = Fe, Co, Ni) are soluble in liquid or supercritical CO₂ (”︁scCO₂”︁”︁) without any reaction with the solvent. The polymeric compounds zincocene or manganocene form with CO₂ insoluble CO₂ insertion products. As well homoleptic metal carbonyls as a number of ligand-stabilized metal carbonyls are also soluble in scCO₂. Fe(CO)₅ reacts photochemically in this solvent to Fe₂(CO)₉ and thermically to Fe₃(CO)₁₂. The highly reactive (cdt)Ni(0) (cdt: cyclododeca-1,5,9-triene) is soluble in liquid CO₂. A reaction with the solvent could not been observed. Solved in scCO₂ (cdt)Ni reacts thermically to form Ni after a short time. CpCo(cod) catalyzes slowly the cyclo-cooligomerization of hex-3-yne with acetonitrile to form 2,3,4,5-Tetraethyl-6-methylpyridine. Propargylic alcohol reacts under formation of cyclotetrameres with a selectivity of 90% using (cod)₂Ni or (cdt)Ni as catalysts, hex-3-yne in and with carbon dioxide under selective formation of tetraethyl-2-pyrone when the catalyst system R₃P/(cod)₂Ni (R: Me, Et) is used. In situ IR measurements show that the catalytically active species will be desactivated by formation of nickel carbonyl complexes. The catalytic oxidation of cyclooctene to form cycloocteneoxid with t-BuOOH using Titan(IV)-isopropylate as soluble catalyst proceeds less selectively, however in the presence of Mo(CO)₆ the epoxid is formed in good yields and in a highly selective reaction.     

Silica hydride intermediate for octadecylsilica and phenyl bonded phase preparation via heterogeneous hydrosilation in supercritical carbon dioxide

Investigations into the preparation of silica hydride intermediate in supercritical carbon dioxide (sc-CO(2)) that avoids the use of organic solvents such as toluene or dioxane are described. The effects of reaction temperature, pressure and time on the surface coverage of the supercritical fluid generated silica hydride intermediate were studied. Under optimised supercritical conditions of 120°C, 483 bar and 3 h reaction time, silica hydride (Si-H) conversion efficiencies of ca. 40% were achieved for the hydride intermediate prepared from a monofunctional silane reagent (dimethylmethoxysilane). Si-H conversion efficiencies (as determined from (29)Si CP-MAS NMR spectral analysis) for the hydride intermediate prepared from triethoxysilane (TES) in sc-CO(2) were found to be comparable to those obtained using a TES silanisation approach in an organic solvent. (13)C and (29)Si CP-MAS-NMR spectroscopy was employed to provide a complete structural assignment of the silica hydride intermediates. Furthermore, supercritical CO(2) was subsequently employed as a reaction medium for the heterogenous hydrosilation of silica hydride with octadecene and with styrene, in the presence of a free radical initiator. These supercritical fluid generated reversed-phase materials were prepared in a substantially reduced reaction time (3 h) compared to organic solvent based methods (100 h reaction time). Silica functionalisation in sc-CO(2) presents an efficient and clean alternative to organic solvent based methods for the preparation of important silica hydride intermediate and silica bonded stationary phases via a hydrosilation approach.     

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%.     

Effect of supercritical carbon dioxide on the diffusion coefficient of phenol in poly(bisphenol A carbonate)

For some polymers, the rate of solid‐state polymerization (SSP) is higher with supercritical carbon dioxide (scCO₂) as the sweep gas than with atmospheric N₂. One explanation for this higher rate is that the diffusion coefficient of the condensate molecule is higher in the CO₂‐swollen polymer. To investigate this hypothesis, we measured the diffusion coefficient of phenol in poly(bisphenol A carbonate) (BPA‐PC) by carrying out SSP of this polymer under diffusion‐limited conditions. Under these conditions, the diffusion coefficient of the condensate molecule could be calculated from the profile of the molecular weight versus time. The phenol diffusivity was determined between 135 and 180 °C in the presence of N₂ at about 1 bar and in the presence of scCO₂ at about 138, 207, and 345 bar. The diffusion coefficient of phenol was up to 200% higher in scCO₂ than in N₂, depending on the temperature and CO₂ pressure. With both N₂ and scCO₂, the activation energy for phenol diffusion in BPA‐PC was larger than the activation energy for the reaction between hydroxyl and phenyl end groups that occurred during SSP of BPA‐PC. As a result, the overall SSP reaction shifted from diffusion control at low temperatures toward chemical‐reaction control at high temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1143–1156, 2003     

Effect of supercritical CO2 on the copolymerization behavior of cyclohexene oxide/CO2 and copolymer properties with DMC/Salen‐Co(III) catalyst system

The copolymerization of cyclohexene oxide (CHO) and carbon dioxide (CO₂) was carried out under supercritical CO₂ (scCO₂) conditions to afford poly (cyclohexene carbonate) (PCHC) in high yield. The scCO₂ provided not only the C1 feedstock but also proved to be a very efficient solvent and processing aid for this copolymerization system. Double metal cyanide (DMC) and salen‐Co(III) catalysts were employed, demonstrating excellent CO₂/CHO copolymerization with high yield and high selectivity. Surprisingly, our use of scCO₂ was found to significantly enhance the copolymerization efficiency and the quality of the final polymer product. Thermally stable and high molecular weight (MW) copolymers were successfully obtained. Optimization led to excellent catalyst yield (656 wt/wt, polymer/catalyst) and selectivity (over 96% toward polycarbonate) that were significantly beyond what could be achieved in conventional solvents. Moreover, detailed thermal analyses demonstrated that the PCHC copolymer produced in scCO₂ exhibited higher glass transition temperatures (T_g ～ 114 °C) compared to polymer formed in dense phase CO₂ (T_g ～ 77 °C), and hence good thermal stability. Additionally, residual catalyst could be removed from the final polymer using scCO₂, pointing toward a green method that avoids the use of conventional volatile organic‐based solvents for both synthesis and work‐up. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2785–2793     

Supercritical carbon dioxide assisted synthesis of amphiphilic graft copolymers based on poly(styrene-co-maleic anhydride) with methoxyl poly(ethylene glycol) side chains

Supercritical carbon dioxide（scCO₂） was used as a reaction medium in synthesizing amphiphilic graft copolymers composed of poly（styrene-co-maleic anhydride）（SMA） backbones and methoxyl poly（ethylene glycol）（MPEG） side chains via esterification.The synthesized copolymers were characterized by Fourier transform infrared spectroscopy（FTIR）,gel permeation chromatography（GPC）,¹H-NMR,thermo-gravimetric analysis（TGA） and differential scanning calorimetric analysis（DSC）.The gelation phenomenon was suppressed effectively by tuning reaction conditions.The influences of scCO₂ temperature and pressure on the conversion of anhydride were investigated.It was found that the highest conversion ratio occurred at 80℃under a constant pressure of 14 MPa or 26 MPa.With the increase of scCO₂ pressure,the conversion ratio increased first,and then leveled off.The conversion ratio of anhydride could be controlled by regulating the reaction conditions.It was also revealed that using low molecular weight MPEG brought a high conversion ratio of anhydride.     

Grafting of methyl methacrylate onto natural rubber in supercritical carbon dioxide

The grafting of the methyl methacrylate (MMA) monomer onto natural rubber (NR) was carried out by supercritical carbon dioxide (scCO₂) swelling polymerization with benzoyl peroxide (BPO) as an initiator. Fourier transform–infrared spectroscopy (FT–IR) was used to confirm the formation of graft copolymers with the characteristic bands of symmetric C?O and C? O? C stretching vibrations at 1728 cm^?1 and 1147 cm^?1, respectively. The effects of the rubber‐to‐monomer ratio, amount of initiator, reaction time, and pressure on the monomer grafting level (GL) and grafting efficiency (GE) were investigated, and the optimum conditions for the preparation of NR‐g‐MMA were found to be 70:30 of the rubber‐to‐monomer ratio, 1.2% of the initiator content, and the reaction pressure of 23 MPa for 6 h. The thermal behavior of the NR and the different NR/MMA molar ratio grafted copolymer samples was studied by differential scanning calorimetry (DSC). The observed glass transition temperature (T_g) was consistent with the GL. The tensile strength, modulus of elasticity, elongation at break, hardness, and oil resistance of graft copolymers were determined and compared with the values of NR and that of polymerization products prepared in traditional toluene solution. The results showed that the tensile strength, modulus of elasticity, hardness and oil resistance were greatly improved after modification in scCO₂. Copyright © 2007 John Wiley & Sons, Ltd.     

Heterogeneous strong base catalysis in supercritical carbon dioxide by mesoporous alumina and sulfated mesoporous alumina

The development of solid strong base catalysts utilizable in green but acidic medium of scCO₂ is reviewed. The strong base sites on mesoporous alumina and sulfated mesoporous alumina that had been generated by severe treatment at 773 K under vacuum (10^?4 Torr) were not neutralized by the compressed Lewis acidic molecules of CO₂, promoting a representative strong base-catalyzed reaction of the Tishchenko reaction as well as a typical base-catalyzed reaction of the Knoevenagel reaction in scCO₂. Infrared spectroscopy of the adsorbed pyrrole, temperature-programmed desorption of CO₂, and the poisoning by a very weak Brönsted acid of methanol have revealed that the average strengths of the base sites on mesoporous alumina and sulfated mesoporous alumina are weaker than that on conventional γ-alumina like JRC-ALO-4, but that they have a small number of strong base sites which function even in scCO₂ medium. It was found that the addition of a slight amount of THF cosolvent into scCO₂ remarkably accelerates the Tishchenko reaction over sulfated mesoporous alumina; the reaction rate in the scCO₂–THF medium was 1.5-fold and 2-fold faster than those in ordinary organic solvents such as benzene and THF and that in pure scCO₂, respectively. The unique structures of mesoporous alumina and sulfated mesoporous alumina have been fully characterized by N₂ adsorption–desorption measurements and XRD analyses.     

Studies on the oxidative degradation of nylons by nitrogen dioxide in supercritical carbon dioxide

Oxidative degradation of nylons was carried out using nitrogen dioxide (NO₂) as the oxidizing agent and supercritical carbon dioxide (scCO₂) as the reaction medium. Seven typical nylons were studied: three ring opening polymerization type nylons (nylon-6, -11 and -12) and four condensation co-polymerization type nylons (nylon-4/6; -6/6; -6/9 and -6/12). All the nylons decomposed in the NO₂/scCO₂ system under relatively mild conditions (140 °C, 1 h, and 10 MPa) and provided aliphatic α, ω-diacids such as succinic, glutaric and adipic acids in good yields. The product distribution of these α, ω-diacids strongly depended on the reaction conditions such as temperature, time and amount of NO₂, but not on the total pressure. Furthermore, the proportions of the products were affected by the type of nylon. A mechanism is proposed and a detailed discussion regarding the degradation of nylon in the NO₂/scCO₂ system is provided.     

超临界二氧化碳偶合超声预处理强化玉米秸秆酶水解(英)

提出了一个木质纤维素生物质预处理的全绿色加工过程.以玉米秸秆和玉米芯为原料,以超临界CO₂和超声偶合法对木质纤维素进行预处理.超临界CO₂预处理条件为:压力15-25 MPa,温度120₁70℃,含水量50%,反应时间0.5₄ h.超声场功率600W,温度80℃,作用时间2-8 h.用纤维素酶水解反应获得的还原糖总量来评价预处理效果.结果表明,单纯超临界CO₂和超临界CO₂偶合超声预处理都能够提高生物质水解反应还原糖产量.对于玉米芯,超临界CO₂预处理（170℃,20 MPa,3 0min）后,还原糖产率为62%（未预处理的为12%）.对于玉米秸秆（170℃,20 MPa,2.5 h）,还原糖产率为46.4%.对于玉米芯,超临界CO₂偶合超声预处理（600 W,80℃下超声处理6 h,然后用170℃,20 MPa超临界CO₂预处理30 min）后,还原糖产率为87%.对于玉米秸秆,超临界CO₂偶合超声预处理（600 W,80℃下超声处理8 h,然后用170℃,20 MPa超临界CO₂预处理1 h）后,还原糖产率为25.5%.与未处理生物质相比,X射线衍射结果表明玉米秸秆和玉米芯在超临界CO₂和超声预处理后其结晶度没有明显变化.扫描电镜分析则发现木质纤维素的表面积显著增加.