Reactions In Supercritical Carbon Dioxide Research Articles

On-line SFC-UV/Vis-MS using flow selection interfaces to monitor continuous flow single and sequential stage organic reactions in supercritical carbon dioxide

Two flow selection interfaces have been developed for connecting single or linked reactors with on-line SFC equipped with UV/Vis diode-array (DAD) and mass spectrometer detectors coupled in series (SFC-DAD-MS). This process analytical technology system, enabled the study of reactions performed in supercritical fluid carbon dioxide (SF-CO2). Each interface is designed to obtain on-line samples at different reaction progress points. Three single stage electrophilic annulation reactions performed in SF-CO2 using aniline, indole and pyrrole as amine reactants to synthesize N-heterocyclic products within a stirred continuous flow reaction vessel containing montmorillonite K-10 catalyst were monitored. Also, both stages of a two step synthetic procedure conducted within two connected continuous flow reaction coil systems were monitored using on-line SFC-DAD-MS. The first step involved a Knoevenagel reaction in SF-CO2 that provided a continuous feed to perform a second stage acetylation reaction. Use of on-line SFC-DAD-MS enabled early detection and characterization of unexpected by-products.

Molecular Dynamics of Combustion Reactions in Supercritical Carbon Dioxide. 6. Computational Kinetics of Reactions between Hydrogen Atom and Oxygen Molecule H + O2 ⇌ HO + O and H + O2 ⇌ HO2.

Reactions of the hydrogen atom and the oxygen molecule are among the most important ones in the hydrogen and hydrocarbon oxidation mechanisms, including combustion in a supercritical CO2 (sCO2) environment, known as oxy-combustion or the Allam cycle. Development of these energy technologies requires understanding of chemical kinetics of H + O2 ⇌ HO + O and H + O2 ⇌ HO2 in high pressures and concentrations of CO2. Here, we combine quantum treatment of the reaction system by the transition state theory with classical molecular dynamics simulation and the multistate empirical valence bonding method to treat environmental effects. Potential of mean force in the sCO2 solvent at various temperatures 1000-2000 K and pressures 100-400 atm was obtained. The reaction rate for H + O2 ⇌ HO + O was found to be pressure-independent and described by the extended Arrhenius equation 4.23 × 10-7 T-0.73 exp(-21 855.2 cal/mol/RT) cm3/molecule/s, while the reaction rate H + O2 ⇌ HO2 is pressure-dependent and can be expressed as 5.22 × 10-2 T-2.86 exp(-7247.4 cal/mol/RT) cm3/molecule/s at 300 atm.

Study on the Changes of Structures and Properties of PAN Fibers during the Cyclic Reaction in Supercritical Carbon Dioxide.

Thermal pre-oxidation of polyacrylonitrile (PAN) fibers is a time-consuming and energy-consuming step in the production of PAN-based carbon fibers. In this paper, the effect of temperature on the structures and properties of PAN fibers cyclized in the supercritical carbon dioxide (Sc-CO2) medium was studied. The thermal behaviors of the PAN fibers were investigated by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The cyclization reaction was sensitive to the heating temperature and gas atmosphere. The FT-IR results of the PAN fibers treated in the Sc-CO2 confirmed that the degree of cyclization increased with the increase of the cyclization temperature. Compared with the PAN fibers treated in the air, the PAN fibers treated in the Sc-CO2 showed a higher degree of cyclization even at the same temperature. These findings might be related to the osmotic action of Sc-CO2 causing the fibers to be further arranged in a regular manner, which was favorable for the cyclization reaction. Moreover, as one kind of high diffusion and high heat transfer media, the heat release during the cyclization of PAN fibers could be quickly removed by Sc-CO2, which achieved the progress of the rapid-entry cyclization reaction.

Molecular dynamics of combustion reactions in supercritical carbon dioxide. Part 4: boxed MD study of formyl radical dissociation and recombination.

Fossil fuel oxy-combustion is an emergent technology where habitual nitrogen diluent is replaced by high pressure (supercritical) carbon dioxide. The supercritical state of CO2 increases the efficiency of the energy conversion and the absence of nitrogen from the reaction mixture reduces pollution by NOx. However, the effects of a supercritical environment on elementary reactions kinetics are not well understood at present. We used boxed molecular dynamics simulations at the QM/MM theory level to predict the kinetics of dissociation/recombination reaction HCO• + [M] ↔ H• + CO + [M], an important elementary step in many combustion processes. A wide range of temperatures (400-1600K) and pressures (0.3-1000atm) were studied. Potentials of mean force were plotted and used to predict activation free energies and rate constants. Based on the data obtained, extended Arrhenius equation parameters were fitted and tabulated. The apparent activation energy for the recombination reaction becomes negative above 30atm. As the temperature increased, the pressure effect on the rate constant decreased. While at 400K the pressure increase from 0.3atm to 300atm accelerated the dissociation reaction by a factor of 250, at 1600K the same pressure increase accelerated this reaction by a factor of 100. Graphical abstract Formyl radical surrounded by carbon dioxide molecules.

A strategy for environmentally-friendly removal of impurities from cotton based on biocatalytic reaction in supercritical carbon dioxide

A novel and environmentally-friendly strategy for integrated bio-treatment (namely the biodesizing and bioscouring) of grey cotton in one-step to degrade and/or remove impurities was constructed on the basis of catalytic reactions from mixed enzymes, by employing reverse microemulsion in supercritical carbon dioxide fluid (SCF-CO2) media as an alternative to heavily polluting wet-chemical processes. Moreover, a subsequent supercritical washing procedure was also involved. Then the proposed strategy was further explored and characterized by the observation of the formation of reverse microemulsion, impurity removal efficiency and wickability of the treated substrate, the results of static water contact angle measurements, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The results demonstrate that an efficient degradation and/or removal of various impurities could be achieved by the proposed strategy from grey cotton with enhanced properties. A successful formation of microemulsion for transfer of enzymes into supercritical carbon dioxide was observed with the presence of an emulsifying agent of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and the auxiliary of ethanol. The efficiency of impurity removal could also be improved at an appropriate system temperature and composite enzyme dosage, as well as by a subsequent washing in SCF-CO2 media. Furthermore, the results of the static water contact angle measurement, XPS spectra and SEM analysis further confirmed the feasibility, validation and reliability of the constructed strategy. Additionally, an integrated removal mechanism was also proposed for impurity degradation and/or removal from grey cotton, with mixed enzymes transferred by reverse microemulsion in supercritical carbon dioxide media.

Palladium(II) complexes with new bidentate phosphine-imine ligands for the Suzuki C[sbnd]C coupling reactions in supercritical carbon dioxide

Newly designed perfluorinated phosphine-imine ligands (3a-c) have been synthesized from the 3-(heptadecafluorooctyl)aniline and 2-(diaryl)phosphinobenzaldehyde (diaryl: −Ph2, 2a; −(3,5-(CH3)2Ph)2, 2b; −(3,5-(CF3)2Ph)2, 2c) and complexed with dichloro(1,5-cyclooctadiene)palladium(II) to form supercritical carbon dioxide (ScCO2) soluble palladium(II) complexes (4a-c). All compounds were fully characterized using spectroscopic and analytical techniques, including 31P, 1H, 19F, 13C NMR and FTIR spectroscopies and high resolution mass spectroscopy. These palladium(II) complexes having perfluoroctyl ponytails (-C8F17) are soluble in carbon dioxide at >333 K under 122 atm of CO2 pressure. Homogenous palladium catalyzed Suzuki CC coupling reactions using the novel catalysts were carried out at 353 K 135 atm. To the best of our knowledge, we applied the first example of hetereodonor bidentate ligands which are bearing both phosphine and imine group for the palladium catalyzed Suzuki CC coupling reaction in ScCO2 solvent system.

Effect of precursor structure on mixed-crystal phase titanium oxide synthesized by sol-gel reaction in supercritical carbon dioxide

Effects of the precursor structure on crystallinity and morphology of titanium oxide from sol-gel reaction and drying in supercritical carbon dioxide was investigated. The titanium precursors examined in this work are: titanium isopropoxide (TIP), titanium tetrabutoxide (TBO), titanium ethylhexoxide (TEO) and titanium diisopropoxide bis(acetylacetonate) (TDB). A mixed-crystal phases with anatase and rutile phases were formed from the titanium oxide synthesized in supercritical carbon dioxide at the lower calcination temperatures. The formation of the rutile phase in the mixed-crystal titanium oxide was facilitated by using the TEO and TDB precursor with long alkyl chain and acetylacetonate group and the calcination in argon gas. The fibrous titanium oxide was synthesized from the supercritical sol-gel reaction using TIP. The supercritical sol-gel reaction using TBO precursor succeeded the titanium oxide mixed-crystal of anatase and rutile phases with the urchin-like morphology with a surface area of 63 m2 g−1.

Efficient synthesis of isoindoles using supercritical carbon dioxide

Bicyclopyrroles were efficiently converted to the corresponding isoindoles by a retro Diels-Alder reaction in supercritical carbon dioxide. By adding ethylene gas as an oxygen scavenger, the isoindole yield was further improved.

Synthesis of eugenyl acetate by enzymatic reactions in supercritical carbon dioxide

Supercritical carbon dioxide (SC-CO2) as reaction medium has gained attention in the production of terpenic esters catalyzed by lipases. Therefore, this work investigated the production of eugenyl acetate by esterification of eugenol and acetic anhydride in SC-CO2 using two commercial lipases (Lipozyme 435 and Novozym 435) as catalysts. The influence of enzyme concentration (1⿿10% weight/weight), substrates⿿ molar ratio (1:1 to 5:1), temperature (40⿿60°C) and pressure of SC-CO2 (10⿿30MPa) on the esterification rate (X; %) and specific productivity (SP; kg of product/kg of catalyst x hour) were evaluated. A home-made high-pressure stirred-batch reactor (100ml) was used in the experiments. The use of Novozym 435 achieved higher conversion and specific productivity of eugenyl acetate than Lipozyme 435. An excess of acetic anhydride (5:1M/M) and high enzyme concentration (10%) achieved higher esterification rates than the lowest conditions (1% and 1:1M/M). The optimal temperatures and pressure for the synthesis of eugenyl acetate in SC-CO2 were 50 and 60°C at 10MPa, respectively. The phase behavior of the reaction system and the synthesis in organic medium were also studied. Kinetic experiments performed at 40, 50 and 60°C indicated that the reaction follows the simple Ping-Pong Bi-Bi mechanism and the affinity of acetic anhydride to enzyme was larger than that of eugenol.

Dynamic phase behavior during sol-gel reaction in supercritical carbon dioxide for morphological design of nanostructured titania

Dynamic phase behavior during sol-gel reaction in supercritical carbon dioxide is investigated for a morphological design of titania. The sol-gel reactions are conducted using acetic acid (HAc) and titanium tetrabutoxide (TBO) as the precursor of titania at 313–353K and 20.0MPa. It is demonstrated the effects of the precursor concentration and temperature on the swelling ratio of the reaction phase and the formation of the homogeneous phase during the reaction in supercritical carbon dioxide. Nano-spherical titania is formed at the condition of lower precursor concentration and temperature 313K that leads to the larger swelling ratio of the reaction liquid phase. The titania with a hollow urchin-shaped is obtained at 333K with the higher precursor concentration. It is implied that this unique structured titania is produced by the phase separation between supercritical carbon dioxide and water phases which is the byproduct on the reaction.

ChemInform Abstract: Metallic Copper Wire: A Simple, Clear and Reusable Catalyst for the CuAAC Reaction in Supercritical Carbon Dioxide.

An efficient protocol for the CuAAC reaction catalyzed by metallic copper wire for the synthesis of 1,4-disubstituted triazoles has been developed in supercritical carbon dioxide (scCO2) at 50 °C. The protocol could afford the corresponding products in excellent yields with a very easy work-up procedure. The metallic copper wire could be reused for more than 200 runs without decreasing the catalytic efficiency.

SN1 reactions in supercritical carbon dioxide in the presence of alcohols: the role of preferential solvation.

Ethanol () inhibits SN1 reactions of alkyl halides in supercritical carbon dioxide (scCO2) and gives no ethers as products. The unexpected behaviour of alcohols in the reaction of alkyl halides with 1,3-dimethoxybenzene () in scCO2 under different conditions is rationalised in terms of Brønsted and Lewis acid-base equilibria of reagents, intermediates, additives and products in a singular solvent characterised by: (i) the strong quadrupole and Lewis acid character of carbon dioxide, which hinders SN2 paths by strongly solvating basic solutes; (ii) the weak Lewis base character of carbon dioxide, which prevents it from behaving as a proton sink; (iii) the compressible nature of scCO2, which enhances the impact of preferential solvation on carbon dioxide availability for the solvent-demanding rate determining step.

Synthesis of α - mangostin-D-glucoside in supercritical carbon dioxide media.

α-Mangostin, the major xanthone constituent of mangoteen fruit pericarp, has several important pharmaceutical application but its bioavailability is restricted due to its insolubility in water. Herein, we synthesized water soluble α-mangostin-D-glucoside by glycosylation of α-mangostin at hydroxyl group; using amyloglucosidase (3.2.1.3) catalyzed reaction in supercritical carbon dioxide (SC-CO2) media. Response surface methodology (RSM) based on a five-variable central composite rotatable design involving 32 experiments was used to determine the effect of pressure (80-160bar), temperature (35-75°C), enzyme concentration (15-45mg), buffer pH (4.0-8.0) and buffer volume (1.0-5.0mL). Experimental data fitted the second-order polynomial equation as indicated by R(2) value of 0.94. The optimal enzymatic conversion within the experimental range of the variables reached 20.3% at a pressure of 120bar, temperature of 55°C, enzyme concentration of 30mg, buffer volume of 3mL and pH6.0 which is well matched with the predictive yield.

Metallic copper wire: a simple, clear and reusable catalyst for the CuAAC reaction in supercritical carbon dioxide

Relatively mild conditions, easy work-up and a simple purification; the stable and easily obtained catalyst presented here could be reused for more than 200 cycles for a 10 cm length of copper wire.

ChemInform Abstract: Stereodivergent Michael Addition of Diphenylphosphite to α‐Nitroalkenes in the Presence of Squaramide‐Derived Tertiary Amines: An Enantioselective Organocatalytic Reaction in Supercritical Carbon Dioxide.

The first “green” asymmetric organocatalytic reaction in a supercritical carbon dioxide medium was elaborated. Under the proposed conditions (100 bar, 35 °C), α-nitroalkenes enantioselectively accept diphenylphosphite in the presence of bifunctional organocatalysts bearing the tertiary amino group and the squaramide fragment to afford corresponding β-nitrophosphonates in high yields and with enantioselectivities of up to 94% ee. By varying the catalyst structure it is possible to synthesize both β-nitrophosphonate enantiomers under these conditions. A significant potential of the supercritical extraction for product isolation and catalyst recovery was demonstrated.

Stereodivergent Michael addition of diphenylphosphite to α-nitroalkenes in the presence of squaramide-derived tertiary amines: an enantioselective organocatalytic reaction in supercritical carbon dioxide

The first “green” asymmetric organocatalytic reaction in a supercritical carbon dioxide medium was elaborated. Under the proposed conditions (100 bar, 35 °C), α-nitroalkenes enantioselectively accept diphenylphosphite in the presence of bifunctional organocatalysts bearing the tertiary amino group and the squaramide fragment to afford corresponding β-nitrophosphonates in high yields and with enantioselectivities of up to 94% ee. By varying the catalyst structure it is possible to synthesize both β-nitrophosphonate enantiomers under these conditions. A significant potential of the supercritical extraction for product isolation and catalyst recovery was demonstrated.

Diastereomer salt formation of ibuprofen in supercritical carbon dioxide

The first in situ diastereomeric salt formation reaction in supercritical carbon dioxide is reported in this paper. The reaction studied was the salt formation between racemic ibuprofen and (R)-(1)-phenylethylamine, and was combined with supercritical fluid extraction in order to separate the unreacted enantiomers from the formed salts. The effects of pressure, temperature and reaction time were studied in detail. With increasing pressure, the reaction rate and the resolution efficiency at equilibrium increase. With increasing temperature, the optical purity of ibuprofen in the carbon dioxide phase increases, as does the reaction rate.

Lipase-catalyzed synthesis of poly(e-caprolactone) in supercritical carbon dioxide

Abstract In this study, the synthesis of poly(e-caprolactone) by lipase-catalyzed reactions in supercritical carbon dioxide was performed in a batch reactor in order to evaluate the influence of the operating conditions on polymer chain size and on polydispersity index. Firstly, a fractional 2 4−1 factorial design was performed to evaluate the effect of temperature, concentration of enzyme, water content and agitation. Then, a full 2 3 experimental design was carried out to evaluate the effects of pressure, enzyme concentration and water content. The best result was a polymer chain size of 7419.6 g/gmol, obtained in a reaction conducted at 145 bar, 65 °C, 200 rpm, 10 wt% enzyme concentration and at the lowest water content.

ChemInform Abstract: Continuous Reactions in Supercritical Carbon Dioxide: Problems, Solutions and Possible Ways Forward

AbstractReview: 80 refs.

Continuous reactions in supercritical carbon dioxide: problems, solutions and possible ways forward

This Tutorial Review focuses on supercritical carbon dioxide (scCO(2)), and discusses some of the problems that have frustrated its wide use on an industrial scale. It gives some recent examples where strategies have been developed to reduce the energy requirements, including sequential reactions and gas-expanded liquids. It then describes a number of cases where scCO(2) offers real chemical advantages over more conventional solvents, for example by controlled phase separation, tunable selectivity, oxidation and on-line analysis and self-optimisation. Overall, this review indicates where scCO(2) could deliver value in the future.