Decomposition and Oxidation Reactions of Aliphatic Nitro Compounds in Supercritical Water

The reaction kinetics of nitromethane, nitroethane, and 1-nitropropane decomposition and oxidation in supercritical water near the critical point was studied in a flow reactor. The reaction rate constants were calculated assuming first-order reaction. It was found that pressure has a considerable effect on the rates of decomposition of the above nitrogen-containing compounds in supercritical water over a wide pressure range. The reactivity of the above aliphatic nitro compounds in supercritical water in decomposition reactions decreased and in oxidation reactions increased with an increasing number of carbon atoms.     

Kinetics of thermal conversions of monoterpenic compounds in supercritical lower alcohols

The most important information concerning thermal conversions of vegetable terpenes (α-pinene, β-pinene, turpentine, and cis-verbenol) in supercritical lower alcohols is systematized. The kinetics of selected reactions is reported and is compared with the kinetics of the same reactions in the gas and liquid phases. Thermodynamic calculations of the phase states and kinetic parameters are presented for a number of multicomponent multiphase systems containing terpenes and lower alcohols. The effect of the supercritical solvent pressure on the rate and selectivity of the selected reactions is reported.     

The thermolysis of α-pinene and verbenone epoxides in supercritical solvents

Thermal transformations of α-pinene and verbenone epoxides were studied in supercritical solvents with complex compositions, including CO₂, lower alcohols (ethanol and isopropanol), and water, over the temperature and pressure ranges 387–575 K and 135–215 atm. The main product from α-pinene epoxide in a supercritical solvent containing water was campholenic aldehyde and pinocamphone; the total content of these products in the reaction mixture was 80%. Suggestions concerning the mechanism of the thermal isomerization of α-pinene epoxide depending on the acidity of supercritical solvents were made. The direction of verbenone epoxide transformations was independent of the presence of water in the mixture. The main identified products were ketoalcohols with para-menthane and camphane frameworks.     

Toward green catalytic synthesis—Transition metal-catalyzed reactions in non-conventional media

Solvents play a critical role in “greening” synthetic chemistry, and this is also true in catalytic organic synthesis. This review attempts to summarize the progress made in the past a few years on homogeneous and heterogeneous catalytic reactions in the non-conventional solvents, water, ionic liquids, supercritical carbon dioxide and fluorous carbons, with the focus on those catalyzed by transition metal complexes. The reactions covered include hydrogenation, hydroformylation, carbonylation, Heck reactions, Suzuki and Stille couplings, Sonogashira reactions, allylic substitution, olefin metathesis, olefin epoxidation and alcohol oxidation.     

Selective chemical reactions in supercritical carbon dioxide,water, and ionic liquids

Abstract

Alternative solvents such as supercritical carbon dioxide, water, and ionic liquids are receiving an increase of interest as better replacements for conventional solvents in chemical reactions. They have been called sustainable green solvents because they are highly promising reaction mediums for organic synthesis. This review presents an overview of some selected chemical reactions that have been developed in these green solvents with a particular emphasis on metal-catalyzed reactions.     

Reaction Kinetics of 2-Propanol Dehydration in Supercritical Water

A study of the kinetics and mechanism of chemical reactions in supercritical fluids is considered. An experimental procedure was proposed for examining reversible chemical reactions in supercritical water. The reaction kinetics of 2-propanol dehydration in supercritical water was studied. It was found that the uncatalyzed reactions of olefin hydrogenation by hydrogen dissolved in supercritical water occur at high rates near the critical point of water. The experimental data on the dehydration of 2-propanol in supercritical water are adequately described by first-order reaction rate equations. The rate constants and activation energies of 2-propanol dehydration near the critical point of supercritical water were found.     

Vibrational Spectroscopy in Supercritical Fluids: From Analysis and Hydrogen Bonding to Polymers and Synthesis

Supercritical fluids are beginning to be used widely in chemistry. Applications range from extraction and chromatography in analytical chemistry to solvents for reaction chemistry and preparation of new materials. Spectroscopic monitoring is important in much of supercritical chemistry, and vibrational spectroscopy is particularly useful in this context because the vibrational spectrum of a given molecule is usually quite sensitive to the environment of that molecule. Thus, vibrational spectra are excellent probes of conditions within the fluid. In this review, we describe a variety of techniques and cells for IR and Raman spectroscopy in supercritical fluids and illustrate the breadth of applications in supercritical fluids. The examples include: the use of supercritical Xe as a spectroscopically transparent solvent for chemistry and for supercritical fluid chromatography with FTIR detection of analytes; Raman spectroscopy as a monitor for gases dissolved in supercritical CO₂; the effect of solvent density on hydrogen bonding in supercritical fluids and the formation of reverse micelles; IR as a monitor for the supercritical impregnation/extraction of polymers and the reactions of organometallic compounds impreganated into polymers; reactions of organometallic compounds in supercritical fluids; and finally, the use of miniature flow reactors for laboratory-scale preparative chemistry. Overall, our aim is to provide a starting point from which individual readers can judge whether such measurements might usefully be applied to their own particular problems.     

Cu(II) 2-quinoxalinol salen catalyzed oxidation of propargylic,benzylic, and allylic alcohols using tert-butyl hydroperoxide in aqueous solutions

The synthesis of carbonyl compounds by oxidation of alcohols is a key reaction in organic synthesis. Such oxidations are typically conducted using catalysts featuring toxic metals and hazardous organic solvents. Considering green and sustainable chemistry, a copper(II) complex of sulfonated 2-quinoxalinol salen (sulfosalqu) has been characterized as an efficient catalyst for the selective oxidation of propargylic, benzylic, and allylic alcohols to the corresponding carbonyl compounds in water when in combination with the oxidant tert-butyl hydroperoxide. The reactions proceed under mild conditions (70 °C in water) to produce yields up to 99% with only 1 mol % of catalyst loading. This reaction constitutes of a rare example of propargylic alcohol oxidation in water, and it makes this process greener by eliminating the use of hazardous organic solvents. Excellent selectivity was achieved with this catalytic protocol for the oxidation of propargylic, benzylic, and allylic alcohols over aliphatic alcohols. The alcohol oxidation is thought to go through a radical pathway.     

Thermolysis of α-pinene in supercritical lower alcohols

Thermal isomerization of α-pinene in supercritical solvents, viz., ethanol, methanol, and propan-1-ol, was carried out, and differences in the rate and selectivity of the process were revealed. In supercritical ethanol the reaction rate increases sharply and the selectivity remains unchanged with an increase in the temperature (from 290 to 390 °C) or pressure (from 90 to 270 atm). The main reaction products are limonene, isomeric alloocimenes, and pyronenes. The selectivity for limonene in propan-1-ol is higher than in other alcohols when the conversion of α-pinene not higher than 50%. In supercritical ethanol (430 °C, 120 atm, 140 s) limonene is more stable than α-pinene (conversion 8%).     

超临界流体萃取分离离子液体与有机物及其相平衡的研究

离子液体具有一些优良的物理和化学性质,非常有希望成为传统有机溶剂的替代溶剂.但是如何从过程物流中分离和回收离子液体将是其工业化应用的一个很大挑战.蒸馏、液液萃取和超临界萃取是目前已知的三个可行的方法.其中超临界萃取可应用于离子液体与挥发的或相对不挥发的有机物的分离,而且不存在相间交叉污染.本文从二元体系相平衡、三元体系相平衡、模型化研究和萃取实验结果方面介绍了超临界萃取方法的最新研究进展,在此基础上提出了用超临界丙烷替代超临界二氧化碳作为萃取溶剂的新思路,并探讨了该领域今后的研究方向和工业化前景.     

水溶性金属卟啉应用于催化反应的研究进展

综述了水溶性金属卟啉作为催化剂应用于均相或非均相的催化反应的研究进展,重点介绍了水溶性金属卟啉在水或水与有机溶剂混合介质中催化底物氧化反应的催化性能,其中包括烷烃的羟基化,烯烃的环氧化,含氧、含硫及含氮化合物的氧化反应.另外水溶性金属卟啉还可用于催化Suzuki-Miyaura反应、氧化偶联反应、C=C氧化断裂反应等.水溶性金属卟啉催化剂具有水溶性、催化效率高、反应条件温和等优点,因此将在催化反应特别是氧化反应中得到更广泛的应用.     

Extraction of aroma compounds in blackcurrant buds by alternative solvents: Theoretical and experimental solubility study

This study was designed to evaluate the performance of nine alternative solvents (α-pinene, MeTHF, ethyl acetate, methyl acetate, ethyl lactate, butanol, isopropanol, ethanol and CO₂ supercritical fluid) for extracting aromas from blackcurrant buds (Ribes nigrum L) compared to that of n-hexane, commonly used. This study has been performed via experimentation and simulation using Hansen solubility methodology for the comprehension of the dissolving mechanism. Experimentally, the extracts were analysed to compare the solvents performance in terms of aroma compositions. The results indicated that an alternative solvent, i.e. MeTHF, could be the most promising one for n-hexane substitution with good yield and selectivity of aromas.     

Enhanced cage effects in supercritical fluid solvents. the behavior of diffusive and geminate caged-pairs in supercritical carbon dioxide

The behavior of geminate and diffusive radical caged-pairs arising from the photolysis of dicumyl ketone in conventional and supercritical carbon dioxide (SC--CO(2)) solvents has been examined. The results suggest that locally enhanced solvent density about a solute (solvent/solute clustering) can lead to an enhanced cage effect near the critical pressure in supercritical fluid solvents. This enhanced cage effect is similar in magnitude for both diffusive and geminate caged-pairs.     

Autoxidation of cyclic olefins in perfluorinated organic solvents

It is well known that several perfluorinated organic compounds (particularly alcanes and cyclic ethers perfluor$\text{i}$nated) have specific properties like solvents of biatomic gas and oxygen.Since these perfluorinated compounds have also suff$\text{i}$cient capabilities as solvents of several alifatic hydr$\text{o}$carbons and pratically none as solvents of their oxidation products (alcohols, ketones; peroxides, acids, water, etc.), these solvents seem ideal for the studying of oxidation reactions in liquid phase.The kinetics of autoxidation, with O₂ for temperatures between 15°C and 60°C, of cyclohexene and methyl cyclohexenes, have been studied in fluorinated solvents (various mixtures of 3,n-perfluoro-propyl-perfluoro-tetrahydrofuran, and 3,n-perfluoro-buthyl-perfluoro-tetrahydropyran) with formula C₈F₁₆O. This study includes the determination of the kinetic parameters both during the induction phase and during the stationary phase.The above mentioned oxidations we have studied in anal$\text{o}$gous conditions in other solvents (carbon tetrachloride, benzene chloride, etc.). The highest rates observed and the larger selectivity of the fluorinated solvents have been pointed out.     

Investigations on the supercritical fluid extraction of spiked organic pollutants from wet soils

The possibility of a fractionation (sequential extraction) of certain groups of compounds has been investigated during supercritical fluid extraction (SFE) from wet and dry wetland-soils. The classes of compounds considered are chlorinated hydrocarbons on the one hand and nitrogen- or phosphorus-containing pesticides (N/P-pesticides) on the other hand. The results show the great influence of water on the efficiency of the extraction and the limited possibility of attaining a fractionation during the extraction.     

Heterogeneous reactions of epoxides in acidic media

Epoxides have recently been identified as important intermediates in the gas phase oxidation of hydrocarbons, and their hydrolysis products have been observed in ambient aerosols. To evaluate the role of epoxides in the formation of secondary organic aerosols (SOA), the kinetics and mechanism of heterogeneous reactions of two model epoxides, isoprene oxide and α-pinene oxide, with sulfuric acid, ammonium bisulfate, and ammonium sulfate have been investigated using complementary experimental techniques. Kinetic experiments using a fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS) show a fast irreversible loss of the epoxides with the uptake coefficients (γ) of (1.7 ± 0.1) × 10(-2) and (4.6 ± 0.3) × 10(-2) for isoprene oxide and α-pinene oxide, respectively, for 90 wt % H(2)SO(4) and at room temperature. Experiments using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) reveal that diols are the major products in ammonium bisulfate and dilute H(2)SO(4) (<25 wt %) solutions for both epoxides. In concentrated H(2)SO(4) (>65 wt %), acetals are formed from isoprene oxide, whereas organosulfates are produced from α-pinene oxide. The reaction of the epoxides with ammonium sulfate is slow and no products are observed. The epoxide reactions using bulk samples and Nuclear Magnetic Resonance (NMR) spectroscopy reveal the presence of diols as the major products for isoprene oxide, accompanied by aldehyde formation. For α-pinene oxide, organosulfate formation is observed with a yield increasing with the acidity. Large yields of organosulfates in all NMR experiments with α-pinene oxide are attributed to the kinetic isotope effect (KIE) from the use of deuterated sulfuric acid and water. Our results suggest that acid-catalyzed hydrolysis of epoxides results in the formation of a wide range of products, and some of the products have low volatility and contribute to SOA growth under ambient conditions prevailing in the urban atmosphere.     

Supercritical fluid injection of high-molecular-weight polycyclic aromatic compounds in capillary supercritical fluid chromatography

A sample introduction system for capillary supercritical fluid chromatography, which allows the dissolution of the sample in the supercritical mobile phase before being introduced into the column, was constructed and evaluated. Supercritical n-pentane was shown to solvate high-molecular-weight polycyclic aromatic compounds that could not be solvated using typical liquid solvents. In addition, split injection of a supercritical fluid solution was found to be more reproducible than split injections of a liquid solution. The potential of such an injection system was demonstrated, although further developments are needed in order to make the technique of practically utility.     

Ultra‐high performance supercritical fluid chromatography of lignin‐derived phenols from alkaline cupric oxide oxidation

Traditional chromatographic methods for the analysis of lignin‐derived phenolic compounds in environmental samples are generally time consuming. In this work, an ultra‐high performance supercritical fluid chromatography method with a diode array detector for the analysis of major lignin‐derived phenolic compounds produced by alkaline cupric oxide oxidation was developed. In an analysis of a collection of 11 representative monomeric lignin phenolic compounds, all compounds were clearly separated within 6 min with excellent peak shapes, with a limit of detection of 0.5–2.5 μM, a limit of quantification of 2.5–5.0 μM, and a dynamic range of 5.0–2.0 mM (R² > 0.997). The new ultra‐high performance supercritical fluid chromatography method was also applied for the qualitative and quantitative analysis of lignin‐derived phenolic compounds obtained upon alkaline cupric oxide oxidation of a commercial humic acid. Ten out of the previous eleven model compounds could be quantified in the oxidized humic acid sample. The high separation power and short analysis time obtained demonstrate for the first time that supercritical fluid chromatography is a fast and reliable technique for the analysis of lignin‐derived phenols in complex environmental samples.     

Metal(salen)-catalyzed oxidation of limonene in supercritical CO2

Summary The Mn(Salen)Cl and Ni(Salen)-catalyzed oxidation of limonene has been carried out. The catalytic cycle involved PhIO via a rebound mechanism. In all cases the use of organic solvents resulted in reasonable selectivities of oxidized products. The use of supercritical carbon dioxide (SCCO₂) led at least to comparable results in terms of conversions, but showed different selectivities. In ordinary solvents epoxidation appears to predominate over allylic oxidation. This tendency, in SCCO₂, appears only after 4 h of reaction. Shorter reaction times (2 h) appear to lead to opposite selectivity. These results showed the advantages of using SCCO₂ as solvent in these reactions. SCCO₂ is much more compatible with green technology than are organic solvents.     

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。