The First Efficient Iodination of Unactivated Aliphatic Hydrocarbons

No heavy metals, no enzymes, and a simple protocol : the direct iodination of aliphatic hydrocarbons, which has not been possible to date, can now be carried out in multiphase systems [see for example Eq. (1)]. In situ generated tetraiodomethane serves as a key intermediate in this selective radical chain reaction initiated by a single electron transfer. This room-temperature, efficient transformation is highly regioselective, easy to work-up, and hence widely applicable.     

Selective Hydrogen Oxidation in the Presence of C3 Hydrocarbons Using Perovskite Oxygen Reservoirs

Perovskite‐type oxides, ABO₃, can be successfully applied as solid “oxygen reservoirs” in redox reactions such as selective hydrogen combustion. This reaction is part of a novel process for propane oxidative dehydrogenation, wherein the lattice oxygen of the perovskite is used to combust hydrogen selectively from the dehydrogenation mixture at 550 °C. This gives three key advantages: it shifts the dehydrogenation equilibrium to the side of the desired products, heat is generated, thus aiding the endothermic dehydrogenation, and it simplifies product separation (H₂O vs H₂). Furthermore, the process is safer since it uses the catalysts’ lattice oxygen instead of gaseous O₂. We screened fourteen perovskites for activity, selectivity and stability in selective hydrogen combustion. The catalytic properties depend strongly on the composition. Changing the B atom in a series of LaBO₃ perovskites shows that Mn and Co give a higher selectivity than Fe and Cr. Replacing some of the La atoms with Sr or Ca also affects the catalytic properties. Doping with Sr increases the selectivity of the LaFeO₃ perovskite, but yields a catalyst with low selectivity in the case of LaCrO₃. Conversely, doping LaCrO₃ with Ca increases the selectivity. The best results are achieved with Sr‐doped LaMnO₃, with selectivities of up to 93 % and activities of around 150 μmol O m^?2. This catalyst, La_0.9Sr_0.1MnO₃, shows excellent stability, even after 125 redox cycles at 550 °C (70 h on stream). Notably, the activity per unit surface area of the perovskite catalysts is higher than that of doped cerias, the current benchmark of solid oxygen reservoirs.     

Aliphatic and Aromatic Hydrocarbons in the Mediterranean Aerosol

Abstract

The atmospheric transport of organic pollutants over long distances and their effect on the biological cycles of the sea are two major questions of concern in environmental chemistry. These processes are of particular importance in the Mediterranean Sea because of its semi-enclosed characteristics, which determine the accumulation of the pollutants entering into the system.

In order to get some insight into these processes a project (PHYCEMED), was developed for the evaluation of the atmospheric budget of organic and inorganic substances in the Western Mediterranean and for the investigation of the exchange mechanisms of these materials across the air/sea interface.

A high volume air sampling system including a cascade impactor was placed on board of the R/V le Suroit for collecting the acrosols along several transects parallel to the French, Spanish and North-African coasts, facing areas of different population densities and industrial activities. The cruise was realised on October 1983 and the particulate material was fractionated into the following sizes: 7.2, 3.0, 1.5, 0.96, and 0.03 μm. Quantitative and qualitative analyses of the aliphatic and the aromatic hydrocarbons present in these fractions were performed by high resolution gas chromatography and gas chromatography-mass spectrometry.

Total non-aromatic hydrocarbon concentrations are in the range 30-57 ng/m³ (10-14ng/m³ for n-alkanes). The distribution of n-alkanes indicates that most of the aerosol mass is associated with small particles < 1 μm.Polycyclic aromatic hydrocarbons are identified from phenanthrene to benzo(ghi)perylene with fluoranthene and pyrene as dominant compounds. Concentrations for individual PAH vary in the range 4.1 pg/m³ for benzo(a)anthracene up to 100 pg/m³ for fluoranthene. The evaluation of different contributions such as land plant waxes or soil sources and various anthropogenic sources is discussed from n-alkanes and PAH distribution patterns.     

FluorJmetric Estimation of Aliphatic Hydrocarbons in Airborne Particulates

A thin-layer chromatographic method is presented that allows determination of long-chain aliphatic hydrocarbons in the benzene-soluble fraction of airborne particulate extracts by direct scanning in a spectrophotofluorimeter. Silica-gel plates were impregnated with rhodamine 6G, and after development the separated aliphatic hydrocarbon spot was scanned on a scanning spectrophotofluorimeter and measured. The area under the peak was concentration-dependent, with a useful range of analysis from 0.1 meg to at least 10 meg of aliphatics in terms of n-docosane. Urban air samples contained 1.6 to 2.7 meg of aliphatics per cubic meter; nonurban samples had 0.12 to 0.24 meg. Since hydrocarbon carcinogens are ubiquitous, it is suggested that their concentration is of secondary importance in many cases, whereas the much higher concentrations of the cocarcinogens (such as large aliphatic hydrocarbons) and prolonged exposure to them are probably of prime importance. A number of polynuclear aromatic hydrocarbons and pesticides were screened and were found not to interfere with the determination of the aliphatic hydrocarbons. Their chromatographic and fluorimetric properties under experimental conditions are discussed.     

Methane Conversion to Higher Hydrocarbons in the Presence of Carbon Dioxide Using Dielectric-Barrier Discharge Plasmas

Experimental investigation has been conducted to convert methane into higher hydrocarbons in the presence of carbon dioxide within dielectric-barrier discharge (DBD) plasmas. The objectives of cofeed of carbon dioxide are to inhibit carbon deposit and to increase methane conversion. The products from this plasma methane conversion include: (1) syngas (H₂+CO), (2) gaseous hydrocarbons containing ethylene, acetylene, and propylene, (3) liquid hydrocarbons, (4) plasma-polymerized film, and (5) oxygenates. The selectivity of products is subject to the DBD plasma-reactive conditions and catalyst applied. The liquid hydrocarbons produced by this way are highly branched, which represents a better fuel production.     

Silver(I)-promoted Oxidation and Ring-enlargement Reactions of Unstrained Hydrocarbons, Polyphenyl-cyclopentadiene

The activation of carbon-carbon bonds by soluble transitional metal complexes has been one of the most prominent challenges in recent years1-3. Despite the inertness of carbon-carbon bonds, some possible ways to cleave carbon-carbon bonds have been devised, such as relieving ring energy4, inducing aromatic stabilization5, forming stable metallocyclic complexes6, etc. Silver salts, such as silver perchlorate and silver trifluoroacetate, play an important role in carbon-carbon bond activation,…     

Catalytic Oxidation of Indigo Carmine in the Presence of Silver Nanoparticles: Application to Groundwater Analysis

The oxidation of indigo carmine by potassium hexacyanoferrate(III) is catalyzed by trace of silver nanoparticle (AgNP). The reaction is followed UV‐Vis absorption spectrophotometrically by measuring the change in the absorption spectra (λ_max 612 nm). The catalytic oxidation reaction is used for the quantification of indigo carmine. The calibration graph was linear in the concentration range 50 nM—1.8 μM of indigo carmine. The variables affecting the method have been optimized. The method is applied to the determination of indigo carmine in groundwater samples with the satisfactory results.     

Photocatalytic Oxidation of Aromatic Hydrocarbons

In acidic aqueous solutions UO(2)(2+) serves as a photocatalyst (lambda(irr) >/= 425 nm) for the oxidation of benzene by H(2)O(2). Under conditions where 50% of the excited state UO(2)(2+) is quenched by H(2)O(2) (k = 5.4 x 10(6) M(-)(1) s(-)(1)) and 50% by benzene (k = 2.9 x 10(8) M(-)(1) s(-)(1)), the quantum yield for the formation of phenol is 0.70. The yield does not change when benzene is replaced by benzene-d(6), but decreases by a factor of approximately 4 upon the change of solvent from H(2)O to D(2)O. Photocatalytic oxidation of toluene by UO(2)(2+)/H(2)O(2) produces PhCHO, PhCH(2)OH, and a mixture of cresols with a total quantum yield of 0.28 under conditions where 50% of UO(2)(2+) is quenched by H(2)O(2). The quenching of UO(2)(2+) by benzene and substituted benzenes takes place with k > 10(8) M(-)(1) s(-)(1). The system UO(2)(2+)/t-BuOOH/C(6)H(6)/hnu does not result in the oxidation of benzene, but instead yields methane and ethane.     

脂肪醇氨氧化反应制备脂肪腈研究进展北大核心CSCD

脂肪腈是一类非常重要的化工原料和中间体,被广泛应用于医药、农用化学品、染料和合成树脂等领域.在诸多合成脂肪腈的路线中,脂肪醇氨氧化制备脂肪腈的路线使用可源于生物质资源的脂肪醇为原料,有助于“碳中和”和“碳达峰”目标的实现;同时,该反应副产物为水或氢气,符合“绿色”可持续发展的要求,具有重要的研究价值.根据脂肪醇氨氧化制备脂肪腈的过程中是否需要向体系中提供氧气,氨氧化过程可分为需氧氧化-氨化反应和脱氢氧化-氨化反应两类.需氧氧化-氨化反应在均相催化体系和非均相催化体系中均具有相关研究,而脱氢氧化-氨化反应的研究则主要集中在非均相体系中.按照以上分类,综述了脂肪醇氨氧化制备脂肪腈催化体系的研究进展,分析了不同种类催化体系的优势与尚存在的不足,并展望了该反应催化体系未来发展的方向.     

The Catalytic Activity of Transition Metal Compounds in the Liquid-Phase Oxidation of Hydrocarbons

The way in which dissolved transition metal compounds affect the liquid-phase oxidation of hydrocarbons is demonstrated for compounds of cobalt, copper, and manganese. Kinetic investigations on model systems and comparisons with the non-catalyzed reaction show that the catalysts participate in all the oxidation steps.     

渗透汽化分离芳烃/烷烃混合体系的研究进展*

本文对近年来应用于分离芳香烃/ 烷烃混合体系的渗透汽化(简称PV ) 膜材料, 特别是高分子材料进行了较为系统的综述, 并简要概述了渗透汽化膜分离特点、机制以及影响渗透汽化分离过程的主要因素。     

High Temperature Steam Extraction for the Determination of Aliphatic Hydrocarbons in Petroleum Source Rock

A simple method for the extraction of hydrocarbons from petroleum source rock by high temperature steam was investigated and the conditions for maximum yield were determined. The results showed that the temperature and kinetic rates have significant effects. The optimum temperature for the extraction of n-alkanes and isoprenoid hydrocarbons from sedimentary organic rocks was 250 °C. The optimum extraction time for lower and medium molecular weight n-alkanes was 20 min, while the higher molecular weight alkanes were exhaustively extracted after 50 min. The yields of the analytes were much higher with using the high temperature steam extraction than Soxhlet extraction. The recoveries of the n-alkanes for GC–MS analysis from the extractant water by SPME with a PDMS fibre ranged from 90 to 100% and most of the compounds were above 93%.

     

High Temperature Steam Extraction for the Determination of Aliphatic Hydrocarbons in Petroleum Source Rock

A simple method for the extraction of hydrocarbons from petroleum source rock by high temperature steam was investigated and the conditions for maximum yield were determined. The results showed that the temperature and kinetic rates have significant effects. The optimum temperature for the extraction of n-alkanes and isoprenoid hydrocarbons from sedimentary organic rocks was 250 °C. The optimum extraction time for lower and medium molecular weight n-alkanes was 20 min, while the higher molecular weight alkanes were exhaustively extracted after 50 min. The yields of the analytes were much higher with using the high temperature steam extraction than Soxhlet extraction. The recoveries of the n-alkanes for GC–MS analysis from the extractant water by SPME with a PDMS fibre ranged from 90 to 100% and most of the compounds were above 93%.     

The Heavy-Atom Effect on the Photophysics of Aromatic Hydrocarbons in the Presence of Solid Clays

The exchange of the original cation present on a Laponite clay (usually Na⁺) for heavy atoms such as Rb⁺, Cs⁺, and Tl⁺ significantly alters the emission characteristics of some aromatic hydrocarbons (p-terphenyl, naphthalene, pyrene, and biphenyl). The increase of the atomic mass of the cation induces a decrease of the fluorescence emission simultaneous with an increase of the emission in the region of lower energies of the spectra, ascribed to the phosphorescence of those hydrocarbons. Time-resolved experiments for the pyrene–clay system showed a decrease of singlet lifetimes for the heavier atoms. Hydrocarbon aggregates were also detected from both the emission spectra and the time-resolved studies. The “excimer-like” emission showed longer lifetimes (10–25 ns) than the monomolecular hydrocarbons (1–3 ns), as already found for other similar systems. The amount of aggregates increased for the heavier cations due to the smaller surface available on the clay particles. Experiments increasing the amount of Tl⁺ in samples containing a constant concentration of naphthalene allowed evaluation of the distance between the heavy atoms and the probe on the clay surface. The Perrin model treatment was used and resulted in approximately R₀=9.2 Å.