Laboratoire de Génie des Procédés Catalytiques

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNitrogen-Containing Ligands for Asymmetric Homogeneous and Heterogeneous CatalysisFabienne Fache, Emmanuelle Schulz, M. Lorraine Tommasino, and Marc LemaireView Author Information Laboratoire de Catalyse et Synthèse Organique, UMR 5622, UCBL, CPE, 43 Bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France Cite this: Chem. Rev. 2000, 100, 6, 2159–2232Publication Date (Web):May 16, 2000Publication History Received2 December 1999Published online16 May 2000Published inissue 1 June 2000https://pubs.acs.org/doi/10.1021/cr9902897https://doi.org/10.1021/cr9902897research-articleACS PublicationsCopyright © 2000 American Chemical SocietyRequest reuse permissionsArticle Views9177Altmetric-Citations809LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Catalysts,Chemical structure,Ligands,Selectivity,Stereoselectivity Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnantioselective Catalysis Using Heterogeneous Bis(oxazoline) Ligands: Which Factors Influence the Enantioselectivity?Dalit Rechavi and Marc LemaireView Author Information Laboratoire de Catalyse et Synthèse Organique (U.C.B.L.-C.P.E.), 43 bld du 11 nov. 1918, 69622 Villeurbanne Cedex, France Cite this: Chem. Rev. 2002, 102, 10, 3467–3494Publication Date (Web):September 20, 2002Publication History Received15 May 2002Published online20 September 2002Published inissue 1 October 2002https://pubs.acs.org/doi/10.1021/cr020008mhttps://doi.org/10.1021/cr020008mresearch-articleACS PublicationsCopyright © 2002 American Chemical SocietyRequest reuse permissionsArticle Views3064Altmetric-Citations268LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Catalysts,Ligands,Polymers,Stereoselectivity,Styrenes Get e-Alerts

We report in this work the grafting of laponite clay particles with monofunctional γ-methacryloxypropyl dimethyl methoxy silane (γ-MPTDES) and trifunctional γ-methacryloxypropyl trimethoxy silane (γ-MPTMS) coupling agents. The evolution of the grafted amount and of the grafting yield was monitored as a function of the reaction time and of the initial silane concentration. We showed that the grafted amount increased with time and with the silane content up to a plateau value. The amount of chemisorbed silane at saturation varied from 0.56 to 1.9 mmol g−1 depending on the nature of the coupling agent, the reaction time and the grafting conditions. While the trifunctional silane was capable of both reaction with the clay edges and formation of complex polysiloxane oligomers in the bulk which were further deposited on the particulate surface, the monofunctional silane formed a monolayer coverage on the border of the clay plates with the carbonyl groups being directed toward the surface as attested by Fourier transform infrared (FTIR) spectroscopy. The properties of the organosilane-modified laponite were examined by various analytical techniques such as wide-angle X-ray diffraction (WAXD), nitrogen adsorption and thermogravimetric analysis (TGA). The monofunctional silane exhibited nearly no effect on the physicochemical properties of the clay whereas grafting of the trifunctional silane resulted in decreased porosity, increased interlamellar distance and higher hydrophobicity.

Abstract Rosemary oil was extracted by both steam and hydrodistillations then analysed by gas chromatography and gas chromatography–mass spectrometry. The effect of time of extraction enabled us to follow the evolution of the yield and oil composition obtained by both processes. Copyright © 2003 John Wiley & Sons, Ltd.

Starch gelatinization corresponds to a melting phase transition in aqueous medium. Such a transition involves important mass transfer of water. Using a high-pressure bomb including optical ports, the volume variation of starch granules in suspension was related to gelatinization during a high-pressure treatment up to 420 MPa. Microscopic observations of wheat and potato starch granules were compared with macroscopic measurements of compressibility up to 600 MPa and gelatinization intensity using differential scanning calorimetry on treated suspensions. Wheat starch gelatinization started below 300 MPa and was completely achieved at 600 MPa. Potato starch was not altered under 600 MPa. The behavior of the volume variation of starch granules under pressure compared with starch suspensions compressibility could be explained by simultaneous compression and hydration mechanisms. Keywords: Starch gelatinization; high hydrostatic pressure; image analysis

Polyphasic fluid catalysis can be screened by a microreactor, which employs injected catalyst and substrate pulses and a micromixer. Screening both liquid/liquid and gas/liquid processes has been demonstrated to levels of 20 μg rhodium per test and throughput testing frequencies (TTFs) up to 20 h−1. The picture shows a representation of the liquid/liquid apparatus, in which the substrate S and catalyst streams mix by flowing through a micromixer (see scanning electron microscopy image, top right) to form the product P, quantified by standard analytical methods.

Several and recent approaches for the homogeneous-supported catalysts in the fields of hydrogenation using BINAP ligand derivatives and hydrogen transfer reduction with diamines or aminoalcohol ligands are reviewed in order to point out efficient recyclable catalytic systems.

The occurrence of three groups of hazardous organic contaminants (PCBs, PAHs, Me-PAHs) in fifteen watercourses and rivers located in highly urbanized and industrialized zones was studied. The distribution of 62 organic contaminants was determined in three matrices: in the dissolved phase, associated with suspended solid matter (SSM) and in sediment. Their distributions in the aquatic environment depend strongly on their physicochemical properties. Low molecular weight PAHs were predominant in the dissolved phase while those with high molecular weight accumulated preferentially in SSM and sediments. Among the 28 PCBs congeners, only PCB153 was detected. The results showed that the contamination of these areas originated mainly from combustion processes. The three the most polluted sites identified are surrounded by big cities. Ecotoxicological assessment based on the international Sediment Quality Guidelines (SQGs) showed that the toxic effects of the sediment in these watercourses and rivers occurred due to high levels of hydrocarbons.

A safe, straightforward, and atom economic approach for the oxidation of aliphatic aldehydes to the corresponding carboxylic acids within a continuous flow reactor is reported. Typically, the reaction is performed at room temperature using 5 bar of oxygen in PFA tubing and does require neither additional catalysts nor radical initiators except for those already contained in the starting materials. In some cases, a catalytic amount of a Mn(II) catalyst is added. Such a flow process may prove to be a valuable alternative to traditionally catalyzed aerobic processes.

The aminothiol cysteamine, derived from coenzyme A degradation in mammalian cells, presents several biological applications. However, the bitter taste and sickening odor, chemical instability, hygroscopicity, and poor pharmacokinetic profile of cysteamine limit its efficacy. The use of encapsulation systems is a good methodology to overcome these undesirable properties and improve the pharmacokinetic behavior of cysteamine. Besides, the conjugation of cysteamine to the surface of nanoparticles is generally proposed to improve the intra-oral delivery of cyclodextrin-drug inclusion complexes, as well as to enhance the colorimetric detection of compounds by a gold nanoparticle aggregation method. On the other hand, the detection and quantification of cysteamine is a challenging mission due to the lack of a chromophore in its structure and its susceptibility to oxidation before or during the analysis. Derivatization agents are therefore applied for the quantification of this molecule. To our knowledge, the derivatization techniques and the encapsulation systems used for cysteamine delivery were not reviewed previously. Thus, this review aims to compile all the data on these methods as well as to provide an overview of the various biological applications of cysteamine focusing on its skin application.

Abstract The first part of this work deals with flow laws of gas, liquid and mixtures in metallic foam. This experimental work is based on the stationary pressure profile measurement in a channel filled with metallic foam of several grades or materials for several controlled flow rates. Several foam samples with different characteristics (10, 40, 60, 100 ppi) of copper and of nickel are studied. In single‐phase conditions, we evaluate the permeability and inertial the coefficient according to the Forchheimer model. In the gas flow case, compressibility effects are taken into account. Emphasis is given on the relative contributions of inertial and viscous effects. The specific behavior linked to compressibility effect is thoroughly studied. The adiabatic (air‐water) conditions are analyzed; the results are reported in term of biphasic multipliers according to a simple homogeneous model, to study the impact of foam texture and gas quality on flow laws. Several aspects of the two‐phase flow case (i.e. liquid‐vapor) are discussed: phase repartition, pressure drops, characteristic boiling curve …. In single phase conditions, the heat transfer coefficient was improved by two orders of magnitude with the presence of metallic foam with only a limited increase in pressure drop. In biphasic conditions, the study of convective boiling regime also showed significant heat transfer enhancement with very low‐pressure drops. A simple one dimensional homogeneous model was used and allows a good description of global flow behavior across the test section.

The epoxidized group, also known as the oxirane group, can be considered as one of the most crucial rings in chemistry. Due to the high ring strain and the polarization of the C–O bond in this three-membered ring, several reactions can be carried out. One can see such a functional group as a crucial intermediate in fuels, polymers, materials, fine chemistry, etc. Literature covering the topic of epoxidation, including the catalytic aspect, is vast. No review articles have been written on the catalytic synthesis of short size, intermediate and macro-molecules to the best of our knowledge. To fill this gap, this manuscript reviews the main catalytic findings for the production of ethylene and propylene oxides, epichlorohydrin and epoxidized vegetable oil. We have selected these three epoxidized molecules because they are the most studied and produced. The following catalytic systems will be considered: homogeneous, heterogeneous and enzymatic catalysis.

In the present work, a drop tube reactor (DTR) and a horizontal tubular reactor (HTR) were used to study the pyrolysis behaviour of beech wood particles of different sizes under the conditions encountered in industrial fluidized bed gasifiers, namely high external heat flux (105 – 106 W.m-2) and high temperature (800 – 1000°C). The influence of the reactor temperature (800 and 950°C), of particle size (from 350 µm to 6 mm), and of gas residence time (from 1 to 10 s) were examined. Under the explored conditions, when pyrolysis is finished, more than 80 wt.% of virgin wood is converted into gas and less than 13 wt.% remains in solid. In the gas phase, CO is the main gaseous product (50 wt.% of virgin wood), followed by H2 (molar ratios of H2/CO are between 0.35 to 0.55), H2O, CO2 and CH4. Species C2H2, C2H4, C2H6 and C6H6 are present in much lower amounts. The increase of temperature increases the rate of solid devolatilization and favours the cracking reactions of hydrocarbons. The increase of particle size increases the required time for completing pyrolysis. Meanwhile, the results obtained at 950°C show that the final products distribution at the end of pyrolysis is almost the same for the particles between 350 and 800 µm. The increase of the particle size from 800 µm to 6 mm seems to have some influence on the final products distribution. The gas phase reactions mainly change the yields of light hydrocarbons and H2: the increase of gas residence time favours the cracking reactions of hydrocarbons and thus leads to a higher H2 yield.

[reaction: see text] We report here the first heterogenization of a bis(oxazoline) ligand on an inorganic (silica) surface. The activity and enantioselectivity of this new material as a catalyst for the Diels-Alder reaction were checked, and it was shown that under certain conditions enantioselectivities similar to those of the homogeneous catalyst are reached. It was also shown that under these conditions the catalyst can be recycled without loss of activity or selectivity.

A microstructured mesh contactor that can offer residence time of more than minutes is used for gas-liquid-solid hydrogenations and gas-liquid asymmetric hydrogenations. Applications for catalyst/chiral inductor screening and for kinetic data acquisition are demonstrated.

A three-step sintering mechanism is proposed for Co-based catalysts under Fischer–Tropsch reaction conditions. This mechanism includes an intermediate formation of oxide layer on cobalt metal nanoparticles in the presence of water. The partially reversibly oxidized surface accelerates sintering by both reducing the surface energy and enhancing the diffusion rates of cobalt particles. The proposed mechanism is then employed for a fixed-bed unsteady state reactor. The effect of particle growth on the catalytic activity was analyzed within a diverse range of operating conditions (syngas ratio = 1.5–4, water co-feed ratio = 0–6, inert co-feed ratio = 0–6). It is found that, at the same gas space velocity, sintering proceeds faster at higher H2/CO ratios. At the same initial conversion, a low H2/CO syngas ratio increases sintering severity, i.e., catalyst deactivation due to the crystallite growth, as it brings about higher relative water partial pressure. Dilution of syngas with different amounts of inert gas does not affect the cobalt sintering rate. Cobalt sintering proceeds more rapidly if water is co-fed during the reaction.

The mechanism of acceptorless dehydrogenative coupling reaction (ADC) of alcohols to esters catalyzed by aliphatic pincer PHNP ruthenium complexes was experimentally studied. Relevant intermediate species involved in the catalytic cycle were isolated and structurally characterized by single-crystal X-ray diffraction studies, and their reactivity (including toward substrates related to the catalytic process) was probed. VT NMR studies unveiled several chemical exchanges connecting the Ru amido hydride, the Ru alkoxide, and the alcohol substrate. Under catalytic conditions, in situ IR spectroscopy monitoring demonstrated the production of ester via aldehyde as intermediate. A Tishchenko-like pathway is proposed as the main path for the production of ester from aldehyde, involving alkoxide and hemiacetaloxide Ru species (the latter being identified in the reaction mixture by NMR). Catalytic system deactivation under base-free conditions was found to be related to water traces in the reaction medium (either as impurity or derived from aldol reactions) that lead to the formation of catalytically inactive acetato Ru complexes. These react with alkali metal alkoxides to afford catalytically active Ru species. In line with this observation, running the ADC reaction in the presence of water scavengers or alkoxides allows maintaining sustained catalytic activity.

Durch gepulste Katalysator- und Substrateinspeisung wird ein gezieltes Screening bei der Mehrphasen-Fließbettkatalyse ermöglicht. Auf diese Weise konnten mit nur 20 μg Rhodium pro Umlauf und mit „Throughput Testing Frequencies“ von bis zu 20 h−1 Flüssig/flüssig- und Gas/flüssig-Prozesse realisiert werden. Das Bild zeigt, wie Substrat- und Katalysatorstrom in einem Mikromixer (siehe Rasterelektronenmikroskopie-Aufnahme oben rechts) vermischt werden und das Produkt P bilden.

Flow chemistry has changed chemical process designs toward process intensification and is generally considered as green methodology. In this connection, this perspective provides a more critical and holistic view about the sustainability of flow chemistry by introducing both simple and complex holistic tools for environmental quantitative assessment on sustainability and providing examples of how they were used for flow chemistry. The latter also shows a critical assessment of what flow chemistry can add to make chemical processes more sustainable. With the increasing complexity of assessment, green chemistry metrics, life cycle assessment methodology, and circular transition indicators are discussed. In this way, the sustainability of flow chemistry is assessed first on the level of a reaction only and then moving to a process level and beyond. Flow chemists are very aware of the principles of green chemistry and their simple metrics. Yet, they hardly use life cycle assessment, and quantitative circularity analysis has not been made. When those assessments are used, it is usually done by researchers with an ecology background. This perspective aims to make flow chemists aware of the opportunities that complex environmental assessment can provide and that protecting our planet requires a holistic sustainability consideration. The perspective critically states what each of the three types of assessments can do and what their limitations are.

Chirality amplification refers to the ability of a small chiral bias to fully control the main chain helicity of polymers and assemblies. Further implementation of functional chirally amplified helices as switchable asymmetric catalysts, chiral sensors, and circularly polarized light emitters will require a greater control of the energetics governing these chirality amplification effects. In this work, we report on the counterintuitive ability of an achiral molecule to suppress conformational defects in supramolecular helices, thus leading to the emergence of homochirality in a system containing a very small chiral bias. We focus our investigation on supramolecular helices composed of an achiral benzene-1,3,5-tricarboxamide (BTA) ligand, coordinated to copper, and an enantiopure BTA comonomer. Amplification of chirality as probed by varying the amount (sergeants and soldiers effect) or the optical purity (diluted majority-rules effect) of the enantiopure comonomer are modest in this initial system. However, both effects are hugely enhanced upon addition of a second achiral BTA monomer, leading to a perfect control of the helicity either by means of a remarkably low amount of sergeants (0.5%) or a small bias from a racemic mixture of enantiopure comonomers (10% ee). Such an enhancement in the amplification of chirality is only achieved by mixing the three components, i.e. the two achiral and the enantiopure comonomers, highlighting a synergistic effect upon coassembly of the three monomers. Investigation of the role of the achiral additive by multifarious analytical techniques supports its ability to stabilize the helical coassemblies and suppress helix reversals: i.e., conformational defects. Implementation of these helical copper precatalysts in the hydrosilylation of 1-(4-nitrophenyl)ethanone confirms that the effect of the achiral BTA additive is also operative under the conditions of the catalytic experiment. A highly enantioenriched product (90% ee) is produced by a supramolecular catalyst operating with ppm levels of chiral species.