Nickel-katalysierte Dimerisierung von Butenen aus C4-Gemischen mit ionischen Flüssigkeiten - Weiterentwicklungen zur industriellen Anwendung und Untersuchung neuer Selektivitätskonzepte

Linear dimers of butene are important reactants for the production of plasticizers mainly for polyvinylchloride. In industry there exist two routs for large scale synthesis of propene and butene dimers. One is the homogeneous dimersol process published by IFP, the other is a heterogeneous process catalyzed by nickel oxides on supports. Both options have disadvantages and are uneconomic for diluted feeds. That can be overcome by a biphasic reaction mode. In 1990 Chauvin et al. presented a process using acidic ionic liquids. Due to its catalyst immobilization, double bond isomerization and in-situ-separation of polar and unpolar compounds, this process is exceptionally suitable for diluted feedstocks with a thermodynamic composition of butenes. Unlike for propene dimerization, for the reaction with butenes a ligand effect on selectivity was not shown in Chauvin’s system. As a standard catalytic system NiCl2(PPh3)2 in [BMIM]Cl/AlCl3/EtAlCl2 (1:1,2:0,1) was chosen since the ligand PPh3 showed an influence on selectivity of the dimerization. In further studies it was revealed that this influence is dependent on the contact time between catalyst and ionic liquid without butene. Thus the equilibrium of intact and split catalyst complexes, postulated by Chauvin for phosphane ligands in propene dimerization, seems to be valid here as well. ESI-MS-measurements confirmed that free ligands appear in the ionic media only after a minimum contact time. In batch and continuous experiments, the weak organic base tetramethylebenzene (TMB) showed a positive impact on complex stability. The immobilization of this base effect was successful by introducing the aromatic function into an imidazolium side chain [1-methyl-3-propylphenyl imidazolium]Cl. In detailed solubility studies the solution was determined to be very slow. DFT-calculations gave a good agreement of the experimental selectivity results. For the first time, dimerization was successfully carried out in a SILP system. By that, the selectivity was greatly enhanced. Due to the sensible matter of acidity in the nickel catalyzed dimerization, the nature and treatment of the support had tremendous influence on the catalytic activity. A well dried carbon support proved to be suitable for reproducible results whereas silica and alumina supports showed significant variations. Since acidic ionic liquids are sensitive to moisture and harmful to metal equipment, experiments in low coordinating, neutral ILs were carried out. Homogeneuos biphasic catalysis in [EMIM][FAP] showed no activity due to a low catalyst solubility and a non-suitable environment for the complex. In contrast, it was possible to dimerize butene with a SILP-catalyst comprising the very [EMIM][FAP]. The reason is the thin film and thus the good contact between catalyst and co-activating EtAlCl2. SILP-systems with [EMIM][FAP] also showed to be less prone to support fluctuations than the corredspnding systems with acidic ILs. First results in a micro-fixed bed gasphase reactor showed that the catalytic system can be stable in ethene dimerization for more than 150 h. Activation of the catalyst turned out to be the crucial step here. In the fundamental part of this work, two low melting liquid crystalline ionic liquids (ILCs) were synthesized and characterized ([C12C12IM][BF4] and [C12C12IM][ClO4]). For the first time a shear rate dependent viscosity of the ionic liquid mesophase was observed (pseudo-plastic). Stepwise a liquid crystalline SILP-system was developend, disclosing a strong impact to the nature of the support on the visibility of the liquid crystalline phase. On the catalyst side two approaches were made. Carben complexes with structural analogies towards the ILC were synthesized. These catalysts need activation but show advantageous solution effects. A number of self active methallyl catalysts were prepared and these effectively dimerized ethene without activation. The pivotal factor here is temperature stability. With this work new insights into the equilibrium of phosphane ligands on nickel catalysts in acidic ionic liquids were gained. The dimerization was for the first time carried out with a SILP-catalyst both, slurry and in a fixed bed gas phase reactor. Low coordinating neutral ILs like [EMIM][FAP] emerged to be viable. Moreover a liquid crystalline SILP-system was developed and successfully tested in ethene dimerization. Carbene und methallyl nickel complexes were applied.Nach Stein-, Bronze- und Eisenzeit wird die aktuelle Epoche oft das Zeitalter des Kunststoffs genannt. Unter dem Druck immer strengerer Klimaziele ist verständlich, dass die leichten Kunststoffe konventionelle Werkstoffe wie Stahl und Glas immer stärker ersetzen. Um die günstigen Eigenschaften von Kunststoff - Flexibilität und geringes Gewicht - gezielt einstellen zu können, sind spezialisierte Additive und Weichmacher notwendig. Für hochwertige Phthalat-Weichmacher werden wenig verzweigte C8-Alkene aus der Butendimerisierung benötigt. Aufgrund der Verknappung fossiler Rohstoffe zielt die industrielle Forschung verstärkt auf die Nutzbarmachung verdünnter Alken-Restströme, da in diesen beachtliche Werte stecken. Bestehende Verfahren sind für verdünnte Eduktströme wenig wirtschaftlich. Deswegen sind neue Verfahren notwendig. 1990 stellten Chauvin et al. erste Arbeiten zur zweiphasigen Dimerisierung von Alkenen in ionischen Flüssigkeiten (ILs) vor. Für die Dimerisierung von Alkenen hat sich das Übergangsmetall Nickel in lewissauerer Umgebung durch seine hohe Dimerselektivität und Aktivität ausgezeichnet. Screeningversuche ergaben, dass es über den Liganden Triphenylphosphan möglich ist, in [BMIM]Cl/AlCl3/EtAlCl2 (1:1,2:0,1) die Selektivität zu dem zweifach verzweigten Produkt DMH auf 25 % und damit unter den Wert von unmodifiziertem Nickel zu senken. Dieser Effekt ist von der Kontaktzeit zwischen IL und Katalysator abhängig. Aromatische Additive verhindern die völlige Abstraktion des Liganden. In kontinuierlichen Experimenten ist die Entfernung des Liganden eine Funktion des Volumenstroms der organischen Phase. Stetig zugegebene Aromaten führen auch hier zu einer Stabilisierung. Allerdings verstärken Additiven wie TMB den Austrag aktivierender Substanzen. Mit der maßgeschneiderten aromatischen IL 1-Methyl-3-propylphenylimidazoliumchlorid konnten die Nachteile des Leachings bei Beibehaltung aller Vorteile überwunden werden. Die Lösung von Nickelsalzen in aziden ILs ist sehr langsam. Der Nickelgehalt in IL55 beträgt nach 2 min 0,17 mol%, nach 30 min 0,53 mol%, und nach 24 h 1,45 mol% für den Komplex NiCl2(PPh3)2. Der Einfluss auf die Selektivität zu DMH liegt nur am Liganden PPh3, nicht jedoch an der Konzentration des Nickels. In dieser Arbeit wurde erstmals erfolgreich ein SILP-System zur Dimerisierung realisiert. Die Selektivität zu DMH lag damit bei nur 12 %. Die Azidität des Trägermaterials hat einen sehr starken Einfluss auf die Katalyse. Silica- und Alox-Materielien waren problematisch, Kohlenstoffträger besser geeignet. In SILP-Systemen war es erstmals möglich, Ni(II)-Katalysatoren in neutralen ILs wie [EMIM][FAP] einzusetzen. Für eine gleiche Aktivität war hier mehr EtAlCl2 nötig. Ebenfalls erstmals wurden SILP-Systeme zur Dimerisierung von Ethen in der Gasphase entwickelt. Es konnten über 50 h stabile Umsätze erzielt werden. Mit [C12C12IM][BF4] und [C12C12IM][ClO4] wurden zwei flüssigkristalline Dialkyl-substituierte ILs charakterisiert, die mit ca. 50°C (Schmelzpunk) und etwa 70°C (Klärpunkt) erstaunlich niedrige Phasen-übergangstemperaturen haben. Im flüssigkristallinen Bereich (SmA) verhalten sich beide ILs nicht-Newtonsch (pseudo-plastisch). Die Mesogenität von [C12C12IM][BF4] bleibt nach Lösung eines Katalysatorkomplexes und nach Immobilisierung der IL auf einem porösen Träger erhalten. Katalysatoren mit IL-ähnlichen Liganden und Alox- bzw. Kohlenstoffträger waren besonders geeignet. Das entwickelte System wurde in der Dimersierung von Ethen getestet. Bei 30°C und 1 ml/min Ethen wurde über t >3 h ein Umsatz von 30 % erreicht. Da der Einfluss des Co-Katalysators EtAlCl2 auf die Mesophase nur schwer zu bestimmen ist, wurden auch selbstaktive Nickelkomplexe auf Methallyl-Basis untersucht. Mit der Verbindung [(mall)Ni(dppanis)][SbF6] konnten in einem SILP-System in [EMIM][FAP] über 15 h stabile Umsätze gefahren werden. Die Ergebnisse der vorliegenden Arbeit stellen im Hinblick auf eine Verbesserung industrieller Verfahren zu größerer Effizienz und verantwortungsvollem Rohstoffeinsatz interessante Lösungsansätze dar. In einer schnelllebigen Zeit mit häufig wechselnden Bedürfnissen ist es wichtig, kurzfristig auf Marktanforderungen reagieren zu können. Flexible Reaktionssysteme auf Basis flüssigkristalliner Substanzen mit schnell umschaltbaren Selektivitäten scheinen ein Weg zu sein, dies in der Zukunft zu realisieren. Langfristig wird so ein wichtiger Beitrag zur Entstehung einer nachhaltigen Chemieindustrie geleistet

Interaction imaging with amplitude-dependence force spectroscopy

Knowledge of surface forces is the key to understanding a large number of processes in fields ranging from physics to material science and biology. The most common method to study surfaces is dynamic atomic force microscopy (AFM). Dynamic AFM has been enormously successful in imaging surface topography, even to atomic resolution, but the force between the AFM tip and the surface remains unknown during imaging. Here, we present a new approach that combines high accuracy force measurements and high resolution scanning. The method, called amplitude-dependence force spectroscopy (ADFS) is based on the amplitude-dependence of the cantilever's response near resonance and allows for separate determination of both conservative and dissipative tip-surface interactions. We use ADFS to quantitatively study and map the nano-mechanical interaction between the AFM tip and heterogeneous polymer surfaces. ADFS is compatible with commercial atomic force microscopes and we anticipate its wide-spread use in taking AFM toward quantitative microscopy

Long-alkyl-chain-derivatized imidazolium salts and ionic liquid crystals with tailor-made properties

A series of new 1,3-dialkylimidazolium salts with the general formula [CnCnIM][A] (for n = 12; A = PF6−, OTf−, NTf2−; for n = 10, 14, 16, and 18; A = BF4−, ClO4−) has been synthesized. The [C12C12IM][A] salts are ionic liquids at room temperature, whereas all [CnCnIM][BF4] and [CnCnIM][ClO4] (n = 10, 14, 16, 18) salts demonstrate a liquid crystalline phase at elevated temperatures that have a large mesophase window, which varies from 10 to 80 °C with increasing alkyl chain length. In particular, [C10C10IM][BF4] shows liquid crystalline behavior at room temperature and therefore is potentially suitable for application as a pre-organized reaction medium in synthesis and catalysis. Viscosity studies of [C16C16IM][BF4] and the corresponding perchlorate salt demonstrate strong non-Newtonian viscosity behavior for the liquid crystalline state of these ionic liquids

Emerging pharmacotherapy of tinnitus

Tinnitus, the perception of sound in the absence of an auditory stimulus, is perceived by about 1 in 10 adults, and for at least 1 in 100, tinnitus severely affects their quality of life. Because tinnitus is frequently associated with irritability, agitation, stress, insomnia, anxiety and depression, the social and economic burdens of tinnitus can be enormous. No curative treatments are available. However, tinnitus symptoms can be alleviated to some extent. The most widespread management therapies consist of auditory stimulation and cognitive behavioral treatment, aiming at improving habituation and coping strategies. Available clinical trials vary in methodological rigor and have been performed for a considerable number of different drugs. None of the investigated drugs have demonstrated providing replicable long-term reduction of tinnitus impact in the majority of patients in excess of placebo effects. Accordingly, there are no FDA or European Medicines Agency approved drugs for the treatment of tinnitus. However, in spite of the lack of evidence, a large variety of different compounds are prescribed off-label. Therefore, more effective pharmacotherapies for this huge and still growing market are desperately needed and even a drug that produces only a small but significant effect would have an enormous therapeutic impact. This review describes current and emerging pharmacotherapies with current difficulties and limitations. In addition, it provides an estimate of the tinnitus market. Finally, it describes recent advances in the tinnitus field which may help overcome obstacles faced in the pharmacological treatment of tinnitus. These include incomplete knowledge of tinnitus pathophysiology, lack of well-established animal models, heterogeneity of different forms of tinnitus, difficulties in tinnitus assessment and outcome measurement and variability in clinical trial methodology. © 2009 Informa UK Ltd.Fil: Langguth, Berthold. Universitat Regensburg; AlemaniaFil: Salvi, Richard. State University of New York; Estados UnidosFil: Elgoyhen, Ana Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentin

Flexible Strategies for Coping with Rainfall Variability: Seasonal Adjustments in Cropped Area in the Ganges Basin

One of the main manifestations of climate change will be increased rainfall variability. How to deal with this in agriculture will be a major societal challenge. In this paper we explore flexibility in land use, through deliberate seasonal adjustments in cropped area, as a specific strategy for coping with rainfall variability. Such adjustments are not incorporated in hydro-meteorological crop models commonly used for food security analyses. Our paper contributes to the literature by making a comprehensive model assessment of inter-annual variability in crop production, including both variations in crop yield and cropped area. The Ganges basin is used as a case study. First, we assessed the contribution of cropped area variability to overall variability in rice and wheat production by applying hierarchical partitioning on time-series of agricultural statistics. We then introduced cropped area as an endogenous decision variable in a hydro-economic optimization model (WaterWise), coupled to a hydrology-vegetation model (LPJmL), and analyzed to what extent its performance in the estimation of inter-annual variability in crop production improved. From the statistics, we found that in the period 1999–2009 seasonal adjustment in cropped area can explain almost 50% of variability in wheat production and 40% of variability in rice production in the Indian part of the Ganges basin. Our improved model was well capable of mimicking existing variability at different spatial aggregation levels, especially for wheat. The value of flexibility, i.e. the foregone costs of choosing not to crop in years when water is scarce, was quantified at 4% of gross margin of wheat in the Indian part of the Ganges basin and as high as 34% of gross margin of wheat in the drought-prone state of Rajasthan. We argue that flexibility in land use is an important coping strategy to rainfall variability in water stressed regions