Supported Ionic Liquid Phase (SILP) Allylic Alkylation of Amines in Continuous Flow
We present the use of Pd-complex-containing supported ionic liquid phases (SILPs) as a novel approach for continuous-flow allylic alkylation of N-nucleophiles. This immobilization strategy gave simple access to air-tolerating catalyst frameworks, providing rapid and convenient access to various achiral and chiral N-allylation products. Under optimized conditions, the flow-reaction could be maintained for 3.5 hours with constant product output; meanwhile, only a marginal 0.7 wt % of ionic liquid leaching and no detectable palladium-complex leaching could be observed.
Applying ionic liquids as oil additives for gearboxes: Going beyond the state of the art by bridging the nano-scale and component level
Ionic liquids (ILs) have been used effectively in many applications for reducing problems related to friction and wear. In this work, the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied. Two halide-free ILs: P8881(BuO)2PO−2 (1) and P8881(MeO)2PO−2 (2), which are blended at 5 wt% each into a standard non-additivated FVA2 base oil (BO) are examined. Their solid—liquid interface, friction and load-carrying capacity, and wear (scuffing) behavior are studied on the nano-, lab-, and component-scale, respectively, at a different range of temperature and loading conditions by using the atomic force microscopy (AFM), Schwing—Reib—Verschleiß (SRV) friction tests, and Brugger tests, as well as forschungsstelle für zahnräder und getriebebau (FZG) back-to-back gear test rig. The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO. Similarly, IL blends demonstrate a very stable coefficient of friction (COF) of around 0.16, which even decreases with increasing test temperatures ranging from 40 to 120 °C. A clear reduction in COF up to 25% is achieved by adding only 5 wt% of the investigated ILs in the BO, and the Brugger tests also show a pronounced enhancement of load-carrying capacity. Finally, on the component-scale, a significant improvement in gear scuffing performance has been observed for both used IL blends. A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy (TEM) revealed the formation of a phosphate (P—O)-based amorphous tribo-chemical layer of about 20 nm thickness. Therefore, this work may present an approach for ILs to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties, making them an alternative lubricant solution for high load-carrying gearbox applications.
Extraction techniques for bioactive compounds of cannabis
Aitor Sainz Martinez, Olga Lanaridi, Kristof Stagel, Heidi Halbwirth, Michael Schnürch, Katharina Bica-Schröder*
Nat. Prod. Rep. (2023) Advance Article
Historically, cannabis has always constituted a component of the civilized world; archaeological discoveries indicate that it is one of the oldest crops, while, up until the 19th century, cannabis fibers were extensively used in a variety of applications, and its seeds comprised a part of human and livestock nutrition. Additional evidence supports its exploitation for medicinal purposes in the ancient world. The cultivation of cannabis gradually declined as hemp fibers gave way to synthetic fibers, while the intoxicating ability of THC eventually overshadowed the extensive potential of cannabis. Nevertheless, the proven value of certain non-intoxicating cannabinoids, such as CBD and CBN, has recently given rise to an entire market which promotes cannabis-based products. An increase in the research for recovery and exploitation of beneficial cannabinoids has also been observed, with more than 10 000 peer-reviewed research articles published annually. In the present review, a brief overview of the history of cannabis is given. A look into the classification approaches of cannabis plants/species as well as the associated nomenclature is provided, followed by a description of their chemical characteristics and their medically valuable components. The application areas could not be absent from the present review. Still, the main focus of the review is the discussion of work conducted in the field of extraction of valuable bioactive compounds from cannabis. We conclude with a summary of the current status and outlook on the topics that future research should address.
Photocatalyst-free hydroacylations of electron-poor alkenes and enones under visible-light irradiation
Org. Biomol. Chem. (2022) 20, 7245
Herein we present a photocatalyst- and additive-free radical hydroacylation of electron-poor double bonds under mild reaction conditions. Using 4-acyl-Hantzsch ester radical reservoirs, various Michael acceptors, enones and para-quinone methide substrates could be used. The protocol enabled further derivatizations and it could also be extended to a few unactivated alkenes. Moreover, the nature of the radical process was also investigated.
Surface-active ionic liquids: A review
J. Mol. Liq. (2022) 347, 118160
The combination of water and surface-active ionic liquids provides a unique reaction medium, facilitating aggregation and micellization of the ionic liquid to allow for chemical reactions in bulk water. With a growing focus on sustainable technologies, ionic liquids have emerged as tunable solvents for multiple applications but are often too viscous or expensive for use as bulk solvent. As a result, there has been a tremendous increase in interest in the behavior of ionic liquids in the presence of water. It has already been shown that certain ionic liquids act as surfactants in aqueous solutions, enabling the combination of both solvents to afford solvent systems with unique properties. Ultimately, surface-active ionic liquids in water give rise to distinct chemistry of their own compared to traditional molecular solvents, and thus their use is rapidly growing. In this review, the general structure of surface-active ionic liquids and the key features that allow aggregation in water to give micellar structures is discussed. Furthermore, characterization techniques of the formed micelles are presented, discussing aggregation and possible methods of studying micellization behavior. Finally, current applications of surface-active ionic liquids across all fields of chemistry, from traditional organic chemistry to nanoparticle synthesis are presented.
Liquid- and Solid-based Separations Employing Ionic Liquids for the Recovery of Platinum Group Metals Typically Encountered in Catalytic Converters: A Review
ChemSusChem (2022) 15, e202102262
The wide application range and ascending demand for platinum group metals combined with the progressive depletion of their natural resources renders their efficient recycling a very important and pressing matter. Primarily environmental considerations associated with state-of-the-art recovery processes have shifted the focus of the scientific community toward the investigation of alternative recycling approaches. Within this context, ionic liquids have gained considerable attention in the last two decades chiefly sparked by properties such as tunabilty, low-volatility, and relatively easy recyclability. In this review an understanding of the state-of-the-art processes, including their drawbacks and limitations, is provided. The core of the discussion is focused on platinum group metal recovery with ionic liquid-based systems. A brief insight in some environmental considerations related to ionic liquids is also provided while some discussion on research gaps, common misconceptions related to ionic liquids and outlook on unresolved issues could not be absent from this review.
Benign recovery of platinum group metals from spent automotive catalysts using choline-based deep eutectic solvents
Green Chem. Lett. Rev. (2022) 15, 405
The recovery of platinum group metals (PGMs) from secondary raw materials has become a topic ofcritical importance mainly due to the gradual depletion of their natural resources and theircontinuously increasing demand. However, the insufficient recovery of PGMs coupled with thenegative environmental impact of the state-of-the-art recycling procedures mandate theinvestigation and development of alternative recovery processes that will assist in minimizing oreven eliminating these drawbacks. Herein, we present a process for the extraction of platinumgroup metals from spent car catalysts relying on benign deep eutectic solvents (DESs). It isdemonstrated that with addition of small amounts of an oxidizing agent, deep eutectic solventscan act as excellent leaching media for the quantitative extraction of platinum group metals.Despite its inertness towards acidic and oxidizing agents, Rh can be leached in a considerableamount which can be further increased by physical pre-treatment of the spent car catalystmaterial.
Sterically Demanding Flexible Phosphoric Acids for Constructing Efficient and Multi-Purpose Asymmetric Organocatalysts
Angew. Chem. Int. Ed. (2022) 61, e202202189
Herein, we present a novel approach for various asymmetric transformations of cyclic enones. The combination of readily accessible chiral diamines and sterically demanding flexible phosphoric acids resulted in a simple and highly tunable catalyst framework. The careful optimization of the catalyst components led to the identification of a particularly powerful and multi-purpose organocatalyst, which was successfully applied for asymmetric epoxidations, aziridinations, aza-Michael-initiated cyclizations, as well as for a novel Robinson-like Michael-initiated ring closure/aldol cyclization. High catalytic activities and excellent stereocontrol was observed for all four reaction types, indicating the excellent versatility of our catalytic system. Furthermore, a simple change in the diamine’s configuration provided easy access to both product antipodes in all cases.
Photocatalytic Hydroalkylation of Aryl-Alkenes
J. Org. Chem. (2022) 87, 11042
Here, we present a visible light-catalyzed hydroalkylation of aryl-alkenes affording C–C bonds using aryl-alkenes and alkyl iodides. We demonstrate the formation of various hydroalkylation products in excellent yields, with primary, secondary, and tertiary alkyl iodides being tolerated in the reaction. Mechanistic experiments reveal a pathway consisting of halogen atom transfer followed by a radical-polar crossover mechanism delivering the desired hydroalkylation products.
Halide-Free Continuous Synthesis of Hydrophobic Ionic Liquids
ACS Sustainable Chem. Eng. (2022) 10, 11215
Herein, we present a novel approach for the halide-free, continuous-flow preparation of hydrophobic ionic liquids (ILs) relying on the bis(trifluoromethanesulfonyl)imide (bistriflimide, NTf2–) anion. The simple yet fast two-step synthetic route, which involves the formation of different alkyl bistriflimides (R4NTf2), followed by the quaternization with an amine nucleophile, led to the desired ILs in high yields and excellent purities without any byproduct formation. The variable alkyl chain (R4) length and the broad range of the applicable nucleophiles (R1R2R3N) offer considerable flexibility to the synthetic protocol. The quaternization can be performed under solvent-free conditions; moreover, the homogeneous nature of these reactions allows the application of modern continuous-flow technologies. Given these advantages, the methodology can afford not just a fast and efficient alternative for the conventional synthesis of such compounds with reduced waste water production but their negligible halide content might provide a significantly broader application range of the IL products, especially for the field of materials science.
Continuous Formation of Limonene Carbonates in Supercritical Carbon Dioxide
Philipp Mikšovsky, Elias N. Horn, Shaghayegh Naghdi, Dominik Eder, Michael Schnürch, Katharina Bica-Schröder*
Org. Process Res. Dev. (2022) 26, 2799
We present a continuous flow method for the conversion of bioderived limonene oxide and limonene dioxide to limonene carbonates using carbon dioxide in its supercritical state as a reagent and sole solvent. Various ammonium- and imidazolium-based ionic liquids were initially investigated in batch mode. For applying the best-performing and selective catalyst tetrabutylammonium chloride in continuous flow, the ionic liquid was physisorbed on mesoporous silica. In addition to the analysis of surface area and pore size distribution of the best-performing supported ionic liquid phase (SILP) catalysts via nitrogen physisorption, SILPs were characterized by diffuse reflectance infrared Fourier transform spectroscopy and thermogravimetric analysis and served as heterogeneous catalysts in continuous flow. Initially, the continuous flow conversion was optimized in short-term experiments resulting in the desired constant product outputs. Under these conditions, the long-term behavior of the SILP system was studied for a period of 48 h; no leaching of catalyst from the supporting material was observed in the case of limonene oxide and resulted in a yield of 16%. For limonene dioxide, just traces of leached catalysts were detected after reducing the catalyst loading from 30 to 15 wt %, thus enabling a constant product output in 17% yield over time.
Counterion-Enhanced Pd/Enamine Catalysis: Direct Asymmetric α-Allylation of Aldehydes with Allylic Alcohols by Chiral Amines and Achiral or Racemic Phosphoric Acids
J. Org. Chem. (2021) 86, 1, 850
We report a straightforward and efficient Pd/enamine catalytic procedure for the direct asymmetric α-allylation of branched aldehydes. The use of simple chiral amines and easily prepared achiral or racemic phosphoric acids, together with a suitable Pd-source resulted in a highly active and enantioselective catalyst system for the allylation of various α-branched aldehydes with different allylic alcohols. The reported procedure could provide an easy access to both product antipodes. Furthermore, two possible orthogonal derivatizations of the enantioenriched aldehydes were performed without any decrease in enantioselectivity.
Toward the Recovery of Platinum Group Metals from a Spent Automotive Catalyst with Supported Ionic Liquid Phases
ACS Sustainable Chem. Eng. (2021) 9, 375
We present a novel approach for the separation and recovery of Pt and Pd leached from a spent automotive catalyst relying on conventional and polymerized supported ionic liquid phases (SILPs and polySILPs, respectively). A variety of parameters with possible effects on the separation behavior, namely, acidity and concentration of the platinum group metal (PGM) containing solution, as well as different SILP and polySILP loadings, were evaluated for the separation of PGMs in the presence of high concentrations of Al, Fe, Zn, and Ce. The polySILP material demonstrated the ability to separate the PGMs from major accompanying interferences in a single separation step, while problems arising from ionic liquid leaching in the case of SILPs could be avoided. Moreover, the use of supported ionic liquid phases allowed the drastic reduction of the amount of required ionic liquid compared to conventional liquid–liquid separation, while avoiding problems arising from emulsion formation. Subsequent stripping experiments lead to further purification of the PGMs and finally desorption from the solid material into a pure solution. Eventually, the concept of chemisorbed polySILPs provides a new and convenient approach for the recycling of platinum group metals.
A Combined Deep Eutectic Solvent–Ionic Liquid Process for the Extraction and Separation of Platinum Group Metals (Pt, Pd, Rh)
Molecules (2021) 26, 7204
Recovery of platinum group metals from spent materials is becoming increasingly relevant due to the high value of these metals and their progressive depletion. In recent years, there is an increased interest in developing alternative and more environmentally benign processes for the recovery of platinum group metals, in line with the increased focus on a sustainable future. To this end, ionic liquids are increasingly investigated as promising candidates that can replace state-of-the-art approaches. Specifically, phosphonium-based ionic liquids have been extensively investigated for the extraction and separation of platinum group metals. In this paper, we present the extraction capacity of several phosphonium-based ionic liquids for platinum group metals from model deep eutectic solvent-based acidic solutions. The most promising candidates, P66614Cl and P66614B2EHP, which exhibited the ability to extract Pt, Pd, and Rh quantitively from a mixed model solution, were additionally evaluated for their capacity to recover these metals from a spent car catalyst previously leached into a choline-based deep eutectic solvent. Specifically, P66614Cl afforded extraction of the three target precious metals from the leachate, while their partial separation from the interfering Al was also achieved since a significant amount (approx. 80%) remained in the leachate.
Combined ionic liquid and supercritical carbon dioxide based dynamic extraction of six cannabinoids from Cannabis sativa L.
Green Chem. (2021) 23, 10079
The potential of supercritical CO2 and ionic liquids (ILs) as alternatives to traditional extraction of natural compounds from plant material is of increasing importance. Both techniques offer several advantages over conventional extraction methods. These two alternatives have been separately employed on numerous ocassions, however, until now, they have never been combined for the extraction of secondary metabolites from natural sources, despite properties that complement each other perfectly. Herein, we present the first application of an IL-based dynamic supercritical CO2 extraction of six cannabinoids (CBD, CBDA, Δ9-THC, THCA, CBG and CBGA) from industrial hemp (Cannabis sativa L.). Various process parameters were optimized, i.e., IL-based pre-treatment time and pre-treatment temperature, as well as pressure and temperature during supercritical fluid extraction. In addition, the impact of different ILs on cannabinoid extraction yield was evaluated, namely, 1-ethyl-3-methylimidazolium acetate, choline acetate and 1-ethyl-3-methylimidazolium dimethylphosphate. This novel technique exhibits a synergistic effect that allows the solvent-free acquisition of cannabinoids from industrial hemp, avoiding further processing steps and the additional use of resources. The newly developed IL-based supercritical CO2 extraction results in high yields of the investigated cannabinoids, thus, demonstrating an effective and reliable alternative to established extraction methods. Ultimately, the ILs can be recycled to reduce costs and to improve the sustainability of the developed extraction process.
Dynamic streamlined extraction of iridoids, anthocyanins and lipids from haskap berries
LWT (2021) 138, 110633
The European Commission recently authorized the placing of haskap (Lonicera caerulea L.) berries as a novel food on the EU market. It has been suggested that these berries have several health beneficial properties, due to their considerable content of highly valuable secondary metabolites, such as anthocyanins, phenolic acids, iridoids and fatty acids. Herein, we report a dynamic streamlined extraction process for iridoids and anthocyanins with supercritical carbon dioxide and ethanol as modifier. In particular, we have focused on the iridoids loganic acid and loganin, as well as on different hydroxylation patterns of the anthocyanins. The developed multiple step extraction process leads to initial separation of lipids at low ethanolic concentrations (1 vol%), followed by partial extraction of iridoids at 10 vol% ethanol and ultimately to combined extraction of iridoids and anthocyanins at higher ethanol amounts (>10 vol%). The sequential extraction can be performed in a closed system by automated variation of two innocuous solvents, but uses higher solvent amounts. In comparison to conventional ethanolic extraction, the dynamic streamlined yielded 97% of iridoids and about 7% more anthocyanins.
Purification of anthocyanins from grape pomace by centrifugal partition chromatography
J. Mol. Liq. (2021) 326, 115324
The purpose of this work is to integrate the extraction of anthocyanins from grape pomace with a sequential purification process using an aqueous two-phase system (ATPS), and scaled-up in centrifugal partition chromatography (CPC) using as a common solvent the protic ionic liquids based on ethanolammonium and sulfuric acid. The choice of the best operational condition was performed through the selectivity (ratio between the concentration of anthocyanin and total phenolic compounds), which allowed the purification of anthocyanins of 16.36 fold (S/L = 55 mg.mL−1; 35 °C; [PIL] = 12.5%), and 2.21 fold (S/L = 55 mg.mL−1; 25 °C; [PIL] = 12.5%). ATPS based on protic ionic liquid and acetonitrile purified the anthocyanins between 19.30 and 23.88 fold at 25 °C and pressure atmospheric. At 25 °C (limitation of equipment), CPC increased the purification factor to 41.88, although with the decrease of anthocyanin recovery. However, the best operational condition depends on the anthocyanins application.