Improved carbon dioxide absorption in double-charged ionic liquids.

Four divalent ionic liquids based on imidazolium cations with alkyl or ether functionalized side-chains were synthesised and characterized: 3,3'-(tetraethyleneglycol-1,11-diyl)bis(1-methyl-1H-imidazolium)bromide, [tetraEG(mim)2][Br]2, 3,3'-(tetraethyleneglycol-1,11-diyl)bis(1-methyl-1H-imidazolium)acetate, [tetraEG(mim)2][OAc]2, 1-butyl-3-methylimidazolium malonate, [C4mim]2[Mal], and 3-butyl-1-methylimidazolium glutarate, [C4mim]2[Glut]. Their densities vary between 1.1 and 1.5 g cm-3 and their viscosities between 0.2 and 4 Pa s at 353 K. We found that the molar volumes are not additive, especially in the case of the divalent ionic liquids based on the double-charged imidazolium cations, meaning that they cannot be predicted using common group contribution methods. The reason for this behaviour could be explained by the structure of the cations, which is dominated by intramolecular hydrogen bonding. The carboxylate-based divalent ionic liquids absorb reversibly large quantities of carbon dioxide following a chemical mechanism described before. An improved 1 : 1 stoichiometry is achieved both in a double-charged imidazolium acetate ionic liquid and in imidazolium carboxylate salts with double charged anions. This behaviour places these ionic liquids amongst the best performing for carbon dioxide absorption.

Influence of the Use of an Ionic Liquid as Pre-Hydrodistillation Maceration Medium on the Composition and Yield of Cannabis sativa L. Essential Oil.

Cannabis sativa L. is a multi-purpose crop, whose resilience, adaptability and soil-enriching properties make it a low-impact production. In the last years, the cultivation of the "industrial" hemp varieties (THC < 0.2%) has been promoted by many Countries, opening a whole new market of hemp-derived products, such as its essential oil (EO). Its distillation might represent an effective method to exploit a residue of the hemp fiber production (flowers), complying with the guidelines of the circular economy. In the present work, different concentrations of an ionic liquid (IL; 1,3-dimethyl-1H-imidazol-3-ium dimethylphosphate) have been studied as a pre-hydrodistillation maceration medium. The EO yields have been evaluated, and their compositions have been analyzed by GC-EIMS. The use of 100% and 90% IL concentrations gave a hydrodistillation yield increment of 250% and 200%, respectively. The 200% yield increase was maintained when the 100% IL was recycled after the hydrodistillation. The lower IL concentrations incremented the cannabinoid and oxygenated sesquiterpene contents, while the opposite was true for sesquiterpene hydrocarbons. The proposed IL-enhanced hydrodistillation medium applied to hemp, studied for the first time in the present work, might be used to both (i) noteworthy increment the hydrodistillation yield and (ii) modulate the obtained EO composition based on the desired final product.

Nanoscale PDA disassembly in ionic liquids: structure-property relationships underpinning redox tuning.

Nanoscale disassembly of mussel-inspired polydopamine (PDA) in ionic liquids (ILs) was recently shown to induce an electron paramagnetic resonance (EPR)-detectable reorganization of free radical centers in the resulting nanoparticles (NPs) in an IL-controlled manner. Herein, we report electrical impedance spectroscopy (EIS) data showing that PDA NPs produced by suspending samples obtained in Tris and bicarbonate buffer (PDA-T and PDA-C) in different ILs display different redox activity as a result of structural control combined with IL-surface interactions. In particular, susceptibility to oxidation was found to correlate closely with the spin density in an ion pair-tunable fashion in ILs. Structural control over free radical properties and redox behavior of PDA NPs in ILs opens novel perspectives for the rational design of functional nanovectors of possible interest for drug delivery and theranostic applications.

Unexpected Intrinsic Lability of Thiol-Functionalized Carboxylate Imidazolium Ionic Liquids.

New thiol-functionalized carboxylate ionic liquids (ILs), varying both for the cation and for the anion structures, have been prepared as new potential redox switching systems by reacting either 3-mercapto propionic acid (3-MPA) or N-acetyl-cysteine (NAC) with commercially available methyl carbonate ILs. Different ratios of thiol/disulfide ILs were obtained depending both on the acid employed in the neutralization reaction and on the reaction conditions used. Surprisingly, the imidazolium ILs displayed limited thermal stability which resulted in the formation of an imidazole 2-thione and a new sulfide ionic liquid. Conversely, the formation of the imidazole 2-thione was not observed when phosphonium disulfide ILs were heated, thus confirming the involvement of the imidazolium ring in an unexpected side reaction. An insight into the mechanism of the decomposition has been provided by means of DFT calculations.

Remarkable Effect of [Li(G4)]TFSI Solvate Ionic Liquid (SIL) on the Regio- and Stereoselective Ring Opening of α-Gluco Carbasugar 1,2-Epoxides.

Carba analogues of biologically relevant natural carbohydrates are promising structures for the development of future drugs endowed with enhanced hydrolytic stability. An open synthetic challenge in this field is the optimization of new methodologies for the stereo- and regioselective opening of α-gluco carbasugar 1,2-epoxides that allow for the preparation of pseudo mono- and disaccharides of great interest. Therefore, we investigated the effect of Lewis acids and solvate ionic liquids (SILs) on the epoxide ring opening of a model substrate. Of particular interest was the complete stereo- and regioselectivity, albeit limited to simple nucleophiles, toward the desired C(1) isomer that was observed using LiClO4. The results obtained with SILs were also remarkable. In particular, Li[NTf2]/tetraglyme ([Li(G4)]TFSI) was able to function as a Lewis acid and to direct the attack of the nucleophile preferentially at the pseudo anomeric position, even with a more complex and synthetically interesting nucleophile. The regioselectivity observed for LiClO4 and [Li(G4)]TFSI was tentatively ascribed to the formation of a bidentate chelating system, which changed the conformational equilibrium and ultimately permitted a trans-diaxial attack on C(1). To the best of our knowledge, we report here the first case in which SILs were successfully employed in a ring-opening process of epoxides.

Divergent Syntheses of ( Z)-3-Alkylideneisobenzofuran-1(3 H)-ones and 1 H-Isochromen-1-ones by Copper-Catalyzed Cycloisomerization of 2-Alkynylbenzoic Acids in Ionic Liquids.

The cycloisomerization of readily available 2-alkynylbenzoic acids 1 in ionic liquids (ILs) as recyclable reaction media has been studied under the catalytic action of CuCl2. With substrates bearing an aryl group on the triple bond, a mixture of ( Z)-3-alkylideneisobenzofuran-1(3 H)-ones (from 5- exo- dig cyclization) and 1 H-isochromen-1-ones (from 6- endo- dig cyclization) was observed in 1-ethyl-3-methylimidazolium ethyl sulfate (EmimEtSO4), while the reaction turned out to be selective toward the formation of the isobenzofuranone only using N-ethyl- N-methylmorpholinium dicyanamide [Mor1,2N(CN)2] as the solvent. The 5-membered product was also obtained selectively when the substrate bearing a terminal triple bond was employed, either in EmimEtSO4 or Mor1,2N(CN)2. On the other hand, 2-alkynylbenzoic acids bearing an alkyl or an alkenyl group on the triple bond selectively led, in EmimEtSO4, to 1 H-isochromen-1-ones, while the formation of a regioisomeric mixture was observed in Mor1,2N(CN)2. In any case, the solvent/catalyst system could be easily recycled after extraction of the product from the reaction mixture with diethyl ether. DFT calculations have been carried out to clarify the reaction outcome depending on reaction conditions, and the structures of two representative products, which are ( Z)-3-benzylideneisobenzofuran-1(3 H)-one and ( Z)-3-(4-methylphenylmethylidene)isobenzofuran-1(3 H)-one, have been confirmed by X-ray diffraction analysis.

Modifying bis(triflimide) ionic liquids by dissolving early transition metal carbamates.

The authors report the first modification of ionic liquids with metal carbamates. A selection of homoleptic N,N-dialkylcarbamates of group 4 and 5 metals, M(O2CNR2)n, were dissolved in bis(trifluoromethylsulfonyl)imide-based ionic liquids, i.e. [bmim][Tf2N] and [P(oct)4][Tf2N], at 293 K. The resulting solutions were characterized by means of IR, UV and NMR spectroscopy, and the data were compared to those of the respective metal compounds. Notably, the dissolution process did not proceed with the release of any of the original carbamato ligands, thus preserving the intact coordination frame around the metal centre. The solvation process of Ti(O2CNiPr2)4, as a model species, in [bmim][Tf2N] was rationalized by DFT calculations. As a comparative study, solutions of NbF5 and MCl5 (M = Nb, Ta) in [bmim][Tf2N] were also investigated, revealing the possible occurrence of solvent anion coordination to the metal centres.

Formation, Oxidation, and Fate of the Breslow Intermediate in the N-Heterocyclic Carbene-Catalyzed Aerobic Oxidation of Aldehydes.

The reaction paths and intermediate structures related to the formation of the Breslow intermediate and its oxidation along the oxidative/oxygenative lanes have been studied from a mechanistic point of view, with the support of gas-phase and computational studies. The results confirm the occurrence of a single-electron transfer from the Breslow intermediate to the molecular oxygen with formation of a radical couple that recombines either as a peroxide anion 7' to afford the aldehyde-to-carboxylic acid product or as a hydroperoxy derivative 7″ that evolved into an electrophilic acyl azolium, opening to the aldehyde-to-ester conversion. Steric factors enter into determining the different reactivity. All of the intermediates of both catalytic paths have been observed and characterized under mass spectrometric conditions. In particular, for the imidazoline catalyst, the (+)ESI-MS/(MS) detection of the genuine Breslow intermediate was made possible in virtue of its limited reactivity. Mechanistic aspects of the N-heterocyclic carbenes catalyzed aerobic oxidation of aldehydes shares important similarities with that one of the recently revisited benzoin condensation.

Divergent syntheses of iodinated isobenzofuranones and isochromenones by iodolactonization of 2-alkynylbenzoic acids in ionic liquids.

The regiochemical outcome of the iodolactonization of 2-alkynylbenzoic acids, carried out at 100 °C in ionic liquids (ILs) as unconventional solvents and with molecular iodine as the iodine source, in the absence of external bases, was found to be strongly dependent on the nature of the IL medium. In particular, while the use of N-ethyl-N-methylmorpholinium dicyanamide (Mor1,2N(CN)2) promoted the stereoselective formation of (E)-3-(iodomethylene)isobenzofuran-1(3H)-ones, through an anti-5-exo-dig cyclization route, the use of 1-ethyl-3-methylimidazolium ethyl sulfate (EmimEtSO4) tended to favor the 6-endo-dig cyclization mode, with preferential or selective formation of 4-iodo-1H-isochromen-1-ones. In any case, the IL solvent could be easily recycled after extraction of the product from the reaction mixture with diethyl ether. DFT calculations have been carried out to clarify the role of the IL's nature in favoring either the anti-5-exo-dig cyclization route or the 6-endo-dig mode. In the case of iodocyclization of 2-ethynylbenzoic acid, only the 5-exo-dig mode was observed in both EmimEtSO4 and Mor1,2N(CN)2 solvents. The structures of two representative products have been confirmed by X-ray diffraction analysis.

Auto-Tandem Catalysis in Ionic Liquids: Synthesis of 2-Oxazolidinones by Palladium-Catalyzed Oxidative Carbonylation of Propargylic Amines in EmimEtSO4.

A convenient carbonylative approach to 2-oxazolidinone derivatives carried out using an ionic liquid (1-ethyl-3-methylimidazolium ethyl sulfate, EmimEtSO4) as the solvent is presented. It is based on the sequential concatenation of two catalytic cycles, both catalyzed by the same metal species (auto-tandem catalysis): the first cycle corresponds to the oxidative monoaminocarbonylation of the triple bond of propargylic amines to give the corresponding 2-ynamide intermediates, while the second one involves the cyclocarbonylation of the latter to yield 2-(2-oxooxazolidin-5-ylidene)-acetamides. Reactions are carried out using a simple catalytic system consisting of PdI2 in conjunction with an excess of KI, and the catalyst/solvent system could be recycled several times without appreciable loss of activity after extraction of the organic product with Et2O.

Dissolution of metal salts in bis(trifluoromethylsulfonyl)imide-based ionic liquids: studying the affinity of metal cations toward a "weakly coordinating" anion.

Despite the weakly coordinating ability of the bis(trifluoromethylsulfonyl)imide anion ([Tf2N](-)) the corresponding ionic liquids (ILs) are able to dissolve relevant amounts of metal salts having the same anion, M[Tf2N]x. To better understand the metal dissolution process we evaluated the interaction ability of a set of metal cations (Y(III), Al(III), Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Li(I), and Na(I)) toward the [Tf2N](-) anion measuring the relative aptitude to give the corresponding anionic monocharged complex, [M(Tf2N)x+1](-) using the ESI-MS technique. UV-vis and NMR measurements were carried out to verify the consistence between the liquid and the gas phase. Density functional theory calculations have been used to identify the metal-containing species and determine their relative stability. An interesting correlation between interaction ability and chemical properties (Lewis acidity) was found.

Alkylation of Methyl Linoleate with Propene in Ionic Liquids in the Presence of Metal Salts.

Vegetable oils and fatty acid esters are suitable precursor molecules for the production of a variety of bio-based products and materials, such as paints and coatings, plastics, soaps, lubricants, cosmetics, pharmaceuticals, printing inks, surfactants, and biofuels. Here, we report the possibility of using Lewis acidic ionic liquids (ILs) to obtain polyunsaturated ester dimerization-oligomerization and/or, in the presence of another terminal alkene (propene), co-polymerization. In particular, we have tested the Lewis acidic mixtures arising from the addition of a proper amount of GaCl3 (Χ > 0.5) to two chloride-based (1-butyl-3-methylimidazolium chloride, [bmim]Cl, and 1-butylisoquinolium chloride, [BuIsoq]Cl) or by dissolution of a smaller amount of Al(Tf2N)3 (Χ = 0.1) in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][Tf2N]. On the basis of product distribution studies, [bmim][Tf2N]/Al(Tf2N)3 appears the most suitable medium in which methyl linoleate alkylation with propene can compete with methyl linoleate or propene oligomerization.

A recyclable and base-free method for the synthesis of 3-iodothiophenes by the iodoheterocyclisation of 1-mercapto-3-alkyn-2-ols in ionic liquids.

The first example of an iodocyclisation reaction made recyclable by the use of an ionic liquid as the reaction medium is reported. Readily available 1-mercapto-3-alkyn-2-ols were smoothly converted into the corresponding 3-iodothiophenes (50-81% yields, 10 examples) when allowed to react with iodine (1-2 equiv.) in a proper ionic liquid, such as 1-ethyl-3-methylimidazolium ethyl sulfate (EmimEtSO4), as the solvent under mild reaction conditions (25 °C) and in the absence of an external base. The reaction medium can be recycled several times without significantly affecting the reaction outcome. Theoretical calculations have also been performed to investigate the role of the ionic liquid anion in the reaction.

Ecotoxicity of pristine graphene to marine organisms.

The ecotoxicity of pristine graphene nanoparticles (GNC1, PGMF) in model marine organisms was investigated. PGMF resulted more toxic than GNC1 to the bioluminescent bacterium Vibrio fischeri and the unicellular alga Dunaliella tertiolecta on the basis of EC50 values (end-points: inhibition of bioluminescence and growth, respectively). No acute toxicity was demonstrated with respect to the crustacean Artemia salina although light microscope images showed the presence of PGMF and GNC1 aggregates into the gut; a 48-h exposure experiment revealed an altered pattern of oxidative stress biomarkers, resulting in a significant increase of catalase activities in both PGMF and GNC1 1mg/L treated A. salina and a significant increase of glutathione peroxidase activities in PGMF (0.1 and 1mg/L) treated A. salina. Increased levels of lipid peroxidation of membranes was also observed in PGMF 1mg/L exposed A. salina.

Computational studies on organic reactivity in ionic liquids.

Computational studies on organic reactions in ionic liquids (ILs) are analysed from different points of view. Important information about reaction mechanisms in ILs has been obtained from these studies although the theoretical approaches are still not able to give an exhaustive picture of the chemical processes occurring in ionic media. Challenges and perspectives of this investigation field are discussed and the fundamental role played by experimental results in the development of this intriguing sector is pointed out.

Coordination environment of highly concentrated solutions of Cu(II) in ionic liquids through a multidisciplinary approach.

The coordination environment around Cu(II) in highly concentrated solutions of copper(II) salts (CuCl(2) and Cu(Tf(2)N)(2)) in two pure ionic liquids bearing the same anion, namely, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf(2)N]) and 1-butyl-3-methylimidazolium chloride ([bmim]Cl), is investigated by X-ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, EPR spectroscopy and DFT calculations. Moreover, the electrochemical behavior of these mixtures is studied. Whereas reversible reduction of Cu(II) to copper metal can be observed in the 1:1 [bmim][Tf(2)N]:Cu(Tf(2)N)(2) solution, 2:1 and 1:1 [bmim]Cl:CuCl(2) mixtures showed one-electron reduction of Cu(II) to Cu(I) with formation of a permanent deposit of CuCl. XPS, UV/Vis and EPR spectra as well as DFT calculations suggest the formation in [bmim]Cl of dynamic coordination complexes arising from the interaction between CuCl(2) and [bmim](+)Cl(-). The two long-lived situations are probably trigonal and deformed tetrahedral copper(II) chloride coordination complexes ([CuCl(3)](-) and [CuCl(4)](2-), respectively).

Development of a stereoselective Ugi reaction starting from an oxanorbornene ß-amino acid derivative.

We have synthesised a novel oxanorbornene ß-aminoacid derivative and employed it in a stereoselective Ugi reaction. Hypothesis regarding the mechanism taking place during the reaction have been made and validated through the determination of the relative and absolute configuration of the Ugi adducts. Use of the correct choice of solvents can increase stereoselection. The resulting bicyclic peptidomimetics can be used as a novel class of pluripotent substrates to be elaborated according to the synthetic strategies previously elaborated in our laboratories.

Interface properties of ionic liquids containing metal ions: features and potentialities.

Interfaces and surfaces are the regions where important events happen: catalysis, molecular recognition, charge transfer, polymerization, and many other critical processes take place at the boundary between one medium and another. In this article we discuss the interface (liquid/air) properties of ionic liquids (ILs) containing dissolved metal ions with the aim to show the possibility to use metal salts to transform ILs and their surfaces into engineered liquid supports to apply in material sciences, separation procedures or to use as optical devices.

Chiral ionic liquid-mediated photochirogenesis. Enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid.

Enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid (AC-H) and its lithium salt (AC-Li) in chiral ionic liquid (CIL), (R)-1-(2,3-dihydroxypropyl)-3-methylimidazolium acetate {[(R)-GLYMI][AcO]}, gave a mixture of two head-to-tail (HT) and two head-to-head (HH) cyclodimers in HT/HH ratios of 1.3-1.7 (for AC-H) and 2.2-4.3 (for AC-Li) with low enantiomeric excesses (ee) of 0-3% for chiral syn-HT and anti-HH dimers. In contrast, irradiation of AC-H in an aqueous solution, containing cucurbit[8]uril (CB[8]) as a host and [(R)-GLYMI][AcO] or [(R)-GLYMI][Tf(2)N] as a modifier of CB portals, afforded the HH dimers in 91-99% selectivity, although the anti-HH dimer was totally racemic. Interestingly, irradiation of AC-H in a dichloromethane solution, containing [(R)-GLYMI][AcO] as a chiral template, led to the formation of the HH-dimers in 98% selectivity with chiral anti-HH dimer in -14% ee, presumably by the dual ligation of two ACs to a CIL through electrostatic and hydrogen-bonding interactions.

Acute toxicity and biodegradability of N-alkyl-N-methylmorpholinium and N-alkyl-DABCO based ionic liquids.

N-alkyl-N-methylmorpholinium and N-alkyl substituted 1,4-diazabicyclo[2.2.2]octane (DABCO) based ionic liquids (ILs), N-alkyl-DABCO, bearing short alkyl chains are characterised by a low toxicity to Vibrio fischeri, although toxicity significantly increases on increasing the alkyl chain length. Alkyl chain length affects also biodegradability in the 28 days tests; the higher level of biodegradation was found in both the series in the case of the ethyl (C2) derivatives. In the case of N-ethyl DABCO based IL, although biodegradability is still around 40%, and consequently this IL cannot be classified as "readily biodegradable", this value is similar to the more biodegradable functionalized imidazolium based ILs.