Search

The behavior of [H.sub.2]S in several ionic liquids (ILs) is investigated. Results show extremely high solubilities in ILs suggesting the occurrence of specific interactions between H2S and the examined ILs.

Electrospray ionization mass spectrometry (ESI-MS) applied to ionic liquids is used to analyze the relative strength of anion-cation interaction inside the ionic liquids. The low-energy collision dissociation of loosely bonded homologous and mixed complexes has provided some vital information about the magnitude of these interactions.

Michler's ketone (MK) and tetracyanoethene (TCNE) might be used as a UV-vis probe to investigate the solvent properties of ionic liquids (ILs). In molecular solvents, MK and TCNE give an electron donor-acceptor (EDA) complex, a zwitterionic species or a radical ion pair, depending of the aprotic or protic nature of the solvent and on its ionizing power.

Solute-solvent interactions on the keto-enol tautomerism of 2-nitrocyclohexanone in several organic solvents and room-temperature ionic liquids (RTILs) are analyzed in terms of multiparameter equations. Permittivity and cohesive pressure values of the RTILs, unavailable by direct measurements are derived.

The kinetic constants and the activation parameters for the reactions of Br(sub 3)(super -) and ICl(sub 2)(super -) with some alkenes and alkynes in six different ionic liquids (ILs) and in typical molecular solvent for these reactions, 1,2-dichloroethane (DCE) are reported. The results show the potential effects of the cations of the ILs as hydrogen bonding donors in electrophilic addition reactions in ionic liquids and confirm previous data showing that the capability of imidazolium ILs for H-bonding can be exploited to suppress unwanted substitution reactions.

The stereochemical course of the electrophilic iodination and bromination of tri-benzyl-D-glucan under various conditions is compared to that of substituted dihydropyrans 2-5. The factors determining the versatile selectivity of the electrophile approach are discussed in terms of PPFMO theory and of the special mechanisms of glycan reactions.

Results show that trans-(1-methyl-2-adamantylidene)-1-methyladamantane reacts with bromine spontaneously forming a pi-complex, which is converted into an ionic intermediate. The bromination reaction exhibits a marked affect of steric strain on the double bond reactivity.

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. [ABSTRACT FROM AUTHOR]

A kinetic and product investigation of stilbene bromination over a very wide reactivity range indicates that bromine bridging is not the only stereochemistry-determining factor. The stereochemical outcome of bromination is controlled by its association with its nucleophilic partners and its lifetime, as well as by the bridged or unbridged structure of the cationic intermediate. Lifetimes of the ionic intermediates of nucleophilic substitutions influence the pathway followed under specific reaction conditions.

The bromination of cis- and trans-4,4'-dimethoxystibenes with Br2 and tetrabutylammonium tribromide (TBAT) led to the formation of bromocarbenium bromide. Analysis of the activation parameters of 1,2-dichloromethane and chloroform during the formation of bromocarbenium bromide indicated the nucleophilic role of the Br- ion in the TBAT-mediated bromination process. Furthermore, the ionization of the pi-complex to a bromocarbenium-bromide ion pair competed with the formation of a bromocarbenium tribromide ion pair.

The apparent activation energy of the bromination of (E)-2,2,3,4,5,5- hexamethylhex-3-ene (HMH, 2) in 1,2-dichloroethane (DCE) is negative and that of tetraisobutylethylene (TIBE) in acetic acid is slightly positive, and it incorporates the formation of a 2-Br2 charge transfer complex in the first step. In DCE, a second complex containing two Br2 molecules is formed by exothermic affiliation and ionizes to a bromonium ion paired to a tribromide anion stabilized by charge delocalization.

1,2-dichloroethane was analyzed at 5, 25 and 50 degrees Celsius to determine the bromination of 5H-dibenz(b,f)azepine-5-carbonyl chloride. Variation in rate law from overall third order to overall fourth order accompany enhancement in Br2 concentrations and reduction in temperature. The breakdown of the ionic intermediate to 2 is the rate determining process.

The effect of bromide-tribromide-pentabromide equilibrium on stilbene bromination was investigated through the computation of electronic spectra and formation constant of the product from the spectrophotometric data. Results show that the formation of the ionic intermediate can be reversible inspite of the presence of bromide counteranions at low concentrations. It was likewise demonstrated that the predominant products of the reaction was affected by bromine equilibrium.

Chiral ionic liquids (CILs), or ionic liquids (ILs) with chiral additives, are very attractive chiral media for enantioselective electroanalysis, on account of their high chiral structural order at the electrochemical interphase. A family of molecular salts with CIL properties is now introduced, based on the chiral steroid building block of deoxycholic acid implemented either in the anion or cation. Testing them as chiral additives in a commercial achiral IL, they enable voltammetric discrimination of the enantiomers of a model chiral probe on disposable screen-printed electrodes in terms of peak potential differences, which is the most desirable transduction mode of the enantiorecognition event. The probe enantiomer sequence is the same for all selectors, consistent with their sharing the same chiral building block configuration. This proof-of-concept widens the application fields of bile acid derivatives as chiral selectors, while also enriching the still very few CIL families so far explored for applications in chiral electroanalysis. [ABSTRACT FROM AUTHOR]

Three novel deep eutectic solvents (DESs) were prepared with choline acetate (ChOAc) as the hydrogen bond acceptor (HBA) and three hydrogen bond donors (HBD): glycolic acid (GlyA), levulinic acid (LevA) and imidazole (Im). They showed different, albeit remarkable capabilities of dissolving lignin (from 35% to 100%) and hemicellulose (from 40% to 50%). The solubility was first tested on commercially available hemicellulose in neat DES and in DES aqueous solution. The high values of solubility observed (22–45 wt%) demonstrated the potential of DESs as hemicellulose solvents. A proof of concept test was carried out on Kraft cellulose: our systems provided selective solubilisation of lignin and hemicellulose leading to cellulose purification, as demonstrated by the lignocellulosic content before and after the DES treatment. [ABSTRACT FROM AUTHOR]

This study reports an ionic liquid (IL) promoted green method to obtain diaryl thioethers useful as key intermediates for the synthesis of matrix metalloproteinase (MMP) inhibitors. The synthetic pathway includes a sequential Ullmann reaction and Suzuki cross-coupling. The Ullmann conditions were optimized as regards the catalyst, the ionic liquid, reaction time, and temperature. Under optimal conditions (1-butyl-3-methylimidazolium bromide ([BMIM]Br) as solvent; catalyst, Cu; base, K2CO3; reaction time, 22 h; reaction temperature, 150°C) the aryl iodide conversion was 95%. The Suzuki cross-coupling was conducted in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) at 110°C, using Pd(PPh3)4 as catalyst and Na2CO3 as base. For both reactions, a combination of ILs with microwave (MW) irradiation determined a substantial improvement of reaction time and yields compared to conventional heating. This multi-step process reduces reaction times and removes organic solvents providing a more eco-friendly alternative for the synthesis of important pharmaceutical building blocks. [ABSTRACT FROM AUTHOR]

The fungal pathways of melanin synthesis have so far been little considered as a source of bio-inspiration in the field of functional materials, despite the interesting properties exhibited by Ascomycetes melanins from 1,8-dihydroxynaphthalene (1,8-DHN), including the ability to shield organisms from ionizing radiation. Herein, the processing techniques and characterizations of mycomelanin thin films obtained from the solid state polymerization of 1,8-DHN is reported for the first time. Overall, the results highlighted the role of synthetic mycomelanin thin films as a prototype of next generation bioinspired interfaces featuring high structural regularity and ultrasmooth morphology, high robustness against peroxidative bleaching and adhesion under water conditions, good biocompatibility and unprecedented effects in inducing the spontaneous differentiation of embryonic stem cells prevalently towards the endodermal lineages in the absence of added factors. These data open up new avenues towards the applications of this biomaterial in the fields of tissue engineering and regenerative medicine. [ABSTRACT FROM AUTHOR]

Excess entropy scaling relationships for diffusivity of ions in room-temperature ionic liquids are tested using molecular dynamics simulations for a model ionic liquid, dimethyl imidazolium chloride. The thermodynamic excess entropy of the single ions (estimated from the ion-ion pair correlation functions) is shown to be very strongly correlated with the diffusivity. An essential feature of these systems, the fact that the heavier and larger cation has a greater diffusivity with respect to the anion, is correctly captured by the excess entropy calculations, which estimates the diffusivity ratio between the two ions with noticeable precision. [ABSTRACT FROM AUTHOR]

In this work, we study the solvation thermodynamics and other solvation properties of small ions in two room-temperature ionic liquids, dimethyl imidazolium hexafluorophosphate [mmim] [pf6] and dimethyl imidazolium chloride [mmim][cl] with the reference interaction site model (RISM). The nature of the charge affects several aspects of solvation, from electrostriction to the mutual disposition of cations around the solute; nevertheless, the long-range screening behavior of the liquid appears to be insensitive to both charge and dimensions of the solute. The ion solvation is energy driven, as expected for the nature of the solvent, and displays a marked asymmetry between cation and anion solvation chemical potential. Such asymmetry is dependent, even qualitatively, on the ionic liquid chosen as solvent. Partial molar volumes of ions in solution are found to follow the nature of ion-solvent interaction. [ABSTRACT FROM AUTHOR]

The equilibrium constants for ion pair formation of pyridines are analyzed by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water, whereas pyridine basicity is less sensitive to the substituent effect in ionic liquids than in water.