Electrogenerated BF3 From Tetrafluoroborate-Based Ionic Liquids: Theoretical And Experimental Studies Towards Selective Styrene Oxide Isomerization

The anodic oxidation of tetrafluoroborate anion yields the Lewis acid BF3. If this reaction is carried out in an imidazolium ionic liquid, a quite stable system containing BF3 is obtained, whose reactivity is similar to the one of BF3·Et2O, but less harmful. The two reagents’ stabilities were compared by computational analysis, strongly suggesting a higher stability for BF3/BMIm-BF4 system. The effect of substituents on the imidazolium ring and of the electrochemical configuration on BF3 reactivity were studied in a model reaction, styrene oxide isomerization. The experimental conditions were defined for the selective formation of phenylacetaldehyde or of 2-benzyl-4-phenyl-1,3-dioxolane. Moreover, the formation of N-heterocyclic carbene-BF3 adduct was confirmed when carrying out the electrolysis in an undivided cell. Electrogenerated BF3/BMIm-BF4 system demonstrated to be a valid alternative to commercial BF3·Et2O.

Performance and Mechanism of Alkylimidazolium Ionic Liquids as Corrosion Inhibitors for Copper in Sulfuric Acid Solution

The addition of corrosion inhibitors is an economic and environmental protection method to prevent the corrosion of copper. The adsorption, performance, and mechanism of three 1-alkyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4, [HMIM]HSO4, and [OMIM]HSO4) ionic liquids (ILs) on the copper surface in 0.5 M H2SO4 solutions were studied by quantum chemical calculation, quantitative structure-activity relationship (QSAR), and molecular dynamics simulation. It is found that the main reactive site is located on the imidazolium ring (especially the C2, N4, and N7 groups). When the alkyl chain of the imidazolium ring is increasing, the molecular reactivity of the ILs and the interaction between the ILs inhibitor and copper surface are enhanced. The imidazole ring of the ILs tends to be adsorbed on Cu (111) surface in parallel through physical adsorption. The order of adsorption energy is [Bmim]HSO4 < [Hmim]HSO4 < [OMIM]HSO4, which is in agreement with the experimental order of corrosion efficiency. On the imidazole ring, the interaction between the copper surface and the C atom is greater than that between the copper surface and the N atom. It is found that ILs addition can hinder the diffusion of corrosion particles, reduce the number density of corrosion particles and slow down the corrosion rate. The order of inhibition ability of three ILs is [Bmim]HSO4 < [Hmim]HSO4 < [OMIM]HSO4,which agree well with experimental results. A reliable QSAR correlation between the inhibition corrosion efficiency and molecular reactivity parameters of the ILs was established.

Design of metalloporphyrins fused to imidazolium rings for binding DNA G-quadruplexes

Synthesis and characterization of nickel(II) meso-tetraarylporphyrins fused to imidazolium rings across [Formula: see text],[Formula: see text]-pyrrolic positions and X-ray structure of the porphyrin where two opposed pyrrole units are fused to an imidazolium ring are presented. The interactions between these mono-, bis-, tris- and tetrakis(imidazolium) porphyrins with human telomeric DNA G-quadruplexes (G4) were investigated using UV-vis absorption spectroscopy, Circular Dichroism (CD) spectroscopy and Fluorescence Resonance Energy Transfer (FRET) melting assay. Possible binding modes between cationic porphyrins and a selected G4 sequence (d[AG3(T2AG[Formula: see text]]), and relative stabilities of porphyrin/G4 complexes are discussed. Excepting porphyrins fused to one imidazolium ring, the other derivatives interact with G4 structures and their stabilization strongly depends on the porphyrin structure (number and localization of the imidazolium rings).

Pyridine-Imidazlolium Salts: Oxidatively Cleavage of N-C Bond via Nitration

Azaheterocycles derivatives with pyridine-imidazole skeleton are compounds of great value for medicinal chemistry. We report herein the nitration of 1,1′-(pyridine-2,6-diylbis(methylene))bis{3-[2-(4-nitrophenyl)-2-oxoethyl]-1H-imidazol-3-ium} bromide using a typical mixture of nitric and sulphuric acid. The nitration occur with the oxidative cleavage of N–C bond between imidazolium ring and methylene group.

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.

1,3-Bis(2,4,6-trimethylphenyl)imidazolium perchlorate

The title compound, C21H25N2 +·ClO4 −, arose as an unexpected oxidation product of the carbene 1,3-bis(2,4,6-trimethylphenyl)-1,3-dihydro-2H-imidazol-2-ylidine in methanol. It crystallizes with two unique cations and anions in the P-type monoclinic unit cell. The five-membered cationic imidazolium rings are essentially planar and in each imidazolium cation the phenyl rings of the 2,4,6-trimethylphenyl groups are staggered with respect to the imidazolium ring [dihedral angles ranging from 60.9 (3) to 86.3 (3)°]. In the crystal, a hydrogen-bonding network is created via C—H...O interactions between the imidazolium ring H atoms and the perchlorate-anion oxygen atoms. The crystal studied was refined as an inversion twin.

1,3-Bis(2,6-diisopropylphenyl)imidazolium perchlorate

The title salt, C27H37N2 +·ClO4 −, arose as an unexpected oxidation product of the carbene 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene in methanol. The five-membered cationic imidazolium ring is planar by symmetry and the complete cation is generated by a crystallographic twofold axis passing through the central N-bonded C atom and the mid-point of the C=C bond; the Cl atom of the perchlorate anion also lies on the rotation axis. The phenyl rings of the 2,6-diisopropylphenyl groups are each perpendicular to the imidazolium ring [dihedral angle = 90.0 (3)°]. In the crystal, weak C—H...O and bifurcated C—H...(O,O) interactions between the imidazolium ring H atoms and the perchlorate O atoms lead to [001] chains.