Acetate Ionic Liquid Research Articles

Organocatalytic upgrading of the key biorefining building block by a catalytic ionic liquid and N-heterocyclic carbenes

The present study of rapid degradation of the key biorefining building block 5-hydroxymethylfurfural (HMF) in an ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), has led to highly selective and efficient upgrading of HMF to 5,5′-di(hydroxymethyl)furoin (DHMF), a promising C12 kerosene/jet fuel intermediate. This HMF upgrading reaction is carried out under industrially favourable conditions (i.e., ambient atmosphere and 60–80 °C), catalyzed by N-heterocyclic carbenes (NHCs), and complete within 1 h; this process selectively produces DHMF with yields up to 98% (by HPLC or NMR) or 87% (unoptimized, isolated yield). Mechanistic studies have yielded four lines of evidence that support the proposed carbene catalytic cycle for this upgrading transformation catalyzed by the acetate IL and NHCs.

Demonstration of Chemisorption of Carbon Dioxide in 1,3‐Dialkylimidazolium Acetate Ionic Liquids

Real chemistry: Spectroscopic and crystallographic analyses confirm the chemical reaction of CO 2 with carbene present in 1,3- dialkylimidazolium acetate ionic liquids and the supporting role of the acetate ion. When CO 2 was bubbled through [C 2mim][OAc], formation of the corresponding imidazolium carboxylate, [C 2mim +-COO -], could be observed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation and rheological properties of cellulose/chitosan homogeneous solution in ionic liquid

Cellulose/chitosan homogeneous solutions were prepared in 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) ionic liquid. Steady and oscillatory dynamic rheological properties were studied with a Haake Mars-ΙΙΙ rotational rheometer. Rheological results show that cellulose/chitosan [EMIM]Ac solutions are a pseudoplastic liquid, and the viscosity of the solution decreases with increasing of chitosan content. The zero shear rate viscous activation energy of solution is about 52.10 to 62.50KJ/mol, calculated from the Cross and Arrhenius equation. The structural viscosity index of the solution is similar to that of cellulose/N-methylmorpholine-N-oxide solution, which indicates a potential spinnability. The dynamic rheological responses reveal that the Cox-Merz rule holds well with the solutions, and the crossover point of loss modulus and storage modulus shifts to a higher frequency range with increasing temperature.

Solvation of Nucleobases in 1,3-Dialkylimidazolium Acetate Ionic Liquids: NMR Spectroscopy Insights into the Dissolution Mechanism

NMR studies of uracil, thymine, and adenine dissolved in 1-ethyl-3-methyl-imidazolium acetate ([C(2)mim][CH(3)COO]) and 1-butyl-3-methyl-imidazolium acetate ([C(4)mim][CH(3)COO]) show that hydrogen bonds (HB) dictate the dissolution mechanism and that both cations and anions participate in the solvation process. For that, the 1,3-dialkylimidazolium acetate ionic liquids (ILs) were considered to be bifunctional solvation ionic liquids. In the solvation of uracil and thymine, the [CH(3)COO](-) anion favors the formation of hydrogen bonds with the hydrogen atoms of the N1-H and N3-H groups of the nucleobases, while the aromatic protons in the bulky cations ([C(2)mim](+) and [C(4)mim](+)), especially the most acidic H2, interact with the oxygen atoms of the carbonyl groups. In the adenine solvation, while the [CH(3)COO](-) anion favors the formation of hydrogen bonds with the hydrogen atoms of the amino and N9-H groups of adenine, the aromatic protons in the bulky cations ([C(2)mim](+) and [C(4)mim](+)), especially the most acidic H2, prefer to interact with the unprotonated nitrogen atoms (N1, N3, and N7) of adenine. It is clearly demonstrated that hydrogen bonding is the major driving force in the dissolution of nucleobases in 1,3-dialkylimidazolium acetate ILs. Our results show that the ionic liquid must be a good hydrogen bond acceptor and a moderate hydrogen bond donor to dissolve nucleic acid bases. To strengthen the evidence of the proposed mechanism, NMR studies in the absence of deuterated cosolvents have been used, because the use of deuterated solvents could seriously hinder the dissolving capability of the IL for nucleobases.

Active species formed in a Fenton-like system in the medium of triethylammonium acetate ionic liquid for hydroxylation of benzene to phenol

High-valent iron(IV)-oxo species was proved to be the main oxidizing species for hydroxylation of benzene to phenol by a Fenton-like reagent in triethylammonium acetate ionic liquid via UV–vis and ESI-MS characterization, while hydroxyl radical was excluded by detailed investigations. It was found that the formation of hydroxyl radical was prohibited by the reduction of redox potential of Fe(III)/Fe(II) couple in triethylammonium acetate medium, leading to a decreased over-oxidation of benzene than that in aqueous solution. The reaction mechanisms for hydroxylation of benzene, as well as for over-oxidation of phenol by iron(IV)-oxo species were proposed. The latter is partly prohibited by the hydrogen-bond interaction between as-produced phenol and acetate anion of the ionic liquid.

Solubility of CO2in 1-Butyl-3-methyl-imidazolium-trifluoro Acetate Ionic Liquid Studied by Raman Spectroscopy and DFT Investigations

The polarized and depolarized Raman spectra of 1-butyl-3-methyl-imidazolium-trifluoro acetate (Bmim TFA) ionic liquid and of the dense phase obtained after introduction of supercritical carbon dioxide (313K) under pressure (from 0.1 MPa up to 9 MPa) in the ionic liquid have been recorded. The spectrum of the pure ionic liquid has been assigned by comparison with the spectra of ionic liquids sharing the same cation and using literature data concerning the vibrational modes of the TFA anion. It was found that the spectra of the ionic liquid is almost unaffected by the CO(2) dilution. The only noticeable perturbation concerns a weak enhancement of the mode assigned here to the symmetric stretch vibration of the COO group of the TFA anion. The band shape analysis of the ν(CC) band in pure Bmim TFA shows that the carboxylate groups probe a variety of environments which are almost not affected by the dilution in carbon dioxide. The analysis of the Fermi dyad of carbon dioxide shows that this molecule is perturbed upon dilution in the ionic liquid. The spectra suggest the presence of carbon dioxide in two different environments. In the first one, carbon dioxide molecules interact with themselves, whereas in the second environment, this molecule interacts with the COO group of the TFA anion. This is supported by B3LYP-DFT calculations aimed at assessing the interaction between an ion pair dimer and a carbon dioxide molecule. It is shown that dissolved CO(2) molecules preferentially interact with the TFA anion through a weak charge transfer interaction taking place between the carbon atom of CO(2) (acting as a Lewis acid) and a oxygen atom of the COO group of TFA (as a Lewis base). The results show that Bmim TFA is able to accommodate a large amount of carbon dioxide without having its short-range local structure significantly perturbed. Most CO(2) is hosted in the voids existing among the ion pairs, while some also weakly interact with the anion. It is finally argued that the evolution of the local organization of the IL upon carbon dioxide dilution presents similarities with the microsegregation phenomena reported for IL upon increasing the alkyl chains lengths.

Reaction of elemental chalcogens with imidazolium acetates to yield imidazole-2-chalcogenones: direct evidence for ionic liquids as proto-carbenes

Mechanistic analysis of the reaction between elemental sulfur or selenium and 1,3-dialkylimidazolium acetate ionic liquids, in the absence of an external base or solvent, affords evidence for the equilibrium presence of carbene species in these ionic liquids. It demonstrates the potential to control, through anion selection, the concentration of carbene in stable ionic liquids.

Greener approach towards the facile synthesis of 1,4-dihydropyrano[2,3-c]pyrazol-5-yl cyanide derivatives at room temperature

This report describes triethylammonium acetate (TEAA) ionic liquid catalyzed one pot synthesis of 6-amino-4-aryl-5-cyano-3-methyl-1-phenyl-1,4-dihydropyrano[2,3-c]pyrazoles by the reaction of aromatic aldehyde, malononitrile and 3-methyl-1-phenyl-2-pyrazolin-5-one at room temperature. TEAA plays dual role as reaction media and catalyst. It can also be easily recovered and reused in several runs. TEAA provides greener reaction protocol to present methodology which obviates the need of organic solvents, expensive and toxic catalyst.

Henry and Knoevenagel reactions catalyzed by methoxyl propylamine acetate ionic liquid

Henry reactions and Knoevenagel reactions, used to prepare substituted olefins, have been limited by complex catalyst separation. In this article, methoxyl propylamine acetate ionic liquid was used as an environmentally benign catalyst for these reactions under solvent-free condition for the first time. This ionic liquid was shown to effectively catalyze Henry reactions and Knoevenagel reaction of active nitromethane compounds with various aldehydes. Yields from the catalyzed reactions were over 99% under solvent free condition. The process is highly effective, environmentally benign, and very selective. Furthermore, methoxyl propylamine acetate ionic liquid was conveniently separated with the products and easily recycled to catalyze Knoevenagel reaction again with excellent yields.

Triethylammonium acetate (TEAA): a recyclable inexpensive ionic liquid promotes the chemoselective aza- and thia-Michael reactions

A new, highly efficient, inexpensive, recyclable, mild, convenient, and green protocol for chemoselective aza/thia-Michael addition reactions of amines/thiols to α,β-unsaturated compounds using triethylammonium acetate (TEAA) ionic liquid was developed. The catalyst can be recycled ten times and obviate the need for toxic and expensive catalysts.