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Special Issue "Ionic Liquids in Organic Synthesis"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Synthesis".

Deadline for manuscript submissions: closed (31 October 2015)

Special Issue Editor

Guest Editor
Dr. Jason P. Hallett

Department of Chemical Engineering, Imperial College London, South Kensington, London, UK
Website | E-Mail
Interests: ionic liquids; organic synthesis; green chemistry; biorefining

Special Issue Information

Dear Colleagues,

This Special Issue of Molecules is dedicated to the use of ionic liquids as solvents in organic synthesis. Over the past two decades, ionic liquids have risen from being a specialist curiosity to a novel solvent for academic research, to full-blown industrial application. The basis of this has been the ability of chemists to take advantage of the novel properties of these solvents—in particular, their highly tunable nature, which positions ionic liquids as the only truly "designer solvents."

Accompanying this enhanced popularity has been a wide range of applications—nearly every class of reaction has been demonstrated in ionic liquids, with unique benefits reported in the recycling of homogeneous catalysis, the modification of carbohydrates and the use of non-traditional synthetic techniques such as microwaves and ultrasound. Ionic liquids have further positioned themselves as the solvent of choice for environmental applications in organic synthesis—and the range of uses for these solvents is limited only by the ingenuity of the scientists involved.

Dr. Jason P. Hallett
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • ionic liquids
  • organic synthesis
  • green chemistry

Published Papers (11 papers)

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Research

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Open AccessArticle A Sustainable Approach to the Stereoselective Synthesis of Diazaheptacyclic Cage Systems Based on a Multicomponent Strategy in an Ionic Liquid
Molecules 2016, 21(2), 165; doi:10.3390/molecules21020165
Received: 14 December 2015 / Revised: 21 January 2016 / Accepted: 26 January 2016 / Published: 29 January 2016
PDF Full-text (1737 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The microwave-assisted three-component reactions of 3,5-bis(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones, acenaphthenequinone and cyclic α-amino acids in an ionic liquid, 1-butyl-3-methylimidazolium bromide, occurred through a domino sequence affording structurally intriguing diazaheptacyclic cage-like compounds in excellent yields. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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Open AccessArticle Unimolecular Solvolyses in Ionic Liquid: Alcohol Dual Solvent Systems
Molecules 2016, 21(1), 60; doi:10.3390/molecules21010060
Received: 2 November 2015 / Revised: 12 December 2015 / Accepted: 24 December 2015 / Published: 6 January 2016
Cited by 1 | PDF Full-text (1023 KB) | HTML Full-text | XML Full-text
Abstract
A study was undertaken of the solvolysis of pivaloyl triflate in a variety of ionic liquid:alcohol solvent mixtures. The solvolysis is a kΔ process (i.e., a process in which ionization occurs with rearrangement), and the resulting rearranged carbocation intermediate reacts
[...] Read more.
A study was undertaken of the solvolysis of pivaloyl triflate in a variety of ionic liquid:alcohol solvent mixtures. The solvolysis is a kΔ process (i.e., a process in which ionization occurs with rearrangement), and the resulting rearranged carbocation intermediate reacts with the alcohol cosolvent via two competing pathways: nucleophilic attack or elimination of a proton. Five different ionic liquids and three different alcohol cosolvents were investigated to give a total of fifteen dual solvent systems. 1H-NMR analysis was used to determine relative amounts of elimination and substitution products. It was found, not surprisingly, that increasing the bulkiness of alcohol cosolvent led to increased elimination product. The change in the amount of elimination product with increasing ionic liquid concentration, however, varied greatly between ionic liquids. These differences correlate strongly, though not completely, to the Kamlet–Taft solvatochromic parameters of the hydrogen bond donating and accepting ability of the solvent systems. An additional factor playing into these differences is the bulkiness of the ionic liquid anion. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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Open AccessArticle Reduced Reactivity of Amines against Nucleophilic Substitution via Reversible Reaction with Carbon Dioxide
Molecules 2016, 21(1), 24; doi:10.3390/molecules21010024
Received: 6 November 2015 / Revised: 7 December 2015 / Accepted: 13 December 2015 / Published: 23 December 2015
Cited by 2 | PDF Full-text (983 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The reversible reaction of carbon dioxide (CO2) with primary amines to form alkyl-ammonium carbamates is demonstrated in this work to reduce amine reactivity against nucleophilic substitution reactions with benzophenone and phenyl isocyanate. The reversible formation of carbamates has been recently exploited
[...] Read more.
The reversible reaction of carbon dioxide (CO2) with primary amines to form alkyl-ammonium carbamates is demonstrated in this work to reduce amine reactivity against nucleophilic substitution reactions with benzophenone and phenyl isocyanate. The reversible formation of carbamates has been recently exploited for a number of unique applications including the formation of reversible ionic liquids and surfactants. For these applications, reduced reactivity of the carbamate is imperative, particularly for applications in reactions and separations. In this work, carbamate formation resulted in a 67% reduction in yield for urea synthesis and 55% reduction for imine synthesis. Furthermore, the amine reactivity can be recovered upon reversal of the carbamate reaction, demonstrating reversibility. The strong nucleophilic properties of amines often require protection/de-protection schemes during bi-functional coupling reactions. This typically requires three separate reaction steps to achieve a single transformation, which is the motivation behind Green Chemistry Principle #8: Reduce Derivatives. Based upon the reduced reactivity, there is potential to employ the reversible carbamate reaction as an alternative method for amine protection in the presence of competing reactions. For the context of this work, CO2 is envisioned as a green protecting agent to suppress formation of n-phenyl benzophenoneimine and various n-phenyl–n-alky ureas. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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Open AccessArticle Development of an Analytical Method Based on Temperature Controlled Solid-Liquid Extraction Using an Ionic Liquid as Solid Solvent
Molecules 2015, 20(12), 22137-22145; doi:10.3390/molecules201219842
Received: 5 August 2015 / Revised: 29 October 2015 / Accepted: 19 November 2015 / Published: 10 December 2015
Cited by 1 | PDF Full-text (1292 KB) | HTML Full-text | XML Full-text
Abstract
At the present paper, an analytical method based on temperature controlled solid-liquid extraction (TC-SLE) utilizing a synthesized ionic liquid, (N-butylpyridinium hexafluorophosphate, [BPy]PF6), as solid solvent and phenanthroline (PT) as an extractant was developed to determine micro levels of Fe
[...] Read more.
At the present paper, an analytical method based on temperature controlled solid-liquid extraction (TC-SLE) utilizing a synthesized ionic liquid, (N-butylpyridinium hexafluorophosphate, [BPy]PF6), as solid solvent and phenanthroline (PT) as an extractant was developed to determine micro levels of Fe2+ in tea by PT spectrophotometry. TC-SLE was carried out in two continuous steps: Fe2+ can be completely extracted by PT-[BPy]PF6 or back-extracted at 80 °C and the two phases were separated automatically by cooling to room temperature. Fe2+, after back-extraction, needs 2 mol/L HNO3 as stripping agent and the whole process was determined by PT spectrophotometry at room temperature. The extracted species was neutral Fe(PT)mCl2 (m = 1) according to slope analysis in the Fe2+-[BPy]PF6-PT TC-SLE system. The calibration curve was Y = 0.20856X − 0.000775 (correlation coefficient = 0.99991). The linear calibration range was 0.10–4.50 μg/mL and the limit of detection for Fe2+ is 7.0 × 10−2 μg/mL. In this method, the contents of Fe2+ in Tieguanyin tea were determined with RSDs (n = 5) 3.05% and recoveries in range of 90.6%–108.6%. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
Open AccessArticle Adsorption Kinetics at Silica Gel/Ionic Liquid Solution Interface
Molecules 2015, 20(12), 22058-22068; doi:10.3390/molecules201219833
Received: 3 September 2015 / Revised: 30 October 2015 / Accepted: 19 November 2015 / Published: 10 December 2015
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Abstract
A series of imidazolium and pyridinium ionic liquids with different anions (Cl, Br, BF4, PF6) has been evaluated for their adsorption activity on silica gel. Quantification of the ionic liquids has been performed
[...] Read more.
A series of imidazolium and pyridinium ionic liquids with different anions (Cl, Br, BF4, PF6) has been evaluated for their adsorption activity on silica gel. Quantification of the ionic liquids has been performed by the use of RP-HPLC with organic-aqueous eluents containing an acidic buffer and a chaotropic salt. Pseudo-second order kinetic models were applied to the experimental data in order to investigate the kinetics of the adsorption process. The experimental data showed good fitting with this model, confirmed by considerably high correlation coefficients. The adsorption kinetic parameters were determined and analyzed. The relative error between the calculated and experimental amount of ionic liquid adsorbed at equilibrium was within 7%. The effect of various factors such as initial ionic liquid concentration, temperature, kind of solvent, kind of ionic liquid anion and cation on adsorption efficiency were all examined in a lab-scale study. Consequently, silica gel showed better adsorptive characteristics for imidazolium-based ionic liquids with chaotropic anions from aqueous solutions in comparison to pyridinium ionic liquids. The adsorption was found to decrease with the addition of organic solvents (methanol, acetonitrile) but it was not sensitive to the change of temperature in the range of 5–40 °C. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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Open AccessArticle Alkylation of Methyl Linoleate with Propene in Ionic Liquids in the Presence of Metal Salts
Molecules 2015, 20(12), 21840-21853; doi:10.3390/molecules201219805
Received: 5 November 2015 / Revised: 20 November 2015 / Accepted: 27 November 2015 / Published: 7 December 2015
Cited by 1 | PDF Full-text (3586 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
Open AccessArticle A Simple, Effective, Green Method for the Regioselective 3-Acylation of Unprotected Indoles
Molecules 2015, 20(10), 19605-19619; doi:10.3390/molecules201019605
Received: 5 October 2015 / Revised: 22 October 2015 / Accepted: 22 October 2015 / Published: 27 October 2015
Cited by 5 | PDF Full-text (873 KB) | HTML Full-text | XML Full-text
Abstract
A fast and green method is developed for regioselective acylation of indoles in the 3-position without the need for protection of the NH position. The method is based on Friedel-Crafts acylation using acid anhydrides. The method has been optimized, and Y(OTf)3 in
[...] Read more.
A fast and green method is developed for regioselective acylation of indoles in the 3-position without the need for protection of the NH position. The method is based on Friedel-Crafts acylation using acid anhydrides. The method has been optimized, and Y(OTf)3 in catalytic amounts is found to be the best catalyst together with the commercially available ionic liquid [BMI]BF4 (1-butyl-3-methylimidazolium tetrafluoro-borate) as solvent. The reaction is completed in a very short time using monomode microwave irradiation. The catalyst can be reused up to four times without significant loss of activity. A range of substituted indoles are investigated as substrates, and thirteen new compounds have been synthesized. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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Open AccessArticle Preparation of Thermo-Responsive Poly(ionic liquid)s-Based Nanogels via One-Step Cross-Linking Copolymerization
Molecules 2015, 20(9), 17378-17392; doi:10.3390/molecules200917378
Received: 11 August 2015 / Revised: 11 September 2015 / Accepted: 14 September 2015 / Published: 18 September 2015
Cited by 5 | PDF Full-text (1745 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this study, thermo-responsive polymeric nanogels were facilely prepared via one-step cross-linking copolymerization of ethylene glycol dimethacrylate/divinylbenzene and ionic liquid (IL)-based monomers, 1,n-dialkyl-3,3′-bis-1-vinyl imidazolium bromides ([CnVIm]Br; n = 6, 8, 12) in selective solvents. The results revealed that stable and blue
[...] Read more.
In this study, thermo-responsive polymeric nanogels were facilely prepared via one-step cross-linking copolymerization of ethylene glycol dimethacrylate/divinylbenzene and ionic liquid (IL)-based monomers, 1,n-dialkyl-3,3′-bis-1-vinyl imidazolium bromides ([CnVIm]Br; n = 6, 8, 12) in selective solvents. The results revealed that stable and blue opalescent biimidazolium (BIm)-based nanogel solutions could be obtained without any precipitation when the copolymerizations were conducted in methanol. Most importantly, these novel nanogels were thermo-response, and could reversibly transform to precipitation in methanol with temperature changes. Turbidity analysis and dynamic light scatting (DLS) measurement illustrated that PIL-based nanogel solutions presented the phase transform with upper critical solution temperature (UCST) in the range of 5–25 °C. The nanogels were characterized using Fourier transform infrared (FTIR), thermogravimetric analyses (TGA), and scanning electron microscopy (SEM). In addition, BIm-based nanogels could also be used as highly active catalysts in the cycloaddition reaction of CO2 and epoxides. As a result, our attributes build a robust platform suitable for the preparation of polymeric nanomaterials, as well as CO2 conversion. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
Open AccessArticle Eco-Friendly Synthesis of a New Class of Pyridinium-Based Ionic Liquids with Attractive Antimicrobial Activity
Molecules 2015, 20(8), 14936-14949; doi:10.3390/molecules200814936
Received: 16 June 2015 / Revised: 30 July 2015 / Accepted: 5 August 2015 / Published: 14 August 2015
Cited by 8 | PDF Full-text (713 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The present study reports a green synthesis of a new family of ionic liquids (ILs) based on functionalized 4-dimethylaminopyridinium derivatives. The structures of 23 newly synthesized ILs (224) were confirmed by FT-IR, 1H-, 13C-, 11B-, 19
[...] Read more.
The present study reports a green synthesis of a new family of ionic liquids (ILs) based on functionalized 4-dimethylaminopyridinium derivatives. The structures of 23 newly synthesized ILs (224) were confirmed by FT-IR, 1H-, 13C-, 11B-, 19F-, and 31P-NMR spectroscopy and mass spectrometry. The antimicrobial activity of all novel ILs was tested against a panel of bacteria and fungi. The results prove that all tested ILs are effective antibacterial and antifungal agents, especially 4-(dimethylamino)-1-(4-phenoxybutyl) pyridinium derivatives 5 and 19. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)

Review

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Open AccessReview Application of Ionic Liquids in Pot-in-Pot Reactions
Molecules 2016, 21(3), 272; doi:10.3390/molecules21030272
Received: 20 November 2015 / Revised: 1 February 2016 / Accepted: 18 February 2016 / Published: 26 February 2016
Cited by 1 | PDF Full-text (1632 KB) | HTML Full-text | XML Full-text
Abstract
Pot-in-pot reactions are designed such that two reaction media (solvents, catalysts and reagents) are isolated from each other by a polymeric membrane similar to matryoshka dolls (Russian nesting dolls). The first reaction is allowed to progress to completion before triggering the second reaction
[...] Read more.
Pot-in-pot reactions are designed such that two reaction media (solvents, catalysts and reagents) are isolated from each other by a polymeric membrane similar to matryoshka dolls (Russian nesting dolls). The first reaction is allowed to progress to completion before triggering the second reaction in which all necessary solvents, reactants, or catalysts are placed except for the starting reagent for the target reaction. With the appropriate trigger, in most cases unidirectional flux, the product of the first reaction is introduced to the second medium allowing a second transformation in the same glass reaction pot—albeit separated by a polymeric membrane. The basis of these reaction systems is the controlled selective flux of one reagent over the other components of the first reaction while maintaining steady-state catalyst concentration in the first “pot”. The use of ionic liquids as tools to control chemical potential across the polymeric membranes making the first pot is discussed based on standard diffusion models—Fickian and Payne’s models. Besides chemical potential, use of ionic liquids as delivery agent for a small amount of a solvent that slightly swells the polymeric membrane, hence increasing flux, is highlighted. This review highlights the critical role ionic liquids play in site-isolation of multiple catalyzed reactions in a standard pot-in-pot reaction. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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Open AccessReview Room Temperature Ionic Liquids as Green Solvent Alternatives in the Metathesis of Oleochemical Feedstocks
Molecules 2016, 21(2), 184; doi:10.3390/molecules21020184
Received: 30 September 2015 / Accepted: 25 January 2016 / Published: 6 February 2016
Cited by 5 | PDF Full-text (2560 KB) | HTML Full-text | XML Full-text
Abstract
One of the most important areas of green chemistry is the application of environmentally friendly solvents in catalysis and synthesis. Conventional organic solvents pose a threat to the environment due to the volatility, highly flammability, toxicity and carcinogenic properties they exhibit. The recently
[...] Read more.
One of the most important areas of green chemistry is the application of environmentally friendly solvents in catalysis and synthesis. Conventional organic solvents pose a threat to the environment due to the volatility, highly flammability, toxicity and carcinogenic properties they exhibit. The recently emerged room temperature ionic liquids (RTILs) are promising green solvent alternatives to the volatile organic solvents due to their ease of reuse, non-volatility, thermal stability and ability to dissolve a variety of organic and organometallic compounds. This review explores the use of RTILs as green solvent media in olefin metathesis for applications in the oleochemical industry. Full article
(This article belongs to the Special Issue Ionic Liquids in Organic Synthesis)
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