Bronsted Acidic Ionic Liquids Research Articles

Structures and hydrogen bonds of -SO3H functionalized acid ionic liquids

Brønsted acidic ionic liquids (BAILs) are clean and versatile replacements for traditional homogeneous acid catalysts and have attracted much attention as efficient catalysts for the synthesis of valuable chemicals. It’s critically important to understand the structural properties of BAILs from the molecular level. In this work, we studied a series of −SO3H functionalized acidic ionic liquids by density functional theory (DFT) calculations, and the most stable geometries were obtained by global semiempirical quantum mechanical search. The most stable structures of cations are formed when more intramolecular H-bonds exist. For BAILs clusters, intramolecular and intermolecular H-bonds coexist and play a critical role in the stability of the system. The interaction energy decreases with increasing alkyl chain length. When the alkyl chain was replaced by −SO3H groups, the interaction energy increased due to more H-bonds formed with the anions. The quasi-3D network is formed in the BAILs clusters and the electrostatic interaction plays a critical role in stabilizing the ion clusters. This work helps to understand the microcosmic interactions of BAILs in-depth and design them in a “task-specific” way.

In-situ approach to porous nitrogen-doped carbon nanosheets functionalized by Brønsted acidic ionic liquids for microwave-assisted upgrading fructose to 5-hydroxymethylfurfural

In the search for robust and recoverable supported Brønsted acidic ionic liquids (BAILs) catalysts for efficient upgrading bio-sugars to value-added chemicals, an in-situ strategy of supramolecular preorganization-thermal polycondensation is designed to fabricate porous ultrathin nitrogen-doped carbon nanosheets (NCNSs), and then BAILs-functionalized NCNSs catalysts are prepared via successive quaternary ammonization by sultones and anion exchange with Brønsted acids. By adjusting the molar composition of the starting monomers, the textural properties of NCNSs supports are tuned; and by functionalization with different sultones (1,3-propanesultone and 1,4-butanesultone) and organic (trifluoromethanesulfonic acid and p-toluenesulfonic acid) or inorganic (H2SO4 and H3PO4) acids, the surface hydrophobicity and Brønsted acid strength of the catalysts are regulated. The catalysts are applied in microwave-assisted upgrading fructose to 5-hydroxymethylfurfural, and influences of Brønsted acid nature, surface hydrophobicity and textural properties on the catalytic performance are explored. For the most active [C4SO3HN][OTf]-NCNSs-MA-3 catalyst with the advantages of superstrong Brønsted acidity, higher surface hydrophobicity and perfect porous ultrathin sheet-like nanostructure, the conversion of fructose and the yield of 5-hydroxymethylfurfural of 100% and 87.7% are achieved after microwave irradiation for 15 min, outperforming Amberlyst-15 resin and HY zeolite. The catalysts also demonstrate the robust catalytic reusability, and after five consecutive catalytic runs, the obvious activity loss hardly occurs, along with little acid sites leaching.

N−SO3H Functionalised Brønsted Acidic Ionic Liquid Catalysed Sequential One‐Pot Synthesis of 2‐Amino‐3‐Cyanopyridines via Claisen‐Schmidt Condensation Under Solvent‐free Condition

AbstractThis work presents a simple approach for the synthesis of 2‐amino‐3‐cyanopyridines via a one pot two‐step sequential route catalysed by direct N‐−SO3H functionalised Brønsted acidic ionic liquids (BAILs). Herein, catalytic activities of four BAILs namely ([TSPi][Cl]2, [DSIM][TFA], [EDSIM][TFA] and [DBDSA][TFA]) were explored and among them [TSPi][Cl]2 was found to be the most efficient reusable homogeneous catalyst. This process involves the ionic liquid catalysed in situ generation of chalcones from Claisen‐Schmidt condensation between aromatic aldehydes and acetophenone/4‐Cl acetophenone, followed by multicomponent reaction (MCR) with malononitrile and ammonium acetate using the same IL catalyst to selectively produce 2‐amino‐3‐cyanopyridine derivatives in a solvent‐free medium at 80 °C within 30–60 minutes in high yields (96–86 %). This amalgamation of MCR with ionic liquids and solvent‐free conditions makes the present work more compliant with the protocols of Green Chemistry.

Kinetics and mechanism of esterification of palmitic acid with ethanol in the presence of Brønsted acidic ionic liquids as catalyst

Abstract The present work is focused on the kinetics and mechanisms of palmitic acid and ethanol esterification reaction using Brønsted acidic ionic liquids (BAILs) as catalysts. The experiments were performed in an isothermal batch reactor and progress of reaction has been monitored by measuring the water content using Karl Fischer Titrator. The experimental data has been investigated by integral method of data analysis to determine the kinetics. The kinetics from the experimental data revealed that the reaction is non-elementary, and a suitable mechanism was proposed. The importance of activity coefficients was also studied using UNIFAC and modified UNIFAC programme.

Protic Brønsted acidic ionic liquids with variable acidity for efficient conversion of xylose and hemicellulose to furfural

Furfural (FF) is an important platform molecule originated from biomass, but it’s synthesis through the traditional acid-catalyzed dehydration reaction of xylose and hemicellulose remains problematic due to the poor activity and equipment corrosion. Therefore, a series of [HSO4]-based protic Brønsted acidic ionic liquids (BAILs) are employed as green catalysts to achieve efficient and sustainable preparation of FF from xylose or hemicellulose in this work. Furfural yields of 75.4% or 80.4% were achieved under optimal operating conditions with [Hpy][HSO4] as catalyst, hemicellulose or xylose as substrates, higher than those catalysed with most ionic liquids reported so far. The chemical structures of BAILs were confirmed by NMR and FT-IR spectroscopy, and the Hammett acidity (H0) were determined using UV–vis spectroscopy with 4-nitroaniline as probe. The acidity of BAILs were tuned through methyl substitution on the pyridinium ring, and its effect on the catalysis performance was investigated. In addition, the reaction constants and the corresponding activation energies of BAILs for dehydration of xylose to FF were calculated by kinetic equations. Overall, the highly efficient catalysis performance, good recyclability and low cost enables [Hpy][HSO4] to be potentially applied for large-scale preparation of FF.

PolyE-IL Is an Efficient and Recyclable Homogeneous Catalyst for the Synthesis of 5-Hydroxymethyl Furfural in a Green Solvent.

5-Hydroxymethyl furfural (5-HMF) is a potential platform molecule with multidimensional applications and can be produced from biomass-based hexose sugars. In the present article, polyethyleneimine (PEI)-functionalized polymeric Bronsted acid ionic liquid (PolyE-IL) catalyst has been explored for fructose dehydration in the presence of isopropyl alcohol (IPA) as a green and low-boiling-point (LBP) organic solvent. The use of homogeneous PolyE-IL catalyst provides several specific advantages in terms of high yield, conversion, selectivity, ease of catalyst separation, recycle and reuse, and so forth. PEI with various Bronsted acid counterions such as H2SO4, H3PO4, TsOH, TfOH, and TFA provides the corresponding variables of PolyE-IL such as [PEI]+[HSO3]-, [PEI]+[H2PO4]-, [PEI]+[CF3CO2]-, [PEI]+[TfO]-, and [PEI]+[TsO]-, which are tested for fructose dehydration in the presence of IPA. Of the tested catalysts, only PolyE-IL with [HSO4]-, [CF3CO2]-, [TfO]-, and [TsO]- counterions showed the formation of 5-HMF. [PEI]+[HSO4]- showed the maximum yield of 5-HMF (61%) and selectivity (70%) with (87%) fructose conversion. Thus, further process optimization study was conducted to obtain the maximum yield, conversion, and selectivity. The intensified process provides a maximum yield of 5-HMF of 75% with 85% fructose conversion and 90% selectivity. The catalyst recyclability study showed the consistency in 5-HMF yield (75%), conversion (85%), and selectivity (90%) for five consecutive recycle runs. However, the study of reaction kinetics showed the first-order kinetics with an activation energy of 12.4 kJ/mole by using [PEI]+[HSO4]- catalyst. Thus, the use of an easily recyclable and robust catalyst provides an efficient route for production of 5-HMF in the presence of a green solvent.

Groebke‐Blackburn‐Bienaymé Multicomponent Reaction Catalysed by Reusable Brønsted‐Acidic Ionic Liquids

AbstractIn the present work, the use of Brønsted acidic ionic liquids (BAIL) as catalysts for Groebke‐Blackburn‐Bienaymé (GBB) multicomponent reactions was systematically investigated. A series of four 1‐(butyl‐4‐sulfonic)‐3‐methylimidazolium salts bearing different anions was easily prepared and screened as acidic catalysts for this transformation. The best reaction conditions were stablished as 20 mol % of catalyst [(SO3H)4C4C1Im][OTf] in refluxing EtOH or MeOH under conventional heating and in sealed tube at 150 °C for 1–4 hours under microwave heating, affording a series of imidazo‐fused heterocycles in moderate to excellent yields (42–93 %). The homogeneous BAIL catalyst could be recycled and reused in four consecutive reaction cycles, despite of a laborious recovery procedure employed. This approach represents the first example of a task‐specific reusable homogeneous Brønsted acidic catalyst in GBB reactions and opens new opportunities for the exploration of acidic ionic liquid phases as catalysts for this fascinating multicomponent reaction.

Iridium-Functionalized Cellulose Microcrystals as a Novel Luminescent Biomaterial for Biocomposites

Microcrystalline cellulose (MCC) is an emerging material with outstanding properties in many scientific and industrial fields, in particular as an additive in composite materials. Its surface modification allows for the fine-tuning of its properties and the exploitation of these materials in a plethora of applications. In this paper, we present the covalent linkage of a luminescent Ir-complex onto the surface of MCC, representing the first incorporation of an organometallic luminescent probe in this biomaterial. This goal has been achieved with an easy and sustainable procedure, which employs a Bronsted-acid ionic liquid as a catalyst for the esterification reaction of -OH cellulose surface groups. The obtained luminescent cellulose microcrystals display high and stable emissions with the incorporation of only a small amount of iridium (III). Incorporation of MCC-Ir in dry and wet matrices, such as films and gels, has been also demonstrated, showing the maintenance of the luminescent properties even in possible final manufacturers.

2-Hydroxyethylammonium Bisulfate (2-HEAS) as a Brønsted Acidic Ionic Liquid Catalyst for Esterification

Brønsted acidic ionic liquids (BAILs) with great variety as effective catalysts for the synthesis of valuable chemicals such as esters have attracted particular attention. In this work, an ionic acid 2-hydroxyethylammonium bisulfate (2-HEAS) was successfully synthesized and used to catalyze esterification reactions. The powerful FTIR and NMR techniques were used to determine the ionic liquid properties. All results and data showed that the ionic liquid has been synthesized successfully. The catalytic activity of IL during esterification of acetic acid in the presence of various alcohols was investigated. The impacts of a few imperative parameters such as reaction time and temperature, molar ratio of acid to alcohol, and catalyst dosage were investigated. The results showed that the 2-HEAS catalyst is suitable for esterification of methanol, ethanol, and butanol. Furthermore, the esterification efficiencies of methyl acetate, ethyl acetate, and butyl acetate produced were high and quantitative. Moreover, a homogeneous catalyst was employed to separate esters from the reaction medium. Additionally, the catalyst was easily removed from products and was reusable six times.

Brønsted acidic ionic liquid‐catalyzed and ultrasound‐promoted transesterification of fish oil with ethanol

AbstractFour typical Brønsted acidic ionic liquids (BILs) and concentrated sulphuric acid (H2SO4) were used to catalyze the transesterification of fish oil with ethanol to produce fatty acid ethyl ester (FAEE) in this work. The experimental results show that the imidazole BILs lead to fewer side reactions and higher product quality than H2SO4. Molecular dynamics (MD) simulations indicate that [PSMim][HSO4] molecules can be enriched at the interface and enhance the contact of eicosapentaenoic acid triglyceride (EPATG, a typical component of fish oil) and ethanol. And ester groups of EPATG tend to expose more to ethanol in the BILs system, which facilitates the occurrence of transesterification. However, H2SO4 has no positive effect on the distribution of the two reactants. For the transesterification, the interfacial property affects the catalytic activity a lot, instead of catalyst acidity. Also, the reaction rate is accelerated, obviously, by ultrasound‐led liquid–liquid phase emulsification.

A polymeric Brønsted acid ionic liquid mediated liquefaction of municipal solid waste

The rapid industrialization and population explosion continuously generate massive amounts of municipal waste. Several conventional processes are in practice for the treatment of municipal waste, but the requirement of stringent operating conditions, incomplete conversion, longer processing time and emission of toxic gases, etc., are the major associated barriers. Thus, there is an urgent requirement for a sustainable, environmentally feasible process that can process waste into energy and fuel products. In the present manuscript, polyethylenimine functionalized polymeric Bronsted acid ionic liquid (PolyE-IL) catalysts have been explored for the Catalytic Thermo Liquefaction (CTL) of organic biodegradable municipal solid waste (MSW). A series of PolyE-IL catalysts with variable counter ions were examined for CTL of MSW. Of all the tested PolyE-IL catalysts, the integration of [PEI]+[HSO4]- gave excellent MSW conversion (>85%) and yield (>80%) of liquefied products (CTL-Oil) under non-stringent reaction conditions and without any formation char and gases. The influence of reaction conditions such as catalyst concentration, reaction temperature, time, slurry concentration, and type of feedstock of conversion and yield are studied. The column adsorption and membrane separation process was integrated to facilitate the catalyst and CTL-Oil separation. A series of commercially available hydrophobic resins were tested to separate catalyst and CTL-Oil. ICT005 showed the highest adsorption efficiency of all tested resins with 35.46 mg/mL of binding capacity and Kd of 0.02159. The physicochemical properties of CTL-Oil were studied in detail by using various analytical tools, which exhibited that CTL-Oil comprises a mixture of small and large molecular weight organic compounds and has a calorific value of 4000 kcal/kg; hence it could be used for further energy and fuel applications. Thus, the reported CTL process can be beneficial to resolve both environmental and fossil fuel dependency issues simultaneously by converting MSW into CTL-Oil.

Fabrication of Brønsted acidic ionic liquids functionalized organosilica nanospheres for microwave-assisted fructose valorization

A series of Brønsted acidic ionic liquids (BAILs) functionalized hollow organosilica nanospheres ([C3/4Im][OTs/OTf]-Si(Et)Si, C3/4 = Pr/BuSO3H) were synthesized by two steps. The process involved the preparation of hollow nanosphere supports via a toluene-swollen sol-gel co-condensation of 1,2-bis(trimethoxysilyl)ethane and 3-chloropropyltriethoxysilane in the presence of F127, and followed by a successive quaternary ammonization and protonation with imidazole, 1,3-propane/1,4-butane sultone and trifluoromethane sulfonic acid/p-toluenesulfonic acid. The adjustable acid property, hollow inner diameter (5–15 nm) and shell thickness (5–9 nm) of [C3/4Im][OTs/OTf]-Si(Et)Si are achieved by introducing different organic acids and controlling toluene concentration, respectively. The [C3/4Im][OTs/OTf]-Si(Et)Si were applied in selective conversion of fructose to 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF) under microwave heating. Under the optimized conditions, the [C4Im][OTs]-Si(Et)Si3.0 nanospheres with the largest inner diameter and the smallest shell thickness exhibit the highest HMF yield (79.4%, 15 min) in fructose dehydration. And the [C3Im][OTf]-Si(Et)Si0.5 nanospheres with the highest acid strength possess the highest EMF yield (70.4%, 30 min) in fructose ethanolysis. The high Brønsted acid-site density and acid strength of [C3/4Im][OTs/OTf]-Si(Et)Si catalysts accompanied by high microwave heating energy lead to excellent dehydration/ethanolysis activity. The product selectivity strongly depended on the BAILs structures and morphological characteristics of the catalyst. More importantly, the [C3/4Im][OTs/OTf]-Si(Et)Si can be reused three times without changes in leaching of BAILs, due to strong covalent bond between BAILs and silicon/carbon framework. This work will provide a simple strategy of chemically bonded BAILs on suitable supports as efficient solid acids, and an approach of combining morphology-controlled solid acids with microwave-heating for catalytic conversion of biomass/derivatives to fuels and value-added chemicals.

Effect of molecular structure of cation and anions of ionic liquids and co-solvents on selectivity of 5-hydroxymethylfurfural from sugars, cellulose and real biomass

The concept of biorefinery still requires advancements in process development for energy and materials. Ionic liquids have been successfully used for several biorefinery applications including high yield synthesis of biofuels and value added platform chemicals. Designing suitable ionic liquid that is efficient in terms of cost as well as product selectivity is still highly needed. This study is carried out to check the effect of different anions of Bronsted acidic ionic liquids (BAILs), Bronsted Lewis acidic ionic liquids (BLAILs), Lewis acidic ionic liquids (LAILs) as well as organic electrolyte solutions (OES) for 5-HMF selectivities from monosaccharides, polysaccharides as well as lignocellulosic composite. Different variables and parameters such as Lewis acidity of anions, alkyl side chain of ionic liquid, metal chloride type and loading, time, temperature, substrate loading, polar protic and aprotic solvents are thoroughly studied for process optimization. Polar protic solvents added in [C1C4SO3HPy] based ionic liquids with CH3COO− and Cl− anions yielded 94 and 80% 5-HMF from fructose and glucose respectively in the presence of AlCl3 as Lewis acid. C4SO3H side chain yielding high from fructose and glucose is inefficient for conversion of cellulose and lignocellulose. High product selectivity from these biopolymers is achieved using butyl side chain with 3-methylpyridinium cation and chlorochromate anion.

PH of Single and Double Salt SO3H-Functionalized Brønsted Acidic Ionic Liquids

Acidic ionic liquids are widely utilized as catalysts in acid-catalyzed reactions. The acidity of SO3H-functionalized Bronsted acidic ionic liquids (S-BAILs) in aqueous solutions was systematically...

Synthesis of N-arylacetamides via amination of aryltriazenes with acetonitrile under metal-free and mild conditions

A transition-metal-free synthetic strategy has been developed for the synthesis of N-aryl amides. The present amination reaction of aryltriazenes with acetonitrile was carried out with acetonitrile as nitrogen donor, stable aryltriazenes as aryl precursors by the cleavage of CN bond, water as oxygen source, and Brønsted acidic ionic liquids (BAILs) as potential promoter under ambient conditions. Remarkably, the practicality of this method was further proved through the reusability of the promoter BAILs. The environmentally benign nature, stable and readily available starting materials make the protocol more attractive for preparing N-aryl amides than traditional methods.

Solvent-free synthesis of 4-substituted coumarins catalyzed by novel brønsted acidic ionic liquids with perchlorate anion: a convenient and practical complementary method for pechmann condensation

Herein, three novel sulfonic-functionalized Bronsted acidic ionic liquids containing perchlorate anion counterparts were prepared and well characterized using FTIR, 1H and 13C NMR, Electro-Spray Ionization Mass Spectrometry (ESI-MS), elemental analysis (CHNS) and TG techniques. These ionic liquid catalysts were prepared through simple and ecofriendly procedures and then applied as efficient catalysts with high yields under solvent-free conditions for the synthesis of 4-substituted coumarins through the Pechmann condensation of different phenols and β-ketoesters. Compared to previous works, the proposed method offers several benefits, such as cleaner reactions, decreased reaction times, high yields, and the lack of laborious workup or purification procedures. Particularly, these catalysts make the condensation of less activated phenols feasible. Besides the described benefits, this advanced protocol was applied successfully for the synthesis of coumarins from γ-lactones such as 3-acetyldihydrofuran-2(3H)-one. The simplicity in operation, applicability and feasibility of this protocol for diverse substrates make it an efficient alternative to conventional methods.

Introduction of novel brønsted acidic ionic liquids with perchlorate counter-anion for one-pot synthesis of symmetric 3,3′-diaryloxindoles

In this work, three novel 1,4-butane sultone-based Bronsted acidic ionic liquids with Perchlorate conter-anion are prepared. These newly introduced ionic liquids were synthesized from a two-steps reaction. The reaction includes ring opening of 1,4-butane sultone using 1,4-dimethylpiperazine or 1,10-phenantroline as nitrogen nucleophile sources to obtain zwitterions and then follow by acidification treatment with perchloric acid to obtain three novel Bronsted acidic ionic liquids. The prepared task specific ionic liquids and their stable intermediates were characterized by FT-IR, 1HNMR, 13C-NMR, UV–Vis, TGA and CHNS analysis techniques. The prepared ionic liquids are fully water soluble and have good thermal stability up to 200 °C or higher. Their catalytic efficiency was checked for the preparation of symmetric 3,3′-diaryloxindoles compounds. It was found that the introduced acidic ionic liquids are completely green, environmental benign, task specific and have high catalytic stability. These novel acidic ionic liquids are simply separable by extraction from organic phase by solving in water up to six consecutive runs and give the target products in short reaction times at high yields.

Intriguing role of novel ionic liquids in stochastic degradation of chitosan

Green technique for hydrolysis of chitosan was developed using novel Brønsted Acidic Ionic Liquids (BAILs) as homogenous reusable catalysts. Efficiency of BAILs in controlling stochastic and irregular breakdown of chitosan was compared with that of mineral acids. Structural elucidation of the novel BAILs was performed using H1-NMR evaluation and supplemented using mass spectroscopy. Additionally, thermal characterization was conducted using TGA-DTA analysis, while acidity was estimated by deriving the Hammet acidity function. BAILs investigated in this work enabled consistent production of LMWCS variants, with minimum formation of residual impurities. Around 80 % reduction in molecular weight was noted as compared to original under extreme conditions employed. Further, Box-Behnken Design (BBD) was implemented to optimize effect of processing parameters for conversion of chitosan to low molecular weight congeners.

Solvent‐free synthesis of compounds containing chromene core catalyzed by novel Brønsted acidic ionic liquids‐ClO4

AbstractA series of novel sulfonic acid‐functionalized Brønsted acidic ionic liquids (BAILs) with perchlorate counter anion are introduced. These ionic liquid catalysts were prepared through simple and eco‐friendly procedures in high yields. Various analytical techniques such as Fourier transform infrared, 1H and 13C NMR, electro‐spray ionization mass spectrometry, elemental analysis (CHNS), and thermogravimetric techniques were used for well characterization of these catalysts. Next, the prepared BAILs were applied as efficient catalysts with high yields under solvent‐free conditions for the synthesis of chromenes. The proposed method offers several superiorities, such as high yields, decreased reaction times, cleaner reactions, and the lack of laborious workup or purification procedures. The simplicity in operation, applicability, and feasibility of this protocol for diverse substrates makes it an efficient alternative to conventional methods.

Theoretical Investigation of the Mechanism, Performance and Kinetic Experimental Phenomena on Brønsted Acidic Ionic Liquids Catalyzed Dehydration of Sorbitol to Isosorbide

AbstractThe dehydration of sorbitol to isosorbide catalyzed by Brønsted acidic ionic liquids (BILs) have been investigated in detail by performing density functional theory (DFT) calculations. It is found that the double dehydration processes involve an intrinsically consistent molecular mechanism: protonation followed by cyclization, and that throughout most of elementary steps, the sulfonic group in the cation of BIL functions as a Brønsted acid/base catalyst, and the anion participates in the reaction as a nucleophile. For 1‐propylsulfonic acid‐3‐methylimidazolium trifluoromethanesulfonate ([C3SO3Hmim]CF3SO3)‐catalyzed reaction, the calculated free energy barrier of the first dehydration step is higher than that of the second dehydration step, rationalizes well the experimentally observed kinetics that the latter has a larger rate constant than the former. In addition, the association energy of [C3SO3Hmim]CF3SO3 with sorbitol is larger than that with either 1,4‐sorbitan or isosorbide, which is consistent with observed association equilibrium constants. BIL carrying a methyl group at the C2 position of imidazolium ring, [C3SO3Hdmim]CF3SO3, shows much better catalytic performance than other tested BILs. The effectiveness of the catalytic system is attributed to the widely distribution of hydrogen‐bonding interactions in transition states and the superior nucleophilicity of the CF3SO3 anion.