Halogen-free Ionic Liquid Research Articles

Tribological performance of phosphonium-based halogen-free ionic liquids as lubricant additives

In recent years, ionic liquids have shown great potential as an additive in lubricants. However, most of the explored ionic liquids for machining applications contain halogen-based anions, which are sensitive to moisture and have a tendency to produce harmful halogen acids (HX) after reacting with water/moisture. These acids are harmful to the environment and can corrode the working surfaces. This study investigates the effectiveness of halogen-free ionic liquids as potential additives to vegetable oil (canola oil). Two halogen-based ionic liquids (1-methyl 3-butylimidazolium tetrafluoroborate [BMIM BF4] and 1-methyl 3-butylimidazolium hexafluorophosphate [BMIM PF6]) and one halogen-free ionic liquids (trihexyl tetradecyl phosphonium bis (24,4-trimethylpentyl) phosphinate P6,6,6,14 [i(C8)2PO2]) were blended individually with canola oil. The percentage ratio of ionic liquid to canola oil is 1:99. Dynamic viscosity and contact angles of different lubricants were measured. Sliding tests were conducted in various conditions; dry, canola oil, and three different blends of ionic liquid with canola oil. Further, to connect tool-chip tribology with machining, turning experiments were carried out under similar lubricating conditions. Results show that the sliding friction, pin surface temperature, and wear were reduced by 48.1%, 44%, and 69.6%, respectively, due to better lubricating ability and spreading tendency of halogen-free ionic liquid blended with canola oil. The microscopic analyses of pin surfaces and the morphology of counter disc surfaces further supported better lubrication between the sliding pair. For P6,6,6,14 [i(C8)2PO2] ionic liquid blended with canola oil, the average cutting temperature and machined workpiece surface roughness reduces by 43.6% and 62.4% compared to dry machining.

Influence of a halogen free ionic liquid on the rheological and tribological characteristics of canola oil

PurposeThis paper aims to develop vegetable oil-based environmentally acceptable lubricants with a halogen-free ionic liquid (IL) as a substitute for petroleum-based lubricants.Design/methodology/approachThe rheological and tribological characteristics of canola oil influenced by 1-ethyl-3-methylimidazolium dicyanamide as an additive along with surfactants have been experimentally investigated. The viscosities of prepared bio-ionic lubricants have been evaluated at a constant shear rate of 100 per second with a temperature ramp from 30°C to 100°C and also by varying shear rate from 1 to 103 per second at constant temperatures of 40°C and 100°C. The solubilization and absorbance of bio-ionic lubricants have been studied by using dynamic light scattering and ultraviolet–visible spectroscopy. Friction and wear effects of bio-ionic lubricants have been evaluated using ball-on-disc tribotester at different speeds and loads.FindingsThe rheological properties of canola oil have been significantly improved with addition of IL. Minimum coefficient of friction and wear have been observed at an optimum concentration of 2 Wt.% of IL. Atomic force microscopy reveals that worn-out surface of ball lubricated with canola oil containing 2 Wt.% IL has smooth surface.Originality/valueThis study demonstrates that halogen-free has the potential to accommodate as an incipient class of EALs.

Machining of titanium alloys using phosphonium-based halogen-free ionic liquid as lubricant additives

PurposeNowadays, ionic liquids (ILs) are used as lubricant additives because of their ability to improve tribological characteristics. However, majority of the ILs contains halogen-based anions. They are extremely sensitive to moisture and produce detrimental halides and halogen acids when reacted with moisture and water. These halides and halogen acids are harmful to the health and environment of the operator’s. This paper aims to study four different lubricants including two halogen-based ILs blended in canola oil and two phosphonium-based halogen-free ILs blended in canola oil and in pure canola oil.Design/methodology/approachViscosity and contact angle were measured by using rheometer and contact angle goniometer, respectively. Machining experiments were performed using turning centre with four different lubricants at two different cutting speeds and temperatures, and the machining forces, tool morphology and roughness of the machined surface were analysed.FindingsThe results showed that the inclusion of 1% phosphonium-based halogen-free ILs blended in canola oil increased the viscosity by 44.8% and reduced the cutting and thrust force by 21.7% and 26.8%, respectively, compared to pure canola oil lubricant. Microscopic analysis of tool showed lower adhesive and abrasive wear when machined with phosphonium-based halogen-free ILs blended in canola oil. The workpiece surface roughness reduced by 32% for phosphonium-based halogen-free ILs blended in canola oil compared with pure canola oil.Originality/valueHalogen-free ILs are possible green lubricants, as they do not contain harmful elements such as F, S, B and Cl like halogen-based ILs. To the best of the authors’ knowledge, this is presumably the first work which shows machining performance of halogen-free ILs as lubricant additives.

HALOGEN FREE [HNMP]+CH3SO3 - IONIC LIQUID MEDIATED BIFUNCTIONALIZED NAPHTHOQUINONE-DIHYDROPYRIMIDIN-(1H)-ONE HYBRIDS AND EVALUATION OF ITS ANTIMICROBIAL POTENTIAL

An efficient halogen free ionic liquid (HFIL) N-methyl-2-pyrrolidonium methane sulfonate [HNMP]+[CH3SO3]- catalyzed Biginelli reaction is reported to synthesize naphthoquinone fused dihydropyrimidin-(1H)-ones (DHPM’s). Diversifying this naphthoquinone constituent provides an access to new and interesting DHPM’s for pharmacological profiling. A series of bifunctionalized naphthoquinone-dihydropyrimidin-(1H)-one conjugates (4a-4l) were synthesized and evaluated for their antimicrobial potential against selected bacterial and fungal pathogenic strains. The resulting naphthoquinone fused dihydropyrimidin-(1H)-one hybrids showed significant activities against all the tested Gram positive (Staphylococcus aureus, Bacillus subtilis) and Gram negative (Escherichia coli, Pseudomonas aeruginosa) bacterial pathogens and fungal strains of Aspergillus niger and Aspergillus flavus. Among the series, the DHPM conjugate 4k>4j>4e>4h samples exhibited highest activities against all the tested strains that proved to be important candidates in the drug development against various life threatening diseases. Presently, one-pot, three-component methodology have been developed for the synthesis of bifunctionalized naphthoquinone linked dihydropyrimidin-(1H)-one are being explored for bio-active asymmetric Biginelli scaffolds.

Micro- to Nano- and from Surface to Bulk: Influence of Halogen-Free Ionic Liquid Architecture and Dissociation on Green Oil Lubricity

Four nonhalogenated ionic liquids (ILs) based on the same phosphonium cation are investigated in terms of the anion suitability for enhancing the lubricity of a biodegradable oil. For all test conditions, typical for industrial machine components, the lubrication is shown to be governed by nonsacrificial films formed by the physisorption of ionic species on the tribo-surfaces. The anionic structure appears to have an important role in the formation of friction modifying films. The orthoborate ILs exhibit the formation of robust ionic boundary films, resulting in reduced friction and better wear protection. On the contrary, the surface adsorption of phosphinate and phosphate ILs appears to antagonistically disrupt the intrinsic lubrication properties of the biodegradable oil, resulting in high friction and wear. Through additional investigations, it is postulated that the higher dissociation of orthoborate ILs in the biodegradable oil allows the formation of hierarchical and electrostatically overscreened layer structures with long-range order, whereas the ILs with phosphate and phosphinate anions exhibit low dissociation in biodegradable oil, possibly due to the ion pairs being surrounded by a hydrocarbon halo, which presumably results in weak adsorption to form a mixed interfacial layer with no long-range order.

A systematic approach of using green solvent for the extraction of Pb (II) from aqueous solution

In this article, the extraction behavior of halogen-free ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, was investigated in the separation of lead from the aqueous solution. Experimental parameters include time, impact of pH, feed concentration, amount of ionic liquid, ionic strength, and temperature were optimized for the evaluation of the lead extraction. From the optimum conditions, it was emanated that the maximum extraction efficiency of lead was 97% with the feed concentration of 10 ppm in an equilibrium time of 60 min at the pH of 5 and 2 g of the ionic liquid, respectively. Furthermore, the extraction results revealed that the higher efficiency was achieved without the addition of salt and that the extraction process was spontaneous and endothermic in nature. The metal complexation was formed by the exchange of ionic liquid anion to the aqueous phase, and thereby, the extraction mechanism was proposed. The ionic liquid in the organic phase was stripped using sodium sulfate as a stripping agent. FTIR analysis confirmed the recoverable ionic liquid and effectively reused it five times in the course of extraction. From the analysis, it was authenticated that the ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, was an effective extractant for the elimination of lead (II) and could be employed for the tertiary treatment of industrial wastes.

Comparing tribology properties of halogen-free ionic liquid, halogen-containing ionic liquid, and PAO 10 lubricants for steel–Al2024 friction contact at room temperature and high temperature

Halogen-free, N/P-containing ionic liquid (NP-IL) was synthesized by combining bis-quaternary ammonium cations with phosphate ester anions and were compared to polyalphaolefin 10 (PAO 10), and a halogen-containing IL (BMIMPF6). The corrosive properties of the NP-IL, BMIMPF6, and PAO 10 lubricants were evaluated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The corrosion performance tests show that NP-IL has better corrosion resistance than that of BMIMPF6 due to its halogen-free characteristics. The tribological performances of NP-IL, BMIMPF6, and PAO 10 were evaluated by Optimol SRV-V oscillating friction tester. The lubricant mechanism of NP-IL was evaluated using SEM, EDS, X-ray photoelectron spectroscopy (XPS), and by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). From the results, the NP-IL was found to be a suitable lubricant for steel–Al2024 friction contacts. During friction, the IL forms a surface-protective film thought tribochemistry, which contributes to reduce-friction (RF) and anti-wear (AW).

Bmim]HSO4-Catalyzed Synthesis of Tetrasubstituted Imidazoles as Potential Mutant Isocitrate Dehydrogenase 1 Inhibitors

An ecofriendly, simple, and efficient one-pot protocol has been developed for the synthesis of 1,2,4,5-tetrasubstituted imidazoles by the reaction of benzil, aryl aldehydes, aliphatic or aromatic amines, and ammonium acetate, catalyzed by the acidic halogen-free ionic liquid [bmim]HSO4 under solvent-free conditions. The advantages of the proposed protocol include high yields, short reaction time, operational simplicity, and recyclability of the catalyst. Eight previously unknown tetrasubstituted imidazoles were synthesized, among which those bearing a cyclopropyl substituent on N1 can be considered as potential mutant isocitrate dehydrogenase 1 (IDH1) inhibitors.

Effect of the TiO2 Anchoring of a Hydrophobic Ionic Liquid in a Fully Aqueous DSSC

This article describes the effect on the efficiency of a fully aqueous dye-sensitized solar cell (DSSC) after the anchoring of the hydrophobic and halogen-free ionic liquid (IL) trioctylmethyl ammonium dodecanedioate (DTMA) on its titanium oxide (TiO2) photo-anode surface. In comparison with nontreated DTMA DSSCs, efficiency increments of 137% and 176% were observed when azo dye Red Reactive 2 and N3 dye were employed as sensitizers, respectively. Since V OC and I SC were increased, it was concluded that DTMA reinforced the dye-TiO2 anchoring, shifted negatively the levels of photo-anode conduction bands, improved electron injection, and reduced recombination losses.

Lipophilic halogen-free ionic liquid with antibacterial and anti-biofilm activities against Pseudomonas aeruginosa

A halogen-free ionic liquid (IL) designed with long alkyl chain anion is reported. 1-methylimidazolium stearate (MIM stearate) synthesized through Bronsted acid-base reaction has shown improved lipophilic character and is able to penetrate bacterial cell walls. Antimicrobial activities against Gram-negative bacteria, Escherichia coli, and Pseudomonas aeruginosa were observed. Anti-biofilm assays showed effectivity against the biofilm of Pseudomonas aeruginosa. At 50 µg/mL the %biofilm inhibition of MIM stearate towards P. aeruginosa biofilm formation is comparable to the Bromofuran positive control. Brine shrimp lethality assay showed weak toxicity indicating the IL to be safe and benign. The synthesized MIM stearate showed good promise as an antimicrobial and anti-biofilm agent.

Facile Construction of Novel Fused Chromeno[2,3-d]Thiazolo[3,2-a]Pyrimidine Derivatives in Biocompatible Ionic Liquid under Solvent-Free Conditions

A simple and efficient three-component reaction is reported between 2,3-dihydro-7-hydroxythiazolo[3,2-a]pyrimidin-5-one, dimedone and aromatic aldehydes for synthesis of biologically important novel heterocycles containing thiazolo[3,2-a]pyrimidine and chromene as biologically active moieties. The SO3H-functionalised halogen-free ionic liquid [MIM(CH2)4SO3H][HSO4-] is found to be an environmentally benign catalyst for this reaction without using any solvent. This SO3H-functionalised ionic liquid could be recovered and used at least four times without considerable reduction in activity. Good functional group tolerance, broad scope of usable substrates and good to excellent yields of products are the other prominent features of the present synthetic protocol.

Novel phosphorus-containing halogen-free ionic liquid toward fire safety epoxy resin with well-balanced comprehensive performance

Most flame retardants used in epoxy resin (EP) inevitably affect its curing process, mechanical properties as well as transparency. To solve this problem, a novel phosphorus-containing halogen-free ionic liquid ([Dmim]Tos), composed of imidazole cation modified with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and tosylate anion, has been designed and used as a flame retardant for EP. DSC non-isothermal curing scans show that [Dmim]Tos has accelerating effect on the curing of EP. The addition of [Dmim]Tos enhances not only the crosslinking density but also the modulus of EP. The unnotched izod impact strength and the glass transition temperatures (Tgs) of EP/[Dmim]Tos are a little lower than pure EP because of the plasticization of unreacted [Dmim]Tos. Due to the good affinity with epoxy resin, low [Dmim]Tos addition almost has no effect on the transparency of EP. Besides, incorporation of 4 wt% [Dmim]Tos into EP makes it pass UL-94 V-0 level and increases the LOI value to 32.5%. Cone calorimeter test indicates the peak heat release rate (p-HRR) of EP/4.0[Dmim]Tos reduces by 37% compared with EP. The flame-retardant mechanism of EP/[Dmim]Tos has been investigated in detail. It is found that the flame-retardant action of [Dmim]Tos on EP is in the gas phase for quenching effect of phosphorus-based radicals and the condensed phase for dehydration of phosphorous fragments.

Tribological Performance of Halogen-Free Ionic Liquids in Steel–Steel and DLC–DLC Contacts

ABSTRACTThe tribological performance of halogen-free ionic liquids at steel–steel and diamond-like carbon (DLC)–DLC contacts was investigated. Hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (ta-C) were used as test specimens. Friction tests were carried out on steel–steel, a-C:H–a-C:H, and ta-C–ta-C contacts by using a reciprocating cylinder-on-disk tribotester lubricated with two different types of halogen-free ionic liquids: 1-ethyl-3-methylimidazolium dicyanamide ([BMIM][DCN]) and 1-butyl-3-methylimidazolium tricyanomethanide ([BMIM][TCC]). From the results of friction tests, the ta-C–ta-C tribopair lubricated with [BMIM][DCN] or [BMIM][TCC] exhibited an ultralow friction coefficient of 0.018–0.03. On the other hand, ultralow friction was not observed at the steel–steel and a-C:H–a-C:H contacts. Measurements obtained with a laser scanning microscope and an atomic force microscope (AFM) showed that a chemical reaction film, derived from the ionic liquid lubricant used, was formed on the steel surfaces. However, this chemical reaction film was not observed on either of the DLC surfaces. The AFM results showed that there were high-viscosity products on the ta-C surfaces, that the wear tracks on the ta-C surfaces exhibited low frictional properties, and that the ta-C surfaces were extremely smooth after the friction tests. Based on these results, it was concluded that an ionic liquid–derived adsorbed film formed on the ta-C surface and resulted in the ultralow friction when lubricated with a halogen-free ionic liquid.

Systematic study of the effects of novel halogen-free anionic surface active ionic liquid on interfacial tension of water/model oil system

In this investigation, a novel anionic- halogen-free ionic liquid (IL), 1-butyl-3-methylimidazolium dodecyl sulfate ([C4mim][C12SO4]), was synthesized and examined for possible application in the chemical enhanced oil recovery (EOR) processes. In this way, the effects of [C4mim][C12SO4] and NaCl concentrations, temperature and model oil type (aliphatic and aromatic hydrocarbons) on interfacial tensions (IFTs) between [C4mim][C12SO4] solutions and model oils were systematically investigated. It is surprisingly revealed that the novel SAIL [C4mim][C12SO4] is highly effective in reducing the IFT of aromatic hydrocarbon/water system, and ultra-low IFT can be achieved in the presence of salinity at higher temperature. Moreover, the interaction energies between [C4mim][C12SO4] and different model oil molecules were calculated using molecular mechanics, which could further interpret the reasons of ultra-low IFT.

Synthesis, optical properties, dyeing study of dihydropyrimidones (DHPMs) skeleton: Green and regioselectivity of novel Biginelli scaffold from Lawsone

Ionic liquids have increased popularly in last couple of decades as solvent for its greener approach. Here a novel three-component, one-pot condensation yielding 4-phenyl-3,4-dihydrobenzo[g]quinazoline-2,5,10(1H)-trione is reported in halogen free ionic liquid (HFIL). Components of reaction are aldehyde, urea, and β-keto esters in presence of HFIL N-methyl-2-pyrrolidonium hydrogen sulfate [HNMP]+[HSO4]−. Comparative reactions were performed under conventional heating and sonication in HFIL. Solvent utility of HFIL makes purification and separation process artless task offering an advantage of five times recyclability without degrading its activity. The use of HFIL is advantageous over conventional solvent due to very short reaction time and halogen-free volatile solvent utility and recyclability. Latterly these compounds applied as disperse dye on polyester and nylon fiber were found to give moderate color and fastness properties.

New ionic liquid lubricants derived from nonnutritive sweeteners

Two series of halogen-free ionic liquid (IL) lubricants, 1-alkyl-3-methylimidazolium saccharinates and acesulfamates, were prepared from nonnutritive sweeteners saccharin sodium and acesulfame potassium. The kinematic viscosity, viscosity index, thermal and hydrolysis stabilities, corrosion and tribological properties of the ILs were systematically evaluated. As compared with conventional halogen-containing ILs, these ILs are resistant to hydrolysis and cause no corrosion to the rubbed metallic surface because of their halogen-free characteristic. They were proved to be good lubricants not only for steel/steel friction pairs but also for steel/copper friction pairs. They can be used as ‘green’ alternatives to conventional halogen-containing IL lubricants as they are environmentally friendly with good biodegradability and reduced toxicity.

Brønsted acidic hydrogensulfate ionic liquid immobilized SBA-15: [MPIm][HSO4]@SBA-15 as an environmentally friendly, metal- and halogen-free recyclable catalyst for Knoevenagel–Michael-cyclization processes

The Brønsted acidic imidazolium-based metal-free and halogen-free ionic liquid hydrogen sulfate was immobilized on nanoporous silica SBA-15. The structures of synthesized catalysts were investigated using different characterization techniques, including FT-IR, small angle XRD, SEM, TEM and TGA. The [MPIm][HSO4]@SBA-15 is used as an alternative to conventional catalysts in the Knoevenagel–Michael-cyclization processes for the synthesis of tetrahydrochromenes and hexahydroquinoline carboxylates via a multicomponent procedure. The reaction time is reduced drastically and the reaction is progressed in an environmentally friendly way. The immobilized catalyst can be recycled without substantial loss of activity after seven runs.

1,1′-Butylenebis(3-methyl-3H-imidazol-1-ium) dihydrogensulfate as a halogen-free and reusable binuclear Brönsted ionic liquid catalyzed the synthesis of pyrano[4,3-b]pyran derivatives

1,1′-Butylenebis(3-methyl-3H-imidazol-1-ium) dihydrogensulfate as an efficient, halogen-free and reusable binuclear Bronsted ionic liquid catalyzed the synthesis of pyrano[4,3-b]pyran derivatives at 60 °C under solvent-free conditions. This method has the advantages of high yield, clean reactions, simple methodology and short reaction time. The ionic liquid could be recycled without significant loss of activity. The structure of the compounds was confirmed by IR, 1H NMR, 13C NMR, mass and elemental analysis.

3-Methyl-1-sulfonic acid imidazolium hydrogen sulfate-catalyzed three-component, one-pot synthesis of 13-aryl-12H-benzo[f]indeno[1,2-b]quinoline-12-one derivatives

3-Methyl-1-sulfonic acid imidazolium hydrogen sulfate, an efficient, halogen-free, and reusable Bronsted ionic liquid, catalyzed the synthesis of 13-aryl-12H-benzo[f]indeno[1,2-b]quinoline-12-one derivatives by one-pot condensation of 2-naphthylamine, aromatic aldehydes, and 2H-indene-1,3-dione under solvent-free conditions. This method has the advantages of high yields, clean reaction, simplicity, and short reaction time. The catalyst can be recycled and reused four times without significant loss of activity.

An efficient and ecocompatible synthesis of annulated benzothiazoloquinazolines in SO3H-functionalized ionic liquid

Structurally diverse annulated benzothiazoloquinazolines have been synthesized by an environmentally benign, efficient, and convenient synthesis involving three-component domino reaction of 2-aminobenzothiazoles, α-tetralone, and furan-2-carbaldehyde/p-methoxybenzaldehyde using an SO3H-functionalized halogen-free ionic liquid ([MIM(CH2)4SO3H][HSO4]) as a catalyst and a reaction medium.