A green and novel procedure for the preparation of ionic liquid

A green and novel procedure is described for the preparation of a series of ionic liquid containing alkylimidazolium-based or N-alkylpyridinium-based cations and hexafluorophosphate-based or tetrafluoroborate-based anions in one-pot solvent-free conditions to give excellent yields with shortened time.     

Preparation and characterization of novel organosoluble and thermally stable poly(benzimidazole-amide)s bearing phthalimide pendent groups

Novel aromatic poly(benzimidazole-amide)s, PBAs, have been synthesized by direct polycondensation of a new dicarboxylic acid, N-[3,5-bis(5-carboxylic acid-2-benzimidazole) phenyl]phthalimide (1), containing performed benzimidazole rings and a phthalimide pendent group with various aromatic diamines. The dicarboxylic acid was synthesized by reaction of 5-(N-phthalimide)isophthalic acid with 4-methyl-1,2-phenylenediamine in polyphosphoric acid, followed by its oxidation into relative dicarboxylic acid. To study the structure-property relationships of 1,3-bis(5-carboxylic acid-2-benzimidazole)benzene (2, as a reference) this compound was also synthesized. The chemical structure of 1 and 2 were confirmed by the spectroscopic methods and elemental analyses. The characterization of the polymers was performed with inherent viscosity measurements, solubility tests, FT-IR, Ultraviolet and ¹H NMR spectroscopy and thermogravimetry. The polymers were obtained in quantitative yields with inherent viscosities between 0.53 and 0.91 dl g⁻¹. The effects of the phthalimide pendent group on the polymer properties such as solubility and thermal behavior were investigated and compared with those of the corresponding unsubstituted poly(benzimidazole-amide)s. The modified poly(benzimidazole-amide)s showed enhanced solubilities in some solvents, such as m-cresol and pyridine, in comparison to the unmodified analogues. In addition, the incorporation of the pendent phthalimide groups in the poly(benzimidazole-amide)s backbone increased remarkably the thermal stability of the polymer. The glass transition temperature and 10% weight loss temperature of the poly(benzimidazole-amide)s were in range of 291-334 °C and 466-540 °C, respectively, in nitrogen.     

A new green approach for the synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthene-11-one derivatives using task specific acidic ionic liquid[NMP]H_2PO_4

12-Aryl-8,9,10,12-tetrahydrobenzo[a]xanthene-11-one derivatives were synthesized by a convenient and environmentally benign procedure involving multicomponent condensation reactions of substituted aromatic aldehydes with 2,7-dihydroxynaphthalene/2-naphthols/2,6-dihydroxynaphthlene and cyclic 1,3-dicarbonyl compounds in task specific acidic ionic liquid[NMP]H_2PO_4 at 80 ℃.This protocol has proved to be efficient in terms of good yields,operational simplicity,easy workup,recyclability of reaction medium/catalyst,and short reaction time.     

Use of ionic liquid and microwave irradiation as a convenient, rapid and eco-friendly method for synthesis of novel optically active and thermally stable aromatic polyamides containing N-phthaloyl-l-alanine pendent group

An efficient, fast and easy method for synthesis of new optically active and thermally stable aromatic polyamides (PAs) containing pendent phthalimide group and l-alanine flexible side spacer using room temperature ionic liquid (RTIL) by microwave irradiation has been investigated. The results found that RTIL efficiently absorb microwave energy, thus leading to a very high heating rate. All the PAs showed excellent solubility and readily dissolved in various organic solvents. Thermogravimetric analysis (TGA) exhibited that polymers were stable, with 10% weight loss recorded above 373 and 418 °C in the nitrogen atmosphere. In order to see the efficiency of microwave irradiation, this method was compared with polycondensation of the same monomers in RTILs using conventional heating.     

Preparation of alkaline anion exchange membranes based on functional poly(ether-imide) polymers for potential fuel cell applications

A novel poly(ether-imide)-based alkaline anion exchange membrane with no free base has been prepared and characterized for its ionic conductivity in water, which is a critical metric of its applicability in a liquid-fed direct methanol fuel cell. The poly(ether-imide)-based membranes were prepared by chloromethylation, quaternization and alkalization of commercial poly(ether-imide) and the derivatives were characterized by NMR. The chemical and thermal stabilities were investigated by measuring changes of ionic conductivities when the membranes were placed in various alkaline concentrations and temperatures for 24 h. The membranes were stable at all concentrations of KOH at room temperature, but not at elevated temperatures. The membranes were stable in 1.0 M KOH solution up to 80 °C without losing membrane integrity. The measured conductivity of the formed membrane ranged from 2.28 to 3.51 × 10⁻³ S/cm at room temperature. This preliminary study indicates that functionalized poly(ether-imide) has suitable conductivity suggesting that it can be used as an alkaline anion exchange membrane in fuel cell applications.     

A novel type of Si-containing poly(urethane-imide)s: synthesis, characterization and electrical properties

A novel type of a Si-containing poly(urethane-imide) (PUI) was prepared by two different methods. In the first method, Si-containing polyurethane (PU) prepolymer having isocyanate end groups was prepared by the reaction of diphenylsilanediol (DSiD) and toluene diisocyanate (TDI). Subsequently the PU prepolymer was reacted with pyromellitic dianhydride (PMDA) or benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl pyrolidone (NMP) to form Si-containing modified polyimide directly. In the second method, PU prepolymer was reacted with diaminodiphenylether (DDE) or diaminodiphenylsulfone (DDS) in order to prepare an amine telechelic PU prepolymer. Finally, the PU prepolymer having diamine end groups was reacted with PMDA or BTDA to form a Si-containing modified polyimide. Cast films prepared by second method were thermally treated at 160 °C to give a series of clear, transparent PUI films. Thermogravimetric analysis indicated that the thermal degradation of PUI starts at 265 °C which is higher than degradation temperature of conventional PU, confirming that the introduction of imide groups improved the thermal stability of PU.To characterize the modified polyimides and their films, TGA, FTIR, SEM and inherent viscosity analyses were carried out. The dielectrical properties were investigated by the frequency-capacitance method. Dielectric constant, dielectric breakdown strength, moisture uptake and solubility properties of the films were also investigated.     

Design and synthesis of fused-ring chiral ionic liquids from amino acid derivatives

Six novel imidazolium salts, which contain a chiral moiety as well as a fused-ring system, have been designed, synthesized, and fully characterized. The synthesis of these ionic liquids is concise and practical due to the commercial availability of the starting materials. These imidazolium compounds were readily prepared from 1-methyl-2-imidazoliumcarboxaldehyde and chiral amino alcohols. Salts that contain the PF₆ anion were solids, but salts with the NTf₂ anion were liquids at room temperature. We envision that these new chiral imidazolium compounds can serve as effective reaction media as well as chiral catalysts for asymmetric reactions, which are presently being investigated in our lab.     

Green approach for the conversion of olefins into vic-halohydrins using N-halosuccinimides in ionic liquids

Alkenes undergo smooth bromo- and iodohydroxylation with N-bromo- and N-iodosuccinimides/water, respectively, using the air and moisture stable ionic liquid [bmim]BF₄ as a novel recyclable reaction medium in high to quantitative yields. N-Halosuccinimides show enhanced reactivity in ionic liquids thereby reducing the reaction times and improving the yields considerably.     

Facile synthesis and properties of a new generation of soluble and thermally stable polyimides

A new diamine, 1,4-phenylene bis((E)-1-(4-chloro-3-aminobenzylidene) thiourea) (PCABT), containing phenylthiourea and azomethine groups was prepared from the reduction of dinitro compound, 1,4-phenylene bis((E)-1-(4-chloro-3-nitrobenzylidene)thiourea), PCNBT. The structures of resulting monomers were characterized by elemental analysis, FTIR, ¹H and ¹³C NMR techniques. Afterwards, this diamine was reacted with various aromatic dianhydrides (ODPA, BTDA and 6FDA) in glacial acetic acid to afford poly(phenylthiourea azomethine imide)s (PPTAIs) with η_inh of 1.59-1.66 dL/g, depending on the dianhydride used. The ensuing PPTAIs exhibited ample solubility in organic solvents (DMAc, DMF, DMSO and NMP) and were obtained in quantitative yields. Also, all polyimides were amorphous according to wide-angle X-ray determination. GPC measurements of polymers revealed M_w around 69,000-72,000. Moreover, thermogravimetric analyses indicated that PPTAIs were fairly stable up to 550 °C, and 10% weight loss temperatures were recorded in the range of 563-578 °C (N₂ atmosphere). Ultimately, these polyimides own high glass transition temperatures about 281-285 °C.     

A facile and highly efficient protocol for synthesis of poly(ether sulfone)s in ionic liquid/zwitterion

A benign approach for efficient preparation of poly(ether sulfone)(PES)(η_(inh) = 0.10-0.31 dL×g~(-1)) has been presented by using ionic liquid(IL)/zwitterion(ZI) as reaction medium. It has been found that the interaction between 4,4′-dihydroxydiphenylsulfone(Bisphenol-S) and ZI at elevated temperatures results in efficient reduction of dehydration time, which is confirmed by TGA curves, melting point of the mixture and FTIR spectra. Furthermore, no agglomeration is observed at dehydration stage, which is attributed to the high solubility of Bisphenol-S dipotassium salt in IL/ZI. This also makes the polymerization temperature(150 °C) much lower than a conventional method(220-300 °C). In order to demonstrate the efficiency of IL/ZI as reaction medium, the polymerization was also performed in sulfolane under the same reaction condition as that in IL/ZI.     

Degradation study on the thermally stable nickel phthalocyanine sheet polymer

Poly (nickel phthalocyanine) which has exceptional thermal stability is synthesized. Knowledge of modes of degradation of this polymer is found to be necessary for its high temperature applications. This polymer showed very high thermal stability with maximum polymer decomposition temperatures (PDT_max) of 500 °C in air and 890 °C in N₂, with char yield 93% at 800 °C. Because of its excellent thermal stability, degradation study with MS as well as GC–MS techniques were found to be very difficult. The present publication deals with MS and GC–MS studies of nickel phthalocyanine sheet polymer at high temperatures ranging from 700 to 1000 °C. Tentative mechanisms are proposed for its modes of fragmentations and based on GC–MS studies, the most probable degradation products are identified.     

A green approach for efficient synthesis of N-substituted pyrroles in ionic liquid under microwave irradiation

A rapid synthesis of N-substituted pyrroles has been described by the reaction of 4-hydroxyproline with isatins in ionic liquid under microwave irradiation. The recovered ionic liquid was reused for six cycles. The reaction proceeds without the addition of any acid promoter     

Three-component coupling reactions in ionic liquids: One-pot synthesis of isoxazolidines

1-Butyl-3-methylimidazolium based ionic liquids are found to accelerate significantly the intermolecular 1,3-dipolar cycloaddition of nitrones derived in situ from aldehydes and phenyl hydroxylamine, with electron deficient olefins to afford enhanced rates and improved yields of isoxazolidines with high regio- and diastereoselectivity.     

Facile ionic liquid-mediated,three-component sequential reactions for the green,regio- and diastereoselective synthesis of furocoumarins

An environmentally friendly approach to the diastereoselective synthesis of trans-4-oxo-3-aryl-3,4-dihydro-2H-furo[3,2-c]coumarin-2-carbonitriles, trans-2-benzoyl-3-(aryl)-2H-furo[3,2-c]chromen-4(3H)-ones and trans-ethyl-4-oxo-3-(aryl)-3,4-dihydro-2H-furo[3,2-c]chromene-2-carboxylates in good yields is described. The method is based on the sequential multicomponent reactions of 4-hydroxycoumarin, aromatic aldehydes and in situ generated cyanomethylpyridinium, phenacylpyridinium/(2-ethoxy-2-oxoethyl)pyridinium ylides, in the presence of the ionic liquid [BMIm]OH, which functions both as a catalyst and the reaction medium.     

Evaporation of ionic liquids at atmospheric pressure: study by ion mobility spectrometry

A conventional ion mobility spectrometry (IMS) was used to study atmospheric pressure evaporation of seven pure imidazolium and pyrrolidinium ionic liquids (ILs) with [Tf₂N], [PF₆], [BF₄] and [fap] anions. The positive drift time spectra of the as-received samples measured at 220 °C exhibited close similarity; the peak at reduced mobility K₀ = 1.99 cm² V⁻¹ s⁻¹ was a dominant spectral pattern of imidazolium-based ILs. With an assumption that ILs vapor consists mainly of neutral ion pairs, which generate the parent cations in the reactant section of the detector, and using the reference data on the electrical mobility of ILs cations and clusters, this peak was attributed to the parent cation [emim]. Despite visible change in color of the majority of ILs after the heating at 220 °C for 5 h, essential distinctions between spectra of the as-received and heated samples were not observed. In negative mode, pronounced peaks were registered only for ILs with [fap] anion.     

Synthesis of star polymeric ionic liquids and use as the stabilizers for high internal phase emulsions

A series of well-defined core cross-linked star (CCS) polymeric ionic liquids (PILs) were synthesized via a three-step approach. First, the styrenic imidazole-based CCS polymer (S-PVBnIm) was prepared by the RAFT-mediated heterogeneous polymerization in a water/ethanol solution, followed by the quaternization of S-PVBnIm with bromoalkanes and anion exchange. The CCS polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained CCS polymers were used as the effective emulsifiers for oil-in-water high internal phase emulsions (HIPEs). Multiple oils with different polarity including n-dodecane, undecanol, toluene and octanol were emulsified using 0.5 wt% S-PVBnIm aqueous solution under the acidic condition to form HIPEs with long-term stabilities. The excellent emulsification properties of CCS PILs were demonstrated by HIPE formation for a variety of oils. The properties of HIPEs in terms of emulsion type and oil droplet size were characterized by the confocal laser scanning microscopy (CLSM). The intriguing capability of CCS PILs to stabilize HIPEs of various oils holds great potentials for the practical applications.     

An efficient and green sonochemical synthesis of some new eco-friendly functionalized ionic liquids

Considerable stress to replace a lot of volatile organic compounds which were used as solvents in synthetic organic chemistry has been done for many chemical industries. A suitable solution for these problems is found by using the ionic liquids as a clean medium of working and avoiding the solvent effect. The present work describes a facile and green ultrasound-assisted procedure as an environmentally friendly alternative to traditional methods for the preparation of a series of 26 new functionalized imidazolium-based ionic liquids. Their structures were characterized by FT-IR, ¹H, ¹³C, ¹¹B, ¹⁹F, ³¹P NMR and mass spectra.     

Synthesis, characterization, and catalytic activity of ionic liquids based on biosources

New room-temperature ionic liquids were synthesized from natural and easily available feedstocks (choline hydroxide and amino acids) following an economical and green route in which the only by-product was water. They were successfully applied as catalysts for the Knoevenagel test reaction between benzaldehyde and different active methylene compounds, at room temperature and under solvent-free conditions, to produce α,β-unsaturated carbonyl compounds, exhibiting good conversions and high selectivities. The catalytic role of cholinium and aminoacetate ions in the Knoevenagel condensation is discussed.     

Ionic liquid accelerated intramolecular hetero-Diels-Alder reactions: a protocol for the synthesis of octahydroacridines

2-Azadienes derived in situ from arylamines and (R)-(+)-citronellal/3-methylcitronellal undergo intramolecular [4+2] hetero-Diels-Alder reactions in the air and moisture stable ionic liquid [bmim]BF₄ in the absence of any acid catalyst to afford 1,2,3,4,4a,9,9a,10-octahydroacridine derivatives in high to quantitative yields.     

A new fluorinated anion for room-temperature ionic liquids

A new room-temperature ionic liquid (RTIL) consisting of the fluorinated anion bis(trifluoromethyl)-phosphinate((CF₃)₂PO₂⁻) coupled with the 1-butyl-3-methyl-imidazoliuim (BMIM) cation has been synthesized and characterized by physicochemical and electrochemical means including differential scanning calorimetry (DSC), thermogravimetric analysis, viscosity, conductivity and cyclic voltammetry measurements. Properties are compared with those of the known RTIL consisting of BMIM coupled with the bis(trifluoromethyl)-sulfonylimide (TFSI) anion.