Synthesis and Characterization of Novel Bronsted-Lewis Acidic Ionic Liquids

To meet the demands of some kinds of reactions catalyzed simultaneously by Br?nsted acid and Lewis acid catalyst, two novel Br?nsted-Lewis acidic ionic liquids, 1-carboxyethylene-3-(4-zinc acetate sulfobutyl) imidazolium chloride ([CH3COO-Zn-O3S-bim-CH2CH2COOH]Cl) and 1-(1,2-dicarboxy) ethylene-3-(4-zinc acetate sulfobutyl) imidazolium chloride ([CH3COO-Zn-O3S-bim-C4H5O4]Cl) were synthesized, in which both Br?nsted and Lewis acidic sites existed in the cation. The structures of the ionic liquids were determined by means of FT-IR, 1H NMR and elemental analysis. The results of Py-IR analysis indicated that the two novel ionic liquids have both Br?nsted and Lewis acid properties. The acid strength values (H0) of the ionic liquids were measured utilizing the UV-visible spectroscopy combined with Hammett indicator method, and the acid amount of them was determined by acid-base titration.

Brφsted-acidic ionic liquids as efficient catalysts for the synthesis of polyoxymethylene dialkyl ethers

Acetalation of formaldehyde(HCHO)with dialkyl formal or aliphatic alcohol to prepare polyoxymethylene dialkyl ethers(RO(CH2O)nR,n≥1)catalyzed by Br?nsted‐acidic ionic liquids has been developed.The correlation between the structure and acidity activity of various ionic liquids was studied.Among the ionic liquids investigated,1‐(4‐sulfonic acid)butyl‐3‐methylimidazolium hydrogen sulfate([MIMBs]HSO4)exhibited the best catalytic performance in the reaction of diethoxymethane(DEM1)with trioxane.The influences of ionic liquid loading,molar ratio of DEM1to HCHO,reaction temperature,pressure,time,and reactant source on the catalytic reaction were explored using[MIMBs]HSO4as the catalyst.Under the optimal conditions of n([MIMBs]HSO4):n(DEM1):n(HCHO)=1:80:80,140°C,and4h,the conversion of HCHO and selectivity for DEM2?8were92.6%and95.1%,respectively.The[MIMBs]HSO4catalyst could be easily separated and reused.A feasible mechanism for the catalytic performance of[MIMBs]HSO4was proposed.

Brnsted Acidic Ionic Liquids: Efficient and Recyclable Catalytic Systems for Beckmann Rearrangement

Six Brnsted acidic ionic liquids（ILs） 1a―1f were synthesized and used as the dual solvent-catalyst systems for Beckmann rearrangement reactions. Among ILs 1a―1f, IL 1a exhibited the highest catalytic activity and successfully catalyzed the Beckmann rearrangement of ketoximes, and the corresponding amides were obtained in good to excellent yields（74%―92%）. In addition, IL 1a could be recovered easily and reused at least three times without any loss of catalytic activity.

BrФnsted Acidic Ionic Liquids: Novel Efficient, Cost-effective and Reusable Solvent-catalysts for Ritter Reaction

Several Bronsted acidic ionic liquids（ILs） were synthesized and used as dual solvent-catalysts for the Ritter reaction of benzonitrile with tert-butanol. In particular, IL11（[NSPTEA][OTF]） showed excellent catalytic activity for the Ritter reaction. In the presence of IL11, various nitriles and tertiary alcohols as well as secondary alcohols were converted smoothly to the corresponding amides in good to excellent yields. In addition, this cost-effective ionic liquid [NSPTEA][OTF] was easily separated from the reaction mixture by extraction with a small amount of water, and was recycled five times without any significant loss in activity.

Effect of various functional groups on biodiesel synthesis from soybean oils by acidic ionic liquids

Preparation of biodiesel from soybean oils catalyzed by five acidic ionic liquids with three cationic functional groups was investigated. The improvement of the catalytic activities was affected by various functional groups including pyridine group, N- methylimidazole group, triethylamine group. Among them [C4SO3Hpy]HSO4 with pyridine group showed better catalytic activity with the biodiesel yield of 94.5%, and still yielded more than 90% after six successive uses. The possible mechanism was also discussed by two reaction paths in detail.

Lewis Acidic Guanidinium Ionic Liquids: Novel, Efficient and Recyclable Catalysts for Aminolysis of Epoxides

Lewis acidic guanidinium ionic liquid（LAGIL） 2c was used as a novel, efficient and recyclable catalyst for aminolysis of epoxides under solvent-free and room temperature conditions, giving the corresponding β-amino alcohols with moderate to excellent regioselectivity（up to 91：9） in high yields（up to 97%）. In addition, LAGIL 2c was recycled three times without any loss of catalytic activity and selectivity to the product.

Epoxidation of Unsaturated Fatty Acid Methyl Esters in the Presence of SO_3H-functional Brφnsted Acidic Ionic Liquid as Catalyst

The epoxidation of unsaturated fatty acid methyl esters(FAMEs)by peroxyacetic acid generated in situ from hydrogen peroxide and acetic acid was studied in the presence of SO3H-functional Brnsted acidic ionic liquid (IL)[C3SO3HMIM][HSO4]as catalyst.The effects of hydrogen peroxide/ethylenic unsaturation ratio,acetic acid concentration,IL concentration,recycling of the IL catalyst,and temperature on the conversion to oxirane were studied.The kinetics and thermodynamics of unsaturated FAMEs epoxidation and the kinetics of oxirane cleavage of the epoxidized FAMEs by acetic acid were also studied.The conversion of ethylenic unsaturation group to oxirane, the reaction rate of the conversion to oxirane,and the rate of hydrolysis(oxirane cleavage)were higher by using the IL catalyst.

Application of Bronsted acid ionic liquids as green catalyst in the synthesis of 2-propanol with reactive distillation

Five Br?nsted acidic ionic liquids(ILs) were prepared and characterized by FT-IR,~1H NMR and ^(13)C NMR. Their catalytic activities for the synthesis of 2-propanol(IPOH) via transesterification of isopropyl acetate(IPAc) with methanol(Me OH) were investigated. Among all the tested ILs, [Ps-mim]HSO_4 performed best and was used as catalyst for further studies. The reaction kinetics were carried out to correlate the parameters in a homogeneous second order kinetic model. It has been found that there is close agreement between the calculated and experimental values. The high-pressure batch reactive distillation experimental apparatus was set up in order to enhance the conversion of IPAc. A high conversion of IPAc of 99.4% was obtained under the optimal reaction conditions. The catalyst [Ps-mim]HSO_4 can be recycled easily by a rotary evaporator and reused without any further treatment. The catalyst had been repeatedly used for four times and no obvious changes in the structure of catalyst could be observed.

Transesterification of palm oil to biodiesel using Brφnsted acidic ionic liquid as high-efficient and eco-friendly catalyst

The transesterification of palm oil and methanol catalyzed by Br?nsted acidic ionic liquids was investigated. Four eco-friendly Br?nsted acidic ionic liquids were prepared and their structures were characterized by NMR, FT-IR and TG–DTG. The results demonstrated that [CyN_(1,1)PrSO_3H][p-TSA] was more efficient than the other ionic liquids and chosen as catalyst for further research. The influences of various reaction parameters on the conversion of palm oil to biodiesel were performed, and the orthogonal test was investigated to seek the optimum reaction conditions, which were illustrated as follows: methanol to oil mole ratio of 24:1, catalyst dosage of 3.0 wt% of oil, reaction temperature of 120 °C, reaction time of 150 min, and the biodiesel yield achieved 98.4%. In addition, kinetic study was established for the conversion process, with activation energy and preexponential factor of 122.93 k J·mol^(-1) and 1.83 × 10^(15), respectively. Meanwhile, seven-time recycling runs of ionic liquid were completed with ignorable loss of its catalyst activity. The refined biodiesel met the biodiesel standard EN 14214.

Swelling acidic poly(ionic liquid)s as efficient catalysts for the esterification of cyclohexene and formic acid

Acidic poly(ionic liquid)s(PILs)with swelling ability were synthesized by free radical copolymerization of N-vinylimidazolium ionic liquids,divinylbenzene(DVB)and sodium acrylate(NaAA),and further acidification by sulfuric acid.The swelling ability of acidic PILs was greatly affected by cross-linker content and chain length of 3-alkyl-substituents on imidazolium.Cross-linked network structures could be observed from the cryogenic scanning electron microscopy(cryo-SEM)images of the swollen acidic PILs in formic acid.Acidic PILs with network structures in swollen state exhibited excellent activities in the esterification of cyclohexene and formic acid,and the catalytic activities were in positive correlation with their swelling abilities.Acidic PIL with 3-octyl-substituent and 2.5 mol%DVB(PIL-C8-2.5DVB-HSO4)had the highest swelling ability in formic acid and exhibited comparable catalytic activities with homogeneous catalysts such as sulfuric acid and p-toluenesulfonic acid.

Olefin oligomerization via new and efficient Bronsted acidic ionic liquid catalyst systems

Olefin oligomerization reaction catalyzed by new catalyst systems（a Br？nsted‐acidic ionic liquid as the main catalyst and tricaprylylmethylammonium chloride as the co‐catalyst） has been investigat‐ed. The synthesized Br？nsted acidic ionic liquids were characterized by Fourier transform infrared spectroscopy（FT‐IR）, ultraviolet‐visible spectroscopy（UV）, ^1H nuclear magnetic resonance（NMR）, and ^13 C NMR to analyze their structures and acidities. The influence of different ionic liquids, ionic liquid loading, different co‐catalysts, catalyst ratios（mole ratio of ionic liquid to co‐catalyst）, reac‐tion time, pressure, temperature, solvent, source of reactants, and the recycling of catalyst systems was studied. Among the synthesized ionic liquids, 1‐（4‐sulfonic acid）butyl‐3‐hexylimidazolium hydrogen sulfate（[HIMBs]HSO4） exhibited the best catalytic activity under the tested reaction con‐ditions. The conversion of isobutene and selectivity of trimers were 83.21% and 35.80%, respec‐tively, at the optimum reaction conditions. Furthermore, the catalyst system can be easily separated and reused; a feasible reaction mechanism is proposed on the basis of the distribution of experi‐mental products.

The alcoholysis of acetonitrile prompted by Brфnsted acidic ionic liquid [HSO_3-pmim]HSO_4

BrФnsted acidic ionic liquids based on imidazolium cation were employed as a series of environmentally benign catalysts and mediums in the alcoholysis of acetonitrile to synthesize ester. The results showed that BrФnsted acidic ionic liquid [HSO3- pmim]HSO4 was an efficient catalyst and medium for the alcoholysis of acetonitrile which could be recycled easily without obvious decline in catalytic activity, the highest yield could reach 85%.

Preparation of fructone catalyzed by water-soluble Brφnsted acid ionic liquids

Fructone （2-methyl-2-ethylacetoacetate-1, 3-dioxolane）, a flavouring material, has been synthesized from ethyl acetoacetate and glycol using five water-soluble Brφnsted acid ionic liquids as catalysts for the first time. The used Brφnsted acid ionic liquids include [Hmim]Tfa, [Hmim]Tsa, [Hmim]BF4, [Bmim]HSO4, [Bmim]H2P04, and [Hmim]BF4 showed the highest catalytic activity for the preparation of fructone. After reaction, the product could be isolated from the reaction system automatically, and the ionic liquid could be directly reused without dehydration.

Facile Aldol Reaction Between Unmodified Aldehydes and Ketones in Bronsted Acid Ionic Liquids

A series of condensation reactions of unmodified ketones and aromatic aldehydes to prepare α,β-unsaturated carbonyl compounds by means of Aldol reactions in Bronsted acid ionic liquids（BAILs）was explored.1-Butyl-3-methylimidazolium hydrogen sulphate（BMImHSO4）acting as an effective media and catalyst in aldol reactions was compared with other BAILs,with the advantages of high conversion and selectivity.The product was easily isolated and the left ionic liquid can be readily recovered and reused at least 3 times with almost the same efficiency.The scope and limitation of the present method were explored and the possible catalytic mechanism was speculated.

Honeycomb-structured solid acid catalysts fabricated via the swelling-induced self-assembly of acidic poly(ionic liquid)s for highly efficient hydrolysis reactions

The development of heterogeneous acid catalysts with higher activity than homogeneous acid catalysts is critical and still challenging.In this study,acidic poly(ionic liquid)s with swelling ability(SAPILs)were designed and synthesized via the free radical copolymerization of ionic liquid monomers,sodium p-styrenesulfonate,and crosslinkers,followed by acidification.The 31P nuclear magnetic resonance chemical shifts of adsorbed trimethylphosphine oxide indicated that the synthesized SAPILs presented moderate and single acid strength.The thermogravimetric analysis results in the temperature range of 300–345°C revealed that the synthesized SAPILs were more stable than the commercial resin Amberlite IR-120(H)(245°C).Cryogenic scanning electron microscopy testing demonstrated that SAPILs presented unique three-dimensional(3D)honeycomb structure in water,which was ascribed to the swelling-induced self-assembly of the molecules.Moreover,we used SAPILs with micron-sized honeycomb structure in water as catalysts for the hydrolysis of cyclohexyl acetate to cyclohexanol,and determined that their catalytic activity was much higher than that of homogeneous acid catalysts.The equilibrium concentrations of all reaction components inside and outside the synthesized SAPILs were quantitatively analyzed using a series of simulated reaction mixtures.Depending on the reaction mixture,the concentration of cyclohexyl acetate inside SAPIL-1 was 7.5–23.3 times higher than that outside of it,which suggested the high enrichment ability of SAPILs for cyclohexyl acetate.The excellent catalytic performance of SAPILs was attributed to their 3D honeycomb structure in water and high enrichment ability for cyclohexyl acetate,which opened up new avenues for designing highly efficient heterogeneous acid catalysts that could eventually replace conventional homogeneous acid catalysts.

Br?nsted acidic ionic liquid catalyzed synthesis of benzo[a]carbazole from renewable acetol and 2-phenylindoles in a biphasic system

An efficient metal-free strategy for the synthesis of pharmaceutically relevant benzo[α]carbazoles from the derivatives of readily available 2-phenylindole and bio-renewable acetol in an aqueous biphasic system was developed. This protocol employed a sulfone-containing Bronsted acidic ionic liquid as the catalyst, which could be used for five times without a noticeable decrease in its activity and selectivity. Various substituted 2-phenylindoles and α-hydroxyketones participated in the reaction smoothly, with water as the sole byproduct. Mechanistically, the reaction involved the conventional carbon-nucleophile-induced Heyns-type rearrangement and downstream intramolecular olefination.

Synthesis of 2-Methyl-4-methoxyaniline from o-Nitrotoluene Using Pt/C and Acidic Ionic Liquid as Catalyst System

2-Methyl-4-methoxyaniline （MMA） was synthesized by one-pot method through the hydrogenation and Bamberger rearrangement of o-nitrotoluene in methanol using acidic ionic liquid and 3% Pt/C as catalyst system. The effects of ionic liquid type, dosage of ionic liquid and 3% Pt/C, reaction temperature and reaction pressure on o-nitrotoluene conversion and MMA selectivity were investigated. The results indicated that the imidazolium-based acidic ionic liquid which contains SO3H-functionalized cation showed higher selectivity to MMA than other acidic ionic liquids used in this work. Using 1-（propyl-3-sulfonate）-3-methylimidazolium hydrosulfate （[HSO3-pmim][HSO4]） as the acid catalyst, the selectivity to MMA was as high as 67.6% at 97.8% of o-nitrotoluene conversion. As 3% Pt/C increased from 0.01 g to 0.025 g, the selectivity to MMA decreased from 73.4% to 62.5%, because of the hydrogenation of intermediate o-methyl-phenylhydroxylamine to o-toluidine becoming more dominant. An increase in hydrogen pressure also had obviously dramatic effect in lowering the MMA selectivity. After easy separation from the products, the catalyst system could be reused at least 3 times.

One-pot conversion of cyclohexanol to ε-caprolactam using a multifunctional Na_2WO_4-acidic ionic liquid catalytic system

Na2WO4‐acidic ionic liquid was used as a simple, ecofriendly, recyclable and efficient catalytic system for the one‐pot conversion of cyclohexanol to ε‐caprolactam. The effect of the structure of the ionic liquid on the catalytic activity of this system was investigated, and the results revealed that sulfonic acid‐functionalized ionic liquids with HSO4? as an anion gave the best results. The highly efficient performance of this catalyst system was attributed to the phase‐transfer behavior of the cation of the ionic liquid, the improved coordination of the substrate to bisperoxotungstate duringthe oxidation reaction, and the stabilization of the intermediate formed during the Beckmann rearrangement.

An efficient method to synthesize HMX by nitrolysis of DPT with N_2O_5 and a novel ionic liquid

A novel polyethylene glycol （PEG）-200-based dicationic acidic ionic liquid （PEG200-DAIL） was used to synthesize HMX from DPT by nitrolysis with N2O5. It was found that either N2O5 or PEGzoo-DAIL could improve the yield. Furthermore, the combined use of PEG200-DAIL and N2O5 could increase the yield of HMX to 64% with the used quantity of HNO3 decreased dramatically.

Bronsted acidic ionic liquid [C_3SO_3HDoim]HSO_4 catalyzed one-pot three-component Biginelli-type reaction: An efficient and solvent-free synthesis of pyrimidinone derivatives and its mechanistic study

A series of Bronsted acidic ionic liquids（ILs） were prepared and used for Biginelli-type condensation reaction among aromatic aldehydes, urea or thiourea and cyclopentanone. Through this reaction, the synthesis of various pyrimidinones could be achieved. Of interest, it was found that the reaction was efficiently catalyzed by a novel, eco-friendly functionalized IL [C3SO3HDoim]HSO4, which could be reused for at least 7 times without significantly loss of catalytic activity. The reaction proceeded efficiently at 80℃ to afford the desired products in good yield（up to 96%）. In addition, a possible mechanism that accounted for the IL [C3SO3HDoim]HSO4-catalyzed reaction was proposed.