Separation and Purification Technology 63(2008)710–715Contents lists available at ScienceDirectSeparation and PurificationTechnologyj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /s e p p urShort communicationHighly efficient extraction of phenols and aromatic amines into novel ionic liquids incorporating quaternary ammonium cationVladimir M.Egorov,Svetlana V.Smirnova,Igor V.Pletnev ∗Department of Chemistry,M.V.Lomonosov Moscow State University,1/3Leninskiye gory,119992Moscow,Russiaa r t i c l e i n f o Article history:Received 13May 2008Received in revised form 26June 2008Accepted 28June 2008Keywords:Ionic liquidsLiquid–liquid extraction PhenolsAromatic aminesa b s t r a c tTwo novel hydrophobic room temperature ionic liquids (RTIL)incorporating quaternary ammonium cations:tetrahexylammonium dihexylsulfosuccinate (THADHSS)and trioctylmethylammonium salicylate (TOMAS)have been obtained.The mutual solubility of the both RTILs with water and their Reichardt’s polarity index have been measured.The extraction of aromatic amines and phenols into novel RTILs and two 1-alkyl-3-methylimidazolium bis (trifluoromethanesulfonyl)amides has been studied.The depen-dences of RTIL–water distribution ratio for the studied liquids on the phase volume ratio,the time of phase contact,pH value of aqueous solutions and the solute concentration have been obtained.In some cases,the solute distribution ratios for ammonium-based RTILs are as high as n ×104that is much greater than for imidazolium ones.Notably,unlike the case of imidazolium-based RTILs,the quantitative extraction into ammonium RTILs is achieved even at the phase volume ratio V RTIL :V w =1:20.©2008Elsevier B.V.All rights reserved.1.IntroductionRoom temperature ionic liquids (RTIL),which are organic or organoelement salts liquid at room temperature,have nowadays a growing diversity of applications in chemistry and technology [1,2].The advantages of room temperature ionic liquids include wide liq-uid range,high heat capacity,high thermal and chemical stability [3,4].As opposed to conventional organic solvents,most RTILs are non-flammable,have low vapor pressure and good electrochemical properties (electric conductivity,wide electrochemical window)[2–5].It is important that modification of cationic or anionic parts of RTIL may enable a fine-tuning of physical and chemical properties [6,7].Room temperature ionic liquids is an attractive alternative to conventional organic solvents in organic synthesis [1],catalysis [8],biopolymers processing [9–11],electrochemistry and electro-analysis [5,12–14],biochemistry [15],analytical chemistry [16].Furthermore,RTILs have a considerable potential as extraction sol-vents and may serve as a key to the design of more environmentally benign separation processes.However,the most abundant 1,3-dialkylimidazolium ionic liq-uids have some limitations on use,the most important being their high cost.That is why the search for new cheaper ionic liquids with improved characteristics is of current interest.As was indicated∗Corresponding author.Tel.:+74959395464;fax:+74959394675.E-mail address:pletnev@analyt.chem.msu.ru (I.V.Pletnev).elsewhere [17,18],some quaternary ammonium or phosphonium-based RTILs look the promising alternative:they are relatively cheap and easy to synthesize;some of them are water-immiscible and suitable for solvent extraction.A large number of publications devoted to liquid–liquid sep-arations with the use of RTILs have appeared within last years.The applications include extraction of simple substituted arenes [19,20],alcohols [21],carboxylic acids [22,23],and metal ions [24,25];aromatics/aliphatics separations [26,27]and fuel desul-furization [28,29].Extraction of various biological substances is another popular subject [30–32].It is worthy of mention that the majority of papers employ only imidazolium-based RTILs as extrac-tion solvents.Gathering a large array of experimental data on the extraction of representative solutes into different RTILs may give a useful information about the influence of solute/solvent structure on the partitioning of organic compounds.Phenols and aromatic amines may well serve as such representative solutes,since a wide vari-ety of substituted compounds are readily available to examine the role of structural details.Additionally,the data on the extraction of phenols have been previously reported for dialkylimidazolium hexafluorophosphate RTILs (our work [33]),and the extraction of phenols and amines has been reported for tetrafluoroborate ones [34].We report herein on the synthesis and properties of two novel hydrophobic RTILs incorporating quaternary ammo-nium cations,tetrahexylammonium dihexylsulfosuccinate (THADHSS)and trioctylmethylammonium salicylate (TOMAS).1383-5866/$–see front matter ©2008Elsevier B.V.All rights reserved.doi:10.1016/j.seppur.2008.06.024V.M.Egorov et al./Separation and Purification Technology63(2008)710–715711These two RTILs along with two imidazolium-based RTILs,1-hexyl-3-methylimidazolium and1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amides(HMImTf2N and DMImTf2N, respectively),have been tested as extraction solvents for recovery of aromatic amines and phenols from aqueous solution.2.Experimental2.1.ReagentsTetrahexylammonium bromide(Aldrich,99%),Aliquat®336 (trioctylmethylammonium chloride,Aldrich),sodium dihexylsul-fosuccinate(Technolog Ltd.,Russia),sodium salicylate(Panreac, RFE,USP,BP,Ph.Eur.),and2,6-diphenyl-4-(2,4,6-triphenylpyridin-1-yl)-phenolate monohydrate(Reichardt’s dye,Sigma–Aldrich, 70%)were used as received.1-Hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide(99%)was purchased at Sol-vent Innovation GmbH,Germany.1-Decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide was synthesized in the Dr.A.V.Yatsenko’s group at the Department of Chemistry of the MSU.The studied solutes,phenol,4-nitrophenol,2,4-dinitrophenol,2,6-dinitrophenol,picric acid,1-naphthol,2-naphthol,aniline hydrochloride,p-toluidine,3-nitroaniline,and tryptamine hydrochloride were of reagent grade purity.Potas-sium ferrocyanide,4-aminoantipyrine,amidopyrine(analytical reagent grade),and iron(III)sulfate(reagent grade)were used for spectrophotometrical measurements.Nitric and sulfuric acids (0.1and3M),potassium hydroxide(0.1and3M),phosphate(pH 6.86)and borate(pH9.18)buffer solutions were used for pH anic solvents,acetone(reagent grade),acetoni-trile(HPLC grade),chloroform(reagent grade)were used without additional purification.Water was freshly distilled before use.2.2.Preparation of quaternary ammonium RTIL2.2.1.Tetrahexylammonium dihexylsulfosuccinate19.42g(0.05mol)of sodium dihexylsulfosuccinate(NaDHSS) was dissolved in80ml of water at50◦C upon shaking.After complete dissolution of NaDHSS,equimolar amount(21.73g)of tetrahexylammonium bromide was added to the solution.The mixture was stirred for20min forming two phases where upper phase is RTIL.Aqueous phase was separated and RTIL phase was repeatedly rinsed with triple volume of fresh water10times upon vigorous shaking.The presence of NaBr in wash water was mon-itored by reaction with silver nitrate.After that the upper phase was collected and centrifuged for several hours to settle the emul-sion of water.A clear,colorless,viscous liquid was obtained.1H NMR(500MHz,CDCl3,␦/ppm relative to TMS):0.88(t;18H),1.33 (m;36H),1.55(m;12H),3.2(m;12H),4.1(m;3H).13C NMR (126MHz,DMSO-d6,␦/ppm relative to TMS):13.64,13.69,13.71 (CH3);20.91,21.76(C*H2CH3);21.87,24.82,24.85,25.34,27.95, 27.99,30.47,30.75,30.82(various CH2CH2);34.01(OOCC*H2CH);57.63(CHSO3);61.30(CH2N);63.89(CH2O);168.31,170.97(COOR).2.2.2.Trioctylmethylammonium salicylate40.42g(0.1mol)of trioctylmethylammonium chloride (Aliquat®336)was dissolved in200ml of acetone,and equal molar amount of sodium salicylate(16.01g)was added to the solution.The mixture was shaken for5h and left overnight.After that the precipitate wasfiltered off and acetone was evaporated fromfiltrate using rotary evaporator.The obtained RTIL was then rinsed with distilled water10times,and the upper RTIL phase was then centrifuged for several hours to settle the emulsion of water.Elemental analysis of the product yielded zero inorganic ash content.A clear,slightly yellowish,viscous liquid was obtained.1H NMR(500MHz,CDCl3,␦/ppm relative to TMS):0.88(t;9H),1.22(m;30H),1.53(m;6H),2.98(s;3H),3.13(m;6H),6.86(t;1H),6.92(d;1H),7.38(t;1H),7.88(d;1H),15.6(s;1H).13C NMR (126MHz,DMSO-d6,␦/ppm relative to TMS):13.80(C*H3C);21.93 (C*H2CH3);21.25,25.68,28.27,28.32,31.04(various CH2CH2);47.41(CH3N);60.50(CH2N);115.35,115.62,120.73,129.73,130.88 (aromatic C);163.17(COH);171.00(COO).1H and13C NMR data were recorded with NMR spectrometer DRX500(Bruker,Germany).2.3.Polarity measurementsFor solvatochromic polarity measurements a pinch of Reichardt’s dye on the tip of a spatula was added to3ml of studied solvent in a glass test-tube.If necessary,the mixture was ultrasonicated to completely dissolve the dye.After that the UV–vis spectrum of the solution was measured relative to distilled water(SF103spectrophotometer,Akvilon,Russia).The Dimroth–Reichardt polarity parameter E T(30)was calculated using the following equation:E T(30),kcal mol−1=28591max(1) where max is a maximum absorbance wavelength[35].2.4.Solubility measurementsThe solubility of THADHSS in water was measured conductimet-rically.A solution of THADHSS was prepared by dissolving a known amount of THADHSS in0.5L of deionized water.Then a series of cal-ibration solutions was made by dilution of the above solution,and their conductivity and the conductivity of the saturated THADHSS solution were measured.The solubility of TOMAS in water was determined spectrofluo-rometrically by salicylate( ex=305nm, em=405nm).The measurement of water content in water-saturated quater-nary ammonium RTILs was made using coulometric Karl Fischer titrator“Expert-007”(Econiks-Expert,Russia).2.5.Extraction procedureThe extraction was carried out in10ml polypropylene cen-trifuge test-tubes at ambient temperature(20±3◦C).The proper volumes of RTIL and pH-adjusted aqueous solution of studied com-pound were placed in a test-tube and shaken for the time necessary for extraction equilibrium to be achieved.Unless otherwise men-tioned,the phase volume ratio V IL:V w was1:3for imidazolium and 1:20for quaternary ammonium RTILs.After the necessary shaking time had elapsed,the systems with quaternary ammonium RTIL were centrifuged for2min(the centrifugation is not imperative but desirable as quaternary ammonium RTILs tend to adhere onto walls of test-tube after shaking).After that the necessary volume of aqueous phase was taken,and pH value was measured(pH-meter pH-410;combined glass microelectrode ESLK-13.7,Akvilon,Rus-sia).Finally,the determination of the solute in the aqueous phase was performed.The recovery(R,%)and the distribution ratio(D)of a solute were calculated using the following equations:R(%)=1−C wC0w100(2) D=C oC w=R100−RV wV o(3) where C0w and C w are the initial and equilibrium concentrations of the studied solute in aqueous phase,respectively(mol L−1),V w and712V.M.Egorov et al./Separation and Purification Technology63(2008)710–715V o denote the volumes of aqueous and RTIL phases,respectively (ml).The studied solutes were monitored spectrophotometrically or spectrofluorometrically[36,37].Spectroscopic measurements were performed using spectrophotometer UV-2201or spectrofluorime-ter RF-5301PC(Shimadzu,Japan),quartz cells.Concentrations of nitrocompounds were determined by their own absorbance after adding3M KOH to pH11–12.The absorbance was measured at400nm(4-nitrophenol),359nm(2,4-dinitrophenol),360nm (2,6-dinitrophenol),356nm(picric acid),365nm(3-nitroaniline). For spectrophotometrical determination of phenol and naphthols, 1.0ml of borate buffer solution(pH9.18),0.1ml of2%wt aque-ous K3Fe(CN)6,and0.1ml of2wt%aqueous4-aminoantipyrine were added to2.5ml of the studied solution.After5min,the absorbance was measured at510nm.For determination of aromatic amines,1ml of phosphate buffer solution,0.3ml of0.1M aqueous amidopyrine and1ml of2wt%K3Fe(CN)6were added to2.5ml of amine solution.After20min,the absorbance was measured at535nm.Tryptamine was determined spectrofluorimetrically at ex=279nm( em=359nm).Spectrophotometrical determination of salicylate in aqueous solutions after contact with TOMAS was car-ried out using freshly prepared5×10−3mol L−1(Fe3+)solution of iron(III)sulfate;2ml of5×10−3mol L−1Fe3+solution were added to2ml of salicylate solution(pH2–3);the absorbance was mea-sured at525nm[36].3.Results and discussion3.1.Properties of the quaternary ammonium RTILsTOMAS and THADHSS are clear liquids with densities slightly less than1g cm−3(0.945and0.975,respectively).Freezing points of the both RTILs are below−10◦C.The liquids are immiscible with water.1H and13C NMR spectra confirmed the identity of the obtained RTILs,and the molar cation–anion ratio calculated from1H NMR data was exactly1:1for the both RTILs.Solubility of THADHSS in water was found to be (8.6±0.2)×10−5mol L−1.Solubility of TOMAS is(2.0±0.2)×10−4mol L−1.These values are up to two orders of magnitude lower than that of common hydrophobic imidazolium-based RTILs[38].This significantly decreases a possible RTIL loss during extraction.The obtained RTILs are hydrolytically stable at pH2–13.Solubility of water in THADHSS and TOMAS is ca.5and7wt%, respectively(Karl Fischer titration).After shaking the RTILs with water,no emulsification was observed in both aqueous and RTIL phases.3.2.Polarity of THADHSS and TOMASPolarity is an important property of a solvent,which affects dif-ferent types of interactions between solvent and solute molecules. There exist several experimental methods for quantitative eval-uation of polarity:inverse gas chromatography,kinetic method, refractive index measurement[39].One of the most popular approaches refers to solvatochromism measured for a specific probe molecule,in particular,Reichardt’s betaine dye.The maxi-mum absorbance wavelength of this dye lies in visible spectrum and strongly depends on the nature of a solvent.In the present study we have measured the Dimroth–Reichardt’s polarity E T(30)of the novel RTILs,and three commonly used organic solvents(acetone,acetonitrile,and chloroform).The results along with literature data are shown in Table1.Table1max and E T(30)values for several solventsSolvent max(nm)E T(30)(kcal mol−1)Acetone67842.2Acetonitrile63045.4Chloroform69841.0 Dichloromethane[40]70040.8HMImTf2N[41]55251.8BMImPF6[40]a54552.5THABzO[35]b65143.9Ethanol[40]54652.4THADHSS(satd.with H2O)61546.5TOMAS(satd.with H2O)59348.2a1-Butyl-3-methylimidazolium hexafluorophosphate.b Tetrahexylammonium benzoate.The E T(30)values for THADHSS and TOMAS are close to each other and comparable with those for the other known ammonium-based RTILs[35].As compared to imidazolium-based RTILs(typical E T(30)values are in between49and60[35]),the novel ionic liquids are less polar.All the measurements and literature data are given for room temperature.It is important to mention that the E T(30)values were measured for water-saturated THADHSS and TOMAS,as they are directly related to the polarity of solvents in extraction conditions.On the basis of polarity measurements one may conclude that the novel RTILs would have solvation/extraction proper-ties different from both conventional extraction solvents and imidazolium-based ionic liquids.As is shown below(see extrac-tion data in Section3.4),there exists no quantitative relationship between E T(30)and extraction efficiency for corresponding RTIL. However,one may note that the lower E T(30)value the more effi-cient is extraction,in general.3.3.Extraction studies3.3.1.Optimization of extraction conditionsThe influence of phase contact time,phase volume ratio and concentration of an inorganic electrolyte(NaCl)on the distribution ratio has been studied on the example of2,4-dinitrophenol.The appropriate values of thefirst two parameters are shown in Table2.As can be seen from Table2,the time of phase contact,which is necessary to achieve extraction equilibrium,is less for the qua-ternary ammonium RTILs.Previously our group has shown that the optimal phase contact time for extraction into imidazolium-based ionic liquids weakly depends on the structure of extracted polar aromatic compound[33].That is why,and also for conditions uni-fication,in all the further experiments the phase contact time for all systems was15min.Like for the other previously studied imidazolium-based RTILs[33],the distribution ratio of2,4-dinitrophenol into both HMImTf2N and DMImTf2N dramatically decreases with increasing phase volume ratio.The3:1phase volume ratio has been chosen as optimal in order to maintain an acceptable distribution coefficientTable2Phase contact time and phase volume ratio for extraction of2,4-dinitrophenol (5×10−4mol L−1;pH2)RTIL Phase contacttime(min)Phase volumeratio(V w:V RTIL) THADHSS520:1TOMAS1020:1HMImTf2N153:1DMImTf2N153:1V.M.Egorov et al./Separation and Purification Technology 63(2008)710–715713and at the same time to minimize the quantity of RTIL,which is necessary for an extraction run.On the contrary,in the case of quaternary ammonium RTILs,the distribution ratio of 2,4-dinitrophenol weakly depends on the phase volume ratio up to 50:1.The value 20:1has been chosen for further experiments with the both quaternary ammonium RTILs in order to decrease the consumption of RTIL while sustaining a good recovery.The concentration of introduced inorganic electrolyte (NaCl)from 5×10−4to 0.5mol L −1has practically no effect on the dis-tribution ratio of 2,4-dinitrophenol.3.3.2.The effect of pH on the recovery of aromatic compoundsAll the studied solutes can be divided into two types based on their acid-base behaviour:phenols and aromatic amines.3.3.2.1.Extraction of phenols.The pH dependence of the distribu-tion ratio of unsubstituted phenol for all studied RTILs is shown in Fig.1.As can be seen,the maximal distribution ratio is observed at acidic pH,where the molecular form of phenol is predomi-nant.Upon the increase in pH the recovery of phenol into the imidazolium-based RTILs dramatically decreases,and at pH >12becomes negligible (R <10%).This is a typical behaviour for parti-tioning of phenol into imidazolium RTILs [33,34].The extraction ability of HMImTf 2N is close to that of DMImTf 2N (though less hydrophobic HMImTf 2N has a small advantage).The distribution ratios of phenol for the ammonium-based RTILs are approximately 0.5and 1order of magnitude (TOMAS and THADHSS,respectively)higher than for the imidazolium-based RTILs.The observed pH dependence of extraction clearly shows that phenol is preferably partitioned into all RTILs in undissociated (molecular)form.However,even at pH 12the recovery of phenol into the ammonium RTILs remains rather significant (R ∼40–50%,see Fig.1).In the case of nitrophenols pH value has small effect on the recovery into quaternary ammonium RTILs,whereas pH depen-dences of distribution ratio of nitrophenols into imdazolium-based RTILs have a trend similar to that for phenol.The aforementioned results clearly point to the possibility of phenolates extraction (anion-exchange)into the quaternary ammonium RTILs,in addi-tion to extraction of a neutral solute.Naturally,the contribution of ion-exchange recovery of ionized phenols should be higher at pH >pK a of solute.Expectedly,the efficiency of anion-exchange extraction into the quaternary ammonium RTILs is higher for more hydrophobic nitrophenols than for phenol.The similarbehaviourFig.1.The effect of pH on distribution ratio of phenol (1×10−4mol L −1)into differ-entRTILs.Fig.2.The increase of salicylate concentrations in aqueous phase after extraction at various pH (solid line)in comparison to calculated initial concentration of 2,4-dinitrophenolate (C total =5×10−4mol L −1;dashed line)in aqueous phase.has been previously observed for the partitioning of picric acid between water and BMImPF 6[33].In order to confirm a contribution of anion exchange to extraction,the concentration of salicylate in aqueous phase after extraction of 2,4-dinitrophenol (5×10−4mol L −1)into TOMAS was monitored.Evidently,anion-exchange extraction of dinitrophe-nolate should be accompanied by a release of stoichiometric quantity of RTIL anion,salicylate,to an aqueous phase.The measured concentration of salicylate after extraction at differ-ent pH was compared with the concentration of salicylate in solutions,which had also been in contact with TOMAS but did not contain 2,4-dinitrophenol (pH values of these solu-tion pairs were approximately the same).Corresponding plot is presented in Fig.2(concentration of 2,4-dinitrophenolate in aqueous phase is calculated with the use of literature pK a ,see Table 3).As can be seen,the increase in aqueous salicylate concentra-tion is higher at higher pH;at pH >7it is nearly equal to the total concentration of 2,4-dinitrophenol.Note that at pH >72,4-dinitrophenol exists mostly as anion,and its recovery into TOMAS is ca.100%.In other words,the increase of aqueous salicylate concen-tration exactly matches the concentration of extracted solute.This proves that the anion exchange mechanism is operative at pH >pK a (solute).3.3.2.2.Extraction of aromatic amines.The extraction of four aro-matic amines into RTILs has been investigated.Fig.3presents theTable 3Extraction of the studied phenols and aromatic amines into quaternary ammonium RTILs (V w :V RTIL =20:1)SolutepK a [42]log D log P OW [43,44]THADHSSTOMAS Phenol10.0 2.5 2.1 1.464-Nitrophenol 7.14 3.6 3.4 1.912,4-Dinitrophenol 4.08 4.1 3.5 1.672,6-Dinitrophenol 4.15 4.0 3.6 1.372,4,6-Trinitrophenol 0.69 3.9 3.8 1.331-Naphthol 9.85 3.8 3.4 2.852-Naphthol 9.63 3.7 3.2 2.70Aniline4.63 1.9 1.80.903-Nitroaniline 2.47 2.3 2.3 1.37p-Toluidine5.07 2.0 2.0 1.39Tryptamine10.23.52.61.55714V.M.Egorov et al./Separation and Purification Technology 63(2008)710–715Fig.3.The effect of pH on distribution ratio of aniline (1×10−4mol L −1)into differ-ent RTILs.pH dependence of the distribution ratio of aniline for all studied RTILs.Three of the studied amines incorporate NH 2group bonded to an aromatic ring,and one (tryptamine)has an aliphatic NH 2group and indole aromatic ring.The pH dependence of extraction of aniline into imidazolium-based RTILs is typical for amines [33,34].Noteworthy,a less hydrophobic HMImTf 2N is a better extraction solvent for aniline than DMImTf 2N.The extraction of aniline into THADHSS and TOMAS is much better than into imidazolium-based RTILs.The characteristic trend of pH dependence for the extraction of aniline,p-toluidine,and m-nitroaniline into the novel RTILs is observed.Tryptamine is efficiently extracted into both THADHSS and TOMAS,but at the optimal pH the distribution ratio of tryptamine for THADHSS is approximately one order of magnitude higher than for TOMAS.For all the ionic liquids studied,the pH profile of aniline extrac-tion is similar to that common for molecular solvents (i.e.efficient extraction takes place at pH >pK a of amine),which is indicative of neutral solute recovery.Unlike phenols,aromatic amines are poorly extracted in ionizedform.parison of distribution data for RTIL/water and 1-octanol/water systems (the trendline is shown for HMImTf 2N).parison of distribution ratios of several compounds for THADHSS and TOMAS (see also Table 3).parative analysis of the extraction resultsThe results obtained in the present work show that the newly obtained quaternary ammonium-based RTILs are much more effi-cient extraction solvents towards the studied aromatic compounds than common imidazolium-based RTILs.The extraction data for non-nitrated phenols and aromatic amines show that the maximal recovery is achieved for molecular forms of these compounds,the decrease in recovery closely corresponding to the respective pK a values.The data on partitioning of the studied phenols and aro-matic amines into quaternary ammonium RTILs are summarized in Table 3.The partitioning of neutral substituted aromatic molecules into imidazolium-based RTILs is often attributed to specific –inter-actions between imidazolium ring and aromatic ring of extracted compound [19,45]or to the ability of imidazolic proton at C2to form hydrogen bonds [46].However,in the case of THADHSS and TOMAS such interactions are unlikely.We suggest that dispersive interactions of solute molecules with cation of RTIL may be a driv-ing force for the preferential partitioning of phenols and aromatic amines into quaternary ammonium RTILs.It is interesting to correlate distribution ratio of organic com-pounds with 1-octanol/water partition coefficients,log P OW .Fig.4shows plot of logarithm of the maximal distribution ratio for the studied compounds (log D )into different RTILs vs.log P OW [43,44].As is clearly seen,the extraction ability of the imidazolium-based RTILs is inferior to the extraction ability of the novel quaternary ammonium RTILs and,in some cases,to that of 1-octanol.Noteworthy,there is a correlation between log P OW and log D for imidazolium-based RTILs (see a trendline in Fig.4).This corresponds well to the literature data [19,33].However,for the novel RTILs a log D –log P OW correlation is poor.This may be because of difference in extraction mechanisms between imidazolium and quaternary ammonium RTILs.At the same time,there exists a good correlation between log D obtained for the same solutes with use of THADHSS and TOMAS (Fig.5).This suggests that solvation/extraction patterns for the two ammonium RTILs be similar (note that,in general,THADHSS is more efficient extraction solvent than TOMAS).4.ConclusionsTwo novel quaternary ammonium based room temperature ionic liquids (THADHSS and TOMAS)have been synthesized andV.M.Egorov et al./Separation and Purification Technology63(2008)710–715715characterized.The Dimroth–Reichardt’s polarities of the novel RTILs,E T(30),are higher than those for the studied molecular sol-vents,but less than for imidazolium ionic liquids.Extraction of11aromatic compounds(phenols and aro-matic amines)into two imidazolium-based RTILs(HMImTf2N and DMImTf2N)and into the novel RTILs has been studied.The best recovery into the novel RTILs has been observed for nitrophenols and naphthols.The recovery of the aforementioned compounds is high(>50%at V IL:V w=1:20)in the whole studied pH range. 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