Nucleophilicity in ionic liquids. 2.(1) Cation effects on halide nucleophilicity in a series of bis(trifluoromethylsulfonyl)imide ionic liquids

In this work, the nucleophilicities of chloride, bromide, and iodide have been determined in the ionic liquids [bmim][N(Tf)(2)], [bm(2)im][N(Tf)(2)], and [bmpy][N(Tf)(2)] (where bmim = 1-butyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bmpy = 1-butyl-1-methylpyrrolidinium, and N(Tf)(2) = bis(trifluoromethylsulfonyl)imide). It was found that in the [bmim](+) ionic liquid, chloride was the least nucleophilic halide, but that changing the cation of the ionic liquid affected the relative nucleophilicities of the halides. The activation parameters DeltaH(), DeltaS(), and DeltaG() have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.     

Kinetic study of the addition of trihalides to unsaturated compounds in ionic liquids. Evidence of a remarkable solvent effect in the reaction of ICl2-

The kinetic constants and activation parameters for the reactions of Br(3)(-) and ICl(2)(-) with some alkenes and alkynes have been determined in the ionic liquids [bmim][PF(6)], [emim][Tf(2)N], [bmim][Tf(2)N], [hmim][TF(2)N], [bm(2)im][Tf(2)N], and [bpy][TF(2)N] (where emim = 1-ethyl-3-methylimidazolium, bmim = 1-butyl-3-methylimidazolium, hmim = 1-hexyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bpy = butylpyridinium, PF(6) = hexafluorophosphate, and Tf(2)N = bis(trifluoromethylsulfonyl)imide) and in 1,2-dichloroethane. The rates of both reactions increase on going from 1,2-dichloroethane to ILs. Evidence suggests that, while the hydrogen bonding ability of the imidazolium cation is probably the main factor able to increase the rate of the addition of ICl(2)(-) to double and triple bonds, this property has no effect on the electrophilic addition of Br(3)(-) to alkenes and alkynes. Furthermore, in the case of the ICl(2)(-) reaction, the hydrogen bonding ability of ILs can be exploited to suppress the unwanted nucleophilic substitution reaction on the products by the Cl(-) anion.     

Ionic liquids/[bmim][N3] mixtures: promising media for the synthesis of aryl azides by SNAr

The nucleophilic aromatic substitution of some activated aryl or heteroaryl halides has been performed in ionic liquid solution, using the 1-butyl-3-methylimidazolium azide as a nucleophile. The reaction course was studied varying the structures of both substrates and ionic liquids. In particular, in the latter case, the reaction of 2-bromo-5-nitrothiophene was carried out in five different ionic liquids ([bmim][BF 4], [bmim][PF 6], [bmim][NTf 2], [bm 2im][NTf 2], and [bmpyrr][NTf 2]). Finally, for all the substrates considered, a comparison with data obtained in MeOH solution in the presence of NaN 3 was also performed. Data collected indicate that in some cases it is possible to obtain aromatic or heteroaromatic azide derivatives in satisfactory yield by means of a S NAr reaction using [bmim][N 3] as the nucleophile.     

Nucleophilicity in ionic liquids. 3. Anion effects on halide nucleophilicity in a series of 1-butyl-3-methylimidazolium ionic liquids

We have continued the study of halide nucleophilicity in ionic liquids, concentrating on the effect of changing the anion ([BF(4)](-), [PF(6)](-), [SbF(6)](-), [OTf](-), and [N(Tf)(2)](-)) when the cation is [bmim](+) (where bmim = 1-butyl-3-methylimidazolium). It was found that the nucleophilicities of all the halides were lower in all of the ionic liquids than in dichloromethane. Changing the anion affected the order of halide nucleophilicity, e.g., in [bmim][BF(4)] the order of nucleophilicity was Cl(-)>Br(-)>I(-) while in [bmim][N(Tf)(2)] the order was Cl(-)相似文献   

Manipulating solute nucleophilicity with room temperature ionic liquids

In this work we report the effect of ionic liquids on a class of charge-neutral nucleophiles. We have studied the reactions of (n)butylamine, di-(n)butylamine, and tri-(n)butylamine with methyl p-nitrobenzenesulfonate in [bmpy][N(Tf)(2)], [bmpy][OTf], and [bmim][OTf] (bmpy = 1-butyl-1-methylpyrrolidinium; bmim = 1-butyl-3-methylimidazolium) and compared their reactivities, k(2), to those for the same reactions in the molecular solvents dichloromethane and acetonitrile. It was shown that all of the amines are more nucleophilic in the ionic liquids than in the molecular solvents studied in this work. Comparison is also made with the effect of ionic liquids on the reactivity of chloride ions, which are deactivated in ionic liquids. The Eyring activation parameters revealed that changes in the activation entropies are largely responsible for the effects seen. This can be explained in part by the differing hydrogen-bonding properties, as shown by the Kamlet-Taft solvent parameters, of each of these solvents and the formation of hydrogen bonds between the solvents and the nucleophiles.     

Acetyl nitrate nitrations in [bmpy][N(Tf)2] and [bmpy][OTf], and the recycling of ionic liquids

In this work we have examined the nitration by acetyl nitrate of a range of activated and deactivated aromatic substrates in two ionic liquids and compared the results to the same reaction in dichloromethane. Both ionic liquids are stable to the reaction conditions, and in both ionic liquids the yields of reaction are higher after unit time than the same reactions in dichloromethane, although the regioselectivity is little affected by solvent choice. This result gives further support to the suggestion that in the ionic liquid, acetyl nitrate dissociates to give the nitronium ion, and that this is the effective nitrating agent here. However, it is shown that [bmpy][N(Tf)(2)] is a better solvent for aromatic nitration than [bmpy][OTf]. This is due to the ease of formation of nitronium ion in the former ionic liquid, and is consistent with the fact that [bmpy][N(Tf)(2)] is a weaker hydrogen bond acceptor solvent than [bmpy][OTf]. Finally, a method by which [bmpy][N(Tf)(2)] may be recovered and reused for aromatic nitration has been demonstrated.     

Thermal effect on C-H stretching vibrations of the imidazolium ring in ionic liquids

We have studied temperature dependent IR spectra of the C-H stretching modes of the imidazolium ring in [bmim][PF(6)], [bmim][Tf(2)N], [emim][Tf(2)N], [hmim][Tf(2)N], and [bmim][BF(4)]. Temperatures in this study are from 278 to 348 K at an interval of 10 K. Spectra of the C-H stretching modes have been deconvoluted using our previous computer program of the Voigt-lineshape function. Frequency shifts, Lorentzian spectral widths, and band absorbance were examined as a function of temperature. In order to interpret the observed behaviors, we have developed a simple mechanical model as well as a chemical equilibrium model. The model analyses suggest that enthalpy changes for the cluster and/or ion-pair breaking reactions in the liquid state are several kJ mol(-1) endothermic, and the degree of dissociations of ion pairs or hydrogen bonded clusters is in the range from 0.3 to 0.9 with different magnitudes for the five ionic liquids.     

A metallacage encapsulating chloride as a probe for a solvation scale in ionic liquids

With the purpose of assessing the reactivity of chloride ions dissolved in ionic liquids (ILs), a relative scale for the solvation of chloride is given for a series of ILs based on the bis(trifluoromethane)sulfonimide ([Tf(2)N]) anion and different cations, 1-butyl-3-methylimidazolium ([bmim]), 1-butyl-2,3-dimethylimidazolium ([bdmim]), 1-butyl-1-methylpyrrolidinium ([bmpy]), 1-butylpyridinium ([bpy]), 1-pentyl-1,1,1-triethylammonium ([C(5)e(3)am]), and 1-(2-hydroxy)ethyl-3-methylimidazolium ([mimeOH]). Insights into the solvation of chloride are achieved by the thermodynamic study of the reaction of dissociation of a chloride-templated nickel(II) metallacage performed at various temperatures by UV-visible spectroscopy in each IL. The order of chloride solvation [C(5)e(3)am][Tf(2)N] < [bmpy][Tf(2)N] < [bmim][Tf(2)N] 相似文献   

The effect of different interfaces and confinement on the structure of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide entrapped in cationic and anionic reverse micelles

The behavior of the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf(2)N]) entrapped in two reverse micelles (RMs) formed in an aromatic solvent as dispersant pseudophase: [bmim][Tf(2)N]/benzyl-n-hexadecyldimethylammonium chloride (BHDC)/chlorobenzene and [bmim][Tf(2)N]/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT)/chlorobenzene, was investigated using dynamic light scattering (DLS), FT-IR and (1)H NMR spectroscopies. DLS results reveal the formation of RMs containing [bmim][Tf(2)N] as a polar component since the droplet size values increase as the W(s) (W(s) = [[bmim][Tf(2)N]]/[surfactant]) increases. Furthermore, it shows that the RMs consist of discrete spherical and non-interacting droplets of [bmim][Tf(2)N] stabilized by the surfactants. Important differences in the structure of [bmim][Tf(2)N] entrapped inside BHDC RMs, in comparison with the neat IL, are observed from the FT-IR and (1)H NMR measurements. The electrostatic interactions between anions and cations from [bmim][Tf(2)N] and BHDC determine the solvent structure encapsulated inside the nano-droplets. It seems that the IL structure is disrupted due to the electrostatic interaction between the [Tf(2)N](-) and the cationic BHDC polar head (BHD(+)) giving a high ion pair degree between BHD(+) and [Tf(2)N](-) at a low IL content. On the other hand, for the AOT RMs there is no evidence of strong IL-surfactant interaction. The electrostatic interaction between the SO(3)(-) group and the Na(+) counterion in AOT seems to be stronger than the possible [bmim](+)-SO(3)(-) interaction at the interface. Thus, the structure of [bmim][Tf(2)N] encapsulated is not particularly disrupted by the anionic surfactant at all W(s) studied, in contrast to the BHDC RM results. Nevertheless, there is evidence of confinement in the AOT RMs because the [bmim](+)-[Tf(2)N](-) interaction is stronger than in bulk solution. Thus, the IL is more associated upon confinement. Our results reveal that the [bmim][Tf(2)N] structure can be modified in a different manner inside RMs by varying the kind of surfactant used to create the RMs and the IL content (W(s)). These facts can be very important if these media are used as nanoreactors because unique microenvironments can be easily created by simply changing the RM components and W(s).     

New method of fluorination using potassium fluoride in ionic liquid: significantly enhanced reactivity of fluoride and improved selectivity

We have found the new nucleophilic fluorination reaction of some halo- and mesylalkanes to the corresponding fluoroalkanes with KF in the presence of [bmim][BF4] under various reaction conditions. 2-(3-Methanesulfonyloxypropoxy)naphthalene (1) was used as a model compound to optimize this fluorination reaction. Whereas the fluorination of the mesylate 1 with KF in an organic solvent such as CH3CN at 100 degrees C occurred hardly even after 24 h, the same reaction in ionic liquids, [bmim][BF4], as a reaction solvent was completed within 1.5 h, affording the wanted product 2-(3-fluoropropoxy)naphthalene 2a (85%) together with the alkene byproduct 2c (10%). Very interestingly, however, the addition of water (5 equiv) completely eliminated the formation of the undesired alkene 2c and thus gave higher yield of 2a (92%, entry 2). The use of acetonitrile as a cosolvent did not affect the reactivity of the fluorination. The presence of a proper amount of cosolvent was rather desirable (94% yield of 2a). We performed fluorination reactions with other ionic liquids ([bmim][PF6], [bmim][SbF6], [bmim][OTf], and [bmim][N(Tf)2], and two other cosolvents, to find the optimal ionic liquid and cosolvent. Nine different compounds were examined, including the 10 g-synthesis of 2-(fluoromethyl)naphthalene in 93% of isolated yield.     

Growth of sputter-deposited gold nanoparticles in ionic liquids

The growth of gold nanoparticles (NPs) synthesized by sputter deposition on an ionic liquid surface is studied in situ in the bulk phase of the ionic liquids (ILs) 1-butyl-3-methylimidazolium dicyanamide [C(1)C(4)Im][N(CN)(2)], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [C(1)C(4)Im][Tf(2)N], 1-butyl-3-methylimidazolium tetrafluoroborate [C(1)C(4)Im][BF(4)], 1-butyl-3-methylimidazolium hexafluorophosphate [C(1)C(4)Im][PF(6)] and 1-butyl-3-methylimidazolium triflate [C(1)C(4)Im][TfO]. It is found that primary nanoparticles with a diameter smaller than 2.5 nm are present in the sample immediately after sputtering. Growth of these primary particles proceeds after the end of the sputtering process and stops when the nanoparticles reach a certain size. Depending on the viscosity of the ionic liquid this growth process can proceed several hours to several days. The growth speed is fastest for the least viscous ionic liquid and follows the trend [C(1)C(4)Im][N(CN)(2)] > [C(1)C(4)Im][Tf(2)N] > [C(1)C(4)Im][TfO] > [C(1)C(4)Im][BF(4)] > [C(1)C(4)Im][PF(6)]. It is also found that a higher concentration of sputtered gold results in faster growth of the gold nanoparticles. A discussion on the growth mechanism of sputtered gold NPs is included.     

Kemp elimination: a probe reaction to study ionic liquids properties

The amino induced elimination of benzisoxazole into the relevant o-cyanophenolate ion (Kemp elimination) has been studied in [bmim][BF 4] solution at 298 K. To have information about the interactions between reactants and ionic liquid, the reaction has been carried out at different temperatures (293-313 K). Several primary, secondary, and tertiary amines have been used to study the effect of amine structure on the reaction rate. The collected data show that the amine structure seems to have a crucial role in determining the reaction rate. Furthermore, as different cation or anion structures of an ionic liquid can significantly affect its properties, the title reaction has been performed in four different ionic liquids ([bmim][PF6], [bmim][NTf 2], [bm 2im][NTf 2], and [bmpyrr][NTf 2]), using pyrrolidine and piperidine as model amines. An H-donor negative solvent (MeOH and [bmim][NTf 2]) effect on reaction rate was detected. Finally, a narrow range of activation parameters was calculated both for the reaction induced by different amines and for pyrrolidine and piperidine, in the presence of different ILs. This fact suggests the occurrence of an "early" transition state.     

Molecular dynamics simulation studies of the influence of imidazolium structure on the properties of imidazolium/azide ionic liquids

Atomistic molecular dynamics simulations were performed on 1-butyl-3-methyl-imidazolium azide [bmim][N(3)], 1-butyl-2,3-dimethylimidazolium azide [bmmim][N(3)], and 1-butynyl-3-methyl-imidazolium azide [bumim][N(3)] ionic liquids. The many-body polarizable APPLE&P force field was augmented with parameters for the azide anion and the bumim cation. Good agreement between the experimentally determined and simulated crystal structure of [bumim][N(3)] as well as the liquid-state density and ionic conductivity of [bmmim][N(3)] were found. Methylation of bmim (yielding bmmim) resulted in dramatic changes in ion structuring in the liquid and slowing of ion motion. Conversely, replacing the butyl group of bmim with the smaller 2-butynyl group resulted in an increase of ion dynamics.     

The glass transition and the distribution of voids in room-temperature ionic liquids: a molecular dynamics study

The glass transition in prototypical room temperature ionic liquids has been investigated by molecular dynamics simulations based on an Amber-like empirical force field. Samples of [C(4)mim][PF(6)], [C(4)mim][Tf(2)N], and [C(3)mim][Tf(2)N] have been quenched from the liquid phase at T = 500 to a glassy state at T ～ 0 K in discontinuous steps of 20 K every 1.2 ns. The glass temperature estimated by simulation (T(g) = 209 K for [C(4)mim][PF(6)], T(g) = 204 K for [C(4)mim][Tf(2)N], and T(g) = 196 K for [C(3)mim][Tf(2)N]) agrees semi-quantitatively with the experimental values (T(g) = 193÷196 K for [C(4)mim][PF(6)], T(g) = 186÷189 K for [C(4)mim][Tf(2)N], and T(g) = 183 K for [C(3)mim][Tf(2)N]). A model electron density is introduced to identify voids in the system. The temperature dependence of the size distribution of voids provided by simulation reproduce well the experimental results of positron annihilation lifetime spectroscopy reported in G. Dlubek, Y. Yu, R. Krause-Rehberg, W. Beichel, S. Bulut, N. Pogodina, I. Krossing, and Ch. Friedrich, J. Chem. Phys. 133, 124502 (2010), with only one free parameter needed to fit the experimental data.     

Uranyl complexation by chloride ions. Formation of a tetrachlorouranium(VI) complex in room temperature ionic liquids [Bmim][Tf2N] and [MeBu3N][Tf2N

The tetrachlorouranium(VI) complex is formed in [Bmim][Tf2N] and [MeBu3N][Tf2N] from a uranium(VI) solution in the presence of a stoichiometric quantity of chloride ions. The [UVIO2Cl4]2- absorption and emission spectra show bands splitting in comparison with the [UVIO2]2+ spectra, as observed in the solid state, organic solvents, and chloroaluminate-based ionic liquids. The fluorescence lifetime of [UO2Cl4]2- in [MeBu3N][Tf2N] is 0.7 +/- 0.1 mus. The reduction potential of this complex is -1.44 and -1.8 V vs Ag/Ag+ respectively in [Bmim][Tf2N] and [MeBu3N][Tf2N] and does not depend on the chloride concentration. The mechanism proposed for the redox process is a monoelectronic reduction to form [UVO2Cl4]3-, followed by a chemical reaction. The tetrachlorouranium(V) complex seems more stable in [Bmim][Tf2N] than in [MeBu3N][Tf2N]. The electrochemical analysis put in evidence specific interactions of the ionic liquid cation with the uranium anionic species.     

Thermodynamic modeling of hydrogen sulfide solubility in ionic liquids using modified SAFT-VR and PC-SAFT equations of state

Equations of state based on the statistical associating fluid theory for potentials of variable range (SAFT-VR) and the perturbed chain statistical associating fluid theory (PC-SAFT) have been used to model the PVT behavior of ionic liquids and the solubility of H₂S in six imidazolium-based ionic liquids. The studied systems included [bmim][PF6], [hmim][PF6], [bmim][BF4], [hmim][BF4], [bmim][NTF2] and [hmim][NTF2] at various temperatures and pressures.For pure components, parameters of the models have been obtained by fitting the models to experimental data on liquid densities; the average relative deviation between the calculated and experimental densities for ionic liquids is less than 2.42% in the PC-SAFT model and 5.44% in the SAFT-VR approach, the latter which incorporates the square-well potential for short-range interactions. In both models an additional term has been added to account for dipole-dipole interactions between solute molecules resulting from the permanent charges on the chain molecules of the solvents. The model parameters have also been correlated as functions of the molecular weight of the solvents. For binary mixtures of ionic liquids and H₂S, the association interactions between H₂S molecules and between the ionic liquids and H₂S molecules have also been taken into account in both approaches, using binary interaction coefficients. The results show an average deviation of less than 5% in the calculation of the mole fraction of H₂S in the ionic liquids. The effect of inclusion of the polar term has been studied for binary systems in both models.     

Thermochemistry of imidazolium-based ionic liquids: experiment and first-principles calculations

In this work the molar enthalpy of formation of the ionic liquid 1-ethyl-3-methylimidazolium dicyanoamide in the gaseous phase [C(2)MIM][N(CN)(2)] was measured by means of combustion calorimetry and enthalpy of vaporization using transpiration. Available, but scarce, primary experimental results on enthalpies of formation of imidazolium based ionic liquids with the cation [C(n)MIM] (where n = 2 and 4) and anions [N(CN)(2)], [NO(3)] and [NTf(2)] were collected and checked for consistency using a group additivity procedure. First-principles calculations of the enthalpies of formation in the gaseous phase for the ionic liquids with the common cation [C(n)MIM] (where n = 2 and 4) and with the anions [N(CN)(2)], [NO(3)], [NTf(2)], [Cl], [BF(4)] and [PF(6)] have been performed using the G3MP2 theory. It has been established that the gaseous phase enthalpies of formation of these ionic liquids obey the group additivity rules.     

Enzymatic polyester synthesis in ionic liquids

The enzymatic synthesis of polyesters by ring-opening polymerization (ROP) and polycondensation in three ionic liquids, i.e., [bmim][Tf₂N], [bmim][PF₆] and [bmim][BF₄] was investigated. For the enzymatic ROP of ε-caprolactone it was found that [bmim][PF₆] and [bmim][BF₄] result in an inhomogeneous reaction mixture upon polymerization, causing polymerization characteristics similar to bulk polymerization. In contrast, for [bmim][Tf₂N] characteristics similar to toluene were observed. Molecular weights of 7000-9500 g/mol were obtained. In the polycondensation of dimethyl adipate and dimethyl sebacate, respectively, with 1,4-butanol the low volatility of ionic liquids was successfully utilized to perform the reactions in an open vessel at temperatures close to the boiling point of the condensation by-product. Molecular weights up to 5400 g/mol were obtained. This, in combination with the tunable solvent hydrophilicity of ionic liquids could offer an advantage in the polymerization of highly polar monomers with low solubility in organic solvents.     

Homogeneous enzymatic reactions in ionic liquids with poly(ethylene glycol)-modified subtilisin

Subtilisin Carlsberg was covalently modified with comb-shaped poly(ethylene glycol) (PM13). PM13-modified subtilisin (PM13-Sub) was readily solubilized in three different ionic liquids (ILs), i.e., [Emim][Tf2N], [C2OC1mim][Tf2N] and [C2OHmim][Tf2N]. Analysis of homogeneous enzymatic reactions in the ILs revealed that PM13-Sub exhibited excellent catalytic performance while the native enzyme suspended in ILs showed no activity. Hydrophobicity of ILs slightly affected enzyme activity, and the relatively hydrophobic IL [Emim][Tf2N] was the preferred medium for enzymatic reactions, similar to enzymatic reactions in conventional organic solvents. Enzyme activity was much higher in [Emim][Tf2N] than in conventional organic solvents, and excellent activity was associated with unique properties of ILs such as hydrophobicity and high polarity. Furthermore, PM13-Sub showed good stability in [Emim][Tf2N], and maintained 80% of its initial activity after 60 h.     

Study of aromatic nucleophilic substitution with amines on nitrothiophenes in room-temperature ionic liquids: are the different effects on the behavior of para-like and ortho-like isomers on going from conventional solvents to room-temperature ionic liquids related to solvation effects?

The kinetics of the nucleophilic aromatic substitution of some 2-L-5-nitrothiophenes (para-like isomers) with three different amines (pyrrolidine, piperidine, and morpholine) were studied in three room-temperature ionic liquids ([bmim][BF4], [bmim][PF6], and [bm(2)im][BF4], where bmim = 1-butyl-3-methylimidazolium and bm(2)im = 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamic parameters, a useful instrument to gain information concerning reagent-solvent interactions, the reaction was carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids than in conventional solvents (methanol, benzene), a dependence of rate constants on amine concentration similar to that observed in methanol, suggesting a parallel behavior. The above reaction also was studied with 2-bromo-3-nitrothiophene, an ortho-like derivative able to give peculiar intramolecular interactions in the transition state, which are strongly affected by the reaction medium.