Electrophilic nitration of aromatics in ionic liquid solvents.

Potential utility of a series of 1-ethyl-3-methylimidazolium salts [emim][X] with X = OTf-, CF3COO-, and NO3- as well as [HNEtPri2][CF3COO] (protonated Hünig's base) ionic liquids were explored as solvent for electrophilic nitration of aromatics using a variety of nitrating systems, namely NH4NO3/TFAA, isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH, Cu(NO3)/TFAA, and AgNO3/Tf2O. Among these, NH4NO3/TFAA (with [emim][CF3COO], [emim][NO3]) and isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH (with [emim][OTf]) provided the best overall systems both in terms of nitration efficiency and recycling/reuse of the ionic liquids. For [NO2][BF4] nitration, the commonly used ionic liquids [emim][AlCl4] and [emim][Al2Cl7] are unsuitable, as counterion exchange and arene nitration compete. [Emim][BF4] is ring nitrated with [NO2][BF4] producing [NO2-emim][BF4] salt, which is of limited utility due to its increased viscosity. Nitration in ionic liquids is surveyed using a host of aromatic substrates with varied reactivities. The preparative scope of the ionic liquids was also extended. Counterion dependency of the NMR spectra of the [emim][X] liquids can be used to gauge counterion exchange (metathesis) during nitration. Ionic liquid nitration is a useful alternative to classical nitration routes due to easier product isolation and recovery of the ionic liquid solvent, and because it avoids problems associated with neutralization of large quantities of strong acid.     

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.     

Lyotropic liquid-crystalline phases formed by Pluronic P123 in ethylammonium nitrate

Aggregation of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer, Pluronic P123, is promoted in a room temperature ionic liquid, ethylammonium nitrate (EAN). A series of lyotropic mesophases including normal micellar cubic (I1), normal hexagonal (H1), lamellar (Lalpha), and reverse bicontinuous cubic (V2) are identified at 25 degrees C by using polarized optical microscopy and small-angle X-ray scattering techniques. Such self-assembly behavior of P123 in EAN is similar to those observed in H2O or 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMim(+)][PF6(-)]) systems except for the presence of the V2 phase in EAN and the absence of the I 1 phase in [BMim(+)][PF6(-)]. This suggests that the ionic solvent of EAN plays similar roles as H2O and [BMim(+)][PF6(-)] during the aggregation process and solvates the PEO blocks through hydrogen-bond interaction. Furthermore, the hydrogen bonds are considered to form between the ethylammonium cations and oxygen atoms of the PEO blocks as confirmed by Fourier transform infrared spectra of P123-EAN assemblies. This deduction is also consistent with the results from differential scanning calorimetry and thermogravimetric analysis. The additional V2 phase appearing in the P123-EAN system is attributed to the higher affinity for the relatively hydrophobic PPO blocks to EAN than to water, which might reduce the effective area of the solvophilic headgroup and increase the volume of the solvophobic part. The obtained results may help us to better understand the self-assembly process for amphiphilic block copolymers in protic solvents.     

Abnormal Temperature Dependence of the Viscosity of Ethylammonium Nitrate–Methanol Ionic Mixtures

The shear viscosities of ionic fluids composed of ethylammonium nitrate (EAN) and methanol (MeOH) have been investigated as a function of the shear rate, the composition of the mixtures (quoted as x, the mole fraction of EAN), and the temperature (T) in the range 293–328 K. At low content of EAN (0.2 x 0.4), the solutions exhibit a non-Newtonian and a non-Arrhenius behavior. The viscosities of these solutions increase with the temperature when T > 313 K, but they are independent of the temperature at x = 0.6 and decrease for x > 0.6. Excess viscosities and excess Gibbs energies for the viscosity give evidence of the formation of strong hydrogen bonded complexes in solution for x < 0.6 and T > 318 K. For these systems, any increase in temperature favors the formation of hydrogen bonds between EAN and MeOH.     

The Synthesis and Application of Novel Nitrating and Nitrosating Agents

Alcohols and phenols are efficiently nitrated with thionyl chloride nitrate or thionyl nitrate, even in the presence of an aromatic moiety. While thionyl chloride nitrate is suitable for nitration of primary OH-groups in carbohydrates, thionyl nitrate is reactive enough to react with secondary OH-groups as well. These reagents permit the highly selective nitration of the 5′-,2′5′- and 3′, 5′-OH-groups of ribonucleosides to produce either mono-or diprotected nitro derivatives in high yields. Carbon acids and the enol form of some ketones are efficiently nitrated with trifluoromethanesulfonyl nitrate/potassium tert-butoxide. Lutidine N-oxide (2,6-(CH₃)₂C₅H₃N O) was found to have a marked effect on nitration reactions. Similarly, thionyl chloride nitrite and thionyl nitrite exhibit an excellent capacity for nitrosation of the aforementioned substrates.     

Volatile Times for the Very First Ionic Liquid: Understanding the Vapor Pressures and Enthalpies of Vaporization of Ethylammonium Nitrate

A hundred years ago, Paul Walden studied ethyl ammonium nitrate (EAN), which became the first widely known ionic liquid. Although EAN has been investigated extensively, some important issues still have not been addressed; they are now tackled in this communication. By combining experimental thermogravimetric analysis with time of flight mass spectrometry (TGA‐ToF‐MS) and transpiration method with theoretical methods, we clarify the volatilisation of EAN from ambient to elevated temperatures. It was observed that up to 419 K, EAN evaporates as contact‐ion pairs leading to very low vapour pressures of a few Pascal. Starting from 419 K, the decomposition to nitric acid and ethylamine becomes more thermodynamically favourable than proton transfer. This finding was supported by DFT calculations, which provide the free energies of all possible gas‐phase species, and show that neutral molecules dominate over ion pairs above 500 K, an observation that is in nearly prefect agreement with the experimental boiling point of 513 K. This result is crucial for the ongoing practical applications of protic ionic liquids such as electrolytes for batteries and fuel cells because, in contrast to high‐boiling conventional solvents, EAN exhibits no significant vapour pressure below 419 K and this property fulfils the requirements for the thermal behaviour of safe electrolytes. Overall, EAN shows the same barely measurable vapour pressures as typical aprotic ionic liquids at temperatures only 70 K lower.     

Evidence for the formation of UO2(NO3)4(2-) in an ionic liquid by EXAFS

The complexation between uranium(vi) and nitrate ions in a hydrophobic ionic liquid (IL), namely [BMI][NO(3)] (BMI = 1-butyl-3-methylimidazolium(+)), is investigated by EXAFS spectroscopy. It was performed by dissolution of uranyl nitrate UO(2)(NO(3))(2)·6H(2)O or UO(2)(Tf(2)N)(2) (Tf(2)N = bis(trifluoromethylsulfonyl)imide (CF(3)SO(2))(2)N(-)). The formation of the complex UO(2)(NO(3))(4)(2-) is evidenced.     

Phase behavior and microstructure of microemulsions with a room-temperature ionic liquid as the polar phase

Microemulsions of nonionic alkyl oligoethyleneoxide (CiEj) surfactants, alkanes, and ethylammonium nitrate (EAN), a room-temperature ionic liquid, have been prepared and characterized. Studies of phase behavior reveal that EAN microemulsions have many features in common with corresponding aqueous systems, the primary difference being that higher surfactant concentrations and longer surfactant tailgroups are required to offset the decreased solvophobicity the surfactant molecules in EAN compared with water. The response of the EAN microemulsions to variation in the length of the alkane, surfactant headgroup, and surfactant tailgroup has been found to parallel that observed in aqueous systems in most instances. EAN microemulsions exhibit a single broad small-angle X-ray scattering peak, like aqueous systems. These are well described by the Teubner-Strey model. A lamellar phase was also observed for surfactants with longer tails at lower temperatures. The scattering peaks of both microemulsion and lamellar phases move to lower wave vector on increasing temperature. This is ascribed to a decrease in the interfacial area of the surfactant layer. Phase behavior, small-angle X-ray scattering, and conductivity experiments have allowed the weakly to strongly structured transition to be identified for EAN systems.     

Preparative-scale synthesis of amino coumarins through new sequential nitration and reduction protocol

In contrast to the conventional deleterious approach for nitration (for example HNO₃/H₂SO₄) and for reduction (for example Zn/HCl), we hypothesized that sensitive heterocycles such as coumarins could not withstand with those hard conditions. Hence, while studying this reaction sequence to prepare amino coumarins (which is our ongoing project to synthesize antitubercular coumarin agents), we came across mild and greener reagent for nitration using calcium nitrate (Ca(NO₃)₂·4H₂O; lime nitrate), and reduction using d-glucose. These two mild, chemoselective, high yielding methods are discussed herein.     

Structural characterization of zinc(II) chloride in aqueous solution and in the protic ionic liquid ethyl ammonium nitrate by x-ray absorption spectroscopy

Extended x-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the species and structures existing in a series of ZnCl(2)-H(2)O-NaCl solutions with different chloride/zinc ratios and in a solution of ZnCl(2) in the protic ionic liquid ethyl ammonium nitrate (EAN). The average coordination numbers and distances of zinc species were determined from the analysis of the EXAFS data. In aqueous solution the number of chloride ions tightly bounded to Zn(2+) is significantly related to the chloride/zinc ratio, and no inner complex formation between Zn(2+) and Cl(-) ions has been detected for low ZnCl(2) concentration (0.1 and 0.2 M). Conversely, in the same concentration range (0.13 M) the ZnCl(2) species do not dissociate in EAN and the Zn(2+) first coordination shell has two chloride ions and is completed by two oxygen atoms of the nitrate anion. The results of this investigation show that notwithstanding the existence of similar characteristics between EAN and water, the solvation properties of the two solvents are markedly different.     

Surface Esterification of Cellulose by Vapor-Phase Treatment With Trifluoroacetic Anhydride

Vapor-phase esterification of cellulose was achieved by exposing filter paper and tunicate cellulose film to mixed vapor of trifluoroacetic anhydride (TFAA) and acetic acid (AcOH) or TFAA and acetic anhydride (Ac₂O) at room temperature. Both treatments gave high hydrophobicity to the specimens. The hydrophobicity of TFAA/AcOH-treated sample was resistant to water immersion, but that of TFAA/Ac₂O-treated sample was lost due to hydrolysis. In spite of high hydrophobicity, the bulk degree of substitution for acetyl groups was as low as 0.07, indicating localization of acetyl groups on the fibril surfaces. Detection of ester groups by X-Ray photoelectron spectroscopy corroborated this feature. Infrared spectroscopy of tunicate cellulose revealed that the esterification occurred preferentially to the weakly hydrogen-bonded hydroxyl groups. This vapor-phase process is potentially useful in modifying cellulosic materials without immersing in solvents or liquid reagents.     

Excess enthalpy and excess volume for binary systems of two ionic liquids + water

In this work we report the experimental measurements of excess molar enthalpy and excess molar volume, at 298.15 K and atmospheric pressure, on ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) + water mixtures. Positive enthalpies were found for the two systems (maximum, at x ₁ around 0.37 correspond to about 700 and 900 J mol⁻¹ for EAN and PAN respectively). As the hydrophobic/hydrophilic ratio increases, along with the length of the alkyl chain in the ionic liquids, ILs, the specific interactions IL-water become less important. The excess molar volumes, V ^E, are negative over the entire composition range for the two binary mixtures. They have similar values but curves exhibit a different asymmetric shape and around equimolar composition they intersect each other. This behaviour: positive H ^E and negative V ^E, is not very common.     

Reversible Photoresponsive Molecular Alignment of Liquid Crystals at Fluid Interfaces with Persistent Stability

This work demonstrates a noninvasive approach to control alignment of liquid crystals persistently and reversibly at fluid interfaces by using a photoresponsive azobenzene‐based surfactant dissolved in an ionic liquid (IL), ethylammonium nitrate (EAN). As the first report on the orientational behavior of LCs at the IL/LC interface, our study also expands current understanding of alignment control of LCs at the aqueous/LC interface by adding electrolytes into aqueous solutions. The threshold concentration for switching the optical responses of LCs can be changed just by simply manipulating the ratio of EAN to H₂O. This work will inspire fundamental studies and novel applications of using the LC‐based imaging technique to investigate various chemical and biological events in ILs.     

Aromatic hydrocarbon nitration under tropospheric and combustion conditions. A theoretical mechanistic study

The viability of some nitration pathways is explored for benzene (B), naphthalene (N), and in part pyrene (P). In principle, functionalization can either take place by direct nitration (NO2 or N2O5 attack) or be initiated by more reactive species, as the nitrate and hydroxyl radicals. The direct attack of the NO2 radical on B and N, followed by abstraction of the H geminal to the nitro group (most likely accomplished by 3O2) could yield the final nitro-derivatives. Nevertheless, the initial step (NO2 attack) involves significant free energy barriers. N2O5 proves to be an even worst nitrating agent. These results rule out direct nitration at room temperature. Instead, NO3 and, even more easily, HO can form pi-delocalized nitroxy- or hydroxycyclohexadienyl radicals. A subsequent NO2 attack can produce several regio- and diastereoisomers of nitroxy-nitro or hydroxy-nitro cyclohexadienes. In this respect, the competition between NO2 and O2 is considered: the rate ratios are such to indicate that the NO3 and HO initiated pathways are the major source of nitroarenes. Finally, if the two substituents are 1,2-trans, either a HNO3 or a H2O concerted elimination can give the nitro-derivatives. Whereas HNO3 elimination is feasible, H2O elimination presents, by contrast, a high barrier. Under combustion conditions the NO2 direct nitration pathway is more feasible, but remains a minor channel.     

微波辅助合成有机膦功能化离子液体及对稀土离子的萃取

用微波辐射法,合成了5个含有机膦氧基团的离子液体：1-丙基-3-(3-二苯基氧膦基)丙基咪唑双(三氟甲基磺酰基)亚胺盐([PImC3P(O)Ph2][Tf2N])、1-己基-3-(3-二苯基氧膦基)丙基咪唑双(三氟甲基磺酰基)亚胺盐([HImC3P(O)Ph2][Tf2N])、1-丙基-3-(3-苯基乙氧基氧膦基)丙基咪唑双(三氟甲基磺酰基)亚胺盐([PImC3P(O)Ph(OEt)][Tf2N])、1-己基-3-(3-苯基乙氧基氧膦基)丙基咪唑双(三氟甲基磺酰基)亚胺盐([HImC3P(O)Ph(OEt)][Tf2N])和(3-苯基乙氧基氧膦基)丙基三乙胺双(三氟甲基磺酰基)亚胺盐([TENC3P(O)Ph(OEt)][Tf2N])。 用31P NMR、1H NMR、13C NMR、MS及FT-IR对产物结构进行了表征。 研究了这类离子液体对稀土Nd(III)的萃取性能。 结果表明,这类功能化离子液体可作为单一组分萃取稀土而无需加入有机稀释剂,离子液体结构对萃取效率影响很大,相同条件下季铵盐型结构的离子液体[TENC3P(O)Ph(OEt)][Tf2N]对稀土Nd(Ⅲ)的萃取效率最高。 稀土溶液pH值对萃取效率影响显著,近中性条件下(pH=6.63),对稀土Nd(Ⅲ)的萃取率最高。 用pH=1.00的盐酸溶液可以较好的从离子液体相反萃Nd(Ⅲ),反萃率可达94%。     

Separation of uranium from lanthanum in molecular and ionic organic liquids

We have investigated the separation of uranium from lanthanum in two molecular organic liquids (sulfolane, TMSO₂; ethylene carbonate, EC) and in one organic ionic melt: ethylammonium nitrate (EAN). A separation is achieved by chemical oxidation and precipitation of oxides in TMSO₂; in this medium, the part of uranium remaining in solution may be recovered by an electrochemical reduction. In EAN, it is required to add Li₂O to initiate the oxides precipitation: the separation corresponds to the difference between the solubility products of UO₃(s) and La₂O₃(s). Best results are obtained in EC where the insoluble phase corresponds to an U/La ratio equal to 186 instead of 1.7 in the initial conditions.     

Preparation and characterization of ultrathin [Ru(CO)3Cl2]2 and [BMIM][Tf2N] films on Al2O3/NiAl(110) under UHV conditions

Towards a better understanding of the interface chemistry of ionic liquid (IL) thin film catalytic systems we have applied a rigorous surface science model approach. For the first time, a model homogeneous catalyst has been prepared under ultrahigh vacuum conditions. The catalyst, di-μ-chlorobis(chlorotricarbonylruthenium) [Ru(CO)(3)Cl(2)](2), and the solvent, the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][Tf(2)N], have been deposited by physical vapor deposition onto an alumina model support [Al(2)O(3)/NiAl(110)]. First, the interaction between thin films of [Ru(CO)(3)Cl(2)](2) and the support is investigated. Then, the ruthenium complex is co-deposited with the IL and the influence of the solvent on the catalyst is discussed. D(2)O, which is a model reactant, is further added. Growth, surface interactions, and mutual interactions in the thin films are studied with IRAS in combination with density functional (DFT) calculations. At 105 K, molecular adsorption of [Ru(CO)(3)Cl(2)](2) is observed on Al(2)O(3)/NiAl(110). The IRAS spectra of the binary [Ru(CO)(3)Cl(2)](2) + [BMIM][Tf(2)N] and ternary [Ru(CO)(3)Cl(2)](2) + [BMIM][Tf(2)N] + D(2)O show every characteristic band of the individual components. Above 223 K, partial decomposition of the ruthenium complex leads to species of molecular nature attributed to Ru(CO) and Ru(CO)(2) surface species. Formation of metallic ruthenium clusters occurs above 300 K and the model catalyst decomposes further at higher temperatures. Neither the presence of the IL nor of D(2)O prevents this partial decomposition of [Ru(CO)(3)Cl(2)](2) on alumina.     

VO(H2O)5]H[PMo12O40]-catalyzed nitration of alkanes with nitric acid

[VO(H2O)5]H[PMo12O40], which contains vanadyl counter cations and PMo12O40(3-), can act as a catalyst for the nitration of various alkanes including alkylbenzenes using nitric acid as a nitrating agent in acetic acid at 356 K.     

Preparation and Structure of A Novel Ethanolamine-occluding Aluminoarsenate

An aluminoarsenate, Al2As2O3.EAN, denoted as AlAsO4-1 was synthesized from EAN(EAN= ethanolamine), pyroarsenic acid and aluminium-iso-propylate systems. The crystal structure of AlAsO4-1 was determined by single crystal X-ray diffraction method. The compound crystallizes in orthorhombic space group Pcab with the unit cell constants:0 = 8.781(3), 6=10.261(3), c=20. 433(11) A .V = 1840.9 A3, 2=8. The final R and Rw factors are 0. 0401 and 0. 0344, respectively. The framework of AlAsO4-1 contains two types of Al atoms. It is interesting that in the asymmetric unit one of two Al atoms is strictly 4-coordinated and the other is 6-coordinated. The three-dimensional framework is built of two-dimensional nets which consist of 4-membered rings and 8-membered rings. The biggest open channel in the framework runs along [100], in which EAN template is located. Arsenic atoms can function as a component element for construction of three-dimensional net with topological novelty.     

Scandium(III) trifluoromethanesulfonate catalyzed aromatic nitration with inorganic nitrates and acetic anhydride

The rare earth metal(III) trifluoromethanesulfonate (rare earth metal(III) triflate, RE(OTf)3) was found to be an efficient catalyst for aromatic nitration with carboxylic anhydride-inorganic nitrate as the nitrating agent. In the presence of a catalytic amount of RE(OTf)3, the nitration of substituted benzenes proceeded to afford the corresponding nitrobenzenes. Especially, scandium(III) trifluoromethanesulfonate (scandium(III) triflate, Sc(OTf)3) is the most active catalyst among our tested Lewis acids. It was also found that acetic anhydride-Al(NO3).9H2O is the most active nitrating agent in this system.