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Imidazolium-based dicationic ionic liquids (DILs) are gaining considerable space in the field of organocatalysis mainly due to the opportunities in offering new possible applicable structural variations. In addition to the well-known variables which made the ionic liquids (ILs) famous as the type of cation and anion used, the nature of the molecular spacer moiety turns out a further possibility to improve some physicochemical properties, for example, solubility, acidity, electrochemical behavior, and so on. For this reason, this class of ionic liquids has been considered as possible competitors to their corresponding monocationic salts in replacing common catalysts in organic synthesis, particularly in cases in which their bidentate nature could positively affect the catalytic activity. This mini-review is intended to highlight the progress carried out in the last six years in the field of organocatalysis, including DILs as such and as hybrids with polymers, nanomaterials, and composites.

The intermediate di-[EMIM]Cl was synthesized from methyl imidazole and 1,4-dichlorobutane and then reacted with cobalt chloride at 105 °C to prepare a bi-[EMIM]CoCl3 ionic liquid catalyst. The di-[EMIM]CoCl3 catalyst coupled with oxone to remove sulfur-containing organics in octane. The di-[EMIM]CoCl3 catalyst was characterized by HNMR, FTIR, TG, and SEM–EDS. The dibenzothiophene (DBT) was dissolved in octane to prepare a model oil with an initial sulfur content of 500 ppm. Six grams of the model oil was added. The results showed that the optimal dosages of di-[EMIM]CoCl3, oxone (20 wt%), and [BMIM]BF4 extractant were 1 g, 2 g, and 2 g, respectively. At the optimum temperature of 45 °C, 100% of sulfur was removed after 40 min. After di-[EMIM]CoCl3 was recycled five times, the sulfur removal percentage remained above 91%. The sulfur removal percentages for different sulfur-containing organics followed the order of dibenzothiophene (DBT) > benzothiophene (BT) > 4,6-dimethyldibenzothiophene (4,6-DMDBT). The oxidation product was determined to be DBTO2 by GC–MS analysis, and the oxidation mechanism was discussed. The active oxygen atoms of oxone oxidized DBT to form DBTO, and then persulfate oxidized DBTO to DBTO2 via an identical oxidation mechanism.

The cycloaddition of CO2 to epoxides has attracted a great deal of interest in recent years as an atom efficient way to employ this greenhouse gas as a useful C1 building block. While several ionic liquids have been tested as catalysts for the reaction, little attention has been devoted to dicationic ionic liquids (DILs). Herein, the catalytic activity of a panel of structurally-related DILs has been evaluated in the cycloaddition of CO2 to epichlorohydrin, in order to study the influence of the DILs’ structure on their activity. The solubilities of a series of bromide DILs in epichlorohydrin, featuring various linker lengths and imidazolium substituents, were investigated. The bromide Cn(MIM)2 series displayed a limited solubility in this medium, which particularly affected the performances of C3(MIM)2 2Br. However, the addition of 20 mol% of reaction product to the reactants was found to be an effective way to overcome this issue. This way, it was possible to compare the catalytic activity of both soluble and only partially soluble systems in epichlorohydrin. C6(MIM)2 2Br and C5(HIM)2 2Br were found to be the best performing DILs and have been tested, together with monocation C4MIM Br, also on less reactive epoxides. Mono and dicarboxylate (D)ILs instead proved to be less active than the bromide DILs and, when considering their synthesis, thermal stability and moisture sensitivity, ultimately less attractive for the development of future catalysts. Finally, a convenient and operationally simple way of recovering and reusing the bromide DILs at the end of the reaction was also evaluated.

Wettability is an important factor affecting the performance of catalytic oxidative desulfurization. In order to develop an efficient catalyst for the extractive coupled catalytic oxidative desulfurization (ECODS) of fuel oil by H2O2 and acetonitrile, a novel family of imidazole-based polyoxometalate dicationic ionic liquids (POM-DILs) [Cn(MIM)2]PW12O40 (n = 2,4,6) was synthesized by modifying phosphotungstic acid (H3PW12O40) with double imidazole ionic liquid. These kinds of catalysts have good dispersity in oil phase and H2O2, which is conducive to the deep desulfurization of fuel oil. The catalytic performance of the catalysts was studied under different conditions by removing aromatic sulfur compound dibenzothiophene (DBT) from model oil. Results showed that [C2(MIM)2]PW12O40 had excellent desulfurization efficiency, and more than 98% of DBT was removed under optimum conditions. In addition, it also exhibited good recyclability, and activity with no significant decline after seven reaction cycles. Meanwhile, dibenzothiophene sulfone (DBTO2), the only oxidation product of DBT, was confirmed by Gas Chromatography-Mass Spectrometry (GC-MS), and a possible mechanism of the ECODS process was proposed.

Benzimidazole dicationic ionic liquids (BDILs) have not yet been widely explored in spite of their potential. Therefore, two structurally related families of BDILs, paired with either bromide or bistriflimide anions and bearing alkyl spacers ranging from C3 to C6, have been prepared. Their thermal properties have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), while their electrical properties have been assessed by cyclic voltammetry (CV). TG analysis confirmed the higher stability of the bistriflimide BDILs over the bromide BDILs, with minor variation within the two families. Conversely, DSC and CV allowed for ascertaining the role played by the spacer length. In particular, the thermal behavior changed dramatically among the members of the bistriflimide family, and all three possible thermal behavior types of ILs were observed. Furthermore, cyclic voltammetry showed different electrochemical window (C3(C1BenzIm)2/2Tf2N &lt, C4(C1BenzIm)2/2Tf2N, C5(C1BenzIm)2/2Tf2N &lt, C6(C1BenzIm)2/2Tf2N) as well as a reduction peak potential, shape, and intensity as a function of the spacer length. The results obtained highlight the benefit of accessing a more structurally diverse pool of compounds offered by dicationic ILs when compared to the parent monocationic ILs. In particular, gains are to be found in the ease of fine-tuning their properties, which translates in facilitating further investigations toward BDILs as designer solvents and catalysts.

A number of dicationic ionic liquids with a disiloxane linker between imidazolium cations and bis(trifluoromethylsulfonyl)imide anion were synthesized and characterized. Melting points, viscosity, and volatility in a vacuum were measured, the thermal and hydrolytic stability of ionic liquids were also studied. The dependence of the properties on the structure of substituents in the cation of the ionic liquid was demonstrated.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES Ionic Liquids (ILs) have been considered good candidates for thermal storage materials due to their properties of thermal stability, non-flammability, low volatility, low corrosion and high heat capacity. Dicationic ILs imidazolium-based with bromide anions perform better than their monocationic analogues, however these ILs have high toxicity. Considering that alkylcarboxylate anions have high heat capacity and low toxicity, this Thesis presents the synthesis, characterization, study of the thermophysical properties of dicationic ionic liquids (ILs) derived from imidazole ([Cn(MIM)2]2+, n = 4, 6 , 8, 10 carbons in the spacer chain) with anions derived from dicarboxylic acids (oxalic, malonic, succinic, glutaric, adipic and pimelic acids) for thermal storage. ILs were characterized by 1H and 13C nuclear magnetic resonance (NMR), mass spectrometry, infrared, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Thermogravimetric analysis showed that dicarboxylate ILs have thermal stability between 200 - 249 °C and are less stable than their mono- and dicationic analogues with bromide anions. The LIs [C4(MIM)2][Oxa], [C6(MIM)2][Mal], [C6(MIM)2][Adi], [C4(MIM)2][Pim], [C8(MIM)2][Oxa], [C8(MIM)2][Suc], [C10(MIM)2][Oxa] and [C10(MIM)2][Pim] presented crystalline and amorphous structural organization represented by melting point and glass transition (Tg) and the other LIs were totally amorphous. For ILs that exhibited crystalline organization, the heat of fusion increased with the increase in the size of the dication spacer chain. The size of the anion spacer chain did not affect the heat of fusion. The dicarboxylate ILs showed higher heat capacities than monocationic ILs imidazolium-based with bromide anions, but lower in relation to their dicationic analogues with bromide anions. The dicarboxylate ILs showed thermal storage densities (Es) lower than their dicationic analogues derived from imidazole with bromide anions. However, [C6(MIM)2][Mal] and [C6(MIM)2][Pim] showed Es greater than thermal oils commonly used as heat storage materials. All the dicarboxylate ILs studied were soluble in polar protic solvents and in dimethyl sulfoxide. In turn, applications of ILs in solution, particularly applications that depend on the formation of nano-organized structures, such as micelles, depend on studies of the relationship between the structure of the IL and the formation of supramolecular aggregates in solution. Thus, this Thesis also presents a study of the aggregation behavior in aqueous solution of dicationic dicarboxylate ILs with dications [Cn(MIM)2]2+ with n = 8 and 10 carbons in the spacer chain. Electrical conductivity and 1H NMR techniques were used. The results showed that dicarboxylate ILs aggregated more easily than their mono- and dicationic analogues imidazolium-based with a bromide anion. It was not possible to correlate the influence of the dianion spacer chain with the obtained CMC values. Based on the shielding and deshielding behaviors observed for the dication and dianion nuclei, a model of supramolecular self-organization for the formed micelles was proposed. Due to the shielding effect suffered by all the hydrogens of the evaluated dianions, it was proposed that the spacer chain would be oriented in order to interact with the hydrophobic chain of the dication, and the dicarboxylate portions would be interacting with the hydrophilic heads of the dication Líquidos iônicos (LIs) tem sido considerados bons candidatos a materiais de estocagem térmica devido a suas propriedades de estabilidade térmica, não-inflamabilidade, baixa volatilidade, baixa corrosão e alta capacidade calorífica. Os LIs dicatiônicos derivados do imidazol com ânion brometo possuem melhor desempenho que seus análogos monocatiônicos, porém estes LIs apresentam alta toxicidade. Considerando que ânions alquilcarboxilatos apresentam alta capacidade calorifica e baixa toxicidade, esta Tese apresenta a síntese, caracterização, estudo das propriedades termofísicas de líquidos iônicos (LIs) dicatiônicos derivados do imidazol ([Cn(MIM)2]2+ com n = 4, 6, 8, 10 carbonos na cadeia espaçadora) com ânions derivados de ácidos dicarboxílicos (ácidos oxálico, malônico, succínico, glutárico, adípico e pimélico) para estocagem térmica. Os LIs foram caracterizados por ressonância magnética nuclear (RMN) de 1H e 13C, espectrometria de massas, infravermelho, análise termogravimétrica (TGA) e calorimetria exploratória diferencial (DSC). A análise termogravimétrica mostrou que os LIs dicarboxilatos possuem estabilidades térmicas entre 200 - 249 °C e são menos estáveis que seus análogos mono- e dicatiônicos com ânion brometo. Os LIs [C4(MIM)2][Oxa], [C6(MIM)2][Mal], [C6(MIM)2][Adi], [C4(MIM)2][Pim], [C8(MIM)2][Oxa], [C8(MIM)2][Suc], [C10(MIM)2][Oxa] e [C10(MIM)2][Pim] apresentaram organização estrutural cristalina e amorfa, representadas por ponto de fusão e transição vítrea (Tg) e os demais LIs foram totalmente amorfos. Para os LIs que apresentaram organização cristalina, a entalpia de fusão aumentou com o aumento do tamanho da cadeia espaçadora do dicátion. O tamanho da cadeia espaçadora do ânion não afetou a entalpia de fusão. Os LIs dicarboxilatos apresentaram capacidades caloríficas superiores a LIs monocatiônicos derivados do imidazol com ânion brometo, porém inferiores em relação a seus análogos dicatiônicos com ânion brometo. Os LIs dicarboxilatos apresentaram densidades de armazenamento térmico (Es) inferiores a seus análogos dicatiônicos derivados do imidazol com ânion brometo. Porém, [C6(MIM)2][Mal] e [C6(MIM)2][Pim] apresentaram Es superiores a óleos térmicos comumente utilizados como materiais pra estocagem de calor. Todos os LIs dicarboxilatos estudados foram solúveis em solventes polares próticos e em dimetilsulfóxido. Por sua vez, as aplicações de LIs em solução, particularmente as aplicações que dependem da formação de estruturas nano-organizadas, tais como micelas, depende de estudos da relação entre a estrutura do LI e a formação de agregados supramoleculares em solução. Assim, esta Tese também apresenta um estudo do comportamento de agregação em solução aquosa dos LIs dicatiônicos dicarboxilatos com dicátions [Cn(MIM)2]2+ com n = 8 e 10 carbonos na cadeia espaçadora. Foram utilizadas as técnicas de condutividade elétrica e RMN de 1H. Os resultados mostraram que os LIs dicarboxilatos agregam mais facilmente que seus análogos mono- e dicatiônicos derivados do imidazol com ânion brometo. Não foi possível correlacionar a influência da cadeia espaçadora do diânion com os valores de CMC obtidos. A partir dos comportamentos de blindagem e desblindagem observados para os núcleos dos dicátions e diânions um modelo de auto-organização supramolecular para as micelas formadas foi proposto. Devido ao efeito de blindagem sofrido por todos os hidrogênios dos diânions avaliados, foi proposto que a cadeia espaçadora estaria orientada de forma a interagir com a cadeia hidrofóbica do dicátion, e as porções dicarboxilato estariam interagindo com as cabeças hidrofílicas do dicátion.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES This work describes the synthesis, structural characterization, and thermal stability of eight dicationic ionic liquids (DILs) containing the cations 1,4-bis(3-methylimidazolium-1-yl)butane ([Bis(C4MIM)]2+) and 1,10-bis(3- methylimidazolium-1-yl)decane ([Bis(C10MIM)]2+) with the anions butyrate (C3COO-), pentanoate (C4COO-), hexanoate (C5COO-) and heptanoate (C6COO-) and two monocationic ionic liquids (MILs) containing the cation 3-methyl-1-butylimidazolium (C4MIM+) and the anions pentanoate and hexanoate. The thermal characterization of these ILs by TGA showed that DILs with the cation [Bis(C4MIM)]2+ are more stable than DILs with the cation [Bis(C10MIM)]2+ and the MILs, the latter being similar. Only for the DILs with the cation [Bis(C4MIM)]2+ an increase in the anion alkyl chain lead to an increase in thermal stability. DSC analysis (-80 to 130 ° C) showed that the DILs with the cation [Bis(C4MIM)]2+ and the MILs are amorphous solids, while most of the DILs with the cation [Bis(C10MIM)]2+are crystalline solids. The decomposition kinetics of the DILs [bis(C4MIM)][C3COO]2, [Bis(C4MIM)][C6COO]2 and [Bis(C10MIM)][C3COO]2 were analyzed by isothermal and isoconversional methodologies. The isoconversional methodologies were the Friedman, Osawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS). The results of the isothermal analyses indicated that the zero-order reaction model best describes the experimental data. Also, the Ea values indicate that the [Bis(C4MIM)][C3COO]2 has a higher decomposition rate than the others, indicating that the velocity of decomposition is proportional to the molar mass of the ILs. The IL [Bis(C4MIM)][C6COO]2 presented two well-defined decomposition steps in isoconversional analyzes. For this methodology, it was also found that the thermal stability of the ILs is proportional to their molar masses. Ea values varied with conversion indicating that the decomposition of these DILs occurs in several steps, except for the first decomposition step of IL [Bis(C4MIM)][C6COO]2. The lnA value for the first decomposition step of this IL was determined by the compensation effect and the f(α) function follows a similar trend to the theoretical diffusion models. The decomposition products of the isothermal analysis of the DILs [bis(C4MIM)][C3COO]2 and [bis(C10MIM)][C3COO]2 were analyzed by 1H RMN and ESI-MS. In turn, non-isothermal decomposition products were analyzed using TGA-FTIR. The data showed that the DIL [bis(C4MIM)][C3COO]2 decomposes by SN2, E2, and heterocyclic carbenes formation reactions. For the DIL [bis(C10MIM)][C3COO]2 it was not possible to identify the mechanisms of isothermal decomposition. In the case of non-isothermal decomposition, esters were form as products, suggesting that the decomposition occurs by SN2 reactions Este trabalho descreve a síntese, caracterização estrutural e estabilidade térmica de oito Líquidos Iônicos Dicatiônicos (LIDs) contendo os cátions 1,4-bis(3-metilimidazolil-1-íneo)butano ([Bis(C4MIM)]2+) e 1,10-bis(3-metilimidazolil-1-íneo)decano ([Bis(C10MIM)]2+) e os ânions butirato (C3COO-), pentanoato (C4COO-), hexanoato (C5COO-) e heptanoato (C6COO-) e dois Líquidos Iônicos Monocatiônicos (LIMs) contendo cátion 3-metil-1-butilimidazolíneo (C4MIM+) e os ânions pentanoato e hexanoato. A caracterização térmica desses LIs por TGA mostrou que os LIDs com o cátion ([Bis(C4MIM)]2+) são mais estáveis que os LIDs com o cátion ([Bis(C10MIM)]2+ e que os LIMs, sendo que os últimos possuem estabilidade térmica similar. Para os LIDs com o cátion [Bis(C4MIM)]2+ o aumento da cadeia do ânion levou ao aumento da estabilidade térmica. As análises de DSC (-80 até 130 °C) mostraram que os LIDs com o cátion [Bis(C4MIM)]2+ e os LIMs são sólidos amorfos, enquanto que os LIDs com o cátion [Bis(C10MIM)]2+ comportaram-se como sólidos cristalinos. A cinética de decomposição dos LIDs [Bis(C4MIM)][C3COO]2, [Bis(C4MIM)][C6COO]2 e [Bis(C10MIM)][C3COO]2 foram determinadas usando metodologias isotérmicas e isoconversionais. Os métodos isoconversionais utilizados foram os de Friedman, Osawa-Flynn-Wall (OFW) e Kissinger-Akahira-Sunose (KAS). Os resultados das análises isotérmicas indicaram que o modelo ordem de reação com ordem igual a zero é o que melhor descreve os dados experimentais. Além disso, os valores de Ea determinados para os LIDs indicaram que o [Bis(C4MIM)][C3COO]2 se decompõe mais rapidamente (possui menor Ea), indicando que a velocidade de decomposição é proporcional à massa molar dos LIs. O [Bis(C4MIM)][C6COO]2 apresentou duas etapas bem definidas de decomposição nas análises isoconversionais. Os resultados desta análise também mostraram que a estabilidade dos LIs é proporcional às suas massas molares. Os valores de Ea variaram com a conversão indicando que a decomposição dos LIDs ocorre em múltiplas etapas. Exceto para a primeira etapa de decomposição do [Bis(C4MIM)][C6COO]2. Os valores de lnA para a primeira etapa de decomposição do LI [Bis(C4MIM)][C6COO]2 foram determinados pelo efeito de compensação. Para o mesmo LI e mesma etapa determinou-se que a função f(α) segue uma tendência similar aos modelos teóricos de difusão. Os produtos de decomposição da análise isotérmica dos LIDs [Bis(C4MIM)][C3COO]2 e [Bis(C10MIM)][C3COO]2 foram analisados por RMN de 1H e ESI-MS. Por sua vez, os produtos de decomposição não isotérmica foram analisados utilizando TGA-FTIR. Os dados mostraram que o LID [Bis(C4MIM)][C3COO]2 se decompõe por reações de SN2, E2 e formação de carbenos heterocíclicos. Para o LI [Bis(C10MIM)][C3COO]2 não foi possível identificar os mecanismos de decomposição isotérmica. No caso da decomposição não isotérmica se verificou a formação de ésteres como produtos, sugerindo que a decomposição ocorre por reações de SN2.

Dicationic ionic liquids (DILs) are more and more accepted as a new class of high temperature and polar stationary phases for gas chromatography (GC). This study deals with the effect of seven different fluorosulfonyl derivatized anions associated with two dications: 1,3-di(3-methylimidazolium)-2-methylpropane [2mC3(mim)2], and 1,3-di(3-methylimidazolium)-isobutene [i-eneC4(mim)2]. Thermophysical properties of the 14 synthesized DILs were evaluated in terms of melting point, viscosity, and thermal stability. The optimal physicochemical properties of 13 DILs allowed preparing 13 GC capillary columns. Accordingly, the polarity and selectivity of the DILs were evaluated by determining the Rohrschneider-McReynolds constants and the equivalent chain lengths of C18 fatty acid methyl esters (FAMEs). The symmetrical fluoroalkylsulfonyl and the trifluorosulfonate anions seem to produce the most polar DILs. Compared to classical polyethyleneglycol phases, the DILs showed substantially decreased retention of apolar compounds and a much stronger retention of the polar ones. Unique selectivities were observed with unsaturated FAMEs, polyaromatic hydrocarbons, and bacterial specific FAMEs. The two applications presented included a biodiesel and bacterial FAME analyses.

In this study, new quaternary bis(ammonium) salts with alkyl-1,X-bis(dimethyldecylammonium) cation and saccharinate, acesulfamate, lactate and pyroglutamate anions were synthesized and characterized by 1H and 13C NMR spectroscopy. Thermal gravimetric and differential scanning calorimetry analyses confirmed that all salts were thermally stable and the majority of them exhibited melting points below 100 °C. The physicochemical properties (viscosity, density, refractive index values, and solubility) of the obtained salts were determined for three compounds with lactate anions. All the tested salts have suitable properties which, in practical application, will reduce the losses caused by the most important storage insects. Most of the synthesized ionic liquids had comparable or better deterrent activity than azadirachtin—an alkaloid known as the most active antifeedant. Graphical abstract Electronic supplementary material The online version of this article (10.1007/s11696-018-0495-6) contains supplementary material, which is available to authorized users.

Ionic liquids (ILs) are neoteric solvents characterized by unique physicochemical properties and considerable structural variability. The thermal behavior of 24 ILs, belonging to two structurally related families with either bromide or Tf2N as counteranion, was analyzed. For bromide mono- and dicationic ionic liquids (DILs), thermal gravimetric analysis showed similar decomposition events, with only small gain in stability for a few members of the latter class. Conversely, all Tf2N DILs displayed higher stabilities (up to 34 K) than the corresponding monocations, thus highlighting the different role played by the two counteranions. Mono- and dicationic ILs bearing a reactive group on the imidazolium substituent resulted instead the least stable ILs studied. Differential scanning calorimetry analyses of most of the (D)ILs only showed glass transition temperatures, a behavior in agreement with the broad liquid range of ILs. The impact of the cationic structure and/or of the type of anion on the above-mentioned transition temperatures has been studied. The apparent activation energy (Ea) and the fragility index (m) for some (D)ILs have also been obtained. Finally, a few bromide (D)ILs presented peculiar thermal events.

Two new di-cationic imidazolium based ionic liquids (ILs) containing chloride, (bisImCl), or hexafluorophosphate anions (bisImPF6) have been synthesized and characterized by FT-Raman and 1H- and 13C NMR spectroscopies. The p-xylyl group acts a spacer between two imidazolium rings in the cation. The influence of the anions on thermal properties of the compounds has been investigated. Both bisImCl and bisImPF6 have shown good thermal stability up to at least 280 °C. Intermolecular and cation-anion interactions have been investigated by NMR spectroscopy. B3LYP/6-311++G∗∗ calculations have optimized the structure of bisIm cation with both anions. Both Cl are found to be in a monodentate coordination, while in bisImPF6 only one PF6 group presents monodentate coordination. AIM calculations at the same level of theory have evidenced a higher number of interactions in bisImPF6, as compared to bisImCl. A complete assignment of the vibrational frequencies for the cation, bisImCl and bisImPF6 are here reported together with a set of harmonic scaled force constants calculated for the cation and bisImCl. Further, polarizability (α) and the static first hyperpolarizabilities (β) of these ILs are calculated by different DFT functionals in order to understand nonlinear optical (NLO) properties. It is observed an inverse correlation between the predicted β value and the HOMO-LUMO energy difference (Δe) from two state models. The high gap value observed for bisImPF6 justifies its low reactivity, as supported by the high number of interactions predicted for this ionic liquid.

Three phosphonium-based dicationic ionic liquids were synthesized as bis(trifluoromethylsulfonyl) imide salts. The three dications had a nonyl spacer between two identical phosphonium-substituted groups. The three phosphonium moieties were dipropyl(phenyl), diphenyl(propyl), and diphenyl(toluyl). The physicochemical properties of the dicationic ionic liquids were appropriate to prepare 30 m capillary columns that were tested in gas chromatography. A unique selectivity compared to different polysiloxane or polar cyanosiloxane commercial columns was observed for selected mixes of phthalates, polyaromatic hydrocarbons, polychlorobiphenyls, and dioxins. Only minor selectivity variations were observed with the three dicationic ionic liquids. The different number of aromatic rings on the positively charged phosphonium group did not influence the dicationic ionic liquid selectivity significantly.

A series of dicationic ionic liquids (ILs) including [C 4 (MIM) 2 ][PF 6 ] 2 , [C 5 (MIM) 2 ][PF 6 ] 2 , [C 6 (MIM) 2 ][PF 6 ] 2 and [C 4 (PYR) 2 ][PF 6 ] 2 were synthesized. Their thermal stability and melting points were analysed. It was found that dicationic ILs presented important implications in the design of homogeneous and heterogeneous system with water. A homogeneous system of dicationic ILs with water could be formed at a relatively high temperature and then a heterogeneous system was formed when the solution was cooled to a low temperature. The ILs recovered by altering the temperature were obtained in high percentage yields of [C 4 (MIM) 2 ][PF 6 ] 2 (97.6%), [C 5 (MIM) 2 ][PF 6 ] 2 (97.3%), [C 6 (MIM) 2 ][PF 6 ] 2 (98.0%) and [C 4 (PYR) 2 ][PF 6 ] 2 (94.2%). On the other hand, [C 4 (MIM) 2 ][PF 6 ] 2 and [C 5 (MIM) 2 ][PF 6 ] 2 exhibited good solubility in acetonitrile and acetone. A homogeneous system could be achieved with imidazolium-based ILs with a relatively low amount of water and acetonitrile at room temperature. All of the properties of dicationic ILs have a strong correlation with the nature of dications, the linkage chain and the symmetry of dications. Dicationic ILs may provide a new opportunity for some specific applications in order to enable the effective separation and isolation of products.

Dicationic ionic liquids (DILs), a subset of the ionic liquid (IL) family, have attracted growing interest in recent years, and the range of applications within which they are investigated is constantly expanding. However, data which allows structure to property correlation of a DIL is still limited, and thus selecting an appropriate salt to address a specific challenge can be problematic. In comparison to traditional ILs, DILs physico-chemical properties can be tuned by changing the length and type of spacer which connects the cationic heads as well as the type of cation. This in turn could give rise to symmetrical or asymmetrical DILs. In this work, a systematic study of a homogeneous class of 12 dibromide DILs and 12 di-carboxylate salts has been performed. The latter class of DILs were also compared to mono cation derivatives. The different traditional exchange methods to prepare carboxylate DILs have been evaluated and an insight into the drawbacks encountered is also presented. Prepared DILs were characterized (NMR, TGA, DSC) allowing the influence of the structure on their thermal stability to be understood. Most DILs were obtained as solid salts after careful drying. For some of these compounds, a new possible application was studied, namely their use as hydrogen bond acceptors (HBA) of deep eutectic mixtures, showing again some significant structural related effects.

Electrospray ionization mass spectrometry (ESI-MS) with induced collision energy was used to carry out a comprehensive study on the interaction energies between cations and anions of dicationic ionic liquids. The influence of the anion ([Br]-, [NO3]-, [BF4]-, [SCN]- and [Cl]-) and the size of alkyl chain (n = 4,6,8 and 10) in the interaction energy of ionic liquids derived from the 1, n-bis (3-methylimidazolyl-1-yl) alkane with n = 4,6,8 and 10, in the gas phase was investigated. Three experiments were carried out to determine the cation-anion interaction energy: (i) ESI-MS of binary (1:1) mixtures of ionic liquids with different anions or cations; (Ii) ESI-MS of ionic liquid individually with variation of the applied collision energy and determination of the center of mass energy (Ecm) using the relation between the intensity of the precursor ion and the sum of the ions; (iii) the rate of variation of the intensity of the precursor ion as a function of collision energy at different concentrations of all ionic liquids was obtained. From this correlation, the cation-anion dissociation constant of the dicationic ionic liquids was obtained. The results showed the appearance of mixed species (example: [Bis-C8(MIM)22XY]- and [C8(MIM)XY]-) in the binary mixtures. The application of the induced collision energy in the mixtures allowed estimating which anion interacts more effectively with the cation. Also for this experiments, the dicationic ionic liquids with the anions [Cl]-, [Br]- and [NO3]- presented higher cation-anion interaction energy. The increasing order of interaction energy was [BF4]

The structural behavior of geminal dicationic ionic liquid 1,n-bis[3-methylimidazolium-1-yl] alkane bromide ([Cn(mim)2]Br2)/water mixtures has been studied using extended X-ray absorption fine structure (EXAFS) spectroscopy in combination with molecular dynamics (MD) simulations. The properties of the mixtures are investigated as a function of both water concentration and alkyl-bridge chain length. The very good agreement between the EXAFS experimental data and the theoretical curves calculated from the MD structural results has proven the validity of the theoretical framework used for all of the investigated systems. In all the solutions the water molecules are preferentially coordinated with the Br(-) ion, even if a complex network of interactions among dications, anions and water molecules takes place. The local molecular arrangement around the bromide ion is found to change with increasing water content, as more and more water molecules are accomodated in the Br(-) first coordination shell. Moreover, with the decrease of the alkyl-bridge chain length, the interactions between dications and anions increase, with Br(-) forming a bridge between the two imidazolium rings of the same dication. On the other hand, in [Cn(mim)2]Br2/water mixtures with long alkyl-bridge chains peculiar internal arrangements of the dications are found, leading to different structural features of geminal dicationic ionic liquids as compared to their monocationic counterparts.

Two new dicationic ionic liquids were synthesized: bis-methyl imidazolium methylidene hexafluorophosphate [M(CH2)IM2 +][2PF 6 − ] and bis-methyl imidazolium propylidene hexafluorophosphate [M(CH2)3IM2 +][2PF 6 − ]. Their structures were identified by H, C, P, F NMR, FTIR/ATR, and FT-Raman spectroscopies in order to study the effect of cation alkyl chain length on vibration behaviors. Several changes were recorded, which were related to alkyl chain length. A frequency shift was observed in some modes while others remained insensitive. A greater number of peaks was found in the FTIR/ATR spectra and the FT-Raman spectra with increasing alkyl chain length, which indicated that chain length influences the N–C connection twisting. More peaks with strong intensity appeared for longer alkyl chain lengths.

Conselho Nacional de Desenvolvimento Científico e Tecnológico This work reports the study of the molecular structure influence of ionic liquid (IL) derived from 1,8-bis(3-methylimidazolium-1-yl)octane in the aggregates formation in a solution ethanol in water (4,75%) and in ethanol (95%). Was varied the anions (Br-, NO3-, BF4-, SCN- e NTf2-) of IL and the aggregation behavior was investigated by various methods, such as differential scanning calorimetry (DSC), conductivity, surface tension, fluorescence and dynamic light scattering (DLS). In the ethanol in water solution (4,75%), the critical aggregation concentration values (cac) (114 to 205 mM), free energy of aggregation (ΔG°a) ( 15 to 18 kJ/mol) and ionization degree (α) (0,37 a 0,44) for the IL with Br-, NO3-, BF4-, SCN- significantly decreased with the increase of anion hydrophobicity. In ethanol, the cac values (165 to 500 mM) and ΔG°a ( 9 to 11 kJ/mol) also decreased with the increase of anion size and hydrophobicity. The free energy adsorption data (ΔG°ads) (-35 to -39 kJ/mol) demonstrated that the ILs, in general, have a good surfactant activity and this property improve with the decrease in the hydrophobic characteristics of anions. In general, in the solvents used in this study, the hydrodynamic radius (Rh) of aggregates ranged between 200 and 500 nm for all the ILs. The critical packing parameter was determined using data from the X-Ray (of IL 4) and surface tension, and showed that aggregates are micelar. The cac data was obtained by the techniques of conductivity, fluorescence and surface tension. Where, was observed that increasing the anion hydrophobicity of dicationic ILs structure favored the formation of aggregates, while less hydrophobic anions improved the surfactant properties of the IL structures. Este trabalho relata o estudo da influência da estrutura molecular de líquidos iônicos (LI) dicatiônicos, derivados do cátion 1,8-bis(3-metilimidazolil-1-íneo)-octano, na formação de agregados em uma solução etanol em água (4,75%) e em etanol (95%). Variaram-se os ânions (Br-, NO3-, BF4-, SCN- e NTf2-) dos LI e o comportamento de agregação foi investigado através das técnicas de calorimetria exploratória diferencial (DSC), condutividade, tensão superficial, fluorescência e espalhamento de luz dinâmico (DLS). Na solução etanol em água (4,75%), os valores de concentração de agregação crítica (cac) (114 a 205 mM), energia livre de agregação (ΔG°a) ( 15 a 18 kJ/mol) e grau de ionização do contra-íon (α) (0,37 a 0,44) para os LI contendo os ânions Br-, NO3-, BF4-, SCN- diminuíram significativamente com o aumento da hidrofobicidade do ânion. Em etanol, os dados de cac (165 a 500 mM), ΔG°a ( 9 a 11 kJ/mol) para os LI com os ânions Br-, SCN- e NTf2- também diminuíram com o aumento do volume e hidrofobicidade dos ânions. Dados de energia livre de adsorção (ΔG°ads) (-35 a -39 kJ/mol) demonstraram que os LI dicatiônicos, de forma geral, possuem boa atividade tensoativa e esta propriedade aumenta com a diminuição das características hidrofóbicas dos ânions. Em geral, nos solventes utilizados no estudo, o raio hidrodinâmico (Rh) dos agregados variou entre 200 e 500 nm para todos os LI. Valores de parâmetro de empacotamento crítico (Pc) determinados a partir de dados de raios-X e tensão superficial indicaram que os agregados formados são micelares. Os dados de cac obtidos por condutividade, fluorescência e tensão superficial apresentaram-se de forma concordante. Observou-se que o aumento da hidrofobicidade da estrutura do ânion do LI dicatiônico favoreceu a formação dos agregados, enquanto que ânions menos hidrofóbicos melhoraram as propriedades tensoativas das estruturas dos LI.

In this work, binary mixtures of a non-ionic surfactant (Triton X-100) and water were studied with concentrations of 30%wt H2O, showing, lamellar mesophase at temperatures below 10oC. Different dicationic ionic liquids were used for doping these mesophases: 1,n-bis(3-methylimidazolium-1-yl)alkane, 1,n-bis(1-methylpyrrolidinium-1-yl)alkane and 1,n-bis(pyridinium-N-yl)alkane dibromide, where n = 6 and 8. Polarized Optical Microscopy and Small-Angle X-ray Scattering were used for identifying the mesophases and the influence of different dicationic ionic liquids on the lyotropic liquid crystals phase transitions. The addition of dicationic ionic liquids to the lyotropic liquid crystals samples led to changes in transition temperature and in mesophase structure itself (such as characteristic distances).