Carlos A. M. Afonso

5-Hydroxymethylfurfural (HMF) as a building block platform: Biological properties, synthesis and synthetic applications

The biorefinery is an important approach for the current needs of energy and chemical building blocks for a diverse range of applications, that gradually may replace current dependence on fossil-fuel resources. Among other primary renewable building blocks, 5-hydroxymethylfurfural (HMF) is considered an important intermediate due to its rich chemistry and potential availability from carbohydrates such as fructose, glucose, sucrose, cellulose and inulin. In recent years, considerable efforts have been made on the transformation of carbohydrates into HMF. In this critical review we provide an overview of the effects of HMF on microorganisms and humans, HMF production and functional group transformations of HMF to relevant target molecules by taking advantage of the primary hydroxyl, aldehyde and furan functionalities.

Preparation and Characterization of New Room Temperature Ionic Liquids

A new series [C(n)O(m )mim][X] of imidazolium cation-based room temperature ionic liquids (RTILs), with ether and alcohol functional groups on the alkyl side-chain has been prepared. Some physical properties of these RTILs were measured, namely solubility in common solvents, viscosity and density. The solubility of LiCl, HgCl(2) and LaCl(3) in room temperature ionic liquids was also determined. The features of the solid-liquid phase transition were analysed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid. These properties were compared with those reported for the 1-n-alkyl-3-methylimidazolium [C(n )mim][X] series. While the density and solid-liquid phase transition properties are similar for both series, the new RTILs present a considerably lower viscosity and an increased ability to dissolve HgCl(2) and LaCl(3) (up to 16 times higher).

Deep desulfurization of diesel fuel using ionic liquids: current status and future challenges

Deep desulfurization of diesel fuel has attracted the attention of a growing number of scientists and engineers due to the stringent regulations imposed on the presence of sulfur in fuel (10 ppm). To bring down the concentration of sulfur compounds to less than 10 ppm is very challenging and demands newer technologies. Novel processes are being proposed for this purpose. It is observed that ionic liquids as class of green solvents can play a major role in the deep desulfurization of diesel fuel. For this reason, this review focuses on the current status in application of ionic liquids for achieving ultra-low-sulfur diesel (ULSD). To get a comprehensive perspective about the topic, other techniques of desulfurization are also discussed in brief in the introduction. Here we propose that the appropriate removal method should be selected according to different systems. To achieve deep desulfurization using ionic liquids, a better understanding regarding the regeneration of ionic liquids is vitally important.

Highly Selective Transport of Organic Compounds by Using Supported Liquid Membranes Based on Ionic Liquids

The selective separation of organic compounds is a critical issue in the chemical industry. In case of readily crystallized molecules, selective crystallization is the most practical method for selective separation, whereas for solutes that are liquid at room temperature, separation by fractional distillation, solvent extraction, or chromatographic methods are more convenient. Some of the above-mentioned methods are technically demanding, involve considerable energy costs, and/or result in large amounts of waste solvents. Membranes, defined as permeable and selective barriers between two phases, have been successfully applied in a large diversity of separation processes, including bioseparations, in which classical separation methods are less convenient, undesirable or even not applicable. The reason for the successful use of membrane-based separation processes stems from the fact that these processes have a high energy efficiency, can be used under moderate temperature and pressure conditions, do not require any additional separating agents or adjuvants, and therefore they are regarded as environmentally friendly.[1] Solute extraction and recovery by using supported liquid membranes is recognized as one of the most promising membrane-based processes. In a supported liquid-membrane system, a defined solvent or solvent/carrier solution is immobilized inside the porous structure of a polymeric or ceramic membrane, which separates the feed phase (in which the solutes of interest are solubilized) from the receiving phase (in which these solutes will be transferred and, eventually, concentrated). This configuration has attracted a great deal of interest because the amount of solvent/carrier needed is minimal, the solvent/carrier is continuously regenerated as a result of solute transport to the receiving phase, and loss of the solvent/carrier phase is negligible if an appropriate supported liquid membrane is designed.[2] The use of a room-temperature ionic liquid (RTIL) as an immobilized phase in the supporting membrane between two organic phases in the feed and the receiving compartments is particularly interesting owing to the nonvolatile character of RTILs and their solubility in the surrounding phases, which allows very stable supported liquid membranes to be obtained without any observable loss of the RTIL to the atmosphere or the contacting phases. Herein we show the potential for continuous separation of organic compounds based on the selective transport through supported liquid membranes that contain RTILs. RTILs that involve a 1,3-dialkylimidazolium cation are attracting increasing interest as new media, mainly because of the advantage of being nonvolatile. Depending on the anion and on the alkyl group of the imidazolium cation, the RTIL can solubilize supercritical CO2 (scCO2), a large range of polar and nonpolar organic compounds, and also transitionmetal complexes. Simultaneously, they have low miscibility with water, alkanes, and dialkyl ethers[3] and are insoluble in scCO2. As a result of these properties, they are emerging as an alternative recyclable, environmentally benign, reaction medium for chemical transformations, including transitionmetal catalysis[3] and biocatalysis.[3f, 5] Their use has also been successfully extended as a potential stationary phase for gas chromatography,[6] in pervaporation,[7] and for the substitution of traditional organic solvents (OS) in aqueous ±OS[7a, 8] and OS± scCO2 biphasic extractions.[4, 9] It is assumed that the 1,3dialkylimidazolium RTIL are not a statistical aggregate of anions and cations, but instead a more organized structure that contains polar and nonpolar regions as a result of the formation of weak interactions, mainly as hydrogen bonds, with 2-H of the imidazolium ring.[10] The above information prompted us to study the potential of using RTIL in supported liquid membranes for selective separation processes. To illustrate the concept, and as a result of transport studies with representative organic functional compounds, we used a mixture of the organic isomeric amines hexylamine, diisopropylamine, and triethylamine (1:1:1 molar ratio) in diethyl ether in side A of the cell (Figure 1). The two sides of the cell were separated by the RTIL 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) immobilized in the por[5] [Pt2(nBuCS2)4] and [Pt2(nBuCS2)4I2] were prepared by the similar procedures with literature methods using toluene and n-hexane.[4] [6] P. M. Chaikin, R. L. Greene, S. Etemad, E. Engler, Phys. Rev. B 1976, 13, 1627 ± 1632. [7] S. A. Borshch, K. Prassides, V. Robert, A. O. Solonenko, J. Chem. Phys. 1998, 109, 4562 ± 4568. [8] H. Tanaka, K. Marumoto, S. Kuroda, M. Mitsumi, K. Toriumi, unpublished results. [9] O. Kahn, Molecular Magnetism, VCH, New York, 1993, pp. 251 ± 286. [10] Field dependence of M of 1 was also measured near the phasetransition temperature under the magnetic field of H 1 ± 5 T. No variation was observed up to 5 T. [11] a) A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994, 27, 435 (SIR92); b) G. M. Sheldrick, SHELXL-97, University of Gˆttingen, Gˆttingen (Germany), 1997; c) Crystal Structure Analysis Package, Molecular Structure Corporation, 1985, 1999 ; d) A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R. Spagna, J. Appl. Crystallogr. 1999, 32, 115 ± 119 (SIR97). [12] Z. Otwinowski, W. Minor, Methods Enzymol. 1997, 276, 307 ± 326.

More Sustainable Approaches for the Synthesis of N-Based Heterocycles† ‡

Centro de Quı́mica-Fı́sica Molecular (CQFM) and Institute of Nanosciences and Nanotechnology (IN), Departamento de Engenharia Quı́mica e Biológica, Instituto Superior Técnico, 1049-001 Lisboa, Portugal, REQUIMTE, Departamento de Quı́mica, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal, and iMed.UL, Faculdade de Farmácia da Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal

Toxicity assessment of various ionic liquid families towards Vibrio fischeri marine bacteria

The increasing interest on the application of ionic liquids (ILs) to a wide range of processes and products has been hampered by a lack of toxicological data, mainly in what concerns novel cations, such as guanidinium, phosphonium, and functionalized and non-functionalized imidazolium-based ILs. The present study reports the toxicity of five guanidinium-, six phosphonium, and six imidazolium-based ILs, towards the luminescent marine bacteria Vibrio fischeri. These new results clearly show that guanidinium-, unlike the imidazolium- and phosphonium-based ILs, do not follow the trend of increasing toxicity with the increase in the alkyl chain length. Moreover, the introduction of oxygenated groups on the alkyl chains, such as ether and ester, leads to a decrease of the toxicity of guanidinium and also imidazolium compounds. In what respects the effect of the different cations, it is possible to recognize that the phosphonium-based ILs seem to be more toxic when compared to the analog imidazolium-based ILs (with the same anion and alkyl chains).

Impact of ionic liquids in environment and humans: An overview

Ionic liquids enclose a large number of molecular structures consisting of a cation and an anion. Their physical state and their chemical properties can be tuned by different combination of the ions and a large number of ionic liquids have already been reported. Toxicity of ionic liquids is a subject of great importance concerning their likely use as greener solvents and new materials for a broad number of potential applications. This review provides relevant toxicological data published so far about this topic and includes a large range of ionic liquids based on different cations (imidazolium, pyridinium, pyrrolidinium, quaternary ammonium, quaternary phosphonium and guanidinium) and anions (halogens-Br, Cl, bis (trifluoromethyl)sulfonylamide, tetrafluoroborate, hexafluorophosphate, dicyanamide, acesulfame and saccharin, amongst others). In general, toxicity of ionic liquids depends on both ions and the effect of the cation alkyl chain length is very pronounced although the type of anion also exerts impact on the overall toxicity.

Studies on the selective transport of organic compounds by using ionic liquids as novel supported liquid membranes

The possibility of using room-temperature ionic liquids (RTILs) in bulk (nonsupported) and supported liquid membranes for the selective transport of organic molecules is demonstrated. A systematic selective transport study, in which 1,4-dioxane, propan-1-ol, butan-1-ol, cyclohexanol, cyclohexanone, morpholine, and methylmorpholine serve as a model seven-component mixture of representative organic compounds, and in which four RTILs based on the 1-n-alkyl-3-methylimidazolium cation (n-butyl, n-octyl, and n-decyl) are used together with the anions PF(6)(-) or BF(4)(-), immobilized in five different supporting membranes, confirms that the combination of the selected RTILs with the supporting membranes is crucial to achieve good selectivity for a specific solute. The use of the RTIL 1-n-butyl-3-methylimidazolium hexafluorophosphate, immobilized in a polyvinylidene fluoride membrane, allows an extremely highly selective transport of secondary amines over tertiary amines (up to a 55:1 ratio). The selective transport of a given solute through the RTIL/membrane system results from the high partitioning of the solute to the liquid membrane phase which, in the case of amines, is rationalized mainly by the formation of a preferential substrate/H[bond]C(2) hydrogen bonding to the imidazolium cation.

Synthesis and properties of tetra-alkyl-dimethylguanidinium salts as a potential new generation of ionic liquids

New room temperature ionic liquids based on the tetra-alkyl-dimethylguanidinium cation present high stability under thermal, basic, acid, nucleophilic and oxidative conditions, low temperature glass transition phases and peculiar solubility properties in common solvents.

Ionic liquids as a recyclable reaction medium for the Baylis–Hillman reaction

Abstract The Baylis–Hillman reaction using 1,4-diazabicyclo[2.2.2]octane (DABCO) has been shown to be 33.6 times faster in the recyclable ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) than in acetonitrile. Low yields (14–20%) of adducts are obtained from aliphatic aldehydes and moderate to high yields (39–72%) from aromatic aldehydes. Recycling and reuse of the reaction medium was demonstrated.