Room temperature molten salts: neoteric "green" solvents for chemical reactions and processes

Abstract

Líquidos iônicos, em particular aqueles derivados do cátion 1,3-dialquilimidazólio, que possuem uma ampla faixa de temperatura em suas fases líquidas, pressões de vapores muito pequenas, baixas viscosidades e elevada estabilidade térmica e química vêm emergindo como uma nova classe de solventes "verdes" para processos de extração e separação, síntese orgânica e catálise. Os principais resultados obtidos com estes líquidos em Química Limpa nos últimos dois anos são objeto deste artigo de revisão. Ionic liquids, especially those based on the 1,3-dialkylimidazolium cation, with a large range of liquid phase, negligible vapour pressure, low viscosity and high thermal and chemical stability are emerging as a new class of 'green' solvents for extraction and separation processes, organic synthesis and catalysis. The main milestones reached in the last two years, on the use of ionic liquids in green technologies, are reviewed.

Preparation, cation-anion interactions and physicochemical properties of ether-functionalized imidazolium ionic liquids

“…Activated carbon, celite, basic aluminum oxide and silica gel 60 (40-60 µm) were purchased from Merck. A procedure reported previously in the literature was used for the synthesis of 1d, 1 2d 1 and 3d, 1 and the spectral data were in accordance with the literature data.…”

“…Although not further considered in the following discussion, it should be kept in mind that this impurity could affect the phase transitions. [1][2][3] Interestingly, only a glass transition was observed for the 1-alkyl ether RTILs 2a-b, 3a-b and 4a, and 1-alkyl RTIL 3d. 9,28 In other words, crystallization does not occur upon cooling of these RTILs to low temperatures.…”

“…A modified literature procedure was used for the synthesis of 1a-c. 1 Alcohol (1.00 equiv. ), methanesulfonyl chloride (1.05 equiv.…”

“…The class of imidazolium RTILs is used in a wide variety of applications due to their attractive physical and chemical properties, [1][2][3] which include: air and moisture stability, low flammability, thermal stability, a neglectable vapor pressure, being liquid over a wide temperature range, wide electrochemical windows, high conductivities and ionic mobilities, easy recycling, tunable miscibility with water and organic solvents, and being a good solvent for a wide variety of organic and inorganic chemical compounds. As a result, imidazolium RTILs are applied in, for instance, synthetic chemistry, 1,3 (biphasic) catalysis, [2][3][4] extraction/separation processes, 1 material science 1,5 and electrochemistry. 6 The number of imidazolium RTIL applications is expanding rapidly as structural modifications are easily introduced in both the imidazolium cation (especially the 1 and 3 positions of the imidazolium ring) and the anion, which promotes the development of taskspecific RTILs.…”

Aerobic, catalytic oxidation of alcohols in ionic liquids

“…2 Among the various 'mobile' phases that have been used for the immobilization of transition-metal catalyst precursors, ionic liquids (molten salts) are attracting continuous and increasing interest. 3,4 The advent of the air and water stable, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF 4 ) and its analog hexafluorophosphate (BMI.PF 6 ), 5 which possesses a wide range of liquid phase, negligible vapour pressure, low viscosity, high thermal and chemical stability as well as a wide electrochemical window (up to 7V), 6 enables reactions to be performed ranging from DielsAlder type processes to hydroformylations in biphasic conditions. [7][8][9][10] In these biphasic systems the products are easily separated from the reaction mixture by simple decantation or distillation and the recovered catalyst solution can be reused several times without any significant changes in its catalytic performance.…”