(621dh) Syntheses and Characterization of New Ionic Liquids

Literature defines ionic liquids (ILs) or room-temperature ionic liquids (RTILs) as organic salts with melting point below 100 ºC, resulting from the combination of organic cations and various anions. These compounds are divided into two groups: aprotic, also considered as “classic”, and protic, generally prepared by neutralization reaction of an organic Brönsted base and a Brönsted acid, compounds of current interest.

The main combinations involve the quaternarium ammonium salts like n-alkylpyridinium and 1,3-dialkylimidalolium and anions like chloride, bromide, thiocyanate and others. These combinations lead to the production of liquids with different features and applications. ^[1-4]

RTILs are liquid in room temperature, nonvolatile, non-flammable, in some cases stable up to temperatures of 400 °C, potentially recyclable properties and solvable in many organic and inorganic materials. Due to their special physical and chemical properties, they have been widely used as solvents for chemical synthesis, homogeneous catalysis, biocatalysis, nanomaterial preparations, templates for production of porous solids, hydraulic, propellants, thermal, magnetic and optical fluids, composite materials and in various devices and processes. ^[1-2]

As examples may be cited the use of triethylammonium hydrogensulfate in the iodination of alcohols; the triethylamine–bonded sulfonic acid in the preparation of β-acetomido ketones, triethylammonium hydrogensulfate, 2-pyrrolidonium hydrogensulfate, 3-methyl-1-sulfonic acid imidazolium chloride and 1-methylimidazolium hydrogensulfate; as catalysts in the synthesis of 12-aryl-12H-indeno [1,2-b]naphtho[3,2-e]pyran-5,11,13-trione and 13-aryl-indeno[1,2- b]naphtha[1,2-e]pyran-12(13H)-one derivatives and other applications. ^[3]

The present study reports the synthesis and characterization of three new ionic liquids from of carboxylic acids and n-butylmanine. The new ionic liquids were prepared by neutralization acid-base reaction. The RTLIs synthesized were: n-butylammonium methanoate, n-butylammonium octanoate and n-butylammonium decanoate.

In all syntheses, the acid (methanoic acid, octanoic acid and decanoic acid) was added slowly to the amine (n-butylamine) and the temperature maintained between 15 and 20 °C under stirring. After addition of the acid, the ionic liquids remained at rest for 48 hours and subsequently characterized. These compounds were characterized by Infrared Spectroscopy using an Infrared Spectrophotometer Nicolet Model 6700 (Thermo), an ATR mode and Nuclear Magnetic Resonance of Hydrogen and Carbon (H1 NMR and C13 NMR). The H¹NMR and the C¹³NMR spectra were obtained on Bruker Avance III 600 HD spectrometer.

By analyzing the spectra referring to n-butylammonium methanoate, n-butylammonium octanoate and n-butylammonium decanoate, the change in chemical displacement is mainly verified referring to the amino group of n-butylamine after the formation of n-butylammonium ions. This is due to the protonation of the amino group, as well as the change in the multiplicity of the signal regarding the amine hydrogens.

In the amines, integration is observed regarding the presence of two hydrogens and in ionic liquids, regarding the presence of three hydrogens. Changes in the IR-ATR spectra are also verified due to the amino group protonation, which corroborate with the results obtained during the NMR analysis as well as a change in the absorption regarding carbonyl.

These results showed the formation of new ionic liquids with potential applications to be used as solvents in organic reactions.

References

[1] Yue, C.; Fang, D.; Liu, L. F.; Yi, T .F.  J. Mol. Liquids 2011, 163, 99.

[2] Shamsipur, M.; Beigi, A. A. M.; Teymouri, M.; Pourmortazavi, S. M.; Irandoust, M. J. Mol. Liquids 2010, 157, 43.

[3] Olivier-Bourbigou, H. O.; Magna, L.; Morvan, D. Appl Catal A-Gen 2010, 373, 1.

[4] Shaterian, H.R., Mohammadni, M., Moradi, F. J. Mol. Liquids 2012, 172, 88.