Cholinium-amino acid based ionic liquids: a new method of synthesis and physico-chemical characterization

Abstract

In the present work we report the synthesis and physico-chemical characterization in terms of the viscosity and density of a wide series of cholinium-amino acid based room temperature ionic liquids ([Ch][AA] RTILs). 18 different amino acids were used to obtain 14 room temperature ILs. Among the most common AAs, only valine did not form an RTIL but it is a liquid above 80 °C. With respect to the methods reported in the literature we propose a synthesis based on potentiometric titration which has several advantages such as shorter preparation time, stoichiometry within ±1%, very high yields (close to 100%), high reproducibility, and no use of organic solvents, thus being more environmentally friendly. We tried to prepare dianionic ILs with some AAs with two potentially ionisable groups but in all cases the salts were solids at room temperature. All the ILs were characterized by (1)H NMR to confirm the stoichiometry. Physico-chemical properties such as density, viscosity, refractive index and conductivity were measured as a function of temperature and correlated with empirical equations. The values were compared with the data already reported in the literature for some [Ch][AA] ILs. The thermal expansion coefficient αp and the molar volume Vm were also calculated from the experimental density values. Due to the high number of AAs explored and their structural heterogeneity we have been able to find some interesting correlations between the data obtained and the structural features of the AAs in terms of the alkyl chain length, hydrogen bonding ability, stacking and cyclization. Some parameters were also found to be in good agreement with those reported for other ILs. We think that these data can give an important contribution to the understanding of the structure-property relationship of ILs because they focused on the structural effect of the anions, while most data in the literature are focussed on the cations.

Is a medium-range order pre-peak possible for ionic liquids without an aliphatic chain?

“…More specically, the combination of choline with amino-acid anions has been recently exploited to provide ionic liquids with very low toxicity to humans 1,5,9 and to the environment, though endowed of very desirable solvent properties, such as the ability to selectively dissolve lignin and cellulose from biomasses. The absence of well separated domains with cycloalkyl substitution was correlated to some thermodynamic data by our group 24 and was described in a previous structure-activity relationship study by Tao et al 25 Nevertheless, a clear pre-peak is visible in the small-angle X-ray scattering curve (Fig. Among all the liquids of this class, we chose to report the results obtained for an interesting system synthesised in our lab (see ESI †), cholineproline (see Fig.…”

Rheological, Thermodynamic, and Gas Solubility Properties of Phenylacetic Acid‐Based Deep Eutectic Solvents

“…The conductivity values of all DESs follow the same trend and there was no visible difference observed in the conductivity range with different concentrations of acid. The presented DES systems provide a relatively high conductivity in comparison with cholinium‐amino acid‐based ionic liquids at different temperatures reported in , where one of the oxalic acid‐trimethylglycine eutectic mixture had a conductivity of 5.1 mS cm −1 at 303.15 K .…”

Enhanced CO2 Absorption in Organic Solutions of Biobased Ionic Liquids

“…In the specific, the peak related to the carboxylate group (≈1600 cm −1 ) slightly shifts to higher wavenumbers (see Figure 2a,c,d, blue dotted line 1) or modify its shape (see Figure 2b, blue dotted lines 1 and 2), which can be attributed to the formation of the carbamate moiety. 2020, 4,1900067 De Santis et al [20] www.advsustainsys.com here studied the CO 2 fixation occurs via the formation of two different species, carbamate, and carbamic acid. The IR spectra evolution is in accordance with our previous study of Glycine and Proline.…”

“…The synthesis of [Cho][AA] ILs usually relies on the water solution of choline hydroxide, [Cho] [OH]. [18,20,21] In fact, [Cho][OH] solution, which can be purchased or obtained from choline chloride [Cho][Cl] and AgO 2 , is a convenient starting reagent for AAILs synthesis via acid-base titration. Such a synthesis method leads to the production of ILs with very high purity without any byproduct.…”

“…Sustainable Syst. 2020, 4,1900067 De Santis et al [20] www.advsustainsys.com here studied the CO 2 fixation occurs via the formation of two different species, carbamate, and carbamic acid. Indeed, two different reactions occur, as depicted in Scheme 2.…”