Deep Eutectic Solvents or Eutectic Mixtures? Characterization of Tetrabutylammonium Bromide and Nonanoic Acid Mixtures

Abstract

Deep eutectic solvents have quickly attracted the attention of researchers because they better meet the requirements of green chemistry and thus have the potential to replace conventional hazardous organic solvents in some areas. To better understand the nature of these mixtures, as well as expand the possibilities of their use in different industries, a detailed examination of their physical properties, such as density, viscosity, the nature of the interactions between their constituents, the phase diagrams, depression of their melting point, and interpretation of these results is necessary. In this work, the mixtures of tetrabutylammonium bromide (TBAB) and nonanoic acid (NA) in different molar ratios are theoretically and experimentally investigated by applying a phase diagram constructed on the basis of differential scanning calorimetry measurements and COSMO-RS model. Spectral properties are investigated based on Fourier transform infrared spectroscopy and density functional theory. The observed eutectic point indicates the formation of a DES in the TBAB−NA system in a 1:2 molar ratio. This is due to the presence of hydrogen bonds between the carboxyl group from the NA molecule and the bromine atom from the TBAB molecule. Other eutectic mixtures are most likely the solutions of TBAB in NA, in which hydrogen bonds predominate between acid molecules.

Estimating the phase diagrams of deep eutectic solvents within an extensive chemical space

“…It should be noted, however, that many eutectic points of the ideal mixture model were located below 298 K (Table 1 ), i.e., a liquid at room temperature. Therefore, assessing DES formation by merely observing solid-to-liquid transformations would result in the misclassification of ideal eutectic mixtures, or even regular solutions, as DESs, as has been the case in previous studies 13 , 14 . Basic information from the eutectic point data is summarized in Table 1 .…”

Demystifying the phase diagrams of deep eutectic solvents within an extensive chemical space

“…It should be noted, however, that many eutectic points of the ideal mixture model were located below 298 K, i.e., a liquid at room temperature. Therefore, assessing DES formation by merely observing solid-to-liquid transformations would result in the misclassi cation of ideal eutectic mixtures, or even regular solutions, as DESs, as has been the case in previous studies 12,13 . Basic information from the eutectic point data is summarized in Table 1.…”

“…The DES de nition proposed by Martins et al is favored by many researchers 6,7,[11][12][13] because it clearly distinguishes ideal eutectic and deep eutectic phenomena from a thermodynamic standpoint.…”

Unexpectedly Superhigh Toxicity of Superbase-Derived Deep Eutectic Solvents albeit High Efficiency for CO2 Capture and Conversion

“…DESs are the liquid mixture of two or more compounds interacting through hydrogen bonds or halogen bonds. ,, The individual compounds are known as hydrogen bond donors (HBDs) or hydrogen bond acceptors (HBAs). Not only DESs show similar benign properties to the ionic liquids (ILs), such as low volatility, low flammability, and low melting point, but also it has the unique advantages of a simple synthesis procedure, high atomic utilization rate, and high product purity. − Due to these favorable properties of DESs, they have been paid much attention in many areas. − ,− …”