Search

Ionic liquids (ILs) are neoteric solvents characterized by unique physicochemical properties and considerable structural variability. The thermal behavior of 24 ILs, belonging to two structurally related families with either bromide or Tf2N as counteranion, was analyzed. For bromide mono- and dicationic ionic liquids (DILs), thermal gravimetric analysis showed similar decomposition events, with only small gain in stability for a few members of the latter class. Conversely, all Tf2N DILs displayed higher stabilities (up to 34 K) than the corresponding monocations, thus highlighting the different role played by the two counteranions. Mono- and dicationic ILs bearing a reactive group on the imidazolium substituent resulted instead the least stable ILs studied. Differential scanning calorimetry analyses of most of the (D)ILs only showed glass transition temperatures, a behavior in agreement with the broad liquid range of ILs. The impact of the cationic structure and/or of the type of anion on the above-mentioned transition temperatures has been studied. The apparent activation energy (Ea) and the fragility index (m) for some (D)ILs have also been obtained. Finally, a few bromide (D)ILs presented peculiar thermal events. [ABSTRACT FROM AUTHOR]

Among the alternative mineral tanning agents investigated for replacing chromium, titanium (IV)-based salts are one of the most promising ones for the development of novel and cleaner tanning processes in the leather industry. The molecular mechanism of the solvation of titanyl salts and their interaction with masking agents was investigated in the present work. A computational study based on the quantum mechanical density functional theory was carried out, focusing on the behavior of complexes between titanyl oligomers of suitable length and different masking agents. The optimized structure of a titanyl octamer was calculated. Different carboxylic acids, and their corresponding anions, containing at least two polar functional groups suitable for the complexation of the titanyl, were considered as masking agents: glycolic, lactic, malic, citric, and phthalic acid. The most significant geometric and energetic parameters of the different titanyl-masking agent complexes were calculated. The results obtained indicate that the lactic acid system shows the best binding energies and the best flexibility. The OH-CRR'-COOH structure appears to be well fitted to complex the titanyl chain. The effect of the R and R' sidechains on complex stabilization seems to be related to electrostatic factors (presence of charge) rather than to steric hindrance. [ABSTRACT FROM AUTHOR]

The nature of solvation of Reichardt's dye in ionic liquids is investigated through semiempirical calculations. We build on the basis of electrostatic considerations a cluster of three ionic pairs that represent the first solvation shell of the dye. The spatial organization of this shell is a balance between sterical, electrostatic and, in the case of functionalized ionic liquids, specific interactions. This model is not sufficient to obtain values of ET(30) quantitatively comparable to the experimental ones, but some qualitative features can be rationalized. The resulting scenario of solute-solvent interactions is different with respect to molecular solvents. Thus, we suggest caution in comparing ionic and molecular solvents through solvatochromic scales. [ABSTRACT FROM AUTHOR]

The Diels-Alder reaction between cyclopentadiene and three dienophiles (acrolein, methyl acrylate and acrylonitrile) in different room temperature ionic liquids containing imidazolium-based cations ([HBIM]+, [BMIM]+ and [BM2IM]+) has been studied at the DFT level using a supermolecular approach. An analysis of the theoretical results shows that the ionic liquid cation coordination affects the equilibrium geometries and electronic structures of the reacting species throughout the reaction pathway leading to changes in reactivity and selectivity. They also indicate that the strong asynchronicity of the Diels-Alder reactions in ionic liquids is due to the polarisation effect of the cation. [ABSTRACT FROM AUTHOR]

Some clusters of Reichardt’s dye with two ion pairs have been studied at the TD-DFT level in order to understand the effect of the ionic liquid anion on solvatochromism. Coherently with the experimental data, the anion effect results substantially related to the anion size, although generally less important than the cation effect. Only small anions, such as halogenides, show a significant effect. [ABSTRACT FROM AUTHOR]