Synthesis of lipophilic antioxidant tyrosol laurate using imidazolium ionic liquid [Bmim]HSO4 as a catalyst

Tyrosol is a natural phenolic compound with potent antioxidant properties in the field of food manufacturing. However, the low lipophilicity of tyrosol limited its application. Therefore, the construction of tyrosol laurate (Tyr-L) could effectively overcome the limitations of tyrosol. In this work, four ionic liquids (ILs) were applied for TYr-L preparation. Among them, the 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4) showed the best catalytic performance. The maximum TYr-L yield was achieved (94.24 ± 1.23 %) under the optimal conditions (reaction temperature 119 °C, substrate ratio 1:6.7, IL dosage 9.2 %, and reaction time 12 h). The kinetic and thermodynamic parameters were also evaluated and it was found that Ea, ΔH, ΔS, and ΔG were 80.81 kJ·mol-1, 77.63 kJ·mol-1, -82.08 J·(mol·K)-1, and 109.89 kJ·mol-1, respectively. The acidic [Bmim]HSO4 demonstrated excellent reusability and stability, even after 6 cycles. Furthermore, TYr-L showed superior ABTS radical scavenging ability, which could be further applied in various industrial processes.

The Electrochemical Behavior of Unmodified and Pd-NPs Modified AB5 Hydrogen Storage Alloy in Selected Protic and Aprotic Ionic Liquids (ILs): Towards ILs-Based Electrolytes for Ni-MH Batteries

The objective of this work was to study the electrochemical behavior of AB₅ alloy and its composite with Pd nanoparticles in selected ionic liquids. The protic ionic liquid (diethylmethylammonium triflate) and the mixture of aprotic ionic liquid (1-ethyl-3-methylimidazolium methanesulfonate) with parent superacid were used as electrolytes in the process of hydrogen electrosorption in AB₅ alloy electrodes. The impact of the surface modification of AB₅ electrode with Pd nanoparticles has been checked. The studies revealed that the highest hydrogen absorption capacity can be obtained in Pd-NPs-AB₅ electrode in DEMA-TFO. It was found that the surface modification with Pd-NPs facilitates the activation of the electrode and results in stabilization of the plateau potential of discharging. The studies show that more effort should be put into the synthesis of less corrosive tailored ionic liquids suitable to be used as electrolytes in hydride batteries.

Regulating the Acidity of SO3 H-Functionalized Ionic Liquids: Hydrogen Bonding or Electrostatic Potential?

The SO₃ H-functionalized ionic liquids (ILs) with high acidity are important catalysts for acid-catalyzed reactions. However, the acidity of these ILs have been found to decrease due to intramolecular hydrogen bonds (H-bonds). In this work, a series of anionic SO₃ H-functionalized ILs were designed and the factors resulting in weak acidity were investigated, including H-bonds strength and electrostatic potential on the leaving proton (ESPLP). Using catalytic experiment, atoms in molecules topology analysis and electrostatic potential calculation, it was found that the acidity of ILs was correlated with the value of ESPLP rather than the H-bond strength. Meanwhile, there were several ways to increase the acidity of anionic SO₃ H-functionalized ILs, such as enhancing the electron-withdrawing ability of cation, introducing H-bond acceptor sites on cation or separating the intramolecular H-bonds through substitution position. These strategies made the conversion of TBA in Friedel-Crafts alkylation increase from 19 % to 84 %.

The Distance between Minima of Electron Density and Electrostatic Potential as a Measure of Halogen Bond Strength

In this study, we present results of a detailed topological analysis of electron density (ED) of 145 halogen-bonded complexes formed by various fluorine-, chlorine-, bromine-, and iodine-containing compounds with trimethylphosphine oxide, Me3PO. To characterize the halogen bond (XB) strength, we used the complexation enthalpy, the interatomic distance between oxygen and halogen, as well as the typical set of electron density properties at the bond critical points calculated at B3LYP/jorge-ATZP level of theory. We show for the first time that it is possible to predict the XB strength based on the distance between the minima of ED and molecular electrostatic potential (ESP) along the XB path. The gap between ED and ESP minima exponentially depends on local electronic kinetic energy density at the bond critical point and tends to be a common limiting value for the strongest halogen bond.

Phosphine oxides as NMR and IR spectroscopic probes for geometry and energy of PO···H–A hydrogen bonds

In this work we evaluate the possibility to use the NMR and IR spectral properties of P=O group to estimate the geometry and strength of hydrogen bonds which it forms...

Highly Efficient Extraction Procedures Based on Natural Deep Eutectic Solvents or Ionic Liquids for Determination of 20-Hydroxyecdysone in Spinach

A novel, efficient extraction procedure based on natural deep eutectic solvents (NADES) and ionic liquids (ILs) for determination of 20-hydroxyecdysone (20-E) in spinach has been developed. NADES, the first green extraction agent, with different hydrogen bond donors and acceptors are screened in order to determine extraction efficiencies. NADES consisting of lactic acid and levulinic acid at a molar ratio of 1:1 exhibits the highest yields. ILs, the second green extraction agent, with various cations and anions are also investigated, where [TEA] [OAc]·AcOH, χAcOH = 0.75 displays the highest recovery. Moreover, NADES-SLE and IL-SLE (SLE, solid-liquid extraction) parameters are investigated. Using the obtained optimized method, the recoveries of the target compound in spinach are above 93% and 88% for NADES-SLE and IL-SLE procedure, respectively. The methods display good linearity within the range of 0.5-30 μg/g and LODs of 0.17 µg/g. The proposed NADES-SLE-UHPLC-UV and IL-SLE-UHPLC-UV procedures can be applied to the analysis of 20-E in real spinach samples, making it a potentially promising technique for food matrix. The main advantage of this study is the superior efficiency of the new, green extraction solvents, which results in a significant reduction of extraction time and solvents as compared to those in the literature.

Study of interactions between Brønsted acids and triethylphosphine oxide in solution by 31P NMR: evidence for 2 : 1 species

The variation of the 31P chemical shift of triethylphosphine oxide in CDCl3 solution with a series of Brønsted acids at different molar ratios allows the determination of the value for the 1 : 1 species (δ1 : 1), which is much lower than the reported value at infinite dilution. This value correlates with the pKa of the acid in two zones, for acids stronger and weaker than TEPO-H+. The acid strength also controls the exchange rate in solution. The evolution of the chemical shift at high acid/TEPO molar ratios indicates the existence of a second TEPO-acid interaction, which is also dependent on the acid strength. This interaction is much more favorable in the case of a diacid, which shows chemical shift higher than expected for its pKa1 value.

Protic Ionic Liquids Based on Oligomeric Anions [(HSO4)(H2SO4)x]− (x = 0, 1, or 2) for a Clean ϵ-Caprolactam Synthesis

Inexpensive Brønsted acidic ionic liquids, suitable for industrial-scale catalysis, are reported as reaction media and catalysts for the Beckmann rearrangement of cyclohexanone oxime to ϵ-caprolactam. A family of protic ionic liquids was synthesised from nitrogen bases (1-methylimidazole, N,N,N-triethylamine, N-methylpyrrolidine, 2-picoline) and sulfuric acid by proton transfer in a simple, inexpensive, solvent-free, one-step process. The density, viscosity, conductivity, and ionicity of the synthesised ionic liquids were determined. Variation in the molar ratio of sulfuric acid (χH2SO4=0.67 and 0.75) was used to tune the acidity of these protic ionic liquids, which showed extremely high catalytic activity in the Beckmann rearrangement of cyclohexanone oxime to ϵ-caprolactam. Both the structure of the cation and the sulfuric acid molar ratio strongly affect the rearrangement of cyclohexanone oxime. The most active ionic liquid, based on the 1-metyhylimidazolium cation, χH2SO4=0.75, afforded high conversion of oxime combined with very good selectivity under mild conditions (110°C, 15min). The product could be extracted from the reaction mixture, eliminating the need for the neutralisation step that exists in conventional processes. The combination of affordable catalyst and process advantages leads to a greener alternative, competitive against existent industrial applications.

Chiral protic imidazolium salts with a (-)-menthol fragment in the cation: synthesis, properties and use in the Diels-Alder reaction

New chiral protic imidazolium salts containing a (1R,2S,5R)-(-)-menthol substituent in the cation and four different anions (chloride, hexafluorophosphate, trifluoromethanesulfonate and bis(trifluoromethylsulfonyl)imide) were efficiently prepared and extensively characterized. Detailed NMR analysis was performed, and a comparison of the chemical shifts of the protons and carbons of the imidazolium cation as a function of the combined anion was discussed. The specific rotation, solubility in commonly used solvents, thermal properties including phase transition temperatures, and thermal stability were also determined. Three of the synthesized tertiary salts (Cl, PF6 or OTf anion) were crystalline solids; 1-H-3-[(1R,2S,5R)-(-)-menthoxymethyl]-imidazolium bis(trifluoromethylsulfonyl)imide, (-)[H-Ment-Im][NTf2] was a liquid at room temperature. The chiral protic salts were used in a Diels-Alder reaction as a test reaction, and the results were compared with those from aprotic chiral ionic liquids having the same chiral substituent in the cation (1R,2S,5R)-(-)-menthol with a bis(trifluoromethylsulfonyl)imide anion. Both protic and aprotic chiral salts, used in a Diels-Alder reaction, were pure (-)-enantiomers, which was determined by NMR with Δ-TRISPHAT tetrabutylammonium salt as a chiral shift reagent. Protic salts offered distinctly higher endo/exo ratios than aprotic ones, but an enantiomeric excess was not obtained. The stereoselectivity reached the same high level even after the fourth recycle of (-)[H-Ment-Im][NTf2] in the reaction of ethyl-vinyl ketone with cyclopentadiene at temperature of -35 °C.

Applying neutron diffraction with isotopic substitution to the structure and proton-transport pathways in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

Neutron diffraction with isotopic substitution has been applied to examine the potential for complex-ion formation in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids.

Protonation versus Oxonium Salt Formation: Basicity and Stability Tuning of Cyanoborate Anions

Anhydrous H[BH₂ (CN)₂ ] crystallizes from acidic aqueous solutions of the dicyanodihydridoborate anion. The formation of H[BH₂ (CN)₂ ] is surprising as the protonation of nitriles requires strongly acidic and anhydrous conditions but it can be rationalized based on theoretical data. In contrast, [BX(CN)₃ ]^- (X=H, F) gives the expected oxonium salts (H₃ O)[BX(CN)₃ ] while (H₃ O)[BF₂ (CN)₂ ]/H[BF₂ (CN)₂ ] is unstable. H[BH₂ (CN)₂ ] forms chains via N-H⋅⋅⋅N bonds in the solid state and melts at 54 °C. Solutions of H[BH₂ (CN)₂ ] in the room-temperature ionic liquid [EMIm][BH₂ (CN)₂ ] contain the [(NC)H₂ BCN-H⋅⋅⋅NCBH₂ (CN)]^- anion and are unusually stable, which enabled the study of selected spectroscopic and physical properties. [(NC)H₂ BCN-H⋅⋅⋅NCBH₂ (CN)]^- slowly gives H₂ and [(NC)H₂ BCN-BH(CN)₂ ]^- . The latter compound is a source of the free Lewis acid BH(CN)₂ , as shown by the generation of [BHF(CN)₂ ]^- and BH(CN)₂ ⋅py.

Brønsted acidic ionic liquid-catalyzed dehydrative formation of isosorbide from sorbitol: introduction of a continuous process

A highly efficient synthesis of isosorbide from sorbitol was developed using Brønsted acidic ionic liquids (BILs) as the catalyst for the first time.

Synthesis of chlorostannate(ii) ionic liquids and their novel application in the preparation of high-qualityl-lactide

A highly efficient approach for the resynthesis ofl-lactideviathe prepolymer route using chlorostannate(ii) ionic liquids as catalysts has been established.

Ionic liquids as solvents for the Knoevenagel condensation: understanding the role of solvent–solute interactions

The hydrogen bond basicityβof ionic liquids, as demonstrated by the NMR studies and the Kamlet–Taft linear solvation energy relationship, was confirmed to be the dominant solvent descriptor determining the rate of the Knoevenagel condensation.