Inexpensive and tuneable protic ionic liquids based on sulfuric acid for the biphasic synthesis of alkyl levulinates

Synthesis and characterization of ammonium-based protic ionic liquids for carbon dioxide absorption

A series of ammonium-based protic ionic liquids (APILs) namely ethanolammonium pentanoate [ETOHA][C5], ethanolammonium heptanoate [ETOHA][C7], triethanolammonium pentanoate [TRIETOHA][C5], triethanolammonium heptanoate [TRIETOHA][C7], tributylammonium pentanoate [TBA][C5] and tributylammonium heptanoate [TBA][C7] was synthesized via proton transfer. Their structural confirmation and physiochemical properties namely thermal stability, phase transition, density, heat capacity (Cp) and refractive index (RI) have been determined. Specifically, [TRIETOHA] APILs have crystallization peaks ranging from -31.67 to -1.00 °C, owing to their large density values. A comparison study revealed the low Cp values of APILs in comparison to monoethanolamine (MEA) which could be advantageous for APILs to be used in CO2 separation during recyclability processes. Additionally, the performance of APILs toward CO2 absorption was investigated by using a pressure drop technique under a pressure range of 1-20 bar at 298.15 K. It was observed that [TBA][C7] recorded the highest CO2 absorption capacity with the value of 0.74 mole fraction at 20 bar. Additionally, the regeneration of [TBA][C7] for CO2 absorption was studied. Analysis of the measured CO2 absorption data showed marginal reduction in the mole fraction of CO2 absorbed between fresh and recycled [TBA][C7] thus proving the promising potential of APILs as good liquid absorbents for CO2 removal.

The structure of protic ionic liquids based on sulfuric acid, doped with excess of sulfuric acid or with water

Neutron scattering with isotopic substitution was used to study the structure of concentrated sulfuric acid, and two protic ionic liquids (PILs): a Brønsted-acidic PIL, synthesised using pyridine and excess of sulfuric acid, [Hpy][HSO₄]·H₂SO₄, and a hydrated PIL, in which an equimolar mixture of sulfuric acid and pyridine has been doped with water, [Hpy][HSO₄]·2H₂O. Brønsted acidic PILs are excellent solvents/catalysts for esterifications, driving reaction to completion by phase-separating water and ester products. Water-doped PILs are efficient solvents/antisolvents in biomass fractionation. This study was carried out to provide an insight into the relationship between the performance of PILs in the two respective processes and their liquid structure. It was found that a persistent sulfate/sulfuric acid/water network structure was retained through the transition from sulfuric acid to PILs, even in the presence of 2 moles (∼17 wt%) of water. Hydrogen sulfate PILs have the propensity to incorporate water into hydrogen-bonded anionic chains, with strong and directional hydrogen bonds, which essentially form a new water-in-salt solvent system, with its own distinct structure and physico-chemical properties. It is the properties of this hydrated PIL that can be credited both for the good performance in esterification and beneficial solvent/antisolvent behaviour in biomass fractionation.

Dialkyl Succinates and Adipates as Alternative Plasticizers-Even More Efficient Synthesis

As a result of strict regulations of phthalate plasticizers, alternative non-phthalate forms are desired and increasingly used. This work presents a synthetic method for alternative plasticizers (dialkyl succinates and adipates) via esterification of succinic and adipic acid with alcohols: butan-1-ol and 2-ethylhexan-1-ol. Ionic liquids were synthesized by the reaction of triethylamine with over-equimolar (1:2.7) amounts of sulfuric(VI) acid, which were used as an acidic catalyst and solvent. The two-phase liquid–liquid system was formed during the reaction due to immiscibility of the esters with the ionic liquid. This phenomenon is a driving force of this process, shifting the equilibrium toward the product formation. As a result, dialkyl succinates and adipates were obtained in high yields (99%) and selectivities (>99%), under mild reaction conditions at 70–80 °C and using a 4:1 molar ratio of alcohol to acid and 15 mol% of catalyst. The catalyst was recycled 10 times without any loss of activity. This alternative method is highly competitive: it involves a simple procedure for product isolation as well as a high yield and purity of the resulting esters. These advantages make this method sustainable and promising for industrial applications.

Synthesis, Characterisation, and Determination of Physical Properties of New Two-Protonic Acid Ionic Liquid and its Catalytic Application in the Esterification

A new ionic liquid was synthesised, and its chemical structure was elucidated by FT-IR, 1D NMR, 2D NMR, and mass analyses. Some physical properties, thermal behaviour, and thermal stability of this ionic liquid were investigated. The formation of a two-protonic acid salt namely 4,4′-trimethylene-N,N′-dipiperidinium sulfate instead of 4,4′-trimethylene-N,N′-dipiperidinium hydrogensulfate was evidenced by NMR analyses. The catalytic activity of this ionic liquid was demonstrated in the esterification reaction of n-butanol and glacial acetic acid under different conditions. The desired acetate was obtained in 62–88% yield without using a Dean–Stark apparatus under optimal conditions of 10 mol-% of the ionic liquid, an alcohol to glacial acetic acid mole ratio of 1.3:1.0, a temperature of 75–100°C, and a reaction time of 4h. α-Tocopherol (α-TCP), a highly efficient form of vitamin E, was also treated with glacial acetic acid in the presence of the ionic liquid, and O-acetyl-α-tocopherol (Ac-TCP) was obtained in 88.4% yield. The separation of esters was conducted during workup without the utilisation of high-cost column chromatography. The residue and ionic liquid were used in subsequent runs after the extraction of desired products. The ionic liquid exhibited high catalytic activity even after five runs with no significant change in its chemical structure and catalytic efficiency.