Extremely Low Vapor-Pressure Data as Access to PC-SAFT Parameter Estimation for Ionic Liquids and Modeling of Precursor Solubility in Ionic Liquids.

Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), vastly depends on the quality of the pure-component parameters. The pure-component parameters for low-volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture-independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure-IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor-pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10-5  Pa even at elevated temperatures. In this work, such vapor-pressure data of a series of 1-ethyl-3-methyl-imidazolium-based [C2 mim]-ILs with various IL-anions (e. g. tetrafluoroborate [BF4 ]- , hexafluorophosphate [PF6 ]- , bis(trifluoromethylsulfonyl)imide [NTf2 ]- ) were experimentally determined and subsequently used for PC-SAFT parameter estimation. The so-determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid-density data only for the molecular PC-SAFT and the ion-based electrolyte PC-SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure-component vapor-pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion-specific parametrization in the long term.

Tetrahydrothiophene-Based Ionic Liquids: Synthesis and Thermodynamic Characterizations.

S-alkyltetrahydrothiophenium, [Cn THT]+ bis(trifluorosulfonyl)imide, [NTf2 ]- room temperature ionic liquids (ILs) and tetraphenylborate, [BPh4 ]- salts with alkyl chain lengths from C4 to C10 have been prepared. The ILs and salts were characterized and their purity verified by 1 H- and 13 C-nuclear magnetic resonance, elemental analysis, ion chromatography, Karl-Fischer titration, single crystal X-ray diffraction as well as thermogravimetric analysis. The experimentally determined density and viscosity decrease with increasing temperature. The experimental solubility of the [Cn THT][NTf2 ]-ILs in water (75 to 2.2 mg/L for C4 to C10 ) was modelled with very good agreement by Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT), based on the extremely low vapor pressures for the [Cn THT][NTf2 ]-ILs measured in this work (4.15 to 0.037 ⋅ 10-7 ×psat for C4 to C10 ). PC-SAFT is able to predict and correlate different thermodynamic properties by estimating the Helmholtz residual energy.

Odd-even effect for efficient bioreactions of chiral alcohols and boosted stability of the enzyme.

We describe a holistic approach for achieving a nearly quantitative conversion for an enzymatic reaction while simultaneously increasing the long-term stability of the enzyme. The approach provided chemical control of bioreactions by utilizing newly synthesized tetrahydrothiophene-based ionic liquids (THT ILs). We showcased its power by using THT-ILs as additives at a low concentration (only 10 mmol L-1) in the alcohol dehydrogenase (ADH)-catalyzed synthesis of methylated 1-phenylethanol (Me-PE). We discovered an "odd-even" effect of the IL-cation chain length: Me-PE displayed beneficial interactions with THT ILs having odd-numbered chain lengths and deleterious interactions with those having even-numbered chain lengths. An intermolecular thermodynamic simulation of the bulk phase and critical micelle concentration investigations of the local surroundings of the THT-ILs proved the occurrence of these interactions, and these two methods confirmed the odd-even effect from different perspectives. Additionally, storing the ADH enzyme in pure THT IL at room temperature allowed for a boosted long-term stability of the enzyme (500 times greater than that in aqueous buffer) without the need for freezing.

Aggregation control of Ru and Ir nanoparticles by tunable aryl alkyl imidazolium ionic liquids.

Metal-nanoparticles (M-NPs) were synthesized in a wet-chemical synthesis route in tunable aryl alkyl ionic liquids (TAAILs) based on the 1-aryl-3-alkyl-substituted imidazolium motif from Ru3(CO)12 and Ir4(CO)12 by microwave-heating induced thermal decomposition. The size and size dispersion of the NPs were determined by transmission electron microscopy (TEM) to an average diameter of 2.2(±0.1) to 3.9(±0.3) nm for Ru-NPs and to an average diameter of 1.4(±0.1) to 2.4(±0.1) nm for Ir-NPs. The TAAILs used contain the same bis(trifluoromethylsulfonyl)imide anion but differ in the substituents on the 1-aryl ring, e.g. 2-methyl-, 4-methoxy- and 2,4-dimethyl groups and in the 3-alkyl chain lengths (C4H9, C5H11, C8H17, C9H19, C11H23). All used TAAILs are suitable for the stabilization of Ru- and Ir-NPs over months in the IL dispersion. Different from all other investigations on M-NP/IL systems which we are aware of the particle separation properties of the TAAILs vary strongly as a function of the aryl substituent. Good NP separation can be achieved with the 4-methoxyphenyl- and 2,4-dimethylphenyl-substituted ILs, irrespective of the 3-alkyl chain lengths. Significant aggregation can be observed for 2-methylphenyl-substituted ILs. The good NP separation can be correlated with a negative electrostatic potential at the 4-methoxyphenyl or 4-methylphenyl substituent that is in the para-position of the aryl ring, whereas the 2-(ortho-)methylphenyl group assumes no negative potential. ε-ePC-SAFT calculations were used to validate that the interactions between ILs and the washing agents (required for TEM analyses) do not cause the observed aggregation/separation behaviour of the M-NPs. Ru-NPs were investigated as catalysts for the solvent-free hydrogenation of benzene to cyclohexane under mild conditions (70 °C, 10 bar) with activities up to 760 (mol cyclohexane) (mol Ru)-1 h-1 and over 95% conversion in ten consecutive runs for Ru-NPs. No significant loss of catalytic activity could be observed.

Thermodynamic properties of selenoether-functionalized ionic liquids and their use for the synthesis of zinc selenide nanoparticles.

Three selenoether-functionalized ionic liquids (ILs) of N-[(phenylseleno)methylene]pyridinium (1), N-(methyl)- (2) and N-(butyl)-N'-[(phenylseleno)methylene]imidazolium (3) with bis(trifluoromethanesulfonyl)imide anions ([NTf2]) were prepared from pyridine, N-methylimidazole and N-butylimidazole with in situ obtained phenylselenomethyl chloride, followed by ion exchange to give the desired compounds. The crystal structures of the bromide and tetraphenylborate salts of the above cations (1-Br, 2-BPh4 and 3-BPh4) confirm the formation of the desired cations and indicate a multitude of different supramolecular interactions besides the dominating Coulomb interactions between the cations and anions. The vaporization enthalpies of the synthesized [NTf2]-containing ILs were determined by means of a quartz-crystal microbalance method (QCM) and their densities were measured with an oscillating U-tube. These thermodynamic data have been used to develop a method for assessment of miscibility of conventional solvents in the selenium-containing ILs by using Hildebrandt solubility parameters, as well as for modeling with the electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) method. Furthermore, structure-property relations between selenoether-functionalized and similarly shaped corresponding aryl-substituted imidazolium- and pyridinium-based ILs were analyzed and showed that the contribution of the selenium moiety to the enthalpy of vaporization of an IL is equal to the contribution of a methylene (CH2) group. An incremental approach to predict vaporization enthalpies of ILs by a group contribution method has been developed. The reaction of these ILs with zinc acetate dihydrate under microwave irradiation led to ZnSe nanoparticles of an average diameter between 4 and 10 nm, depending on the reaction conditions.