Salama Omar

Ionic Liquid Mixtures—An Analysis of Their Mutual Miscibility

The use of ionic liquid mixtures (IL-IL mixtures) is being investigated for fine solvent properties tuning of the IL-based systems. The scarce available studies, however, evidence a wide variety of mixing behaviors (from almost ideal to strongly nonideal), depending on both the structure of the IL components and the property considered. In fact, the adequate selection of the cations and anions involved in IL-IL mixtures may ensure the absence or presence of two immiscible liquid phases. In this work, a systematic computational study of the mixing behavior of IL-IL systems is developed by means of COSMO-RS methodology. Liquid-liquid equilibrium (LLE) and excess enthalpy (H(E)) data of more than 200 binary IL-IL mixtures (including imidazolium-, pyridinium-, pyrrolidinium-, ammonium-, and phosphonium-based ILs) are calculated at different temperatures, comparing to literature data when available. The role of the interactions between unlike cations and anions on the mutual miscibility/immiscibility of IL-IL mixtures was analyzed. On the basis of proposed guidelines, a new class of immiscible IL-IL mixtures was reported, which only is formed by imidazolium-based compounds.

Recovery of tyrosol from aqueous streams using hydrophobic ionic liquids: a first step towards developing sustainable processes for olive mill wastewater (OMW) management

Tyrosol is a high-value added polyphenolic compound with inherent antioxidant properties and increasing market demand for pharmaceutical, cosmetic and food industry applications. As a natural occurring antioxidant, the main source of tyrosol is olive mill wastewater (OMW), a by-product of olive oil processing that causes serious environmental issues due to its large volumes with high organic loads. Therefore, the valorization of OMW by recovering valuable antioxidants whilst reducing the overall toxicity of the aqueous stream is an attractive approach to promote sustainable OMW treatment and management. Herein we propose the utilization of hydrophobic ionic liquids (ILs) to replace conventional volatile organic compounds (VOCs) as extraction solvents to recover tyrosol from aqueous solutions. The operating temperature, the solvent to feed ratio, the effect of salt addition, the solvent physical properties and the solvent structure have been studied to optimize the extraction efficiency of tyrosol from water using [P4441][Tf2N], [N4441][Tf2N], and [N8881][Tf2N] ILs. Comprehensive experimental comparisons using ethyl acetate as a benchmark VOC solvent for tyrosol recovery have been performed. Moreover, the regeneration of the ILs and their subsequent recycling into the tyrosol extraction process have been addressed. Results show the capability of the aforementioned ILs to efficiently recover tyrosol under optimum operating conditions. Adding sodium salts, mainly NaCl, was proven to enhance the tyrosol selectivity towards the IL phase. Moreover, the solubility of ILs in the aqueous phase was found negligible, unlike ethyl acetate, and the water solubility in ethyl acetate was notably higher than in the hydrophobic ILs. Furthermore, back-extraction of tyrosol using inexpensive NaOH followed by IL recycling into the extraction process was successfully accomplished. Additional quantum chemical calculations were performed to provide insights into the behaviour of tyrosol–IL systems. Finally, [P4441][Tf2N] was revealed particularly promising for tyrosol recovery, providing similar extraction efficiency as conventional VOC solvents, proven capacity for regeneration and subsequent recycling, and adequate physical properties.

Towards quantifying the role of exact exchange in the prediction hydrogen bond spin-spin coupling constants involving fluorine

The effect of a fraction of Hartree-Fock exchange on the calculated spin-spin coupling constants involving fluorine through a hydrogen bond is analyzed in detail. Coupling constants calculated using wavefunction methods are revisited in order to get high-level calculations using the same basis set. Accurate MCSCF results are obtained using an additive approach. These constants and their contributions are used as a reference for density functional calculations. Within the density functional theory, the Hartree-Fock exchange functional is split in short- and long-range using a modified version of the Coulomb-attenuating method with the SLYP functional as well as with the original B3LYP. Results support the difficulties for calculating hydrogen bond coupling constants using density functional methods when fluorine nuclei are involved. Coupling constants are very sensitive to the Hartree-Fock exchange and it seems that, contrary to other properties, it is important to include this exchange for short-range interactions. Best functionals are tested in two different groups of complexes: those related with anionic clusters of type [F(HF)n](-) and those formed by difluoroacetylene and either one or two hydrogen fluoride molecules.

On the molecular electron structure of three phosphinine‐containing macrocycles

A broad set of structural models and theoretical methods has been successfully used for studying both the molecular electron structure of the silacalix[3]phosphinine and the changes of the macrocycle core under the conditions that frequently correspond to its complexes with metals. The macrocycle core of the silacalix[3]phosphinine and its neutral derivatives are strongly deviated from the main molecular plane. The phosphorous electron lone pairs and the π‐cloud of the phosphinine units give the main contribution to the electron valence structure in the silacalix[3]phosphinine and also in its both oxidized and reduced derivatives. Although the electron lone pairs of the P atoms tend to be strongly repulsive, they are either totally or partially extended above all the fragment of the phosphorous atoms depending on geometrical factors or even strongly coupled with the π‐cloud of the phosphinine units. Electronic processes that take away part of the electron density from the macrocyle favor both its planar configuration and the asymmetric distribution of the valence electrons in the silacalix[3]phosphinine and its derivatives. The limit condition to this effect is the appearance of a new in‐plane σ molecular orbital between the P atoms of two neighboring phosphinine units.

Performance of wave function and density functional methods for water hydrogen bond spin–spin coupling constants

AbstractSpin–spin coupling constants in water monomer and dimer have been calculated using several wave function and density functional-based methods. CCSD, MCSCF, and SOPPA wave functions methods yield similar results, specially when an additive approach is used with the MCSCF. Several functionals have been used to analyze their performance with the Jacob’s ladder and a set of functionals with different HF exchange were tested. Functionals with large HF exchange appropriately predict 1JOH, 2JHH and 2hJOO couplings, while 1hJOH is better calculated with functionals that include a reduced fraction of HF exchange. Accurate functionals for 1JOH and 2JHH have been tested in a tetramer water model. The hydrogen bond effects on these intramolecular couplings are additive when they are calculated by SOPPA(CCSD) wave function and DFT methods. Graphical AbstractEvaluation of the additive effect of the hydrogen bond on spin-spin coupling constants of water using WF and DFT methods.