Insights into the nature of eutectic and deep eutectic mixtures

A stricter definition of a deep eutectic solvent (DES) is urgent, so that it may become a sound basis for further developments in this field. This communication aims at contributing to deepening the understanding of eutectic and deep eutectic mixtures concerning their definition, thermodynamic nature and modelling. The glut of literature on DES applications should be followed by a similar effort to address the fundamental questions on their nature. This hopefully would contribute to correct some widespread misconceptions, and help to establish a stringent definition of what a DES is. DES are eutectic mixtures for which the eutectic point temperature should be lower to that of an ideal liquid mixture. To identify and characterize them, their phase diagrams should be known, in order to compare the real temperature depression to that predicted if ideality is assumed, and to define composition ranges for which they are in the liquid state at operating temperatures. It is also shown that hydrogen bonding between the DES components should not be used to define or characterize a DES, since this would describe many ideal mixtures. The future of deep eutectic solvents is quite promising, and we expect that this work will contribute to the efficient design and selection of the best DES for a given application, and to model properties and phase equilibria without which the process design is impractical.This work was developed in the scope of the Project CICECO – Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (Ref. FCT UID/CTM/50011/2013) and Associate Laboratory LSRE-LCM, POCI-01-0145-FEDER-006984 (Ref. FCT UID/EQU/50020/2013), both financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. This work is also a result of Project “AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145- FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). FCT is also acknowledged for funding the project DeepBinfo:eu-repo/semantics/publishedVersio

Ion speciation: A key for the understanding of the solution properties of ionic liquid mixtures

Recently, combinations of two (or more) ionic liquids, known as ionic liquid mixtures, have become popular and have a broad range of applications. However, the fundamental knowledge on the molecular interactions that exist in ionic liquid mixtures is far from being understood. In this work, the experimental measurement of the water activity coefficient and computational modelling using Conductor-like Screening Model for Real Solvent (COSMO-RS) were carried out to get an insight into the molecular interactions that are present in ionic liquid mixtures in aqueous solution. The results show that the combination of two ionic liquids of different basicity in aqueous solution allows fine tuning of the water activities, covering a wide range of values that could replace several pure fluids. This is an important feature resulting from the unexpected ion speciation of the ionic liquid mixtures in aqueous solution.We thank the CICECO – Aveiro Institute of Materials, POCI-01- 0145-FEDER-007679 (Ref. FCT UID/CTM/50011/2019) and Associate Laboratory LSRE-LCM, POCI-01-0145-FEDER-006984 (Ref. FCT UID/ EQU/50020/2019), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDDER under the PT2020 Partnership Agreement.info:eu-repo/semantics/publishedVersio

Solid-liquid equilibria for hexafluorophosphate-based ionic liquid quaternary mixtures and their corresponding subsystems

The present work describes an experimental study and the thermodynamic modeling for the solid−liquid phase diagram of an ionic liquid quaternary system constituted by hexafluorophosphate ([PF6]−) as the common anion and by 1-methyl-3-propylimidazolium ([C3mim]+), 1-methyl-1-propylpyrrolidinium ([C3mpyrr]+), 1-methyl-3-propylpyridinium ([C3mpy]+), or 1-methyl- 1-propylpiperidinium ([C3mpip]+) as the cations. The Modified Quasichemical Model was used to model the liquid solution, and the Compound Energy Formalism was used for the relevant solid solutions. The liquidus projections of the four ternary subsystems (1) [C3mim][PF6]−[C3mpip][PF6]−[C3mpyrr]- [PF6], (2) [C3mpy][PF6]−[C3mpip][PF6]−[C3mpyrr][PF6], (3) [C3mpip]- [PF6]−[C3mpy][PF6]−[C3mim][PF6], and (4) [C3mpyrr][PF6]−[C3mpy]- [PF6]−[C3mim][PF6] were predicted using a standard symmetric (for systems 3 and 4) or asymmetric (for systems 1 and 2) interpolation method. In order to test the accuracy of the thermodynamic model, two isoplethal sections were experimentally measured in each of the four ternary systems using differential scanning calorimetry. Overall, agreement was very satisfactory, not requiring fitting of any ternary interaction parameters for the liquid solution model. In each of the four calculated ternary liquidus projections, the region of composition corresponding to room temperature ionic liquid mixtures was determined. The global minimum of the liquidus temperature in the complete composition space was calculated to be about −16 °C, with a mole percentage composition of (33.8% [C3mpyrr][PF6] + 33.9% [C3mpy][PF6] + 32.3% [C3mim][PF6]).The modeling part of this project was supported by the Natural Sciences and Engineering Research Council of Canada (Discovery Grant RGPIN 435893-2013). The new DSC measurements in the four ternary subsystems were supported by the laboratories CICECOAveiro Institute of Materials, project POCI-01-0145-FEDER-007679 (ref FCT UID/CTM/ 50011/2019), and Associate Laboratory LSRE-LCM (ref FCT UID/EQU/50020/2019), both financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement, and the project “AIProcMat@N2020Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020” (ref NORTE-01-0145-FEDER-000006) supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). Constructive discussions with Dr. Aım̈ en Gheribi, Prof. Youn- Bae Kang, and Prof. Nick Virgilio were much appreciated.info:eu-repo/semantics/publishedVersio

Sustainable hydrophobic terpene-based eutectic solvents for the extraction and separation of metals

Sustainable hydrophobic eutectic solvents, composed of low-priced and biodegradable terpenes and fatty acids, were used for the extraction and separation of Cu(ii) from other transition metals in mildly acidic solutions. Multiple parameters were evaluated for metal extraction and the hydrophobic eutectic solvent was successfully recovered and reused.This work was part of BATRE-ARES project (ERA-MIN/0001/2015) funded by ADEME and FCT and partly developed in the scope of the project CICECO – Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013). C. M. S. S. Neves acknowledges FCT for the postdoctoral grant (SFRH/BPD/109057/2015). M. A. R. Martins acknowledges financial support from NORTE 2020 (NORTE-01-0145-FEDER- 000006) and DeepBiorefinery (PTDC/AGRTEC/1191/2014) projects.info:eu-repo/semantics/publishedVersio

The impact of oligomeric anions on the speciation of protic ionic liquids

The synthesis of protic ionic liquids based in carboxylate anions, too often admitted as being straightforward, is actually challenging and must be carefully addressed. This review discusses the importance of oligomeric anions, in particular those based on carboxylates, in the behavior and nature of protic ionic liquids. There is strong evidence in the literature that the synthesis, and subsequent purification, of protic ionic liquids involving carboxylic acids, leads to structures in the liquid phase with an acid:base proportion different from the expected 1:1 stoichiometry. The formation of the oligomeric anions, mostly dependent on the proton transfer from the Brønsted acid to the Brønsted base, may lead to a higher ionicity that suggests the formation of true ionic liquids. It is here stressed the relevance of deepening the understanding of the interactions between the species and the speciation of the liquid phase, combining experimental and theoretical approaches to establish foundations for insightful advances in the area.This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020 , CIMO-Mountain Research Center, UIDB/00690/2020 , and CIQUP, University of Porto (Projects: PEstUID/QUI/00081/2013 ) financed by national funds through the Portuguese Foundation for Science and Technology (FCT) /MCTES. This work was also developed within the scope of the Indo- Portuguese Program for Cooperation in Science & Technology DST/INT/Portugal/P-01/2017 , financed by FCT and the Government of India. P.J.C. acknowledge FCT for his contract under the Investigator FCT 2015 contract number IF/00758/2015 .info:eu-repo/semantics/publishedVersio

Solid-liquid phase behavior of eutectic solvents containing sugar alcohols

Mixtures of carbohydrates are often reported in the literature as deep eutectic solvents yet, in most cases, their solid–liquid phase diagrams are poorly characterized and no evidence is available to validate this classification. In this work, the phase diagrams of the binary systems composed of the sugar alcohols mannitol or maltitol and meso-erythritol, xylitol, or sorbitol, were experimentally determined. The results obtained reveal that these systems have a thermodynamic ideal behavior, questioning their classification as deep eutectic solvents and showing that intermolecular hydrogen bonding between the components of a mixture is not a sufficient condition to prepare deep eutectic solvents. The phase diagrams of the systems composed of mannitol or maltitol and cholinium chloride were also measured in this work. In sharp contrast to the mixtures composed solely by sugar alcohols, and unlike numerous other choline-based eutectic systems reported in the literature, these systems revealed significant deviations to thermodynamic ideality, leading to significant melting temperature depressions. The Cl-OH interaction between cholinium chloride and the sugar alcohols is identified as the main reason for these deviations to ideality, paving the way for the rational choice of hydrogen bond acceptors to prepare deep eutectic solvents.This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, and CIMO-Mountain Research Center, UIDB/00690/2020, both financed by national funds through the Portuguese Foundation for Science and Technology(FCT)/MCTES. L.P.S. acknowledges FCT for her PhD grant (SFRH/BD/135976/2018).info:eu-repo/semantics/publishedVersio

Eutectic mixtures based on polyalcohols as sustainable solvents: screening and characterization

Despite some promising potential applications of eutectic systems containing choline chloride ([Ch]Cl) and a polyalcohol, a detailed investigation of the thermodynamic behavior of these systems is still missing. In this work, the solid-liquid equilibria phase diagrams of binary systems containing [Ch]Cl and one from six different polyalcohols (ethylene glycol (EG), 1,3-propanediol, glycerol (Gly), meso-erythritol, xylitol, and sorbitol) were measured in the full composition. Except for the mixtures with Gly or EG, a quasi-ideal behavior in the [Ch]Cl solubility curve is observed. In the polyalcohol solubility curve, the mixtures present small negative deviations from ideality, except for [Ch]Cl + EG, which is slightly positive. The solid-liquid phase diagrams show a large liquid composition window, and not a fixed stoichiometry for the eutectic points, where the mixtures can be used as solvents close to, or below, room temperature. Aiming at their application, viscosities and densities were measured at the eutectic point in the temperature range from 278.15 to 373.15 K. All systems present densities and viscosities higher than water, which is directly related to the strong interactions between the components. Solvatochromic parameters were measured to characterize the solvents, and they show that solvent tunability can be achieved by varying the polyalcohol mole fraction.This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, and CIMO-Mountain Research Center, UIDB/00690/2020, both financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project Nº 022161 (cofinanced by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). L.P.S. acknowledges FCT for her PhD grant (SFRH/BD/135976/2018).info:eu-repo/semantics/publishedVersio

Terpenes solubility in water and their environmental distribution

Terpenes and terpenoids belong to the largest and most diverse class of natural products. Due to the increasing importance of their applications and the emerging perception of their impact on the environment, the available physico-chemical characterization is insufficient. In this work the water solubility of geraniol, linalool, DL-citronellol, thymol, eugenol, carvacrol and p-cymene, in the temperature range from (298.15 to 323.15) K, and at atmospheric pressure, is studied. Due to the low solubility of these compounds a novel technique was adopted for their measurements and validated using the aqueous solubility data for sparingly soluble aromatic compounds. The thermodynamic properties of solution were derived from the experimental data at infinite dilution. It is shown that the solubility of terpenes in water is an endothermic process confirming the existence of UCST phase diagrams, and only for carvacrol and eugenol is entropically driven. The experimental information is shown in a two-dimensional chemical space diagram providing indications to their probable distribution in the environment once released.Thisworkwas developed in the scope of the project CICECO - Aveiro Institute ofMaterials, POCI-01-0145-FEDER-007679, and Associate Laboratory LSRE-LCM, POCI-01-0145-FEDER-006984, both funded by FEDER under the PT2020 Partnership Agreement - Programa Operacional Competitividade e Internacionalização (POCI) - and by national funds through FCT - Fundação para a Ciência e a Tecnologia. M.A.R.M acknowledges FCT for her PhD grant (SFRH/BD/87084/2012).info:eu-repo/semantics/publishedVersio

Octanol–water partition coefficients and aqueous solubility data of monoterpenoids: experimental, modeling, and environmental distribution

Terpenes and terpenoids encompass one of the most extensive and valuable classes of secondary metabolites. Their ten-carbon-containing oxygenated representatives, monoterpenoids, are the main components of plant essential oils, being widely exploited in the cosmetic, pharmaceutical, and food industrial areas. Due to its widespread use, it is crucial to investigate their environmental distribution. Thus, new water solubility data were obtained for six monoterpenoids ((1R)-(+)-camphor, (S)-(+)-carvone, eucalyptol, (1R)- (−)-fenchone, L-(−)-menthol, and (−)-menthone) at 298.2 and 313.2 K. Furthermore, octanol−water partition coefficients of 12 monoterpenoids (the six mentioned above plus carvacrol, (±)-β-citronellol, eugenol, geraniol, linalool, and thymol) were measured at 298.2 K. The COSMO-RS thermodynamic model and other more empirical approaches were evaluated for the description of the solubilities and partition coefficients, showing reliable predictions. Lastly, the distribution of the monoterpenoids in the different environmental compartments was assessed through an intuitive two-dimensional chemical space diagram based on the physicochemical equilibrium information reported.This work was developed within the scope of the project CIMO-Mountain Research Center, UIDB/00690/2020, and CICECO-Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology (FCT)/MCTES. S.M.V.-B. thanks FCT and the European Social Fund (ESF) for his Ph.D. grant (SFRH/BD/138149/2018). M.C.d.C. would also like to thank CNPq (306666/ 2020-0) and FAPESP (2014/21252-0).info:eu-repo/semantics/publishedVersio

Selecting Critical Properties of Terpenes and Terpenoids through Group-Contribution Methods and Equations of State

The knowledge of critical properties is fundamental in engineering process calculations for the estimation of thermodynamic properties and phase equilibria. A literature survey shows a large number of methods for predicting critical properties of different classes of compounds, but no previous study is available to evaluate their suitability for terpenes and terpenoids. In this work, the critical properties of terpenes and terpenoids were first estimated using the group-contribution methods of Joback, Constantinou and Gani, and Wilson and Jasperson. These were then used to calculate densities and vapor pressure through the equations of state Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) and then compared with the experimental values. On other hand, density and vapor pressure experimental data were used to estimate the critical properties directly by the same equations of state (EoSs), allowing a comparison between the two estimation procedures. For this purpose densities for 17 pure terpenes and terpenoids were here measured at atmospheric pressure in the temperature range (278.15 to 368.15) K. Using the first approach, the best combination is the Joback's method with the Peng-Robinson EoS, despite the high relative deviations found for vapor pressure calculations and difficulties to predict density at low temperatures. Following the second approach, the set of critical properties and acentric factors estimated are able to adequately correlate the experimental data. Both equatio ns show a similar capability to correlate the data with SRK EoS presenting a global %ARD of 3.16 and 0.62 for vapor pressure and density, respectively; while the PR EoS presented 3.61 and 0.66, for the same properties, both giving critical properties estimates also closer to those calculated by the Joback method, which is the recommended group-contribution method for this type of compounds.This work was developed in the scope of the projects POCI-01- 0145-FEDER-007679-CICECO-Aveiro Institute of Materials (ref. FCT UID/CTM/50011/2013), POCI-01-0145-FEDER- 006984−Associate Laboratory LSRE-LCM both funded by European Regional Development Fund (ERDF) through COMPETE2020, Programa Operacional Competitividade e Internacionalização (POCI), and by national funds through FCT (Fundação para a Ciência e a Tecnologia). This work is also a result of project “AIProcMat@N2020 (Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020)”, with the reference NORTE-01- 0145-FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through ERDF. M.A.R.M. acknowledges FCT for her Ph.D. grant (SFRH/BD/87084/ 2012) and COST for the STSM Grant from COST action CM1206. P. J. Carvalho also acknowledges FCT for a contract under the Investigador FCT 2015, Contract No. IF/00758/ 2015. A.M.P. acknowledges Infochem-KBC for his Ph.D. grant. The software Multiflash from Infochem-KBC was applied in some of the calculationsinfo:eu-repo/semantics/publishedVersio