Local interactions between unlike molecules (1–2) in solution are commonly measured with spectroscopy and used to estimate local composition. Herein, a viscosity model based on preferential solvation (PS) theory is developed for aqueous and nonaqueous binary liquid mixtures containing a dipolar aprotic solvent that provides local composition considering the hydration or solvation shell around complex (1–2) molecules. Spectral-derived and viscosity-derived local composition distributions showed similar trends with bulk composition, and their correspondence is attributed to characteristics of the hydration or solvation shell. Viscosity-derived local compositions were consistent with literature molecular simulations, whereas spectral-derived local composition distributions contained artifacts. The PS viscosity model is also applicable to nonpolar–polar mixtures for which self-association occurs, and it can be used to estimate solvent mixture dipolarity/polarizability. Since the PS viscosity model only requires bulk viscosity, it may provide a means to estimate microviscosity or the solvent environment around biomolecules.

Mixtures of safe and renewable solvents can replace hazardous solvents presently being used in the manufacture of engineering plastics. In this work, a methodology is proposed for identifying solvent-pair mixtures for preparing polymer precursors, with poly(amic acid) (PAA) being studied as an example. The methodology uses a chemical safety index, Hansen solubility parameters and Kamlet−Taft solvatochromic parameters of the pure and solvent-pair mixtures to identify hydrogen bond acceptor (HBA)−hydrogen bond donor (HBD) solvent-pair combinations. Ten replacement solvent-pairs for PAA syntheses identified were cyclohexanone−methanol, cyclohexanone−ethanol, cyclopentanone−methanol, cyclopentanone−ethanol, γ-butyrolactone−methanol, γ-butyrolactone− ethanol, γ-butyrolactone−water, γ-valerolactone−methanol, γ-valerolactone−ethanol, and γ-valerolactone−water. Homogeneous PAA solutions could be obtained from HBA−HBD solvent-pair mixtures when their solubility parameters were within 21−29 MPa 0.5 and their Kamlet−Taft solvatochromic parameters were π* (>0.67) and β (>0.67) for nonaqueous solutions and π* (>0.68) and β (>0.59) for aqueous solutions. Replacement solvent-pairs, γ-valerolactone−ethanol, γ-valerolactone−water, and γ-butyrolactone−water gave homogeneous precursor solutions that were comparable with commercial solutions prepared with Nmethyl-2-pyrrolidone. The proposed methodology and reported solvatochromic parameters make it is possible to identify other solvent-pair mixtures and new solvent-pairs for preparing polymer precursor solutions used in engineering plastics.

Kamlet-Taft solvatochromic parameters (polarity, basicity, acidity) of hydrogen bond donor (HBD)/acceptor (HBA) mixed-solvent systems, water (H2O)-γ-valerolactone (GVL), methanol (MeOH)-GVL, ethanol (EtOH)-GVL, H2O-γ-butyrolactone (GBL), MeOH-GBL, and EtOH-GBL, were measured over their entire composition region at 25 °C using UV-vis spectroscopy. Basicity of H2O-GVL and H2O-GBL systems exhibited positive deviation from ideality and synergism in the Kamlet-Taft basicity values. The cybotactic region around each indicator in the mixed-solvent systems was analyzed with the preferential solvation model. Both H2O-GVL and H2O-GBL mixed-solvent systems were found to be completely saturated with mutual complex molecules and to have higher basicity than pure water because water prefers to interact with GVL or GBL molecules rather than with itself. Formation of H2O-GVL and H2O-GBL complex molecules via specific hydrogen bond donor-acceptor interactions were confirmed by infrared spectroscopy. In MeOH-GVL or MeOH-GBL mixed-solvent systems, MeOH molecules prefer self-interaction over that with GVL or GBL so that synergistic basicity was not observed. Synergistic basicity and basicity increase for various functional groups of ten mixed-solvent (water-HBA solvent) systems can be quantitatively explained by considering electrostatic basicity and a ratio of the partial excess HBA solvent basicity with the HBA solvent molar volume that correlate linearly with the preferential solvation model complex molecular parameter (f12/1). Analysis of the cybotactic region of indicators in aqueous mixtures with the preferential solvation model allows one to estimate the trends of mixed-solvent basicity.

Hydrogen bond donor/acceptor mixed-solvent systems for solutes that exhibit strong specific interactions are not readily characterized with methods that depend on solvatochromic parameters. In this work, the reaction of two monomers, 4,4′-oxidianiline (ODA) and pyromellitic dianhydride (PMDA), to form the common engineering plastic precursor, poly(amic acid) (PAA), are studied for the tetrahydrofuran (THF) mixed-solvent systems (THF-methanol, THF-ethanol, THF-water) with spectroscopy. Solute-centric (SC) Kamlet−Taft solvatochromic (K-T) parameters for the solvent environment around the monomer are determined using a proposed model that incorporates spectroscopically determined local composition (X L ) around the ODA monomer and the preferential solvation model. For the example reaction to occur under homogeneous conditions, mixed-solvent conditions need have HBA-rich local compositions (0.30 < X HBA L < 0.83), high solute-centric basicity (β SC > 0.60), high solute-centric polarity, (π SC * > 0.63), and low solute-centric acidity (α SC < 0.63). The method developed allows characterization of mixed-solvent effects and can be readily extended to other systems that have strong specific interactions.

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A methodology is presented that allows hazardous dipolar aprotic solvents used in the pharmaceutical processing industries to be replaced with solvent-pair mixtures that consist of a hydrogen-bond donor (HBD) solvent and a hydrogen-bond acceptor (HBA) solvent. The methodology uses the solubility of the active pharmaceutical ingredient (API) in hazardous solvents to estimate the range of required solubility parameters and Kamlet–Taft parameters for the API and then intersects these ranges with the solubility parameters and Kamlet–Taft parameters of the solvent-pair mixtures to identify favorable solvent pairs and possible working compositions. Solvent pairs are ranked according to GSK safety and health scores. The methodology was applied to 13 APIs, where it was found that nonaqueous mixtures (ethanol–isopropyl acetate, ethanol–ethyl acetate, and ethanol–butyl acetate) and aqueous mixtures (water−γ-valerolactone and water–dimethyl sulfoxide) are highly ranked and applicable to many APIs. Solvent pairs were eliminated from consideration due to their inability to simultaneously satisfy Kamlet–Taft acidity, basicity, and polarity parameter constraints. The proposed methodology makes it simple to identify and rank HBD–HBA solvent-pair mixtures for replacement of dipolar aprotic solvents used in the pharmaceutical processing industries.

Hydrogen sulfate ionic liquid additives with aluminum chloride catalyst in ethanol were found to promote efficient (30 min) one-pot, one-step transformation of glucose into 5-ethoxymethylfurfural (5-EMF) in 37% yields. Spectroscopic measurements (FT-IR, 1H NMR) showed that ionic liquids form multiple hydrogen bonds with glucose and promote its ring opening through ionic liquid–AlCl3 complexes to enable formation of 5-EMF via 5-hydroxymethylfurfural (5-HMF). Reactions performed in dimethyl sulfoxide using (protic, aprotic) ionic liquid additives with and without AlCl3 catalyst showed that both the ionic liquid and AlCl3 were required for efficient transformation of glucose into 5-EMF. The proposed reaction mechanism for 5-EMF synthesis in the ethanol–1-butyl-3-methylimidazolium hydrogen sulfate–AlCl3 reaction system consists of ring opening of glucose to form the 1,2-enediol and dehydration to form 5-HMF that is followed by etherification to the 5-EMF product. The reaction system is effective for glucose transformation and has application to biomass-related compounds.

Kamlet–Taft (KT) parameters were measured for four nonaqueous hydrogen bond donor (HBD)–hydrogen bond acceptor (HBA) solvent-pair mixtures: methanol–cyclopentanone, methanol–cyclohexanone, ethanol–cyclopentanone, and ethanol–cyclohexanone to define their solvent polarity as a function of composition. KT mixed-solvent polarities differed greatly from molar average property values. The preferential solvation (PS) model was used to correlate solvent polarity and showed that local compositions of 1:1 (HBD–HBA) complex molecules were highly asymmetric. Trends of KT parameters of both cyclohexanone and cyclopentanone mixtures were similar, although the specific hydrogen bonding interactions of HBD–HBA complex molecules in cyclohexanone mixtures were stronger than those of cyclopentanone mixtures according to density functional theory calculations, infrared spectroscopy, and solution macroscopic properties. Application of the PS model to pharmaceuticals showed that the solvent-pair mixtures have wide-working composition ranges (∼0 < x HBA < ∼ 1) for aspirin, ibuprofen, niflumic acid, p-amino-benzoic, p-hydroxy-benzoic and salicyclic acid, limited composition ranges (Δx HBA ≈ 0.7) for benzoic acid and temazepam, and narrow composition ranges (Δx HBA ≈ 0.3) for others. By comparing mixed-solvent polarity with polarity of solvents being used for material, petroleum, and biomass processing, it can be concluded that cyclic ketone–alcohol mixtures have many applications.