Article pubs.acs.org/jced
Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Thermal and Volumetric Properties of Five Lactones at Infinite Dilution in Water Vladimír Dohnal,* Karel Ř ehaḱ , and Pavel Morav́ ek Department of Physical Chemistry, University of Chemistry and Technology, Prague 6, 166 28, Czech Republic
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ABSTRACT: Mixing enthalpies and densities of highly dilute aqueous solutions of five lactones (namely γ-butyrolactone (GBL), γ-valerolactone (GVL), αangelica lactone (AAL), γ-hexalactone (GHL), and δ-hexalactone (DHL)) were measured as a function of solution composition at several temperatures in the range from (288.15 to 318.15) K using a tandem flow arrangement of isothermal mixing microcalorimeter and vibrating-tube densimeter. The densities of the neat lactones were measured, also. The dissolution of the lactones in water was found to be exothermic (except for AAL at higher temperatures) and accompanied by volume contraction. On the basis of these systematic measurements, reliable values of partial molar excess enthalpy, partial molar volume, and partial molar excess volume of the studied solutes at infinite dilution in water were determined. Precision of our measurements allowed us to evaluate with a good accuracy also respective temperature derivative properties, that is, infinite dilution partial molar excess heat capacity, expansion, and excess expansion. The observed thermodynamic behavior was shown to be governed by hydrogen bonding of water molecules to the oxygen atoms of the lactone group. Several structural effects like those of the alkylation of lactone ring, its enlargement, the introduction of the double bond, and the lactone molecular volume on the determined properties were identified and rationalized on the molecular level. (GHL), and δ-hexalactone (DHL), conducted at four temperatures T = (288.15, 298.15, 308.15, 318.15) K. On the basis of this primary experimental data various thermal and volumetric properties of these lactones at infinite dilution in water are evaluated. Such information is almost totally missing in the literature. The results are briefly discussed, and attempts are made to rationalize them on the molecular level.
1. INTRODUCTION Thermodynamic properties of volatile organic compounds (VOCs) at infinite dilution in water are essential for various industrial and theoretical applications, especially in separation technology, environmental control/protection, and theory of solutions. Being engaged in systematic measurements of these properties over more than two decades, we have furnished a bulk of reliable data involving many classes of VOCs. For their overview and pertinent references we refer the reader to our recent article dealing with alkanones.1 In this work, which is a follow-up to the series, we focus on lactones. Lactones are cyclic oxygenated compounds resulting from intramolecular esterification of hydroxycarboxylic acids. These compounds occur naturally in many fruits and, thanks to their agreeable organoleptic properties, they are widely used as flavor and fragrance agents in the food and cosmetic industries.2 Lower lactones (C4−C6) are strongly polar aprotic liquids capable of solubilizing many substances. In particular, γ-butyrolactone and γ-valerolactone emerge nowadays as versatile and green-platform solvents and chemicals as they can be readily obtained from renewable biomass feedstocks and exhibit favorable toxicological and environmental profiles.3−5 γ-Valerolactone, with respect to its good combustion profile, is also considered as a prospective biofuel.3,6 Here, we report precise excess enthalpy and density measurements for highly dilute aqueous solutions of five lower (C4−C6) lactones, namely γ-butyrolactone (GBL), γvalerolactone (GVL), α-angelica lactone (AAL), γ-hexalactone © XXXX American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Materials. The chemical samples used in this study are specified in Table 1, and the molecular structure of the lactones are shown in Figure 1. The lactones were purchased from Sigma-Aldrich, and their purities declared by the supplier were confirmed by our own gas chromatography assay using a DB-WAX capillary column. No further purification of the lactone samples was attempted except for their drying with molecular sieves. The coulometric Fischer titration using Hydranal Coulomat AK reagent gave water contents not exceeding 0.0005 mass fraction. Water used as solvent was distilled and subsequently treated by a Milli-Q Water Purification System (Millipore, USA). Before measurements, all liquids were partially degassed by vacuum filtration and sonification. 2.2. Apparatus and Procedure. All measurements in this work were made using an automated calo/densimeter which Received: November 30, 2018 Accepted: March 7, 2019
A
DOI: 10.1021/acs.jced.8b01146 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Table 1. Specification of the Chemicals Used in This Work compound, CAS RN γ-butyrolactone, 96-48-0 γ-valerolactone, 108-29-2 α-angelica lactone, 591-12-8 γ-hexalactone, 695-06-7 δ-hexalactone, 823-22-3 water
source, initial purity Sigma-Aldrich, Sigma-Aldrich, Sigma-Aldrich, Sigma-Aldrich, Sigma-Aldrich, tap water
purification method
0.999a 0.995a 0.986a 0.991a 0.995a
dried with molecular sieves dried with molecular sieves dried with molecular sieves dried with molecular sieves dried with molecular sieves distillation, Milli-Q purification
final purity indication water contenta by KF titration: 480 water contenta by KF titration: 120 water contenta by KF titration: 390 water contenta by KF titration: 280 water contenta by KF titration: 360 electrical resistivity: 184 kΩ × m
× × × × ×
10−6 10−6 10−6 10−6 10−6
a
Mass fraction.
has been described by us in detail previously.7 This combined instrument, coupling a modified Calorimetry Science Corp. model 4400 isothermal mixing microcalorimeter and an Anton Paar model DMA5000 vibrating-tube densimeter into a tandem flow assembly, was used to measure simultaneously mixing enthalpies HE and densities of highly dilute solutions as a function of solute mole fraction. The setup further involved a highly asymmetric syringe pumping system for delivering accurate mass flows of the components to be mixed. The residence time of a mixture thus formed in the calo/densimeter did not exceed 30 min, a time short enough to avoid any effect of solute hydrolysis. The calorimetric signal was calibrated using a Joule effect produced by a built-in calibration heater on the pure water solvent. The densimeter was calibrated with water and dodecane density standards.8,9 Additional ad hoc single-fluid adjustments of the densimeter were carried out at each run using baseline signal corresponding to the pure water solvent.
3. RESULTS AND DISCUSSION Densities of the pure lactones were measured at T = (288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K first to provide reliable data for determination of the mass flows of pumped streams and evaluation of excess volumes. The measured density values are listed in Table 2 along with parameters of the polynomial fitting equation and respective standard deviations of fit. As seen, these deviations are for all five lactones very low (
