Thermodynamics of Mixtures Involving Some Linear or Cyclic Ketones and Cyclic Ethers. 2. Systems Containing Tetrahydropyran Pilar Brocos, A Ä ngel Pin ˜ eiro, † Ramo ´ n Bravo, and Alfredo Amigo* Departamento de Fı ´sica Aplicada, Facultad de Fı ´sica, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain Alain H. Roux and Genevie ` ve Roux-Desgranges Thermodynamique des Solutions et des Polyme `res, UMR CNRS 6003, Universite ´ Blaise Pascal, F-63177 Aubie `re Cedex, France Densities F, refractive indices n, and volumetric heat capacities C p / V have been measured at 298.15 K over the whole concentration range for the binary mixtures {tetrahydropyran + 2-pentanone, + 2-heptanone, or + cyclopentanone}. From the experimental data, excess molar volumes V E , excess molar refractions R E , and excess molar isobaric heat capacities C p E were calculated. Deviations of refractive index from ideality were determined by using a deviation function defined on a volume fraction basis, ∆n φ . Excess molar enthalpies H E have been measured at the same temperature for the systems {tetrahydropyran + 2-pentanone, + 2-heptanone, + cyclopentanone, or + cyclohexanone}. The discussion of these quantities entails a comparison with the results obtained in part 1 of this series for a homologous set of systems containing tetrahydrofuran. Introduction In part 1 of this series 1 we have undertaken the study of thermophysical properties of {cyclic ether + (linear or cyclic) ketone} mixtures by focusing our attention on a set of systems having tetrahydrofuran (THF) as a common component. In the present work we are concerned with a homologous set where the common component is tetrahy- dropyran (THP). This choice allows one to make compari- sons with the aim of analyzing the influence of the C-atom number of the monoether on the studied properties. On the other hand, some of us determined, in the past, excess properties of {THF or THP + alkane or + 1-alkanol} mixtures; 2-7 which means interesting data to enrich the discussion are available. In fact, ketones can be visualized as an intermediate case between alkanes (inert compounds) and alkanols (highly self-associated compounds), from the viewpoint of association. We have measured at 298.15 K and atmospheric pres- sure the densities F, refractive indices n, and volumetric heat capacities C p / V of {THP + 2-pentanone, + 2-hep- tanone, or + cyclopentanone} mixtures and the excess enthalpies of {THP + 2-pentanone, + 2-heptanone, + cyclopentanone, or + cyclohexanone}. From the experi- mental data, excess molar volumes V E , excess molar refractions R E , deviations of refractive index from ideality ∆n φ , and excess molar isobaric heat capacities C p E have been calculated. The discussion of results compares the behavior of THF and THP mixtures, examines the influence of the size and shape of the ketone on the excess properties, and analyzes the role of unlike-pair interactions. Besides, the interpretation of the ratio of molar volume to molar refraction V/R as a measure of the degree of free volume appears to be a useful tool for qualitative considerations supporting that discussion. Experimental Section Tetrahydropyran was obtained from Aldrich (purity 99%). The measured density (F) 0.878 91 g‚cm -3 ), isobaric heat capacity (C p ) 149.32 J‚mol -1 ‚K -1 ), and refractive index at the D-line of sodium (n ) 1.418 65) agree closely with literature values at the same temperature (298.15 K). 3,8-11 The experimental volumetric heat capacity C p / V is 1.5237 J‚cm -3 ‚K -1 . In part 1 of this series (Table 1), 1 similar information concerning the ketones was furnished. The liquids were used without further purification other than being kept over molecular sieves to remove water. For calorimetric measurements they also were degassed under vacuum to avoid bubble formation. Liquid mixtures for density, refractive index, and heat capacity measurements were prepared by mass in airtight stoppered bottles, bearing in mind the vapor pressures of the components when establishing the filling sequence. The error in the mole fraction was estimated to be <10 -4 . Experimental densimetric and calorimetric techniques have been described in detail in a previous series. 12-14 The refractometer and its operating mode have been detailed elsewhere. 15,16 Excess enthalpies were measured with a LKB differential calorimeter (model 2107-121) operating under constant flow conditions. Liquids were pumped by the 5 μL heads of two HPLC pumps, with the total flow rate being 0.6 cm 3 ‚min -1 and the error in mole fraction kept less than 10 -3 . Since the residence time in the mixing chamber guaranteeing complete mixing may vary consider- ably with the type of mixture, the optimum flow rate has to be determined experimentally. The apparatus has proved to have an uncertainty less than 0.5% at the * To whom correspondence should be addressed. E-mail: famigo@usc.es. Fax number: +34 981 520 676. † Current address: Laboratorio de Termofı ´sica, Facultad de Quı ´mica, Universidad Nacional Auto ´noma de Me ´xico, Me ´xico D.F. 04510, Mexico 712 J. Chem. Eng. Data 2003, 48, 712-719 10.1021/je025649t CCC: $25.00 © 2003 American Chemical Society Published on Web 03/14/2003