Thermodynamics of Mixing Tetrahydropyran with 1-Alkanols and Excess Enthalpies of Homomorphy-Related Systems

Abstract

Densities (F) and volumetric heat capacities (C p /V) have been measured at 298.15 K over the whole mole fraction range for the binary mixtures {tetrahydropyran + 1-propanol, + 1-butanol, + 1-pentanol, + 1-hexanol, + 1-heptanol, + 1-octanol, + 1-nonanol, or + 1-decanol}. From experimental data, the excess molar isobaric heat capacities (C p E ) were calculated. Excess molar volumes (V E ) are reported for the systems containing 1-propanol, 1-butanol, 1-pentanol, and 1-decanol. In order to assess and compare the different degrees of hetero-association in these mixtures, the corresponding negative enthalpic contributions at equimolar fraction (H int ) have been calculated semiquantitatively by using the apolar homomorph concept. With this aim, excess molar enthalpies (H E ) of {tetrahydropyran + 1-pentanol, + 1-nonanol, or + 1-decanol}, {tetrahydropyran + decane}, and {cyclohexane + 1-pentanol, + 1-heptanol, + 1-nonanol, or + 1-decanol} have been measured at 298.15 K. The results are discussed in terms of molecular interactions. The various steps of W-shape concentration dependence found in the C p E point to the occurrence of local nonrandomness in THP + alkanol mixtures.

Thermodynamics of Mixing Tetrahydrofuran with 1-Alkanols and Excess Enthalpies of Homomorphy-Related Systems

“…But the trend is reversed in a second part, agreeing from this point with the (less usual) behavior of the homologous series containing cyclohexane. 1 Thus, Figure 2 shows that the mixture {cyclopentane + methanol} furnishes the highest equimolar H E value, whereas the lowest one is obtained for the 1-hexanol system. The H E (x ) 0.5) value for 1-decanol is slightly higher than that corresponding to 1-pentanol.…”

“…8 Improvements in the procedure and other specific features have also been reported recently. 1 Liquids were pumped by two Series II digital HPLC pumps from SSI (Scientific Systems Inc.), with a total flow rate of 0.2 cm 3 ‚min -1 . Details about pump calibrations are given elsewhere.…”

“…This work is the second part of a recently published paper dealing with the thermodynamics of binary mixtures containing tetrahydropyran (THP) and 1-alkanols. 1 Now the attention will be fixed on the homologous series having tetrahydrofuran (THF) as a common component. The objective is to gain further insight into the competition between alkanol self-association and heteroassociation that takes place in {cyclic monoether + alkanol} systems as well as to analyze how the size and shape of the ether affect the studied excess properties.…”

“…As in the first part, we remain interested in excess enthalpies, excess volumes, and especially in excess isobaric heat capacities because various steps of W-shape concentration dependence had been unexpectedly found in {THP + alkanol} systems. 1 The amount of available data in the literature is larger in this case, so less experimental measurements were needed to complete the whole picture. In addition, the present work also deals with excess enthalpies of mixtures related by homomorphs to the working systems, to make semiquantitative calculations for assessing the dependence on the alkanol chain length of the degree of THF + alkanol heteroassociation.…”

“…The approach employed with such a purpose provides a useful tool to compare systems within a homologous series. The theoretical background of the method was analyzed in detail in the first part, 1 emphasizing both its underlying assumptions and its limitations and providing guidelines for a proper usage, to avoid common misapplications.…”