A volumetric and acoustic study of pseudo-binary mixtures of (water + 1,3-propanediol + 3-butoxypropan-1-amine) from T = (283.15 to 303.15) K
Introduction
It is well known the importance of polyols, and in particular diols, in many domains. In biophysics and pharmaceutical industry they are used in preventing the denaturation of proteins and as additives to many drugs, food and cosmetic products because they have been considered compatible co-solvents for proteins [1], [2], [3]. In chemical industry and engineering they are used in the production of polyurethanes and polyethers [4], [5] and as compounds that can prevent the freezing of water and oil with several applications in refrigeration and regulation of temperature [6], [7].
Thermophysical and in particular volumetric properties of aqueous mixtures of diols have been measured by various authors since some time ago [8], [9], [10].
Aqueous mixtures of amphiphiles have been one of the main scientific interests of our research group, trying to understand the mutual influence of amphiphiles in the water structure (hydration) or of water on the organic molecules aggregation or conformation [11], [12], [13], [14], [15], [16], [17]. Effects of changing the amphiphilic groups (including different types of amines, hydroxyl and alkoxy), branching or the chain length have been fructuous to clarify types of hydration and aggregation patterns observed with changing composition and temperature. In recent works [18], [19], [20] we have studied volumetric, acoustic and energetic properties of the aqueous binary mixture {water + 3-butoxypropan-1-ol (BPA)} where we could characterize different types of hydration and identify the threshold of aggregation pattern changing, advancing some of their characteristics.
In this work we aim to study the effect of adding a small amount of BPA on thermodynamic properties of the binary mixture {water +1,3-propanediol (1,3-PD)}. Densities and speeds of sound of the ternary (pseudo-binary) mixture, {water (1) +1,3-PD (2) + BPA (3)}, were measured at five different temperatures ranging from T = (283.15 to 303.15) K. Excess molar, volumes, isobaric expansions and isentropic compressions as well as excess partial molar, volumes and isentropic compressions (including values at infinite dilution) were derived and differences between the volumetric behaviour of these pseudo binary mixtures and the binary (water +1,3-PD) mixtures, were compared and interpreted.
Section snippets
Materials and solutions preparation
3-Butoxypropan-1-amine (BPA), CAS Registry No. 16499-88-0, was obtained from Sigma-Aldrich with purity quoted >0.99, in mass fraction, and used without further purification. The water content was determined by Karl-Fischer method and was found to be <0.001 in mass fraction. 1,3-Propanediol (1,3-PD), CAS number 504–63-2, was supplied by Merck, with purity quoted >0.98, in mass fraction, and used without further purification. The water content was determined by Karl-Fischer method and was found
Density and sound speed
Table 2 summarizes the experimental density and experimental differences, Δu = u’−u0, measured in the ternary system {water (1) + 1,3-PD (2) + BPA (3)}, at the five temperatures. u’ refers to the sound speeds of mixtures and pure 1,3-PD and u0 refers to water. The true u values were then obtained adding the reference sound speed values for water (uref [23]) to Δu. This procedure avoids systematic deviations of the sound speed meter.
For the pure 1,3-PD, comparisons with available literature
Excess molar, volumes, isobaric expansions and isentropic compressions
As it is well known, excess molar properties are defined by Eq. (1),where is the difference between values for the molar property of the real mixture, Zm, and those for an ideal mixture, at the same temperature, pressure and composition of the real mixture, . In our case Zm stands for: Vm (molar volume), (molar isobaric expansion), CP,m (molar isobaric heat capacity), (molar isothermal compression) and , (molar isentropic compression) where
Conclusions
Densities and sound speeds were measured in the ternary (pseudo-binary) {water (1) + 1,3-propanediol (1,3-PD) (2) + 3-butoxypropan-1-amine (BPA) (3)} mixtures, across the whole 1,3-PD composition range. The composition of the mixed solvent, {water (1) +BPA (3)}, was fixed at fm = x3/(1−x2) = 0.0062.
This volumetric study aimed to explore the effect of adding a small amount of an amphiphilic molecule, BPA, with a similar structure as 1,3-PD, to the binary {water + 1,3-PD} mixture. Excess molar,
Acknowledgements
Financial support from Fundação para a Ciência e a Tecnologia, Portugal, under projects UID/MULTI/00612/2013 and UID/QUI/00100/2013 is greatly appreciated.
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