The dilution enthalpies of l-prolinol in N,N-dimethylformamide aqueous solutions at T = 298.15 K
Graphical abstract
Highlights
► The enthalpies of dilution were measured for l-prolinol in pure water and N,N-dimethylformamide aqueous solutions at 298.15 K. ► A pseudo phase equilibrium model is proposed and used to interpret the experimental results. ► The enthalpic pairwise interaction coefficients and the molar aggregation enthalpies are determined. ► The results are discussed in terms of the hydrophobic interaction and the interactions between the solvated solutes.
Introduction
l-Prolinol is one kind of chiral chemical reagents used in synthesizing excellent optical materials and chiral drugs [1], [2], [3]. Recently, with the rapid development of asymmetric catalysis, l-prolinol and its derivatives have been widely used in various organic synthesis [4], [5], [6], [7], [8]. These synthesises were frequently carried out in aqueous solutions however, no study on the properties of l-prolinol aqueous solutions has been reported. It is well known that the alcohol-water system shows abnormalities in mixing properties, which may be attributed to the complex aggregations among the alcohol and water molecules resulting in varieties of the structures. l-Prolinol is an alcohol with a pyrrolidine ring, hence assuming it has similar aggregation behaviour but larger hydrophobic interaction in aqueous solutions as compared with the small alcohol molecules. Thus investigation of the behaviour of l-prolinol aqueous solutions is helpful both for its practical application and better understanding of the alcohol-water system.
The N,N-dimethylformamide (DMF) is a typical acylamide with methyl group and peptide analogous structure that has widely attracted attention as a model compound of proteins [9], [10]. Study of the interaction between l-prolinol and DMF possibly provides some information to understand the impact of the alcohol on the properties of the protein [11], [12]. The present study reports the dilution enthalpies of l-prolinol in pure water and DMF aqueous solutions with different compositions of DMF. An abnormal phenomenon in l-prolinol aqueous solutions is found in the low l-prolinol concentration range. A pseudo phase equilibrium model is proposed to simplify the treatment of complex aggregation equilibriums and interpret the abnormality, which together with the McMillan–Mayer approach is used to fit the experimental dilution enthalpies to obtain the enthalpic pairwise interaction coefficients and the molar aggregation enthalpies of l-prolinol in DMF aqueous solutions.
Section snippets
Reagents
Table 1 contains the list of the purity and suppliers of the chemicals used in this work.
Both DMF aqueous solutions and l-prolinol/DMF aqueous solutions were prepared by weighing using a Sartorius Corp. BS 224S electronic balance with an accuracy of ±1 × 10−4 g. The water for preparation of the aqueous solutions was deionised, distilled and degassed before use. The range of the mass fraction (w) of DMF was (0 to 0.4). All the solutions were degassed and used within 12 h after preparation to avoid
Results and discussion
The experimental values of ΔdilHm together with values of the initial and the final molality (mi and mf) of l-prolinol in DMF aqueous solutions with various mass fractions of DMF at T = 298.15 K are listed in table 2. According to the McMillan–Mayer theory [16], the molar excess enthalpy of a solution with molality m can be expressed as a power series of m:
The enthalpic interaction coefficients (hi) determine the enthalpic interactions between two, three, four and more solute
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Projects 20973061 and 21073063).
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Enthalpic pairwise self-interactions of urea and its four derivatives in (dimethylformamide + water) mixtures rich in water at T = 298.15 K
2016, Journal of Chemical ThermodynamicsCitation Excerpt :For the other three compounds, the variations in h2 values are relatively moderate (see scheme 1). The magnitude of h2 coefficient is determined by the competition balance between hydrophobic and hydrophilic interactions of solutes in aqueous solutions [51–56]. Urea-like compounds have been described as both “structure makers” and “structure breakers” with respect to the structure of water in solution [56–60].
Influence of the composition of water-organic mixtures and the properties of organic solvents on thermochemical characteristics of l-methionine dissolution at 298.15 K
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Present address: PetroChina Lanzhou Lubricating Oil R&D Institue, Lanzhou, Gansu 730060, China.