Calorimetric and FTIR study of selected aliphatic heptanols
Graphical abstract
Introduction
Heat capacities belong among the fundamental thermophysical properties. Although extensive collection of critically assessed heat capacity data was published [1], [2], [3] and estimation methods based on this collection were developed [4], [5], new measurements are necessary for alcohols. This group of compounds often exhibit a complex temperature dependence of liquid heat capacity, including inflection points [6], plateau or even maxima [7], [8], [9], [10], [11], [12], which is not captured by the existing estimation methods and which leads to biased estimates with higher uncertainties when compared to other classes of compounds. The present paper is a continuation of our effort [8], [12], [13], [14], [15] to establish reliable heat capacity data for alcohols. For a better understanding of H-bonding, the stretching mode of OH bond of selected alcohols was studied as a function of temperature. The phase behavior was studied using differential scanning calorimetry (DSC) as no literature data were found for 2-methyl-2-hexanol, 5-methyl-2-hexanol, and 2-methyl-3-hexanol.
Section snippets
Samples description
The studied alcohols were of commercial origin. Purification of 1-heptanol was described previously [8]. Remaining alcohols were used as received except drying over 0.4 nm molecular sieves since their purity, as checked by gas-liquid chromatography, was found satisfactory. For 5-methyl-2-hexanol, 2-methyl-3-hexanol, and 2,2-dimethyl-3-pentanol, a mass spectroscopy analysis was performed to identify the main impurities which allowed correcting the heat capacity data for these impurities. Sample
Heat capacities
Experimental heat capacities obtained in this work with Setaram μDSC IIIa, are listed in Table 2 and shown in Fig. 1. For 5-methyl-2-hexanol, 2-methyl-3-hexanol, and 2,2-dimethyl-3-pentanol, the original experimental heat capacities were recalculated using the heat capacities of main impurities (see Table 1) and assuming that excess heat capacity can be neglected. Experimental heat capacities of impurities were not found (with the exception of a single point found for 2-methyl-3-hexanone [22],
Conclusion
This study represents an effort for understanding the complex thermal behavior and the relationship with the isomerization mechanisms in alcohols. The liquid heat capacities of nine selected heptanols (1-heptanol, 3-heptanol, 4-heptanol, 2-methyl-2-hexanol, 5-methyl-2-hexanol, 2-methyl-3-hexanol, 3-ethyl-3-pentanol, 2,2-dimethyl-3-pentanol and 2,4-dimethyl-3-pentanol) were measured using the Tian-Calvet calorimeter (Setaram μDSC IIIa) in the temperature range from 262 K to 382 K. The phase
Acknowledgements
Special thanks to Meredith A. Weber of Special Collections Library, University Libraries, University Park, PA, for providing literature data from Cook [30]. Paulo B. P. Serra acknowledges financial support from specific university research (MSMT No. 20/2016).
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