Elsevier

Fluid Phase Equilibria

Volume 423, 15 September 2016, Pages 43-54
Fluid Phase Equilibria

Calorimetric and FTIR study of selected aliphatic heptanols

https://doi.org/10.1016/j.fluid.2016.04.003Get rights and content

Highlights

  • Heat capacities of selected alcohols were determined by Tian-Calvet calorimetry.

  • Results were compared with selected estimation methods.

  • Phase behavior was explored by differential scanning calorimetry.

  • Calorimetric measurements were complemented by FTIR spectroscopy.

Abstract

Isobaric liquid phase heat capacities of nine selected aliphatic heptanols (1-heptanol, CAS RN: 111-70-6; 3-heptanol, CAS RN: 589-82-2; 4-heptanol, CAS RN: 589-55-9; 2-methyl-2-hexanol, CAS RN: 625-23-0; 5-methyl-2-hexanol, CAS RN: 627-59-8; 2-methyl-3-hexanol, CAS RN: 617-29-8; 3-ethyl-3-pentanol, CAS RN: 597-49-9; 2,2-dimethyl-3-pentanol, CAS RN: 3970-62-5; 2,4-dimethyl-3-pentanol, CAS RN: 600-36-2) were measured with a highly sensitive Tian-Calvet calorimeter in the temperature range from 261 K to 382 K. Experimental heat capacity data were correlated as a function of temperature. For eight compounds, a maximum on temperature dependence of heat capacity was observed. The phase behavior was investigated with a differential scanning calorimeter. Calorimetric measurements were complemented by FTIR spectroscopy from room temperature to a maximum of 428 K. The main aim of this work was to fill the gap in reliable heat capacity data for these compounds and to extend the knowledge base required for a better understanding of alcohols self-association.

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 Osingle bondH 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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