(398d) Determination of Solubilities of Terpenes in Selected Organic Solvents

Monoterpenes, known as constituents of essential oils, are widely found in nature and are expected to be applied to food, cosmetics, and medical technology [1-3]. Monoterpenes can be separated and purified by vacuum distillation or crystallization, but crystallization is more suitable, because many monoterpenes are sensitive for heats. In the crystallization process, solubility data of monoterpenes in various solvents are important for selecting suitable solvents for each monoterpene, and for designing the crystallization process. However, these solubility data are not enough.

In this work, we focused on ethyl lactate and ethyl levulinate as organic solvents for the crystallization of monoterpenes. These solvents are expected to be green and economical alternatives to conventional volatile organic solvents [4]. Especially, ethyl lactate is amphiphilic, and has high intermolecular forces due to hydrogen bonding and van der Waals forces, making it soluble in both water and organic solvents. Thus, ethyl lactate is as useful as alcohols for a wide variety of solutes [5].

We selected thymol, camphor, borneol, 3-bromocamphor, (-)-menthol, and tigrinic acid as monoterpenes and ethyl lactate. The solubilities of these monoterpenes in ethyl lactate and ethyl levulinate was determined using a synthetic method [6, 7]. The usefulness of ethyl lactate and ethyl levulinic acid as solvents for crystallization was also verified by comparing their solubility in ethanol with literature values. Experimental solubility data were correlated by using the NRTL equation. Group contribution methods, i.e., modied UNIFAC (Dortmund) and ASOG, were also
tested for the predictions of solubilities.

References

[1] Marcin Okuniewski, Kamil Paduszyński, Urszula Domańska, Fluid Phase Equilib. 422 (2016) 66-77.

[2] P. Zhu, Y. Chen, J. Fang, Z. Wang, C. Xie, B. Hou, W. Chen, F. Xu, J. Chem. Thermodyn. 92 (2016) 198-206.

[3] J. Chen, J. He, N. Li, H. Zheng, S. Zhao, J. Chem. Eng. Data 64 (2019) 1826-1833.

[4] S. Aparicio, R. Alcaldea, Green Chem. 11 (2009) 65-78 (2009).

[5] M. S. Manic, D. Villanueva, T. Fornari, A. J. Queimada, E. A. Macedo, V. Najdanovic-Visak, J. Chem. Thermodyn. 48 (2012) 93-100.

[6] H. Matsuda, Y. Ohashi, K. Kurihara, K. Tochigi, K. Ochi, Fluid Phase Equilib. 479 (2019) 17-24.

[7] H. Matsuda, Y. Ohashi, T. Tsuji, K. Naito, Y. Kakuta, K. Kurihara, K. Tochigi, Fluid Phase Equilibria, 595 (2025) 114420.