Nonideality and cocrystal formation in L-menthol/xylenol eutectic systems

Nonideality and cocrystal formation affect the solid-liquid equilibria (SLE) in eutectic systems. This study investigates the influence of the molecular structure of xylenol (dimethylphenol) isomers on the nonide-ality and cocrystal formation in eutectic systems containing L-menthol and five different xylenol isomers. Differential scanning calorimetry and powder X-ray diffraction analyses were employed to comprehend the SLE phase diagram of the studied systems. L-Menthol did not form cocrystals with xylenol isomers having a methyl group at position 2. In contrast, two cocrystals were observed in the L-menthol/3,4-xylenol systems at 1:2 and 2:1 ratios, and one cocrystal was observed in the 1:1 L-menthol/3,5-xylenol system. The liquid phase of all systems showed a strong negative deviation from ideality, except the L- menthol/2,6-xylenol eutectic system, which exhibited a near-ideal behavior. The nonideality of the liquid phase was modeled using the conductor-like screening model for realistic solvation (COSMO-RS) using TZVP and TZVPD_FINE parameterizations, finding that COSMO-RS can reasonably describe the liquid phase nonideality and predict the SLE phase diagram of simple eutectic systems and systems with cocrys-tal formation.(c) 2022 Elsevier B.V. All rights reserved.