Crystal Structures and Binary Molten Solid–Liquid Equilibria of tert-Butylmethylphenol Isomers

Single crystals of 2-tert-butyl-5-methylphenol anhydrate and 2-tert-butyl-5-methylphenol quarterhydrate were prepared and presented for the first time in this work. The structures were characterized by single-crystal X-ray diffraction and DSC analysis. The solid–liquid equilibrium (SLE) for 2-tert-butyl-4-methylphenol with 2-tert-butyl-5-methylphenol anhydrate or 2-tert-butyl-5-methylphenol quarterhydrate was studied by the cooling–heating recycling method using a synthetic visual technique at atmospheric pressure (101.6 ± 1.2 kPa). The experimental SLE data for the two binary systems were reported, and both systems showed simple eutectic behavior. The SLE data were further correlated by Wilson and NRTL (nonrandom two-liquid) models, and the optimally fitted parameters of the two systems were presented. Computational studies on geometric optimization and energy calculation were performed using density functional theory, and the lower energy configuration of 2-tert-butyl-5-methylphenol quarterhydrate could explain the spontaneous incorporation of water in the anhydrous form. These novel data provide valuable information in designing and optimizing the melt crystallization process of tert-butylmethylphenol isomers.