Solvation of o-Hydroxybenzoic Acid in Pure and Modified Supercritical Carbon Dioxide, According to Numerical Modeling Data

The dissolution of an elementary fragment of crystal structure (an o-hydroxybenzoic acid (o-HBA) dimer) in both pure and modified supercritical (SC) carbon dioxide by adding methanol (molar fraction, 0.035) at T = 318 K, rho = 0.7 g/cm(3) is simulated. Features of the solvation mechanism in each solvent are revealed. The solvation of o-HBA in pure SC CO2 is shown to occur via electron donor-acceptor interactions. o-HBA forms a solvate complex in modified SC CO2 through hydrogen bonds between the carboxyl group and methanol. The hydroxyl group of o-HBA participates in the formation of an intramolecular hydrogen bond, and not in interactions with the solvent. It is concluded that the o-HBA-methanol complex is a stable molecular structure, and its lifetime is one order of magnitude higher than those of other hydrogen bonds in fluids.