Understanding the solubility behavior of 2,2′-bifuran-5,5′-dicarboxylic acid in different pure solvents

• Solubility of BFDCA in eight process-relevant solvents is reported. • A single BFDCA polymorph was observed across a range of solubility testing. • The σ profile of BFDCA is reported. • Molecular descriptors of solvents are compared to BFDCA solubility data. The molecule 2,2′-bifuran-5,5′-dicarboxylic acid (BFDCA) has attracted significant attention due to its potential as a building block to form biorenewable polymers. However, there is no information available on the solubility of BFDCA in pure solvents, hindering the effective design for reaction, separation, and crystallization processes. The present work evaluated the solubility of BFDCA in eight different solvents at temperatures from 298.15 K to 363.15 K. On a mole fraction basis, the BFDCA solubility from high to low at 298.15 K followed the order: DMAc > DMSO > MeOH > 1-pentanol > 2-propanol > acetic acid > acetonitrile > H 2 O. Additional solubility tests were performed in cyclohexane, acetone, and dichloromethane, but the equilibrium solute concentration was below the detection limit of the instrument in the range of temperatures studied. The sigma (σ) profile of BFDCA shows that this molecule is strongly polar and can behave as a donor and acceptor of hydrogen bonds. A higher screening charge density was found in the hydrogen bonding (HB) donor regions in BFDCA, which would favor the interaction with the solvents’ HB acceptor regions. Correlations between BFDCA solubility and solvent property parameters show that solvents’ HB acceptor propensity and total basicity play an important role in the solute solubility, which agrees with the findings from the σ profile of BFDCA and solvents and linear energy solvation relationships (LSER). However, the dipole moment, dielectric constant, cohesive energy density, and surface tension also influence the BFDCA solubility since the evaluated molecular descriptors are insufficient to explain the solubility behavior in some cases. The Apelblat equation and the NRTL activity coefficient model aptly described the experimentally observed solubility with model fitting, whereas the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) method predicted qualitative trends.