Preferential configurations in the aqueous solutions of dicarboxylic acids, diols and hydroxyacids: Calorimetric studies at 298 K

Abstract

Enthalpies of dilution of binary and ternary aqueous solutions of malonic acid derivatives, α,ω-dicarboxylic acids, α,ω-diols and 2-hydroxyacids have been determined by flow microcalorimetry at 298 K. Enthalpic self- and cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated and interpreted using the “preferential configuration” model. This working model allows the rationalization of the coefficients in terms of nonstatistical interactions in solution. Information is obtained on the influence of the relative position of the functional groups on hydrophobic interactions. When the functional groups are separated, as in α,ω-substances, the hydroxy–carboxy interaction is a better promoter of hydrophobic interactions than hydroxy–hydroxy and carboxy–carboxy interactions. When the two functional groups are on the same carbon atom, as in 2-hydroxyacids, there is an increased cooperativity of hydrophobic interactions compared with malonic acid derivatives (α-dicarboxylic acids). Chiral recognition is not detected in the aqueous solutions of these substances. This failure has been explained in terms of an intramolecular interaction between the hydroxy and carboxy groups which would mask the influence of the chiral carbon atom on the overall interaction.