Solubility and preferential solvation of some n-alkyl-parabens in methanol + water mixtures at 298.15 K

Abstract

Methyl, ethyl and propyl parabens equilibrium solubility was determined in (methanol+water) binary mixtures at 298.15K. The mole fraction solubility of these compounds increased in 503 (from 2.40×10−4 to 0.121), 1377 (from 9.86×10−5 to 0.136) and 4597 (from 3.73×10−5 to 0.171) times when passing from neat water to neat methanol, for methyl, ethyl and propyl parabens, respectively. All these solubility values were correlated with the Jouyban-Acree model. Preferential solvation parameters by methanol (δx1,3) of these parabens were derived from their thermodynamic solution properties using the inverse Kirkwood-Buff integrals (IKBI) method. For all compounds δx1,3 values are negative in water-rich mixtures but positive in mixtures with methanol mole fraction greater than 0.32. It is conjecturable that in the former case the hydrophobic hydration around non-polar groups of parabens plays a relevant role in the solvation. Besides, the preferential solvation of these solutes by methanol in mixtures of similar co-solvent compositions and in methanol-rich mixtures could be explained in terms of the higher basic behaviour of methanol.