Solubility and Solution Thermodynamics of Betaine in Different Pure Solvents and Binary Mixtures

The solubility of betaine in water, methanol, ethanol, n-propanol, 2-propanol, and n-butanol and also in methanol + ethanol and ethanol + water binary mixtures has been experimentally measured using a laser monitoring observation technique. The modified Apelblat equation was used to correlate the solubility of betaine in the studied pure solvents. The solubility of betaine in the binary solvent mixtures was correlated by a hybrid model based on the Jouyban-Acree model and modified Apelblat equation. The associated P-values of terms for model were used to simplify the hybrid model, which reduced the number of the model parameters without affecting the values of mean percentage deviation (MPD) and R-2. With these models the maximum MPD for studied solvents is 1.94. Thermodynamic functions including Delta H-soln(0), Delta G(soln)(0) and Delta S-soln(0) of solution of betaine were obtained from the modified van't Hoff equation. A comparison of the relative contributions by enthalpy (zeta(H)) and entropy (zeta(TS)) was made (with zeta(H) > 0.6 and even up to 0.99 in methanol), which indicated that the main contributor to the positive standard molar Gibbs energy of solution of betaine was enthalpy in both pure solvents and mixtures.