Temperature Dependent Solubility of α-Form L-Glutamic Acid in Selected Organic Solvents: Measurements and Thermodynamic Modeling

In this study the solubility of a-form L-glutamic acid in the six organic solvents methanol, ethanol, 1-propanol, acetone, formic acid, and dimethyl sulfoxide (DMSO) was measured by a static analytic method. The measurements were carried out over the temperature range 278-355 K at around 5 K intervals, and the equilibrium concentration was determined by the gravimetric method. The experimental results show that formic acid has the highest solubility to a-form L-glutamic acid while the other solvents have the solubility order water, acetone, 1-propanol, ethanol, methanol, DMSO, and acetic acid. The hypothetical enthalpy of fusion and melting temperature of L-glutamic acid are estimated. Several commonly used thermodynamic models, including the empirical van't Hoff equation and the Wilson, NRTL, and UNIQUAC equations, were applied to correlate the experimental solubility data. The binary interaction parameters of the above models are found to have a linear dependency on temperature, and the coefficients were regressed. It was found that all these models can satisfactorily reproduce the experimental solubility and the UNIQUAC equation can provide the best correlation results with an overall standard deviation of 2.7 x 10(-5).