Solubility, dissolution thermodynamics and preferential solvation of sulfadiazine in (N-methyl-2-pyrrolidone + water) mixtures

Abstract

Solubility of sulfadiazine in {N-methyl-2-pyrrolidone (NMP) + water} mixtures from 278.15 K to 313.15 K has been determined and correlated by means of the Jouyban-Acree model. Discontinuous solubility trends are observed in NMP-rich mixtures at low temperatures. By using the van't Hoff and Gibbs equations the respective apparent thermodynamic quantities for the dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy, were calculated. Non-linear enthalpy–entropy relationships were observed in the plot of enthalpy vs. Gibbs energy exhibiting negative but variant slopes in the composition region 0.00 < w1 < 0.60 and variant negative and positive slopes in the other mixtures for the first case. Otherwise, a variant negative slope from neat water to w1 = 0.80 but a positive slope from this mixture to neat NMP were observed for the second case. Based on the inverse Kirkwood-Buff integrals it follows that sulfadiazine is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by NMP molecules in mixtures 0.17 < x1 < 1.00 at 313.15 K.