Activity coefficients of the species in the methanol solutions of acetaminophen and two silylated derivatives at 298.15 K

An isopiestic method was used to measure the solvent osmotic coefficients in solutions of acetaminophen, triethylsilylacetaminophen and tertiarybuthyldimethylsilylacetaminophen in methanol at 298.15 K. The experimental data for osmotic coefficients have been correlated and solute unsymmetric convention activity coefficients have been calculated using the nonrandom factor (NRF) model, the nonrandom, two-liquid (NRTL) model, a three-parameter Margules equation, and a fourth-order polynomial equation in terms of molality. Standard deviations are least for the models with more parameters, but all models describe the data within experimental uncertainty. The solute activity coefficients are greater than unity, increasing with molecular size.