Activity and activity coefficient studies of aqueous binary and ternary solutions of 4-nitrophenol, sodium salt of 4-nitrophenol, hydroquinone and α-cyclodextrin at 298.15 K

Abstract

Osmotic coefficient measurements are reported for binary aqueous solutions of 4-nitrophenol, sodium salt of 4-nitrophenol and hydroquinone at 298.15 K. The data are analyzed to obtain activities and activity coefficients of solute as a function of solute concentration using appropriate thermodynamic equations and methods of integration. The measurements of solvent activity are made for ternary aqueous solutions containing fixed concentration of α-cyclodextrin (α-CD) and varying amount of 4-nitrophenol, sodium salt of 4-nitrophenol and hydroquinone. The solvent activity data have been used to obtain the individual activity coefficients of the components as a function of solute concentration at 298.15 K. It is observed that there is a lowering of activity coefficients of the phenols as well as of hydroquinone in presence of α-CD, which is being attributed to incorporation of these solute molecules into the CD cavity to form inclusion complexes. The salting-in constant and thermodynamic equilibrium constant values for the formation of 1:1 complexes have been determined using Dagade and Patil's method based on the application of the McMillan–Mayer virial coefficient theory. The results are further discussed in terms of neutral and anionic complex formation, water structural effects and hydrophobic interactions.