Thermodynamic parameters characterizing 1-(2-pyridylazo)-2-naphthol in thewater-nitrobenzene extraction system

General relations among thermodynamic parameters characterizing chemical eq uilibria including species H(2)A(+), HA, H+ and A(-) in both phases of a tw o-phase water-nitrobenzene extraction system have been derived. From the ex traction measurements, the equilibrium distribution constant of electroneut ral 1-(2-pyridylazo)-2-naphthol (PAN, HA) between the nitrobenzene and aque ous phases has been determined: logK(D)(HA)=4.3. By using this value and fu rther known constants and applying the mentioned relations, the following v alues of dissociation constants of PAN in nitrobenzene saturated with water have been calculated for a temperature of 25 degrees C: pK(d)(nb)(H(2)A(+) )= -logK(d)(nb)(H(2)A(+))=6.8 and pK(d)(nb)(HA) =-logK(d)(nb)(HA)= 18.7.