Thermodynamic analysis of proton dissociation equilibria of some 4-diethylaminoazobenzenes in 20 wt% aqueous methanol solution

Abstract

Proton dissociation of XC₆H₄NCNH₆H₃YNHEt₂(X = H, CO₂H, NO₂, OMe; Y = H, Me, OEt) has been examined at 293.15 K in aqueous sulphuric acid solutions. Equilibrium constants for the proton dissociation of XC₆H₄NHNC₆H₃YNEt₂(X = H, CO₂H, NO₂, OMe; Y = H, Me, OEt) have been measured as a function of temperature, in the range 293–323 K, in 20 wt% aqueous methanol solution. Thermodynamic functions (ΔG°, ΔH°, ΔS°) have been calculated. Experimental data have been discussed and interpreted in terms of linear free energy relationships. Tautomeric equilibrium constants have been evaluated and apparent equilibrium constants separated into the separate contributions of ammonium and azonium forms.