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

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.