Thermodynamics of ionization of some substituted 4-methyl-thioanilines

Ionization constants of chloro, iodo and nitro substituted 4-methyl-thioanilines were determined over the range 30° to 50° using a spectro-photometric method. The results were analyzed in terms of the Harned-Robinson equation and values of heat, free energy and entropy of ionization were calculated. The free energies are additive, except in the case of 3, 5-diiodo-4-methylthioaniline, while the heats and the entropies are not.