Stability of dithranol in aqueous solutions and aqueous-organic solutions

Using a UV method, the effect of pH, temperature and solvent polarity on the stability of dithranol (DT) has been studied. On the dependence log k - pH we composed the reaction of autoxidation of undissociated molecul, monoanion and dianion of DT, described by k(1), k(2) and k(3) micro rate constants, respectively (k(1) < k(2) < k(3)). Considering rate constants k(1)-k(3), thermodynamic parameters of reaction: energy, entropy and enthalpy of activation and the frequency factor were determined. The rate of DT autoxidation increased with increasing of the solvent polarity. To interpretation of this dependence the molar energy of transition E-T, as the measure of the solvent polarity, where choosen.