On the Dissociation of Methyl Orange:Spectrophotometric Investigation in Aqueous Solutions from 10 to 90 deg C and Theoretical Evidence for Intramolecular Dihydrogen Bonding

摘要

The dissociation of methyl orange was investigated by spectrophotometry in aqueous solutions from 10 to 90 deg C and by quantum chemical calculations.Combined chemo-metric and thermodynamic analyses of the spectrophotometric data were used to simultaneously extract the thermodynamic stabilities and the spectrophotometric attributes of the dominant methyl orange species in solutions containing less than 20.00 mmol-kg~(-1) perchloric acid and submillimolal concentrations of methyl orange.The analyses revealed the presence of only one monomeric deprotonated and one monomeric proto-nated species.The spectra did not reveal any evidence for the presence of tautomeric equilibria between the protonated azo and ammonium species in the experimental range studied.Thermodynamic analyses of the temperature-dependent dissociation constants showed the reactions to be endothermic and enthalpy driven with increasing acidity and increasing temperature.