Abstract
The solubilities of 1-aminoanthraquinone (MAAQ), 1, 4-diaminoanthraquinone (DAAQ) and 1, 4, 5, 8-tetraaminoanthraquinone (TAAQ) in water and in the mixtures of water and alcohols such as methanol, ethanol and n-propanol were determined at 20, 25, 30, 40 and 50°C. From the solubility data the thermodynamic parameters for the transfer of aminoanthraquinone compounds (AAQ) from water to the water-alcohol mixtures were calculated.
On the basis of the thermodynamic parameters, the hydrotropic behaviours of alcohol on the AAQ's are discussed. The following results were obtained:
(1) The solubilities of the AAQ's were larger in water-alcohol mixtures than in water. The effects of alcohols on the solubilities of the AAQ's increase in the order of methanol, ethanol and n-propanol.
(2) The free energy changes were negative. As to the number of amino groups in the AAQ and the alcohol, the enthalpy changes were found to vary from about +4.5 to -5.8 Kcal/mol and the entropy changes from about +17 to -13 cal/deg. mol.
(i) The enthalpy and entropy changes of the MAAQ were positive in all the mixtures of water and alcohol.
(ii) The enthalpy and entropy changes of the DAAQ were positive in water-methanol mixtures, and they were negative in water-ethanol and in water-n-propanol mixtures.
(iii) The enthalpy and entropy changes of the TAAQ were negative in all the mixtures of water and alcohols.
(iv) The enthalpy change of AAQ was found to decrease with the increase in the length of alkyl chain of alcohols.
(3) Assuming the presence of ice-like structure of water around the MAAQ and alcohol molecules, the positive enthalpy and entropy changes can be explained by means of hydrophobic interactions between the hydrophobic portions of the MAAQ and alcohol molecules. The negative enthalpy changes for the transfer of the AAQ's cotaining two or four amino groups may suggest that the adduct between the AAQ and alcohol is formed to be hydrated.
