Effect of sulpholan upon dissociation of phenols in alkaline solution

Abstract

The degrees of ionisation of 3,4,5-trimethylphenol and 2,4-di-t-butylphenol have been measured in water–sulpholan mixtures containing hydroxide ion. The solubilities of 3,4,5-trimethylphenol and 2,4,6-trinitroaniline in dilute aqueous sulpholan solutions have also been determined and activity coefficients derived for the neutral compounds. It is shown that the decrease in the degree of ionisation of phenols that accompanies addition of sulpholan to water applies to both ordinary phenols and those containing bulky ortho-substituents. The cause of this decrease can be traced to the large decrease in activity of the neutral compound that accompanies addition of small amounts of sulpholan to water. The differing ionisation behaviour of phenols and aromatic amines is discussed in terms of activity coefficient changes.