Association of crown ethers with anilinium ions in methanol solution and its influence on acid–base equilibria

Abstract

The effect of adding toluene-p-sulphonic acid to p-nitroaniline and acetic acid to p-toluidine in methanol at 25.0 °C has been quantitatively studied by u.v.–visible spectrophotometry in the presence of 15-crown-5, 18-crown-6, and 21-crown-7. From the enhancement of the apparent basicity of the anilines due to complexation of the conjugate acids with crown ethers the association constants between crown ethers and anilinium ions were calculated. The order in the ability to associate, 18-crown-6 > 21-crown-7 > 15-crown-5, was the same in both series. A change of the anilinium ion substituent from p-NO₂ to p-CH₃ had little or no influence upon the association constants.