Solubility of p-nitroaniline and the basic strength of aqueous alcohols (and other oxygen-containing compounds)

Abstract

The solubility at 25°C of p-nitroaniline in aqueous alcohols at concentrations of up to 40 % v/v is reported and activity coefficients are calculated. The rate of increase of the indicator solubility with alcohol concentration diminishes in the order cyclohexanol > n-propanol > isopropanol > ethanol > methanol, and this effect of the alcohol is sufficient to account for the behaviour of the indicator in dilute acid solutions without the assumption of the protonation of the alcohols themselves. Attention is drawn to some weaknesses in the protonation argument.