Ionization and Dissociation of Picric Acid in 4-Methyl-2-pentanone Solutions at Various Water Concentration

The spectrum of picric acid in 4-methyl-2-pentanone solutions which contained the acid and water at several concentrations was determined in the wavelength range from 330 to 500 nm and the data were statistically analyzed. It was concluded that picric acid molecules formed ion pairs together with four water molecules in these solutions and the ion pairs thus formed dissociated partially. Both of the ion pairs and dissociated picrate ions in these solutions had strong absorption in the visible range where no absorption was found with the acid molecules but the spectra of these two species were different. The formation and dissociation constants of the ion pairs were also calculated from the data and the role of water in these chemical reactions was considered.