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Evidences for zwitter ions formation during determination of pKa values for o-amino benzylidene o, m, p- hydroxyl anilines

A.S.P.Azzouz, A.K.E.AL-Abassy

o- Aminobenzylidene o, m, p- hydroxyl anilines as numbered I, II, III respectivelywere prepared by astandardmethod, Their chemical structures were confirmed by physical method, namely by using melting points, UV and IR spectra, beside some chemical tests. The pKa values for imines I, II and III and were determined by using a potentiometric titrationmethod in 10%ethanol at a temperature range (20- 60)ï‚°C. Imines I and III show anomalous pKa values in the range between (5-6.5). These were unexpected results and confirmed by the formation of zwitter ions at all temperatures stated. Imine II showed a similar result at temperatures (20-30)ï‚°C and other different results at other higher temperature range between (40-60)ï‚°C. All evidences supporting zwitter ions formation were given and discussed.