Dissociation constant of m-nitrophenol in 50 wt percent methanol-water solvent from 25 to 40 C and related medium effects

Abstract

The di ssociation co nstant of m-nitrophenol in 50 wt percent methanol-water as solvent ha s been determined at 25, 30, 35, and 40°C. A spectrophotometric method was used, together with acidity functions for buffer so lutions in 50 percent methanol derived from previous emf meas ure ments. Values of the e nthalpy and entropy c hanges on dissociation of the phenol have been calculated. A co mpariso n with co rresponding values for the dissociation of m-nitrophenol in aqueous so lution affords a measure of the med ium effect. The medium effect for m-nitrophenollies intermediate between that for Q·nitrophenol and that for p-nitrophenol.

The dissociation constant of m-nitroanilinium ion in water-tetrahydrofuran solvents at 25 C

“…The dissociation constant of m-nitroanilinium ion in a number of water-tetrahydrofuran solvents was determined by the spectrophotmetric method described in several previous publications [5][6][7][8][9][10]; the notation used in this paper is that used before. The validity of Beer's Law for this system was demonstrated by measurements of optical density of alkaline solutions in 62.5 wt percent tetrahydrofuran with the con-' centration of m-nitroaniline varying from 2 X 10-4 to 8 X lO-4m.…”