Dissociation of some substituted phenols in 50-percent aqueous methanol as solvent

Abstract

The dissociation consta nts of the following substituted phenols in 50 wt percent methanol have been measured at 25°C: o-nitrophenol, p-nitrophenol, 4-methyl-2-nitrophenol, 2,6-di chlorophenol , pentachlorophenol. The respec tive values found, expressed as pK va lues, are 7.91" 7.692 , 8.28" 7.680, and 5.27.. The dissociati o n cons tants of 4-methyl-2-nitrophenol and pentac hlorop henol, again exp ressed as pK valu es, have been meas ured in water as so lve nt a t 25°C and found to be 7.59, and 4.820. respectively. Key Word s: Di ssociati on consta nt , methanol-water mixtures, so lvent effec ts, sub stituted phenols.

Dissociation constants of some substituted nitrophenols in aqueous solution at 25 C

“…The spectrophotometric method of determining the dissociation constant of a weak acid has been described many times [1,2,3,4,5,6,7], For the five phenols with pK values less than 3_5, dilute solutions of hydrochloric acid were found to be suitable media in which to make measurements; for the other seven, with pK values greater than 3,8, succinate buffers were U! ;;ed_ In some cases a small correction was needed for the effect of the phenol on the acidity of the buffer solution; this correction has already been described [9],…”

“…The determination of the dissociation co nstants of a number of substituted phenols by the spectrophotometric method has been described rece ntly [1,2,3,4,5,6,7). 1 The purpose of this paper is to present data for twelve substituted phenols with an indicator range pH 2.1-5.5.…”

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

“…[12]. The quantity t1Go=2.3026RTt1pK is the c hange in Gibbs free e nergy 'for the transfer reaction:…”

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.…”