581. Chemical constitution and the dissociation constants of monocarboxylic acids. Part XV. Steric effects in substituted nitrobenzoic acids

Abstract

The dissociation constants of nine disubstituted benzoic acids, two trisubstituted benzoic acids, and three nitrophenols in water a t 25' have been determined by the conductivity method ; included are two series comprising dinitro-and chloronitro-benzoic acids. The results shed light on the operation of steric effects in the benzoic acid system. DISSOCIATION constants for dimethylbenzoic acids were published in Part XI11 1 and further constants for disubstituted benzoic acids are provided in the present paper. These acids comprise two series possessing a nitro-or chloro-substituent at the 2-position and a

Ionization constants of the six dichloroanilines and the six dichlorophenols in aqueous solution at 25 °C

“…The change results from the use of more recent pK determinations of the mononitrophenols. The value now adopted, 7.230 [3], for o -nitrophenol is in good agreement with pK 7.234 by Judson and Kilpatrick [8] and 7.229 by Dippy, Hughes, and Laxton [28]. The value of pK 8.355 for m -nitrophenol [4] is preferred to the earlier value of 8.399 [10] because the more recent measurements were made in a tris buffer in place of the borax buffer of comparatively low p H used earlier.…”

Die thermodynamischen Aciditätskonstanten von Pikrinsäure und Trinitroresorcin bei 25°

“…Im Fall der Pikrinsaure erweisen sich Messungen im Bereich von 340-400 mp als geeignet. Zur Festlegung der H+-Konzentration wird den stark verdunnten wasserigen Pikrinsaurelosungen (c,= 7,6 . 1 0 -5~) 0,2-1,0 N Perchlorsaure zugesetzt.…”

“…(1) (Gleichung 4) und extrapoliert deren Zwei Literaturangaben iiber den thermodynamischen pK-Wert der Pikrinsaure aus Leitfahigkeitsmessungen, 0,708 [6] und 0,22 [7], weichen stark voneinander ab. Etwas naher bei der kleineren Zahl liegen die Ergebnisse spektrophotometrischer Bestimmungen : 0,38 [8] …”

Spectrophotometric determination of the ionization constant of dimethylpicric acid (2,4,6-trinitro-3,5-xylenol) in water at 25 C

“…On the assumption that the effects of substituents on the ionization constant of phenol are additive, data on the ionization constants of phenol and its monosubstitilted derivatives [ 2 , 3 ] can be used to calculate 1.76 as an approximate p K value for dimethylpicric acid. Alternatively, data for 2,6-dinitrophenol [ 4 ], p -nitrophenol, and 3,5-xylenol [ 5 ] can be combined to give another estimate, 1.05. Combining data for 2,6-dinitrophenol and 4-nitro-3,5-xylenol [ 6 ] yields the estimate 1.96, whereas utilizing data for 2,4-dinitrophenol [ 7 ], o -nitrophenol, and 3,5-xylenol leads to the value 1.50.…”