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

Abstract

The dissociation constants of twelve substituted phenols with a nitro group in the 0-or p-position hav e been determin ed by spectrophotometric measurements in aqueous solution at 25°C.

Spectrophotometric determination of dissociation constants of selected acidic herbicides

“…The observation that dinoseb was a slightly weaker acid than DNOC may be due to greater steric inhibition to solvation of the phenoxide anion by the sec-butyl group. The observed pKa value of 4.46 for DNOC was in very good agreement with that (pKa = 4.47) determined spectrophotometrically by Robinson (1967a), whereas the observed p7fa value (4.62) for dinoseb differed from that (4.40) reported by Weber (1972). The o-bromo (-7, + 7) substituents (2,6-dibromophenol; pKa = 6.69; Robinson, 1967b) and p-cyano (-/, -AT) group (p-cyanophenol; pffa = 7.97; Fickling et al., 1959) of bromoxynil and the chloro (-7, +M) substituents (2,4,6trichlorophenol; pKa = 6.23; Fischer et al, 1967;3,5-dichlorophenol; pKa = 8.18; Robinson, 1964) of pentachlorophenol are acid strengthening.…”

“…Because of conjugation of the phenyl ring with the lone pair of electrons on the phenolic oxygen, both inductive (7) and mesomeric (M) effects of substituents on the phenyl ring determine the acidic strengths of phenol derivatives (phenol; pKa = 10.00; Ko et al, 1964). The pKa values found for dinoseb and DNOC (see Table I) were intermediate between those resulting from the acid strengthening nitro (-/, -M) groups (2,4dinitrophenol; pKa = 4.09; Robinson, 1967a) and the acid weakening 6-alkyl (+/, +M) group (o-cresol; pKa = 10.32; Herington and Kynaston, 1957). The observation that dinoseb was a slightly weaker acid than DNOC may be due to greater steric inhibition to solvation of the phenoxide anion by the sec-butyl group.…”

Synthesis, Basicity, and Dynamics of a Perfluorocyclohexenyl Anion

“…Ratios of anion 9 to its conjugate acid 10 were determined by 19 F NMR integration. In this way, cyclohexene 10 was found to be 53 ± 4 times more acidic in acetonitrile than cresol 15 , the p K a of which is 4.23 in water . This acidity ratio was calculated on the assumption that the decomposition of 9 does not consume base, and the acidity of 10 is somewhat greater yet if it does .…”

Toward a Class-Independent Quantitative Structure−Activity Relationship Model for Uncouplers of Oxidative Phosphorylation

“… a Same references as for log Klipw,HA. b Values in brackets were determined with the uptake estimated by eqs , , and . c Training set (1); test set (0). d Ref . e PhysProp-Database () or KowWin-Demo-Database (). f Ref (defined for a surface of 0.7 nm 2 per lipid molecule and MW 760 g/mol lipid). g This study. h Ref . i Ref (defined for a surface of 0.7 nm 2 per lipid molecule and MW 760 g/mol lipid). j Ref (measured D ow and p K a of 5.3 taken to obtain K ow ). k Ref (defined for a surface of 0.7 nm2 per lipid molecule and MW 760 g/mol lipid). l Ref . m Ref [measured in 50% EtOH/50% H 2 O (v/v)]. n Ref [value for log K ow taken as a mean of refs e (3.56) and n (3.27)]. o Ref . p SPARC p K a -Database (). q Ref . r Ref [value for log K ow taken as a mean of e (4.13) and r (4.24)]. s Ref . t Ref . u Ref . v Taken as an average value of ref and two older unpublished measurements. w Ref . x Ref . y Unpublished measurements. …”