Comparison of the Relative Acidic Strengths of the Isomeric Dinitrophenols in Benzene and Water

Proton transfer rate‐equilibria in apolar aprotic solvents: a historical perspective

“…Simmons et al evaluated equilibrium parameters (log K BHA , ΔH 0 , ΔS 0 ) for proton transfer reactions between 2,4‐, 2,5‐, and 2,6‐dinitrophenols and triethyl‐, tri‐ n ‐propyl‐, and tri‐ n ‐butylamines in chlorobenzene using spectrophotometry of the hydrogen‐bonded ion pair product. They found the strength of these oxygen acids to increase in the order 2,5‐dinitrophenol < 2,4‐dintrophenol < 2,6‐dinitrophenol, the same found in benzene solutions by earlier researchers and the base strength in the order tri‐ n ‐propylamine < tri‐ n ‐butylamine < triethylamine. They could, however, observe no meaningful deuterium isotope effects for the reactions.…”

“…To determine relative strengths of six isomeric (2,3‐, 2,4‐, 2,5‐, 2,6‐, 3,4‐, 3,5‐) dinitrophenols in benzene, they measured log K BHA of their association with triethylamine as the reference base and found 2,6‐dinitrophenol the most acidic and 2,5‐dinitrophenol the least acidic of the isomers. They showed that log K BHA values were not linearly related to p K a values of these phenols and ascribed this to interference of internal hydrogen bonding in ortho ‐nitrophenols with intermolecular hydrogen bonding . A parallel investigation in which another base of comparable strength 1,3‐diphenylguanidine was the reference base led to a similar result.…”

“…Towards developing a scale of strengths of phenolic or carboxylic acids, Davis and her school made intensive studies on proton transfer equilibria in apolar aprotic solvents involving proton donors and acceptors of varying structure over a period of more than two decades. Their pioneering researches towards development of precision methods for determining strengths of acids and also bases in terms of some appropriate ion pair/associate formation constant, log K BHA for acid–base association remains a landmark in area of acid–base behavior in apolar aprotic solvents . To determine relative strengths of six isomeric (2,3‐, 2,4‐, 2,5‐, 2,6‐, 3,4‐, 3,5‐) dinitrophenols in benzene, they measured log K BHA of their association with triethylamine as the reference base and found 2,6‐dinitrophenol the most acidic and 2,5‐dinitrophenol the least acidic of the isomers.…”

Hydrogen-bonded complex-ion-pair equilibriums in 3,4-dinitrophenol-amine-aprotic solvent systems

“…I III relative to dinitrophenols where one or both ortho positions are substituted by a nitro group, but it is known to form an ion pair with triethylamine in benzene. 7 We report below the results of a spectrophotometric study of the formation of hydrogen-bonded and ion-pair complexes of 3,4-dinitrophenol with several aliphatic amines in benzene and in benzene-cyclohexane mixtures.…”

Contribution A L'Étude du Spectre D'Absorption Électronique de Complexes Phenols‐Triéthylamine

“…Cette equation peut se comparer a celle obtenue par Davis pour les constantes de formation des dinitrophenols avec la triethylamine dans le benzene : [21] log K = -0,43 pKa + 5,9 I Ceci montre que la susceptibilite a la substitution diminue dans un solvant aromatique. Ce fait peut s'expliquer par la formation de liens 0-H ... n dont I'existence est suggeree notamment par spectrometrie infrarouge ou la frequence de vibration vOH ; .…”