Dissociation constants of substituted phenols and homoconjugation constants of the corresponding phenol–phenolate systems in acetonitrile

Abstract

Dissociation constants of 25 phenols and homoconjugation constants of 14 phenol-phenolate systems in acetonitrile have been determined from emf measurements. From these results a linear relationship log K t N = 1.9 pKt20 + 8.3 has been derived. Stronger homoconjugation of weaker proton donors has been found to be a result of various (steric, inductive, mesomeric, charge delocalization) effects; however, the increase of homoconjugation constants with electron density at the phenolic oxygen seems to be unquestionable. Ten hydrogen bis-phenolates were prepared to complete this study, some of which crystallized well from water.

Kinetics and Mechanism of Photodegradation of Chlorophenols

“…The product is 4-chlororesorcinol, while simultaneously HCl in stoichiometric amounts appears in the medium [97]. Chlorohydroquinone or hydroxyhydroquinone are not found among the products, which is indicative of an insignificant contribution of photohydrolysis at the 4-position: (42) Irrespective of the presence of dissolved oxygen, the quantum yield of the process for the anionic forms amounts to 0·11 ± 0·02, whereas for the molecular form it is 0·020 ± 0·004. Irradiation of a phenol/3,4-DCP mixture produced a complex mixture of products (including 4-chlororesorcinol) involving a competition between sensitization and radical induction.…”

“…This rate characterizes the actual photochemical reaction and does not depend on the total light absorption by the medium. Other properties of chlorophenols that have been tabulated include surface areas, molecular volumes, polarizabilities, dipole moments, refractivities (all in [35]) and energies of combustion [36][37][38] b Melting points from [39] c pK a values in aqueous solution quoted in [40,41] d Values for some of these compounds in acetonitrile, propylene carbonate and benzonitrile are given in [42] e Solubility in water, pH 4·5-5·1 at 25°C from [41] f Octanol-water partition coefficients from [35] and references therein g Partition coefficients of some of these compounds as functions of pH have also been given in heptane-water and octane-water systems [43] h The effect of added salt on this is given in [44] i Enthalpies for proton dissociation are given in [45] j [46] k [42] l The effect of pH on this solubility is given in [47] In the case when the light absorption by the medium cannot be neglected, the value of W sur is related to the observed rate of photochemical transformation of substance P, (W obs ) by the relation: W sur = αW obs (26) where α is a correction factor depending on the optical density of the medium [59]:…”

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

“…Dissociation constants of many other acids and bases in organic solvents have been determined by potentiometric titration using a glass electrode calibrated with buffers prepared from picric acid or 2,6-dinitrophenol (see, e.g. [21,22,31,32,[34][35][36][37][38][39][40][41][42][43][44] and references cited therein). Typically, a one-point calibration has been applied and correction for the effect of the ionic strength has been done with the aid of the Debye-Hückel theory.…”

Nucleophilic Substitution of Halogens with Amines in 2- and 4-Nitrophenols

“…We decided to use aprotic solvents as the reaction medium, which should decrease the acidity of nitrophenols compared to the protonated alkylamines. According to literature data, changing the solvent from water to acetonitrile reduces the acidity of 2-nitrophenol from pK a 7.2 to 22.4, 9 whereas that of protonated morpholine only from pK a 8.36 to 16.61. 10 Thus, the reaction of 1 with various primary and secondary alkylamines (2.5-fold excess) was carried out in refluxing acetonitrile for one hour giving almost quantitative yields of substitution products 5 ( Table 1).…”