Dissociation Constants Of Benzoic Acids Research Articles

Exploratory analysis in thermodynamics of equilibria. Classification and prediction of benzoic acid strength in aqueous-organic solvents

Decisive rule for classification and prediction of benzoic acid strength from dielectric constant and Kamlet–Taft parameter of the mixed solvents (water–methanol, water–ethanol, and water–2-propanol) has been elaborated basing on the results of multivariate exploratory analysis. The rule has been verified using the independent experimental data on dissociation constant of benzoic acid in water–dioxane and water–dimethylsulfoxide mixtures. Two-parameter linear regression model of the Gibbs energy of benzoic acid dissociation as a function of the properties of aqueous-alcoholic solvents has been built, and the contributions of dielectric and cohesion medium properties to the decrease in the acid strength have been shown.

Determination of stoichiometric dissociation constants of benzoic acid in aqueous sodium or potassium chloride solutions at 25°C

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant K m of benzoic acid in dilute aqueous NaCl and KCl solutions at 25°C from the thermodynamic dissociation constant K a of this acid and from the ionic strength I m of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study and the equations for K m were based on the single-ion activity coefficient equations of the Hiickel type. The existing literature data obtained by conductance measurements and by electromotive force (EMF) measurements on Harned cells were first used to revise the thermodynamic value of the dissociation constant of benzoic acid. A value of K a = (6.326 ± 0.005) x 10 -5 was obtained from the most precise conductivity set [Brockman and Kilpatrick] and this value is supported within their precisions by the less precise conductivity set of Dippy and Williams and by the EMF data set measured by Jones and Parton with quinhydrone electrodes. The new data measured by potentiometric titrations in a glass electrode cell were then used for the estimation of the parameters of the Huckel equations of benzoate ions. The resulting parameters were also tested with the existing literature data measured by cells with and without a liquid junction. The Huckel parameters suggested here are close to those determined previously for anions resulting from aromatic and aliphatic carboxylic acids. By means of the calculation method based on the Huckel equations, K m can be obtained almost within experimental error at least up to I m of about 0.5 mol-kg -1 for benzoic acid in NaCl and KCl solutions.

Correlation of the Hammett Equation with the Solubility and Dissociation Constants of Benzoic Acid in Aquo-ethanolic Solutions

Correlation of the Hammett Equation with the Solubility and Dissociation Constants of Benzoic Acid in Aquo-ethanolic Solutions

Substituent effects. Part 11. Anomalous dissociation constants of benzoic acids in water–organic solvent mixtures. An extended Hammett equation comprising the hydrophobic constant as an additional parameter

Thermodynamic dissociation constants of benzoic acids show deviations from the Hammett equation in ethanol–water and, more strongly, in t-butyl alcohol–water, with maxima at about 40% ethanol–water (16 mol%) and 32% t-butyl alcohol–water (8 mol%). The extended equation Δ=ρσ+hπ, where π is Hansch's hydrophobic constant, covers the experimental data very well; h varies from 0 to – 0.16. Similar behaviour is exemplified for other systems. In the solvents 80% methyl Cellosolve and 65% dimethyl sulphoxide the Hammett equation is followed closely. Some practical implications and an attempt at rationalization are given. Related data from the literature, including recent work of Fan and Jiang, are discussed briefly.

The effects of high concentrations of aqueous tetramethylammonium chloride and other salts on the dissociation of phenylphosphonic acid and on the enolization of acetone

The dissociation constants of benzoic acid and phenylphosphonic acid have been determined in aqueous solutions containing tetramethylammonium chloride at concentrations up to 15 and 13 molal, respectively. The second dissociation constant of phenylphosphonic acid has also been determined in concentrated solutions of alkali halides. Whereas the organic electrolyte increases the observed pK values of the acids, the inorganic electrolyte idecrease them. The rate of enolization of acetone, catalyzed by phenylphosphonate dianion is increased by the presence of tetramethylammonium chloride, but is decreased by the presence of inorganic salts, in accordance with the changes in the apparent acidity constants of phenylphosphonate monoanion that the two different kinds of electrolyte bring about. The slope of the Bronsted plot for the inorganic salts is 0.76; that for the organic electrolyte is 0.46. Non-quaternary ammonium salts also increase the rate of the phenylphosphonate dianion catalyzed enolization of acetone, but this appears to be due to a considerable extent to the formation of reactive iminium ion intermediates.

Conductometric Studies on the Dissociation Constants of Benzoic Acid in 2-Propanol + Water Mixtures

Article Conductometric Studies on the Dissociation Constants of Benzoic Acid in 2-Propanol + Water Mixtures was published on January 1, 1987 in the journal Zeitschrift für Physikalische Chemie (volume 268O, issue 1).

Effects of Solvent Polarity on the Acid Dissociation Constants of Benzoic Acids

The pKa values of benzoic acid, p-methylbenzoic, and p-aminobenzoic acid (PABA) were determined by potentiometric titration in mixtures of 0–0.5 volume fractions of various cosolvents and water. The differences between the aqueous and semiaqueous pKa values were similar for the three solutes at a particular cosolvent-water mixture for most of the cosolvents studied. The largest differences occurred in the dimethyl sulfoxide (Me2SO)-water system, where the pKa changes were larger for PABA than the other two solutes. The data are analyzed by a consideration of both electrostatic and nonelectrostatic medium effects. The electrostatic medium effect was calculated from the Born Equation while any residual pKa change was attributed to nonelectrostatic medium effects. The residual effects were found to correlate well with indexes of solvent hydrogen bond acceptor ability such as HBA and β-values. These results provide a rationale for the use of two solvent polarity indexes for more accurate estimates of pKa values of weak electrolytes in semiaqueous solvent systems. Analysis of solubility data of the salt and acid forms of PABA and benzoic acid in ethanol-water and Me2SO-water mixtures suggests that the higher activity of the anionic form of PABA in Me2SO-water mixtures is primarily responsible for the large pKa changes observed for that solute.

Effect of substituents at the 5-position on the first and second dissociation constants of isophthalic acid

The dissociation constants of benzoic acid and 20 of its meta- or para-substituted derivatives and of isophthalic acid and ten of its 5-substituted derivatives have been measured in 50 wt% aqueous methanol. The Hammett ρ value for benzoic acid is 1.28; for isophthalic acid the ρ values are 1.21 (pK1) and 1.20 (pK2). The σmeta values for hydroxy and acetoxy are –0.01 and +0.29, respectively, in this system. Values for σmeta for CO2H and CO2– are calculated to be +0.28 and –0.20, respectively; however there are indications that these values are not completely structure-independent.

Studies on the Dissociation Constants of Benzoic Acids in Methanol and Water Mixtures by Conductometric Methods

Studies on the Dissociation Constants of Benzoic Acids in Methanol and Water Mixtures by Conductometric Methods

Studies on the dissociation constants of benzoic acid and substituted benzoic acids in ethanol‐water mixtures by conductometric methods

AbstractThe dissociation constants of benzoic acid, m‐fluorobenzoic acid and m‐chlorobenzoic acid in water and ethanol‐water mixtures (8% to 87,6 wt.% of ethanol) have been determined by the conductometric method as suggested by Gelb with slight modification. The results hav been checked by the method suggested by FUOSS and KRAUS.

Secondary carbon-13 isotope effect on the ionization of benzoic acid

The effect of carbon-13 enrichment in the carboxyl group on the dissociation constant of benzoic acid has been determined in the temperature range of 10–30 °C. The isotope effect, K12/K13, decreases from 1.003 at 10 °C to 1.001 at 30 °C. The temperature dependence of the equilibrium isotope effect, measured by e.m.f. methods, could not be reproduced theoretically. The disagreement between experiment and theory is explained by means of a superimposed isotope effect due to solvation.

Dissociation constant of benzoic acid in H2O + D2O mixtures

The dissociation constant of benzoic acid has been determined at 25°C in ordinary water and in H2O + D2O mixtures by conductance measurements and by precise e.m.f. measurements with glass and silver–silver chloride electrodes in a cell without liquid junctions. The isotope effects ΔpKn(=pKn–pKH) obtained by the two methods are in agreement and are shown to support the simple equilibrium theory of solvent isotope effects. The values of pKH and pKD obtained from the e.m.f. measurements are 4.201±0.004 and 4.693±0.004 respectively.

Acid–base equilibria of substituted benzoic acids. Part I

A spectrophotometric determination of the dissociation constants of benzoic acid and its alkyl derivatives has been made. A computer programme has been written to enable the thermodynamic quantities ΔG°, ΔH, and ΔS° to be calculated at a number of selected reference temperatures within a temperature range. The thermodynamic quantities for benzoic acid and some of its alkyl derivatives have been calculated from the dissociation constants obtained in this investigation at temperatures within the range 15–40°C; the corresponding quantities for halogeno-, nitro-, cyano-, and hydroxy-derivatives have been calculated from literature values. The relative strengths of these acids are discussed.

The thermodynamic dissociation constant of benzoic acid and the entropy of the benzoate ion

The thermodynamic dissociation constant of benzoic acid and the entropy of the benzoate ion

Abnormal Strength of 2:6-Dihydroxybenzoic Acids

THE work of W. Ostwald1 showed that the electrolytic dissociation constants of the hydroxybenzoic acids vary greatly with the positions of the hydroxyl groups. Thus the dissociation constants of benzoic acid, and of those mono-, di- and tri-hydroxybenzoic acids, which do not possess a hydroxyl group in the ortho-position to the carboxyl group, have dissociation constants all less than 1 × 104; the dissociation constants of the various hydroxybenzoic acids containing an ortho-hydroxyl group are all of the order of 1 × 103, and 2:6-dihydroxybenzoic acid has a dissociation constant of 5.0 × 102 (see Table 1).

LXXXIV.The determination of the thermodynamic dissociation constant of benzoic acid, at25 °,from conductivity measurements

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