Dissociation constants of substituted benzoic acids in water and in organic solvents

Abstract

Potentiometric titration has been used to measure dissociation constants of 38 monosubstituted benzoic acids in water and in 6 organic solvents (methanol, ethanol, dimethylformamide, acetonitrile, sulfolane, acetone). The results have been analyzed and interpreted from the point of view of substituent and solvent effects on the dissociation of the title substrates. It has been proved that solvents affect not only the reaction constant but also the substituent constant of the Hammett equation.

Carboxylic acid ionization constants by19F NMR spectroscopy

“…The 19 F NMR spectra of 3-and 4-fluorobenzoic acids have previously been measured in acid and base but without a description of their full titration curves. 15 All three isomeric fluorobenzoic acids also showed very good coincidence between 19 17 and for 26 with an NMR-determined pK a = 4.05 vs pK a = 4.15 found for the very similar 4,4,4-trifluorobutanoic acid. 18 Our conclusion from the comparisons with literature pK a s is that 19 F NMR spectroscopy is very well suited for pK a determination in the (strongly) acidic pH range, much as was shown to be for protonated amines in the physiological pH region.…”

Abraham model correlations for transfer of neutral molecules and ions to sulfolane

“…Ludwig et al [43] have determined pK a values for a large number of benzoic acids in sulfolane and in water. These can be used to calculate values of log P for the benzoate ions, log P(A - benzoic acids studied by Ludwig et al [43], we left out benzoic acid itself and 4-nitrobenzoic acid which were outliers by 0.84 and 0.80 log units respectfully.…”

“…These can be used to calculate values of log P for the benzoate ions, log P(A - benzoic acids studied by Ludwig et al [43], we left out benzoic acid itself and 4-nitrobenzoic acid which were outliers by 0.84 and 0.80 log units respectfully. Our fitted value of -11.55 for log P(H + ) compares reasonably well with the only literature value available of -12.08 log units [43]. Use of the latter would not affect the results significantly.…”

Electronic Effects of Nitro, Nitroso, Amino and Related Groups

“…This research group determined the apparent pK a values for a large number of substituted benzoic acids in one-component organic solvents 121 . Their results for m-and p-nitrobenzoic acids are most easily discussed in terms of the relative order of the pK a values.…”

“…As an example of this kind of work, the recent contributions of the group of Ludwig and Pytela will be mentioned briefly. Reference has already been made to the earlier work of these authors in determining the dissociation constants of a large number of substituted benzoic acids in different solvents (Section III.B) 120,121 . The results were treated as a data matrix by the chemometric methods referred to above, and various sets of Hammett values were derived for the 35 substituents involved.…”