Chemometrical Analysis of Substituent Effects. III. Additivity of Substituent Effects in Dissociation of 3,4-Disubstituted Benzoic Acids in Organic Solvents

1994 ◽  
Vol 59 (3) ◽  
pp. 627-638 ◽  
Author(s):  
Oldřich Pytela ◽  
Jiří Kulhánek ◽  
Miroslav Ludwig ◽  
Václav Říha
Keyword(s):  
Dimethyl Sulfoxide ◽  
Organic Solvents ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Proton Donor ◽  
Benzoic Acids ◽  
Correlation Equations ◽  
Hammett Equation ◽  
Validity Range ◽  
Reaction Constants

Sixteen 3,4-disubstituted benzoic acids (with all combinations of CH3O, CH3, Cl/Br, and NO2 substituents) have been synthesized and their dissociation constants measured in seven organic solvents (methanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, 1,2-dichloroethane). The effect of disubstitution and the validity of additive correlation relationships based on the Hammett equation have been analyzed by means of the analysis of variance, comparison of overall residual standard deviations of correlation equations of additive and additive multiplicative type, and application of the Hammett equation with internal (latent, defined in various ways) parameters and external (taken from literature) parameters describing the substituent effects. The effect of disubstitution has been found to be additive and describable within the validity range of the substituent constants adopted - by applying the additivity principle without any additional correction for interactions between the two substituents. The same conclusion has been drawn from the comparison of overall residual deviations in correlation equations for mono- and disubstituted derivatives. The analysis of differences between the reaction constants of the Hammett equation applied to mono- and disubstituted benzoic acids has shown that in organic solvents the solvation of substituents makes various contributions. The substituent influence is stronger in polar aprotic solvents (acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile) than that in the protic, basic, and less polar ones in which the stabilization by hydrogen bond becomes important, the role of proton donor being played either by the solvent itself (methanol) or by its conjugated acid (pyridine) or by a molecule of the dissociating acid as a consequence of homoconjugation (1,2-dichloroethane).

Chemometrical Analysis of Substituent Effects. IV. Additivity of Substituent Effects in Dissociation of 3,5-Disubstituted Benzoic Acids in Organic Solvents

1994 ◽  
Vol 59 (7) ◽  
pp. 1637-1644 ◽  
Author(s):  
Oldřich Pytela ◽  
Jiří Kulhánek ◽  
Miroslav Ludwig
Keyword(s):  
Organic Solvents ◽  
Dissociation Constants ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Specific Solvation ◽  
Reaction Constant ◽  
Substituent Constants ◽  
The Individual

Ten 3,5-disubstituted benzoic acids have been synthesized containing all possible combinations of the following substituents: CH3O, CH3, Cl/Br, NO2. The dissociation constants of these acids have been measured in seven organic solvents (methanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, 1,2-dichloroethane). It has been found that the effect of disubstitution is smaller than that due to interaction of substituents or their solvation and represents only about 0.2% of the effect caused by the individual substituents. The additivity in 3,5-disubstitution is about 2 - 3 times as good as that in 3,4-disubstitution. The quantitative description of substituent effects at the 3 and 5 positions is additive within the range of validity of the Hammett equation irrespective of the type of the substituent constants adopted, the addition of the multiplicative term being statistically insignificant. The solvent effect on 3,4- and 3,5-disubstituted derivatives is somewhat different at the same value of the reaction constant, due predominantly to the specific solvation of the 4-CH3O and 4-NO2 groups.

Solvent Effect on the Hammett Reaction Constant of Substituted Benzoic Acids

1993 ◽  
Vol 46 (1) ◽  
pp. 31 ◽  
Author(s):  
H Bartnicka ◽  
I Bojanowska ◽  
MK Kalinowski
Keyword(s):  
Solvent Effect ◽  
Dimethyl Sulfoxide ◽  
Dissociation Constants ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
P Values ◽  
Reaction Constant ◽  
Substituted Benzoic Acids ◽  
Reaction Constants ◽  
Solvent Acidity

Potentiometric titration has been used to measure dissociation constants of 13 monosubstituted benzoic acids in nitromethane, benzonitrile , acetonitrile , propylene carbonate, acetone, N,N-dimethylformamide, dimethyl sulfoxide, methanol and formamide. The reaction constants of the Hammett equation were found to depend on the solvent acidity and basicity expressed by the α and β parameters of Kamlet and Taft. The p values determined earlier in water and ethanol also obey this rule.

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

1986 ◽  
Vol 51 (10) ◽  
pp. 2135-2142 ◽  
Author(s):  
Miroslav Ludwig ◽  
Václav Baron ◽  
Karel Kalfus ◽  
Oldřich Pytela ◽  
Miroslav Večeřa
Keyword(s):  
Potentiometric Titration ◽  
Organic Solvents ◽  
Solvent Effects ◽  
Dissociation Constants ◽  
Point Of View ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Substituent Constant ◽  
Reaction Constant ◽  
Substituted Benzoic Acids

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.

Chemometric Analysis of Substituent Effects. VI. A Study of ortho Effect in Dissociation of 2,6-Disubstituted Benzoic Acids

1995 ◽  
Vol 60 (5) ◽  
pp. 829-840 ◽  
Author(s):  
Jiří Kulhánek ◽  
Oldřich Pytela
Keyword(s):  
Latent Variables ◽  
Dissociation Constants ◽  
Additive Model ◽  
Substituent Effects ◽  
Point Of View ◽  
Steric Effects ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Substituent Constants ◽  
Substituted Benzoic Acids

Ten 2,6-disubstituted benzoic acids have been synthesized containing all possible combinations of the following substituents: CH3, OCH3, Cl, and NO2. The dissociation constants of these acids have been measured by potentiometric titration in methanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, and 1,2-dichloroethane. The experimental data obtained together with the pK values of 2-substituted benzoic acids in the same solvents have been analyzed from the point of view of ortho effect and additivity of disubstitution. The mutual interaction between substituents was found to represent only 0.12% of the variability due to substitution and to contribute to the overall variability of data less than the interaction between the substituent and solvent by a factor of about 13. The analysis of data by the method of multiple linear regression revealed a contribution of steric effects beside the effects transmitted through the aromatic skeleton. The 2- and 6-substituents effects are additive within the validity of the Hammett equation, and an addition of a multiplicative term describing interactions between the substituents is statistically insignificant. Nonlinear regression has been adopted in the additive model with multiplicative term to find the inner substituent constants including all the effects of substituents from ortho position: the term describing the interaction between 2- and 6-substituents is statistically insignificant in this model. An application of the method of conjugated deviations revealed two statistically significant latent variables. The first one explains 91.5% of the variability of data and is connected with the substituent effects transmitted through the aromatic skeleton. The second one explains 7.5% of variability of data and predominantly reflects the steric effects of substituents.

Further studies an the extended Hammett equation comprising the hydrophobic constant: Reactivity data for benzoic acids, arylacetic acids, β-arylpropionic acids, trans- and cis-cinnamic acids, methyl benzoates; dissociation constants, DDM reaction and alkaline hydrolysis in various water-organic solvent mixtures

1990 ◽  
Vol 55 (1) ◽  
pp. 119-135 ◽  
Author(s):  
Anthonius J. Hoefnagel ◽  
Bartholomeus M. Wepster
Keyword(s):  
Organic Solvent ◽  
Alkaline Hydrolysis ◽  
Dissociation Constants ◽  
Solvent Mixtures ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Cinnamic Acids ◽  
Tert Butanol ◽  
Arylacetic Acids

The extended Hammett eguaition Δ = ρs + hπ comprising the hydrophobic constant π is found to be effective in the title compounds and reactivities in various solvent mixtures. In 32 vol.% tert-butanol-water hmdecreases in the order ArCOOMe (-0.25), cis-ArCH=CHCOOH (-0.18), ArCOOH and ArCH2COOH (-0.16), ArCH2CH2COOH and trans-ArCH=CHCOOH (-0.07). For ArCOOH, mixtures like 40-60% methanol, 50% ethanol, 50% acetone and 50% dioxane give similar hm values of circa -0.05. For ArCH2COOH the effects of 3-iodo and 4-iodo substituents are acid-weakening in 32% tert-butanol. The consequences of the hπ term for ρ, σ, and the averaging of σ values, are discussed.

Dissociation of substituted benzenesulphonamides in water, methanol and ethanol

1984 ◽  
Vol 49 (5) ◽  
pp. 1182-1192 ◽  
Author(s):  
Miroslav Ludwig ◽  
Oldřich Pytela ◽  
Karel Kalfus ◽  
Miroslav Večeřa
Keyword(s):  
Linear Regression ◽  
Multiple Linear Regression ◽  
Potentiometric Titration ◽  
Principal Components ◽  
Dissociation Constants ◽  
Benzoic Acids ◽  
Reaction Constant ◽  
The Media ◽  
Reaction Constants

Thirteen monosubstituted arylsulphonamides (XC6H4SO2NH2) and two 3,4-disubstituted arylsulphonamides (X2C6H3SO2NH2) have been synthetized and their dissociation constants have been measured by potentiometric titration in water, methanol, and ethanol. The Hammett substitution dependences have been calculated for all the media, and changes in the reaction constants due to transition from water to alcohols are discussed in confrontation with analogous dependences of benzoic acids. The reaction constant ρ found in methanol is lower than that in water. The dissociation constants have been treated mathematically by the method of the principal components and by multiple linear regression.

Chemometric Analysis of Substituent Effects. XI. Solvent Effects on Dissociation of 2,6-Disubstituted Benzoic Acids

1997 ◽  
Vol 62 (6) ◽  
pp. 913-924 ◽  
Author(s):  
Jiří Kulhánek ◽  
Oldřich Pytela
Keyword(s):  
Benzoic Acid ◽  
Solvent Effects ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Carbon Chain ◽  
Graphical Analysis ◽  
Point Of View ◽  
Reaction Centre ◽  
Benzoic Acids ◽  
Protic Solvents

Eleven symmetrically 2,6-disubstituted benzoic acids (with the following substituents: OCH3, OC2H5, OC3H7, OCH(CH3)2, OC4H9, CH3, F, Cl, Br, I, and NO2) have been synthesized and their dissociation constants measured potentiometrically in methanol, ethanol, propan-1-ol, propan-2-ol, butan-2-ol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, and 1,2-dichloroethane. The experimental data obtained have been analyzed from the point of view of solvent effects on acidity of the individual derivatives. Different behaviour found with benzoic acid and the disubstituted derivatives in protic solvents is due to changes in solvation. The different character of solvation of benzoic acid and the disubstituted derivatives depends on the type of substitution, being manifested only in 2,6-disubstituted benzoic acids. The graphical analysis has shown a distinct trend in the increase of magnitude of deviation of the point of benzoic acid in the series: propan-2-ol, butan-2-ol, propan-1-ol, ethanol, methanol. This order correlates with the steric demands of carbon chain of the alcohols used. The abnormal behaviour of benzoic acid in the dissociation in these alcohols as compared with that of its 2,6-disubstituted derivatives is due to the different extent of solvation of the reaction centre caused by steric hindrance. Against the expectation, benzoic acid appears to be a weaker acid in protic solvents, whereas its alkoxy derivatives are stronger acids. The solvation also minimizes the inductive effect of alkoxy groups in the symmetrically 2,6-disubstituted derivatives. In aprotic solvents the acidity of 2,6-dialkoxybenzoic acids is also increased, in this case as a result of sterically forced deviation of the reaction centre and/or the substituents out of the plane of benzene ring.

Ortho Effect in Dissociation of Benzoic Acids with Electron-Accceptor Substituents Using the AISE Theory; Relation to para Substitution and Solvent

2002 ◽  
Vol 67 (5) ◽  
pp. 596-608 ◽  
Author(s):  
Oldřich Pytela ◽  
Jiří Kulhánek
Keyword(s):  
Electron Acceptor ◽  
Dissociation Constants ◽  
Electrostatic Force ◽  
Substituent Effects ◽  
Alternative Interpretation ◽  
Ring Closure ◽  
Reaction Centre ◽  
Benzoic Acids ◽  
Carboxylate Group ◽  
The Given

Potentiometric titration at 25 °C has been used to measure the dissociation constants of 2- and 4-substituted benzoic acids with electron-acceptor substituents in methanol, N,N-dimethylformamide, acetonitrile, and acetone. But for a few exceptions, no significant differences have been found between the dissociation constants measured and those given in literature. Using the measured pKa values, those of 3-substituted derivatives taken from literature (measured in the same solvents) and those of 3- and 4-substituted derivatives measured in water, the so far missing substituent constants σi of NO and CH3SO substituents have been determined by Alternative Interpretation of Substituent Effects (AISE). The previously published relationships and the σi constants have been used to calculate the σm and σp constants for the given substituents and compare them with literature. The agreement was the better, the more reliable the corresponding Hammett substituent constant was. Using a non-linear regression model, we have analysed the structure of matrix of pKa values of ten 2-X-benzoic acids (X is electron-acceptor substituent) measured in the given organic solvents and in water. It has been found that in non-aqueous solvents the conjugate base of benzoic acid is stabilised by intramolecular hydrogen bond if X is COOH and SO2NH2 or electrostatic force if X is CH3SO. On the other hand, in water the carboxylate group is out of the plane of the benzene ring due to interaction between the solvated reaction centre and substituent, this being the case with all the substituents except for X = CHO, CH3CO, NO, and CN. In all the solvents used, intramolecular ring closure takes place between the carboxylate group and substituent X = CH3CO, CHO, and NO, this phenomenon being the most important in water.

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