Substituent effects. 7. Microscopic dissociation constants of 4-amino- and 4-(dimethylamino)benzoic acid

1981 ◽  
Vol 46 (4) ◽  
pp. 653-657 ◽  
Author(s):  
B. Van de Graaf ◽  
A. J. Hoefnagel ◽  
B. M. Wepster
Keyword(s):  
Benzoic Acid ◽  
Dissociation Constants ◽  
Substituent Effects

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.

Chemometric Analysis of Substituent Effects. XII. Application of Relationship Between 2- and 4-Substitution of Benzene Ring to Study ortho Effect in Selected Compounds with Different Reaction Centres

1999 ◽  
Vol 64 (10) ◽  
pp. 1617-1628 ◽  
Author(s):  
Oldřich Pytela ◽  
Ondřej Prusek
Keyword(s):  
Hydrogen Bond ◽  
Benzoic Acid ◽  
Electron Pair ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Reaction Centre ◽  
Benzoic Acids ◽  
Hydrogen Bond Formation ◽  
Latent Structures ◽  
Substituted Benzoic Acids

Three model compounds have been selected to study the relationship between ortho and para substitution: benzoic acid, phenol, and aniline. Sixteen substituents have been chosen involving also those capable of potential interaction between ortho substituent and the reaction centre. For the combinations given, literature presents 25 pairs of data obtained by measuring a particular process for both the ortho and para substituted derivatives. The missing dissociation constants of 16 ortho substituted benzoic acids in water and ethanol and 16 para substituted benzoic acids in dimethyl sulfoxide and pyridine have been measured by potentiometric titration. The data matrices were submitted to analysis by the methods of projection of latent structures (PLS) and principal component analysis (PCA). It has been found that the substituent effects from ortho and para positions have the same character unless the ortho substituents interact with the reaction centre. Such interactions can change the experimentally found value by as much as 20% of its magnitude. The most significant interaction is a hydrogen bond formation. Out of the three models studied the most extensive interactions are present in benzoic acid, whereas almost none were observed in aniline. The capability of donation of electron pair to a hydrogen bond decreases in the substituent series COCH3 > SO2CH3 > NO2. The capability of donation of proton to a hydrogen bond with electron-pair donor decreases in the substituent series OH > NHCOCH3 ≈ SH > NH2 > SO2NH2.

Effects of Medium and Substituents on Dissociationof 4,4'-Disubstituted Bis(benzenesulfon)imides

1996 ◽  
Vol 61 (8) ◽  
pp. 1205-1214 ◽  
Author(s):  
Miroslav Ludwig ◽  
Pavel Štverka
Keyword(s):  
Latent Variables ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Principal Component ◽  
H Nmr ◽  
Base Process ◽  
Elemental Analyses ◽  
Substituent Constants ◽  
Model Substances ◽  
Strong Acids

Ten 4,4'-disubstituted bis(arenesulfon)imides of the general formula XC6H4SO2NHSO2C6H4X have been synthesized and their structures confirmed by their 1H NMR spectra. Elemental analyses are presented for the compounds not yet described. The dissociation constants of these model substances have been measured potentiometrically in pyridine, dimethylformamide, methanol, ethanol, propylene carbonate, acetone, acetonitrile, 1,2-dichloroethane and tetramethylene sulfone. The pKHA values obtained have been correlated with three sets of the Hammett substituent constants and the results have been used to discuss the solvent and substituent effects on the dissociation of the compounds studied. Sulfonimides with electron-acceptor substituents behave as rather strong acids in some solvents (pyridine, dimethylformamide, methanol and ethanol), whereas normal substituent dependences are found in other solvents. The experimental data have also been interpreted with the help of the statistical methods based on latent variables. From the calculations it follows that only the first principal component, which correlates well with the substituent constant sets adopted, is statistically significant in describing the substituent effect on the acid-base process studied.

scholarly journals Substituent Effects on the Dissociation Constants of 1-Aryl-5-hydroxy-2-hydroxymethyl-4-pyridones

1983 ◽  
Vol 56 (6) ◽  
pp. 1879-1880
Author(s):  
Kimiaki Imafuku ◽  
Kumio Takahashi ◽  
Hisashi Matsumura
Keyword(s):  
Dissociation Constants ◽  
Substituent Effects

Substituent effects on polarographic reduction of some photographic color intermediates

1976 ◽  
Vol 54 (8) ◽  
pp. 1205-1210 ◽  
Author(s):  
Ahmad S. Shawali ◽  
Bahgat E. El-Anadouli
Keyword(s):  
Dissociation Constants ◽  
Substituent Effects ◽  
Protonated Form ◽  
Acid Dissociation ◽  
Polarographic Reduction ◽  
Substituent Constant ◽  
Acid Dissociation Constants ◽  
Controlled Potential Electrolysis ◽  
Half Wave ◽  
Controlled Potential

Polarographic reduction of two series of benzoylacetanilides has been investigated in 40% (by volume) ethanolic Britton–Robinson buffers. One series (A) contains substituents on the anilide moiety, and the second (B) has substituents on both the anilide and benzoyl moieties. Polarographic controlled-potential electrolysis data indicate that the electroactive species in both series is the protonated form (ArCOCH2CONHAr′)H+. The reduction half-wave potentials of anilides of series A were found to be independent of the nature of the substituent, whereas those of series B show a good linear relationship when plotted vs. the σ substituent constant of the substituent on the benzoyl moiety (ρ = 0.284, r = 0.995). Values of the acid dissociation constants of the keto (K1) and enol (K2) tautomers of the anilides of series A were calculated; unlike their E1/2 values, the pK1 data show a linear correlation with the Hammett substituent constant, σ. The pK2 values show, however, little variation with σ.

A Study of Transmission Effects of Sulfonyl and Carbonyl Groups

1995 ◽  
Vol 60 (5) ◽  
pp. 841-850 ◽  
Author(s):  
Miroslav Ludwig ◽  
Patrik Pařík ◽  
Jiří Kulhánek
Keyword(s):  
Latent Variables ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Principal Component ◽  
Carbonyl Groups ◽  
H Nmr ◽  
Deviation Analysis ◽  
Substituent Constants ◽  
The Difference ◽  
Latent Structures

Seventeen p-substituted N-phenylsulfonylbenzamides of general formulas XC6H4SO2NHCOC6H5 and C6H5SO2NHCOC6H4X have been synthesized and their structure has been confirmed by elemental analysis and 1H NMR spectra. The dissociation constants of all the compounds have been measured by potentiometric titration in methanol, acetonitrile, dimethylformamide, dimethyl sulfoxide, and pyridine. The obtained pKHA values have been correlated with three sets of Hammett substituent constants using simple or double linear regression. The solvent and substituent effects are discussed on the basis of experimental results, and the difference between the substituent effects from sulfonamide and benzamide sections is evaluated. It has been found that due to the extensive delocalization of negative charge in the conjugated base the transmission effects of carbonyl and sulfonyl groups on the transmission of substituent effect are roughly the same. The experimental data have been interpreted by the methods with latent variables: the principal component analysis (PCA), the conjugated deviation analysis (CDA), and the method of projection to latent structures (PLS). The results obtained by these procedures were similar.

Ortho Effect in Dissociation of Substituted N-Phenylbenzenesulfonamides

2001 ◽  
Vol 66 (9) ◽  
pp. 1380-1392 ◽  
Author(s):  
Jiří Nádvorník ◽  
Miroslav Ludwig
Keyword(s):  
Experimental Data ◽  
Latent Variables ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Principal Component ◽  
Steric Effects ◽  
Deviation Analysis ◽  
Acid Base Equilibrium ◽  
The Difference ◽  
Electronic And Steric Effects

Twenty-five 2,2'-disubstituted N-phenylbenzenesulfonamides (2-X-C6H4SO2NHC6H4-Y-2') were synthesised and their purity checked by elemental analysis. This set of model substrates involved all possible combinations of methoxy, methyl, hydrogen, chloro, and nitro substituents. The dissociation constants of the sulfonamides were determined by potentiometric titration in methanol, pyridine, dimethyl sulfoxide, N,N-dimethylformamide, acetone, and acetonitrile. The dissociation constants pKHA obtained were correlated with various sets of substituent constants describing electronic and steric effects of the substituents, and the statistically treated data were used to discuss the contribution of the substituent effects in the dissociation and the difference between the effects transmitted from the two rings. A linear regression model explaining 99% of the variability of experimental data in all the solvents has been found and discussed. Moreover, the experimental data were also interpreted by the methods using latent variables, the principal component analysis (PCA) and conjugated deviation analysis (CDA), and two latent variables were shown to be statistically significant in the description of dissociation. The first obviously describes common action of electronic and steric effects of substituents; the other probably concerns a combined effect of substituent and solvent on the position of acid-base equilibrium.

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