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

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Title:Chemometric Analysis of Substituent Effects. XI. Solvent Effects on Dissociation of 2,6-Disubstituted Benzoic Acids
Creators:
Kulhánek, Jiří
Pytela, Oldřich
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 62, 6, pp. 913-924
Uncontrolled Keywords:Solvation, <i>ortho</i> Effect, Dissociation constants, Substituent effects

Abstract

Eleven symmetrically 2,6-disubstituted benzoic acids (with the following substituents: OCH<sub>3</sub>, OC<sub>2</sub>H<sub>5</sub>, OC<sub>3</sub>H<sub>7</sub>, OCH(CH<sub>3</sub>)<sub>2</sub>, OC<sub>4</sub>H<sub>9</sub>, CH<sub>3</sub>, F, Cl, Br, I, and NO<sub>2</sub>) 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.

Title:Chemometric Analysis of Substituent Effects. XI. Solvent Effects on Dissociation of 2,6-Disubstituted Benzoic Acids
Creators:
Kulhánek, Jiří
Pytela, Oldřich
Uncontrolled Keywords:Solvation, <i>ortho</i> Effect, Dissociation constants, Substituent effects
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:62
Number:6
Page Range:pp. 913-924
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc19970913UNSPECIFIED
ID Code:1173
Item Type:Article
Deposited On:06 Feb 2009 17:07
Last Modified:06 Feb 2009 16:07

Citation

Kulhánek, Jiří; Pytela, Oldřich (1997) Chemometric Analysis of Substituent Effects. XI. Solvent Effects on Dissociation of 2,6-Disubstituted Benzoic Acids. Collection of Czechoslovak Chemical Communications, 62 (6). pp. 913-924. ISSN 0010-0765

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