The separation of polar and steric effects. Part 14. Kinetics of the reactions of benzoic acid and of ortho-substituted benzoic acids with diazodiphenylmethane in various alcohols

The kinetics of decomposition of 1,3-bis(4-methylphenyl)triazene catalyzed with 13 substituted benzoic acids of various concentrations have been measured in 25 vol.% aqueous methanol at 25.0 °C. The rate constants observed (297 data) have be used as values of independent variable in a series of models of the catalyzed decomposition. For the catalytic particles were considered the undissociated acid, its conjugated base, and the proton in both the specific and general catalyses. Some models presumed formation of reactive or nonreactive complexes of the individual reactants. The substituent effect is described by the Hammett equation. The statistically best model in which the observed rate constant is a superposition of a term describing the dependence on proton concentration and a term describing the dependence on the product of concentrations of proton and conjugated base is valid with the presumption of complete proton transfer from the catalyst acid to substrate, which has been proved. The behaviour of 4-dimethylamino, 4-amino, and 3-amino derivatives is anomalous (lower catalytic activity as compared with benzoic acid). This supports the presumed participation of conjugated base in the title process.

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THE TRANSMISSION OF POLAR EFFECTS: PART II. THE KINETICS OF ESTERIFICATION WITH DIAZODIPHENYLMETHANE AND THE IONIZATION OF 3-SUBSTITUTED ACRYLIC ACIDS

Canadian Journal of Chemistry ◽

10.1139/v65-466 ◽

1965 ◽

Vol 43 (12) ◽

pp. 3354-3363 ◽

Cited By ~ 21

Author(s):

Keith Bowden

Keyword(s):

Butyl Alcohol ◽

Polar Effect ◽

Rate Coefficients ◽

Strengthening Effect ◽

Benzoic Acids ◽

Linear Free Energy ◽

Substituted Benzoic Acids ◽

Energy Relations ◽

Acrylic Acids ◽

Kinetics Of

The rate coefficients for the reaction with diazodiphenylmethane in ethanol, t-butyl alcohol, and ethyl acetate at 30° and the pKa values in water at 25° of fourteen 3-substituted acrylic acids have been determined. The effect of substitution is assessed by use of linear free energy relations. A definite incremental acid-strengthening effect solely due to cis-substitution is confirmed. This is not a "bulk" steric effect and is due solely to the orientation of substitution. The polar effect of a substituent is found to be approximately the same from the cis- or trans-position. An attempt is made to test the suggested mechanisms for the transmission of the polar effect. In the reactions studied the transmission of the polar effect in 3-substituted acrylic acid and ortho-substituted benzoic acids is approximately twice that of the meta- or para-substituted benzoic acids. This appears to be reasonably accommodated by a significant field effect.

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Mixed-dimer formation in binary systems of 4-substituted benzoic acids and structure considerations

Canadian Journal of Chemistry ◽

10.1139/v08-008 ◽

2008 ◽

Vol 86 (6) ◽

pp. 525-532 ◽

Cited By ~ 6

Author(s):

Maren Roman ◽

Annett Kaeding-Koppers ◽

Peter Zugenmaier

Keyword(s):

Benzoic Acid ◽

Crystalline Phase ◽

Liquid Crystalline ◽

Binary Systems ◽

Benzoic Acids ◽

Dimer Formation ◽

Crystalline Phases ◽

Cholesteric Phase ◽

Liquid Crystalline Phases ◽

Substituted Benzoic Acids

The phase behavior of binary systems of 4-substituted benzoic acids is governed by the formation of mixed dimers. This study was conducted to determine the effect of the components’ structural difference on mixed-dimer formation in crystalline and liquid-crystalline phases. The phase diagrams of two systems, with 4-[(S)-(–)-2-methylbutoxy]benzoic acid (MBOBA) as one component and 4-(hex-5-enoxy)benzoic acid (HOBA) and 4-(dec-9-enoxy)benzoic acid (DOBA), respectively, as the second component, were determined by differential scanning calorimetry, polarized-light microscopy, and X-ray diffraction. The MBOBA-HOBA system exhibited a cholesteric phase, two solid solutions, and above 58 °C for compositions between 40 and 80 mol% HOBA a crystalline phase of mixed dimers. The MBOBA-DOBA system showed a crystalline phase of mixed dimers at all compositions, a cholesteric phase, and a twisted smectic C phase, which was dominated by mixed dimers at 60 and 70 mol% DOBA. We conclude that liquid-crystalline phases are generally dominated by mixed dimers, but in crystalline phases the formation of mixed dimers is promoted by a greater difference in molecular structure. The crystal structure of two of the pure compounds MBOBA and DOBA and comparable compounds have been determined for an evaluation of the arrangements of the molecules in the crystal and liquid-crystalline state.Key words: benzoic acid, crystal arrangement, phase diagrams, liquid crystal.

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