scholarly journals Investigation of the reactivity of 4-pyrimidinecarboxylic, 6-hydroxy-4-pyrimidinecarboxylic and 5-hydroxyorotic acids with diazodiphenylmethane in various alcohols: Part III

2007 ◽  
Vol 72 (3) ◽  
pp. 205-214 ◽  
Author(s):  
Fathi Assaleh ◽  
Aleksandar Marinkovic ◽  
Sasa Drmanic ◽  
Bratislav Jovanovic
Keyword(s):  
Solvent Effects ◽  
Spectrophotometric Method ◽  
Rate Constants ◽  
Alkyl Group ◽  
Relative Permittivity ◽  
Reaction Rate ◽  
Hydrogen Atoms ◽  
Protic Solvents ◽  
Hydroxybenzoic Acids ◽  
Polar Constant

Rate constants for the reaction of diazodiphenylmethane (DDM) with 4-pyrimidinecarboxylic, 6-hydroxy-4-pyrimidinecarboxylic and 5-hydroxyorotic acids were determined in twelve protic solvents at 30 ?C using the well known UV-spectrophotometric method. The second order rate contants for the examined acids were correlated using the appropriate solvent parameters by the equation log k = log k0 + af(e) + bs * + cngH were f(e) is the Kirkwood function of relative permittivity [(e-l)/(2e + 1 )], s * is the Taft polar constant for the alkyl group R in the alcohol ROH, and nyH is themumber of hydrogen atoms in the (-position in the alcohol. The results obtained for the investigated acids were compared with the corresponding results for benzoic, 2- and 3-hydroxybenzoic acids and the influence of the structure of the investigated acids on the reactivity in hydroxylic solvents is discussed. It was also possible to evaluate and distinguish the specific and non-specific solvent effects and their influence on the reaction rate.

scholarly journals Investigations of the reactivity of pyridine carboxylic acids with diazodiphenylmethane in protic and aprotic solvents, Part I: Pyridine mono-carboxylic acids

2005 ◽  
Vol 70 (4) ◽  
pp. 557-567 ◽  
Author(s):  
Aleksandar Marinkovic ◽  
Sasa Drmanic ◽  
Bratislav Jovanovic ◽  
Milica Misic-Vukovic
Keyword(s):  
Carboxylic Acids ◽  
Rate Constants ◽  
Kinetic Data ◽  
Reaction Rate ◽  
Linear Regression Analysis ◽  
Multiple Linear Regression Analysis ◽  
Aprotic Solvents ◽  
Solvent Parameters ◽  
Protic Solvents ◽  
Pyridine Carboxylic

Rate constants for the reaction of diazodiphenylmethane with isomeric pyridine carboxylic acids were determined in chosen protic and aprotic solvents at 30 ?C, using the well known UV spectrophotometric method. The values of the rate constants of the investigated acids in protic solvents were higher than those in aprotic solvents. The second order rate constants were correlated with solvent parameters using the Kamlet-Taft solvatochromic equation in the form: logk = logk0 + s?*+ a? + b?. The correlation of the obtained kinetic data were performed by means of multiple linear regression analysis taking appropriate solvent parameters. The signs of the equation coefficients were in agreement with the postulated reaction mechanism. The mode of the influence of the solvent on the reaction rate in all the investigated acids are discussed on the basis of the correlation results.

scholarly journals Effects of solvent and structure on the reactivity of 6-substituted nicotinic acids with diazodiphenylmethane in aprotic solvents

2009 ◽  
Vol 74 (12) ◽  
pp. 1359-1370 ◽  
Author(s):  
Sasa Drmanic ◽  
Aleksandar Marinkovic ◽  
Bratislav Jovanovic
Keyword(s):  
Rate Constants ◽  
Substituent Effect ◽  
Reaction Rate ◽  
Linear Regression Analysis ◽  
Multiple Linear Regression Analysis ◽  
Aprotic Solvents ◽  
Solvent Interaction ◽  
Protic Solvents ◽  
Linear Solvation Energy ◽  
Nucleophilic Solvation

The rate constants for the reactions of diazodiphenylmethane (DDM) with 6-substituted nicotinic acids in aprotic solvents at 30?C were determined. The obtained second order rate constants in aprotic solvents, together with literature data for benzoic and nicotinic acids in protic solvents, were used for the calculation of solvent effects, employing the Kamlet-Taft solvatochromic equation (linear solvation energy relationship - LSER) in the form: log k = log k0 + + s?*+ a? + b?. The correlations of the kinetic data were performed by means of multiple linear regression analysis taking appropriate solvent parameters. The sign of the equation coefficients (s, a and b) were in agreement with the postulated reaction mechanism, and the mode of the solvent influences on the reaction rate is discussed based on the correlation results. A similar contribution of the non-specific solvent effect and electrophilic solvation was observed for all acids, while the highest contribution of nucleophilic solvation was influenced by their high acidity. Correlation analysis of the rate data with substituent ?p parameters in an appropriate solvent using the Hammett equation was also performed. The substituent effect on the acid reactivity was higher in aprotic solvents of higher dipolarity/polarizability. The mode of the transmission of the substituent effect is discussed in light of the contribution of solute-solvent interaction on the acid reactivity.

Solvent Effects on the Kinetics and Mechanism of the Acid-Catalysed Hydrolysis of Diterf.-butylsuccinate in Dioxane-Water Mixtures

1985 ◽  
Vol 40 (1) ◽  
pp. 84-91 ◽  
Author(s):  
Adel N. Asaad ◽  
Fayez Y. Khalil
Keyword(s):  
Dielectric Constant ◽  
Solvent Effects ◽  
Rate Constants ◽  
Mixed Type ◽  
Reaction Rate ◽  
Solvent Composition ◽  
Water Molecules ◽  
Molecular Dipole ◽  
First Order ◽  
Hydrolysis Of

The acid-catalysed hydrolysis of ditert.-butylsuccinate in dioxane-water mixtures proceeds via consecutive first-order reactions. The rate constants kI and kII corresponding to the two steps decrease with increasing dioxane content of the medium. After reaching a minimum at 90% (w/w) dioxane, both rate constants increase again with further addition of dioxane. The kinetic ratio kI/kII is smaller than the statistical value 2.0, and is markedly affected both by solvent composition and temperature. The maximum concentration of the intermediate half ester decreases with increasing dioxane content. The observed activation energies EI and EII of the two steps of the reaction are largely dependent on temperature as well as solvent composition indicating a mixed type of bond fission represented by the AAl 1 and AAC 2 mechanisms, whose relative contributions in the overall rate constants kI and kIIcould be calculated on the basis of the number of water molecules incorporated in the corresponding transition states. The effect of bulk dielectric constant on the reaction rate was investigated in the light of the available electrostatic theories and showed the reaction to be an ion-molecular dipole type of interaction. The activation thermodynamic parameters were computed and discussed as criteria of solvent effect and mechanism.

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