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

Abstract

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 k 0 + + sπ* + aα + bβ. 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 σ 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.

Effects of solvent and structure on the reactivity of 2-substituted nicotinic acids with diazodiphenylmethane in aprotic solvents

“…When the obtained correlation results were compared with the previously published results for the corresponding 6-substituted nicotinic acids, 10 it was found that the solvent effect disposition was similar considering the dominant HBA effect. However, the percentage values for the non-specific and the HBD interactions were different, as the proton-donor ability had a larger influence on the 6-substituted acids.…”

“…[1][2][3][4][5] Related to previous studies [6][7][8][9][10] of the chemical behavior of pyridinecarboxylic acid, the reactivity of 2substituted nicotinic acids with the following substituents Cl (chloro), OH (hydroxy), CH 3 (methyl), Br (bromo) and SH (mercapto) was studied in its reaction 570 DRMANIĆ, NIKOLIĆ and JOVANOVIĆ with DDM. [1][2][3][4][5] Related to previous studies [6][7][8][9][10] of the chemical behavior of pyridinecarboxylic acid, the reactivity of 2substituted nicotinic acids with the following substituents Cl (chloro), OH (hydroxy), CH 3 (methyl), Br (bromo) and SH (mercapto) was studied in its reaction 570 DRMANIĆ, NIKOLIĆ and JOVANOVIĆ with DDM.…”

Synthesis, structure and solvatochromic properties of 5-(3- and 4-substituted phenylazo)-4,6-diphenyl-3-cyano-2-pyridones

“…By considering the equilibrium between the 2-pyridone and 2-hydroxypyridine tautomeric forms 15 in solvents of different polarity, it was found that increasing solvent polarity shifted the equilibrium towards the pyridone form. The effects of solvent dipolarity/polarizability and hydrogen-bonding on the absorption spectra of 3-cyano-4,6-diphenyl-5-(3-and 4-substituted phenylazo)-2--pyridones, and many other compounds, 17,18 can be interpreted by means of the linear solvation energy relationship (LSER) concept using a Kamlet-Taft Equation of the type: 19 ν = ν 0 + sπ* + bβ + aα 1, C).…”

The comparative study of linear solvatation energy relationship for the reactivity of pyridine carboxylic acids with diazodiphenylmethane in protic and aprotic solvents

“…The 6-hydroxynicotinic acid, unlike the 2-hydroxynicotinic acid, gave a successful correlation in the same solvents, with the expected arithmetic signs of the coefficients: 6-Hydroxynicotinic acid: 22 log k = -1.92 + (2.37±0.36)π* + (1.99±0.09)α -(2.20±0.51)β (23) R = 0.982, s = 0.26, n = 5 Due to the ability of forming strong hydrogen bonds between the oxygen and nitrogen on both carboxylic acids and the hydroxyl group, both compounds are insoluble in many solvents; however, the set of five solvents given here, in which they both dissolve, was found. The 6-hydroxynicotinic acid, unlike the 2-hydroxynicotinic acid, gave a successful correlation in the same solvents, with the expected arithmetic signs of the coefficients: 6-Hydroxynicotinic acid: 22 log k = -1.92 + (2.37±0.36)π* + (1.99±0.09)α -(2.20±0.51)β (23) R = 0.982, s = 0.26, n = 5 Due to the ability of forming strong hydrogen bonds between the oxygen and nitrogen on both carboxylic acids and the hydroxyl group, both compounds are insoluble in many solvents; however, the set of five solvents given here, in which they both dissolve, was found.…”