The kinetics of the reactions of 2-substituted nicotinic acids with diazodiphenylmethane in various alcohols

Abstract

The rate constants of 2-substituted nicotinic acids in reaction with diazodiphenylmethane (DDM) in eight alcohols at 30ºC have been determined. In order to explain the obtained results through solvent effects, the second order reaction rate constants (k) of the examined acids were correlated using the appropriate solvent parameters by the equation: log k = log k0 + af(e) + bs* + c ngH where f(e) is the measure of solvent ability as a dielectric to stabilize the separation of opposite charges in the activated complex, s* is the measure of solvent ability to stabilize proton in the initial state and ngH represents the ability of protic solvents to form hydrogen bond with the negative end of the ion-pair intermediate. These constants were correlated also by using solvatochromic equation of the form: log k = log k0 + sp* + aa + bb where p* is the measure of the solvent polarity, a represents the scale of the solvent hydrogen bond donor acidities (HBD) and b represents the scale of the solvent hydrogen bond acceptor basicities (HBA). The correlations of the kinetic data were carried out by means of multiple linear regression analysis. The results obtained for 2-substituted nicotinic acids were compared with the results for ortho-substituted benzoic acid under the same experimental conditions.

Keywords

• 2-substituted nicotinic acids
• kinetic measurements
• protic solvents
• solvent parameters
• diazodiphenylmethane