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

The rate constants for the reactions of diazodiphenylmethane (DDM) with 2-substituted nicotinic acids in nine aprotic solvents at 30 degree C were determined. The obtained second order rate constants in aprotic solvents were correlated using the Kamlet-Taft solvatochromic equation in the complete form: log k = log k sub(0) + s capital pi * + a alpha + b beta . The correlations of the kinetic data were realized by means of multiple linear regression analysis. The obtained results were analyzed in terms of the initial and the transition state of the reaction and compared with previously determined kinetic data for nicotinic acid. The signs of the equation coefficients (s, a and b) are in agreement with the reaction mechanism and the influence of the solvent on the reaction rate is discussed based on the correlation results. The mode of the transmission of the sub-stituent effect is discussed in light of the contribution of solute-solvent interaction to the reactivity of the acid. The substituent effect was additionally analyzed by the Hammett equation, log k = rho sigma + log k sub(0).