Kinetics of the reaction between methyl 2,4-dichloro-3,5-dinitrobenzoate and piperidine — Solvent effect

Abstract

The rate constant for the reaction of methyl 2,4-dichloro-3,5-dinitrobenzoate (1) with different piperidine concentrations have been measured spectrophotometrically in nine pure solvents, viz. methanol, ethanol, n-propanol, isopropanol, t-butyl alcohol, acetonitrile, dimethysulphoxide, dioxane and benzene at different temperatures to study the effect of the solvents. The kinetic results postulate three solvation models: (a) alkanol extensively solvating the amine and weakening the intramolecular hydrogen bonding in the intermediate; (b) the non-polar solvents enhance the intramolecular hydrogen bonding in the intermediate increasing the nucleophilicity of amine; (c) the dipolar aprotic solvents solvate the amine and timely solvating the intermediate by intermolecular hydrogen bond. The solvent parameters have been correlated with the rate constant for the reaction through linear free energy relationships. The adequacy of the multi-parametric scales as appropriate approaches to describe the solvent features in microscopic environments has also been analyzed.