Solvent effects on aromatic nucleophilic substitutions. Part 4. Kinetics of the reaction of 1-chloro-2,4-dinitrobenzene with piperidine in protic solvents

Abstract

The kinetics of the reaction between 1-chloro-2,4-dinitrobenzene and piperidine were studied in 2-methylpropan-1-ol, propan-1-ol, propan-2-ol, butan-2-ol, benzyl alcohol, 2-phenoxyethanol, 2-methoxyethanol, and diethylene glycol at 15, 25, and 40 °C. The second-order rate coefficients, k_A, for the reaction in these solvents are not well correlated with the previously found relationship between the parameter E_T(30) and the k_A values for reaction in aprotic non-hydrogen-bond donor solvents.¹ Inter-and intra-molecular hydrogen-bond interactions in the pure solvent and between the solvent and the amine are relevant in determining the reaction rate. The reactivity in hydroxylic solvents is inversely proportional to the hydrogen-bond-donating ability of the solvent. Fifteen (protic and aprotic) solvents are well correlated by Swain's parameters A and B, although caution is recommended when this linear free energy relationship is used.