Abstract
The rate constant of the reaction of 2-chloroquinoxaline with piperidine was measured spectrophotometrically using different aqueous solutions containing DMSO or DMF. Whatever the experimental conditions used, this reaction follows pseudo first order kinetics and is not amine catalyzed. Furthermore, the second order rate constant, k(A), increases with increasing percentage of DMSO in the solution, in contrast to DMF. The k(A) values were then correlated with solvent parameters alpha, beta, pi*, E-T(N) and Y. Plots of log(10) k(A) against the reciprocal of the dielectric constant at 25 degrees C were found to be nonlinear in DMSO, while a linear relationship with a negative slope was found in the case of DMF. This difference between the solvents is presumably due to different solvation pathways between their initial and transition states. Thus, activation parameters Delta H-#, Delta S-# and Delta G(#) were evaluated and discussed to support this hypothesis. Finally, DFT calculations were performed, using the B3LYP functional and 6-311G(d,p) basis set, to determine optimum molecular geometry. IR, NMR spectra for both reactant and product and were then compared with experimental values.