Theoretical, NMR study, kinetics and a mechanistic investigation of the reaction between triphenylphosphine, dialkyl acetylenedicarboxylates and acetyl acetone

In the present work, a quantum mechanical calculation was clarified as to how the ylides exist in solution as a mixture of two geometrical isomers (Z- and E-) in a major or minor form. In addition, kinetic studies were undertaken for the reaction between triphenylphosphine, di-tert-butyl acetylenedicarboxylate in the presence of a protic/nucleophilic reagent, such as acetyl acetone. To determine the kinetic parameters of the reaction, it was monitored by UV spectrometry. The values of the second order rate constant (k2) were calculated using standard equations within the program. At the temperature range studied, the dependence of the second order rate constant (Ln k2) on the reciprocal temperature was in a good agreement with the Arrhenius equation. This provided relevant plots for calculating the activation energy of the reaction. Furthermore, useful information was obtained from studies of the effect of solvents, the structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylate) and also the concentration of reactants on the rate of reaction. The proposed mechanism was confirmed according to the obtained results and steady state approximation. The first and third (k3) steps of the reaction were recognized as the determining rates and fast steps, respectively, on the basis of experimental data.