Mechanistic investigation of the reaction between triphenylphosphine, dialkyl acetylenedicarboxylates and pyridazinone: a theoretical, NMR and kinetic study

Quantum mechanical calculations were used to clarify how the phosphorus ylides exist as a mixture of the two geometrical isomers (Z- and E-) as a major or minor form. In addition, kinetic studies were made for the reaction between triphenylphosphine and di-alkyl acetylenedicarboxylates in the presence of protic/nucleophilic reagent, such as pyridazinone. To determine kinetic parameters, the reaction was monitored by UV spectrophotometry. The values of the second order rate constant (k (2)) were calculated using standard equations. Useful information was obtained from studies of the solvent effect, the structure of reactants (different alkyl groups within the structure of dialkyl acetylenedicarboxylates) 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 (k (2)) and third (k (3)) steps of reactions were recognized on the basis of experimental data as the rate determining and fast steps, respectively.