AIM analysis, synthetic, kinetic and mechanistic investigations of the reaction between triphenylphosphine and dialkyl acetylenedicarboxylate in the presence of 3-methoxythiophenol

Abstract

Triphenylphosphine reacts with dialkyl acetylenedicarboxylates in the presence of 3-methoxythiophenol to generate stable phosphorus ylides. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. Quantum mechanical calculations were employed to check the stability of the two geometrical isomers in phosphorous ylide by natural population analysis (NPA), atoms in molecules (AIM) methods and CHelpG keyword. To determine the kinetic parameters and mechanistic investigation of the reaction, they were monitored by UV spectrophotometry. The second order fits were automatically drawn, and the value of the second order rate constants (k 2) were automatically calculated using standard equations. At the temperature range studied, the dependence of the second order rate constant (ln k 2) on reciprocal temperature was in good agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all the reactions. Furthermore, useful information was obtained from studies of the effect of solvent, structure of reactions (different alkyl groups within the dialkyl acetylenedicarboxylates), and also concentration of reactants on the rate of reaction. The proposed mechanism was confirmed according to the obtained experimental results, and a steady state approximation. The first (k 2) and third (k 3) steps of the reactions were recognized as the rate determining and fast steps, respectively on the basis of experimental data. Also, the activation parameters involving ΔG# , ΔS# and ΔH# were obtained for all the reactions. Triphenylphosphine reacts with dialkyl acetylenedicarboxylates in the presence of 3-methoxythiophenol to generate stable phosphorus ylides. Quantum mechanical calculations were employed to check the stability of the two geometrical isomers of phosphorous ylides.