Quantum mechanical calculation clarified how the ylides exist in solution 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, di-tert-butyl acetylenedicarboxilate in the presence of protic/nucleophilic reagent, such as 2-aminothiophenol. To determine the kinetic parameters of the reaction, it was monitored by UV spectrophotometery. 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 reciprocal temperature was in a good agreement with Arrhenius equation. This provided the relevant plots to calculate the activation energy of the reaction. Furthermore, useful information was obtained from studies of the effect of solvent and concentration of reactants on the rate of reaction. Proposed mechanism was confirmed according to the obtained results and steady state approximation and first step (k2) of reaction was recognized as a rate determining step on the basis of experimental data.
Keywords: Stable phosphorus ylides, dialkyl acetylenedicarboxylates, Z and E isomers, AIM method
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