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Kinetics study of the reaction between triphenylphosphine, dialkyl acetylenedicarboxylates and 2-mercaptobenzimidazole along with theoretical calculations: A mechanistic investigation

Mohammad Zakarianezhad, Hojjat Ghasempour, Sayyed Mostafa Habibi Khorassani, Malek Taher Maghsoodlou

In the recent work, stability of the Z- and the E- isomers were undertaken for the two rotational isomers of phosphorus ylides involving a 2- mercaptobenzimidazole [namely dimethyl 2-(2-mercaptobenzimidazole-syl)- 3-(triphenylphosphanylidene) succinate] by natural population analysis (NPA) and atoms in molecules (AIM) methods. Quantum mechanical calculationwas clarified howthe ylides exist in solution as amixture of the two geometrical isomers (Z- and E-) as amajor orminor form. In addition, kinetic studies were performed for the reaction between triphenylphosphine, dialkyl acetylenedicarboxilate in the presence of SHacid, such as 2-mercaptobenzimidazole by UV spectrophotometery technique. The values of the second order rate constant (k2) were calculated using standard equations within the program. All reactions repeated at different temperature range, the dependence of the second order rate constantwith temperature was in a good agreementwithArrhenius and Eyring equations. This provided the relevant plots to calculate the activation parameters (H, S and G) of all reactions. 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.