The function of triphenylarsine in catalysis of the (Z)-N-vinyl heterocyclic compound: an experimental mechanistic study

In this scrutiny the kinetics and process underlying the interaction between diethyl acetylendicarboxcylate (DEAD) and phthalimide (N-H heterocyclic compound) in methanol environment with triphenylarsine (TPA) as catalyst using UV/vis spectrophotometry. The impact of temperature and solvent on the reaction rate was studied. The reaction followed second-order kinetics, and the respective partial order of DEAD and phthalimide were one and one, accordingly. Furthermore, step۲ of the reaction mechanism was identified as the rate-determining step (RDS). In contrast, previous researches were performed with triphenylphosphine (TPP) as a reactant (not catalyst) instead of TPA, so partial orders in related to DEAD, TPP and different cases of acids were ۱, ۱ and zero, respectively, in addition step۱ was RDS. In recent work, TPA acted as a strong nucleophile, so in accordance with the experimental data was identified as a fast step. As a result of the change from TPP to TPA in the reaction environment, and subsequently its reactivity, the behavior of the kinetics and mechanism of the reaction was also affected. Based on the different mechanisms investigated in this study, activation energy and parameters (Ea, ΔH‡, ΔS ‡ and ΔG‡) were estimated, whereas the comparison of ΔH‡ with value of TΔS‡ revealed that the reaction was entropy-controlled. In addition, higher values of activation free Gibbs energy confirmed that the reaction was chemically controlled. Furthermore, the large negative value of ΔS‡ was indicative of the existence of a mechanism for the reaction.

کلیدواژه ها:

Kinetics ، Mechanism ، UV Spectroscopy ، phthalimide