The catalytic role of triphenylarsine in the formation of (Z)-Nvinyl Inorganic compound: an experimental mechanistic study

In the current work, the kinetics and mechanism of the reaction between dimethyl acetylendicarboxcylate 2 (DMAD) and phthalimide 3 (N-H heterocyclic compound) in methanol environment in the presence of triphenylarsine 1 (TPA) as a catalyst was undertaken using UV/vis spectrophotometry technique, for the generation of N- vinyl heterocyclic compound [1]. The reaction followed second-order kinetics and the partial orders of DMAD and phthalimide are one and one, respectively. Also, the fourth step (step 4, k4) of the reaction mechanism was recognized as a rate determining step (RDS). In the previous works, when triphenylphosphine (TPP) was employed instead of (TPA) as an another reactant (not catalyst) for the similar reaction with DMAD and N-H heterocyclic compounds to yield different ylides, the partial orders in related to DMAD, TPP and different N-H heterocyclic compounds were one, one and zero, respectively. Herein, on the contrary with the current work, the first step (step1, k1) of the reaction mechanism was determined as a rate determining step. In both the previous and current works, TPP or TPA, participates in the first step (step1, k1) of the reaction mechanism in order to react with DMAD, but TPA acts as a more stronger nucleophile than the TPP, hence the rate of the first step (step1, k1) speeds up remarkably in the current work. As a result, this step could not be a rate-determining step as well as the first step of the previous works, so the different reactivity and nucleophicity of TPA in comparison with TPP can influence kinetics and mechanism of the mentioned reaction, herein, this behavior has been described on competitive mechanism. From the temperature, concentration and solvent studies,the activation energy and the relevant activation parameters (Ea, ΔH‡, ΔS ‡ and ΔG‡) were calculated

Keywords:

Kinetics , Mechanism , UV Spectroscopy , phthalimide