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Kinetics and a mechanistic investigation of the reaction between dimethyl acetylenedicarboxcylate (DMAD) and saccharin ( N – H  heterocyclic compound) has been spectrally studied in methanol environment in the presence of triphenylarsine ( TPA ) as a catalyst. Previously, in a similar reaction, triphenylphosphine ( TTP ) (instead of triphenylarsine) has been employed as a third reactant (not catalyst) for the generation of an ylide (final product) while, in the present work the titled reaction in the presence of  TPA  leaded to the especial N-vinyl heterocyclic compound with different kinetics and mechanism. The reaction followed second order kinetics. In the kinetic study, activation energy and parameters (Ea, ΔH ‡ , ΔS ‡  and ΔG ‡ ) were determined. Also, the structural effect of the  N – H  heterocyclic compound was investigated on the reaction rate. The result showed that reaction rate increases in the presence of isatin ( N – H  compound) that participates in the second step (step 2 ), compared to saccharin (another  N – H  compound). This was a good demonstration for the second step (step 2 ) of the reaction that could be considered as the rate- determining step (RDS). As a significant result, not only a change in the structure of the reactant ( TPA instead of TPP ) creates a different product, but also kinetics and the reaction mechanism have been changed.

chemistry central journal

Structural effects on kinetics and a mechanistic investigation of the reaction between DMAD and N–H heterocyclic compound in the presence of triphenylarsine: spectrophotometry approach