Affiliation: Department of Chemistry, The University of Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran.
Sodium acetate effectively catalyzes the three component reaction between 4-nitrobenzaldehyde, malononitrile and dimedone for the formation of corresponding pyran annulated heterocyclic systems. This method offers the advantages of proceeding in neutral and mild environmental conditions, lack of toxicity, short reaction time, giving high to excellent yields of the products and simple work-up. Moreover, for the first time, an investigation of the kinetics and mechanism was made for the reaction between 4-nitrobenzaldehyde 2, malononitrile 3 and dimedone 1 compounds in the presence of sodium acetate as a catalyst. For determining the kinetics parameters of the reactions, they were monitored using UV/Vis spectrophotometery. The second order rate constant (k1) was automatically calculated by the standard equations contained within the program. In the studied temperature range, the second order rate constant depended (Lnk1, Lnk1/T) on reciprocal temperature was in good consistency with Arrhenius and Eyring equations, respectively. This data provided the suitable plots for calculating the activation energy and parameters (Ea, Δ G# , ΔS # and Δ H #) of the reaction. Furthermore, from studying the effect of solvent, concentration and catalyst on the reaction mechanism, useful information was obtained. The results showed that the first step of the reaction mechanism is a rate determining step (RDS). The mechanism which we proposed was confirmed in accordance with experimental data form UV/Vis experiment and also the steady state assumption.