Full Kinetics and a Mechanistic Investigation of the Synthesis of Tetrahydrobenzo[ b]pyrans in the Presence of Sodium Acetate as a Catalyst by a One-pot Three-component Reaction
Sayyed M. Habibi-Khorassani,
Malek T. Maghsoodlou,
Mohammad A. Kazemian,
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, ΔG#, ΔS# and ΔH#) 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.
Keywords: Dimedone, tetrahydrobenzo[b]pyran, Sodium acetate, 4-nitrobenzaldehyde, malononitrile, Kinetics and
Mechanistic Investigation, UV/Vis spectrophotometery.
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