Full Kinetics and Mechanism Investigation for Generating 4-Substituted 1, 4- Dihydropyridine Derivatives in the Presence of Green Catalyst and Aqueous Medium: Experimental Procedure.

Abstract

The main objective of the kinetic investigation of the reaction between ethyl acetoacetate 1, ammoniumacetat 2, dimedone 3, and diverse substitutions of benzaldehyde 4-X, (X= H, NO2, CN, CF3, Cl, CH (CH3)2, CH3, OCH3, OCH3, and OH) for generating 4-substituted 1, 4-dihydropyridine derivatives (product 5) was to recognize the most realistic reaction mechanism. The layout of the reaction mechanism was studied kinetically via a UV-visible spectrophotometry approach. Among the various mechanisms, only mechanism1 (path1) involving 12 steps was recognized as a dominant mechanism (path1). Herein, the reactions between 1 and 2 (kobs= 814.04 M-1.min-1) and also between 3 and 4-H (kobs= 151.18 M-1.min-1) can be accepted as the first and second steps (step1 and step2) of the reaction mechanism, respectively. Amongst all steps, only step9 of the dominant mechanism (path1) comprised substituent groups (X) near the reaction center. Para electron-withdrawing or donating groups on the compound 4-X increased the rate of the reaction 4 times more or decreased 8.7 times less than the benzaldehyde alone. So, this step is sensitive for monitoring any small or huge changes in the reaction rate. Accordingly, step9 is the rate-determining step of the reaction mechanism (path1). The recent result is in agreement with the Hammett description of an excellent dual substituent factor (r = 0.990) and positive value of reaction constant (ρ= +0.9502), which confirms that both the resonance and inductive effects "altogether" contribute to the reaction center of step9 in the dominant mechanism (path1).