Aims and Objective:
The main objective of the kinetic investigation of the reaction among 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 the generation of 4-substituted 1, 4-dihydropyridine derivatives (product 5) was the recognition of
the most realistic reaction mechanism. The layout of the reaction mechanism studied kinetically by means of the UV-visible
spectrophotometry approach.
Materials and Methods:
Among the various mechanisms, only mechanism1 (path1) involving 12 steps was recognized as a
dominant mechanism (path1). Herein, the reaction between reactants 1 and 2 (kobs= 814.04 M-1
.min-1
) and also compound 3
and 4-H (kobs= 151.18 M-1
.min-1
) were the logical possibilities for the first and second fast steps (step1 and step2, respectively).
Amongst the remaining steps, only step9 of the dominant mechanism (path1) had substituent groups (X) near the reaction
centre that could be directly resonated with it.
Results and Discussion:
Para electron-withdrawing or donating groups on the compound 4-X increases the rate of the reaction
4 times more or decreases 8.7 times less than the benzaldehyde alone. So, this step is sensitive for monitoring any small or
huge changes in the reaction rate. For this reason, step9 is the rate-determining step of the reaction mechanism (path1).
Conclusion:
The recent result is the agreement with the Hammett description with an excellent dual substituent factor (r =
0.990) and positive value of reaction constant (ρ = +0.9502) which confirmed both the resonance and inductive effects
“altogether” contributed on the reaction centre of step9 in the dominant mechanism (path1).
