No abstract

In this work, three speculative mechanisms of the reaction between triphenylphosphine and dimethyl acetylendicarboxylate in the presence of 3‐chloropentane‐2,4‐dione were energetically and thermodynamically developed using quantum mechanical calculations and were profoundly compared with stopped‐flow and UV spectrophotometry approaches. The third speculative mechanism that led to the five‐membered ring structure was experimentally and theoretically favorable. The five‐membered ring structure of product was characterized by X‐ray crystallographic data. Also, steps 1 and 2 of the third mechanism were determined as fast and rate‐determining steps, respectively. The experimental kinetic evidence of the formation and decay of intermediate in steps 1 and 2 (fast and rate‐determining steps, respectively) was compatible with theoretical data. Experimental kinetic data were recognized for overall reaction along with activation parameters for fast and rate‐determining steps of the reaction. Theoretical kinetic data (k and Ea) and activation parameters (ΔG≠, ΔS,≠ and ΔH≠) were calculated for each step and overall reactions.

The use of tartaric acid has many advantages such as mild reaction conditions, simple and readily available precursors and inexpensive catalyst. The proposed mechanism was confirmed by experimental results and a steady state approximation.

For the first time, kinetic studies were made of the reactions between triphenyl phosphite 1, dialkyl acetylenedicarboxylates 2 in the presence of NH-acid, such as 3, 4-dicholoro aniline (as a protic/nucleophilic reagent) 3 for the generation of compound 4 with gauche arrangement and [(2S * , 3S * ) or (2R * , 3R * )] configuration. To determine the kinetic parameters of the reaction, monitoring was conducted using UV spectrophotometery. The second order fits were automatically drawn and the values of the second order rate constant (k 2 ) were automatically calculated using standard equations within the program. All reactions were repeated at different temperature ranges, the dependence of the second order rate constant (Ln k 2 ) and (Ln k 2 /T) on the reciprocal temperature were in good agreement with Arrhenius and Eyring equations, respectively. This provided the relevant plots to calculate the kinetic and activation parameters (Ea, ΔH # , ΔS # and ΔG # ) of all reactions. Furthermore, useful information was obtained from studying the of the effect of solvent, structure of reactants (dialkyl acetylenedicarboxylates) and also concentration of reactants on the reaction rates. The proposed mechanism was confirmed according to the obtained results and steady state approximation. The first and third steps (k 2 , k 3 ) of all reactions were recognized as rate determining and a fast steps, respectively on the basis of experimental data. Herein, theoretical calculations have been employed for the assignment of the most stable isomers ([(2S

Extensive kinetic studies were performed to investigate the mechanism of the reaction between 4-methoxybenzaldehyde 1, malononitrile 2, and dimedone 3 in the presence of fructose as a catalyst in a mixture of water and ethanol. The synthesis reaction of tetrahydrobenzo[b]pyran followed second-order kinetics. The partial orders with respect to 1, 2 were one and one, respectively. Temperature effect has been investigated on the reaction rate, and relevant parameters have been determined with two linearized forms of Eyring equation. The proposed mechanism theoretical rate law were compatible with the experimental data. From the temperature, concentration and solvent studies, the activation energy (E a = 70.05 ± 1.39 kJmol