Abstract

Sayyed Mostafa Habibi-Khorassani*, Malektaher Maghsoodluo, Ali Ebrahimi, Younes Ghalandarzehi, Fatemeh Ghodsi and Osman Asheri

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 (k2 ) 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 k2 ) and (Ln k2 /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 (k2 , k3 ) 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* , 3S* ) or (2R* , 3R* )] or [(2S* , 3R* ) or (2R* , 3S* )] of phosphonate ester 4 at both the HF/6-31G(d,p) level and the B3LYP method with 6-311++G(d,p) basis set. The results showed that compound 4 with gauche arrangement and [(2S* , 3S* ) or (2R* , 3R* )] configuration is more stable than the anti arrangement with [(2S* , 3R* ) or (2R* , 3S* )] geometrie. In addition, experimental 1H, 13C and 31P NMR data along with X-ray crystallograpic data of compound 4 is consistent with the results obtained from theoretical calculations.

Stable phosphonate ester; NH-acid; Kinetic studies; AIM

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