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Article info. : 2006; 3(3) (pp 223~232)

 

UV Spectrophotometric Study of the Kinetics and Mechanism of the Reactions between Triphenylphosphine, Dialkyl Acetylenedicarboxylates and NH-Acid

S.M. Habibi Khorassani*, M.T. Maghsoodlou, A. Ebrahimi, H. Roohi and M. Zakarianezhad

Department of Chemistry, University of Sistan and Balouchestan, Zahedan, Iran

(Received 15 March 2006, Accepted 16 April 2006)

To determine the kinetic parameters of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of an NH-acid, such as 2,3-di-hydroxybenzaldehyde, the reactions were monitored by UV spectrophotometry. The second order fits were automatically drawn and the values of the second order rate constants (k2) were calculated using standard equations as part of the program. The dependence of the second order rate constant (lnk2) on the reciprocal temperature was in agreement with the Arrhenius equation, in the temperature range studied, providing the relevant plots to calculate the activation energy of all reactions. Furthermore, we evaluated the effects of solvent, structure of different alkyl groups within the dialkyl acetylenedicarboxylates, and their concentration on the rates of reactions. The proposed mechanism was confirmed by experimental results and steady-state approximation. The first step (k2) of the reaction was recognized as the rate determining step on the basis of experimental data.

Keywords: Phosphorus ylide, NH-acid, UV spectrophotometry, Kinetic parameters, Rate constant

 

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