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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 |
