Stable crystalline phosphorus ylideswere obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of NH-acid, such as 3,6-dibromocarbazole. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carboncarbon partial double bond, resulting from the conjugation of the ylide moiety with the adjacent carbonyl group. To determine the kinetic parameters of the reactions, they were monitored by UV spectrophotometry. The second-order fits were drawn, and the values of the second-order rate constant (k 2 ) were calculated using standard equations within the program. At the temperature range studied, the dependence of the second-order rate constant (ln k 2 ) on reciprocal temperature was in a good agreement with the Arrhenius equation. This provided the relevant plots to calculate the activation energy of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the Correspondence to: Sayyed Mostafa Habibi Khorassani;

The synthesis, theoretical study and a kinetics and mechanistic investigation are described as a one-pot condensation reaction between benzamide and acetylenic esters in the presence of triphenyphosphine to generate a novel stable phosphorus ylides. For the first time, theoretical calculations have been employed to assign the most stable isomers ( Z or E) of phosphorus ylides 4a-c by AIM and NBO theory, in which Z-4(a,b) are the more stable forms, whereas Z-4c appears as a single isomer. In these cases, the 1H, 13C and 31P NMR spectra of these ylides are consistent with the results obtained from theoretical calculations. Kinetic investigation of the new ylides was undertaken by UV. Useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the acetylenic esters), and also the concentration of reactants on the rate of reactions. The proposed mechanism was consistent with the results obtained; from the steady-state approximation, the first step ( k2) of the reaction was recognized as the rate-determining step on the basis of the experimental data.

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