Mechanism Investigation of Stable Phosphorus Ylides Derived from Saccharine in the Presence of Different Dialkyl acetylenedicarboxylates: Experimental and Theoretical Study

Abstract

In the current work, kinetics studies were made of the reactions between triphenylphosphine 1, dialkyl acetylenedicarboxylates 2 in the presence of NH-acid, such as Saccharine 3. The kinetic parameters of all reactions were determined by UV spectrophotometry. The second order fits were drawn and the values of the second order rate constant (k2) were calculated using standard equations. All reactions were repeated at different solvents and temperatures. Dependence of the second order rate constant (ln k2) and (ln k2/T) on reciprocal temperature was in good agreement with Arrhenius and Eyring equations. This provided the relevant plots to calculate the activation parameters (Ea, ΔH#, ΔS# and ΔG#) of all reactions. Furthermore, useful information was obtained from the studies of the effect of solvent, the structure of reactants (dialkyl acetylenedicarboxylates) and also the concentration of reactants on the reaction rates. Proposed mechanism was confirmed according to the obtained results and steady-state approximation. First and third steps (k2 and k3) of all reactions were recognized as a rate-determining and fast steps in the reaction mechanism, respectively, on the basis of experimental data. In addition, theoretical study and the stability of the dichloromethane were undertaken for the two rotational isomers of phosphorus ylides involving Saccharine by natural population analysis and atoms in molecules methods. Quantum mechanical calculations clarified how the ylides exist in solution as a mixture of the two geometrical isomers (Z and E) as a minor or major form.