Water–acetone Media Enforced Chemoselective Synthesis of 2-substituted Pyrrole Stable Phosphorus Ylides from Reaction between Pyrrole and Acetylenic Esters in the Presence of Triphenylphosphine

Kinetic Spectrophotometric Method for the 1,4-Diionic Organophosphorus Formation in the Presence of Meldrum's Acid: Stopped-Flow Approach

The kinetics of the reaction between triphenylphosphine (TPP) and dimethyl acetylenedicarboxylate (DMAD) in the presence of Meldrum’s acid (MA) for the generation of the 1,4-diionic organophosphorus compound has been investigated using the stopped-flow and UV-VIS spectrophotometry techniques. The first step of the reaction between TPP and DMAD for the generation of (I₁) in ethanol was followed by the stopped-flow apparatus. This step was recognized as a fast step. The reaction between the intermediate (I₁) and MA showed first-order kinetics, and it was followed by the UV-VIS spectrophotometry technique. The activation parameters for the slow step of the proposed mechanism were determined using two linearized forms of the Eyring equation. From the temperature, concentration and solvent studies, the activation energy (Ea = 20.16 kJ·mol⁻¹) and the related activation parameters (ΔG^‡ = 71.17 ± 0.015 kJ·mol⁻¹, ΔS^‡ = −185.49 ± 0.026 J·mol⁻¹ and ΔH^‡ =17.72 ± 0.007 kJ·mol⁻¹) were calculated. The experimental data indicated that the reaction was zero-order in MA and second-order overall. The proposed mechanism was confirmed with the observed kinetic data obtained from the UV-VIS and stopped-flow techniques.

Full kinetics investigation of the formation reaction of phosphonate esters in the gas-phase: a theoretical study

In the present work, the proposed multiple-mechanisms have been investigated theoretically for the reaction between triphenyl phosphite and dimethyl acetylenedicarboxylate in the presence of N-H acid such as aniline for generation of phosphonate esters using ab initio molecular orbital theory in gas phase. The profile of the potential energy surface was constructed at the HF/6-311G(d,p) level of theory. The kinetics of the gas phase reaction was studied by evaluating the reaction path of various mechanisms. Between 12 speculative proposed mechanisms {step₁, step₂ (with four possibilities), step₃ (with three possibilities), and step₄} only the third speculative mechanism was recognized as a desirable mechanism. Theoretical kinetics data involving k and E(a), activation (ΔG(‡), ΔS(‡) and ΔH(‡)), and thermodynamic parameters (ΔG°, ΔS° and ΔH°) were calculated for each step of the various mechanisms. Step₁ of the desirable mechanism was identified as the rate determining step. Comparison of the theoretical desirable mechanism with the rate law that has been previously obtained by UV spectrophotometry experiments indicated that the results are in good agreement.

Theoretical, Kinetic and Mechanistic Studies of the Reaction between Dialkyl Acetylenedicarboxylates, Triphenylphosphine and Pyrrole in Organic Solvents

The kinetics of the reaction between triphenylphosphine, dialkyl acetylenedicarboxylates and pyrrole in dry organic solvents at different temperatures have been studied spectrophotometrically. The observed overall second rate constant ( k2)for reaction decreases with decreasing solvent dielectric constant and media temperature; k2 follows the Arrhenius equation, and the overall reaction is first order in both the dialkyl acetylenedicarboxylate and triphenylphosphine concentrations. The proposed mechanism has been evaluated, and the activation parameters Δ G≠, Δ S≠ and Δ H≠ for the first, rate-determining step, as an elementary reaction have been determined on the basis of Eyring equation. In addition, the Z- and E-isomers have been optimized at HF and B3LYP levels with the 6-311++G** basis set; the more stable is the E-isomer, in agreement with experimental data. Furthermore, to better understand the intramolecular interactions, atoms in molecules (AIM) calculations and natural population analysis (NPA) methods have been carried out. The 1H, 13C, and 31P NMR data of these ylides are consistent with results obtained from theoretical calculations.

Synthesis of Stable Phosphorus Ylides from 6-Chloro-2-Benzoxazolinone and Kinetic Investigation of the Reactions by Uv Spectrophotometry

Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reactions between triphenylphosphine and dialkyl acetylenedicarboxylates, in the presence of an NH-acid, such as 6-chlorobenzoxazolinone. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from 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 ( k2) were calculated automatically using standard equations within the program. Over the temperature range studied, the dependence of the second order rate constant (Ln k2) on reciprocal temperature was in a good agreement with the Arrhenius equation, leading to the activation energies of all reactions. Furthermore, useful information was obtained from studies of the effect of solvent, the structure of reactants (different alkyl groups within the dialkyl acetylenedicarboxylates) and also the concentration of reactants on the rate of reactions. The proposed mechanism is consistent with the results obtained and the steady state approximation, and the first step ( k2) of reaction was recognized as the rate-determining step on the basis of experimental data.