Abstract
ABSTRACTThe kinetics and mechanism of the reaction between dimethyl acetylendicarboxylate (DMAD) and Meldrum's acid (MA) in the presence of triphenylarsine (TPA) as a catalyst were investigated in a methanol environment by the UV/vis spectrophotometry technique. In this work, the reaction followed second- order kinetics and the first and second steps of the reaction mechanism were recognized as the fast and rate-determining step (RDS), respectively. A significant point in this reaction “in comparison with previous work” is related to the change in behavior of the kinetics and reaction mechanism in the presence of triphenylarsine (TPA). Activation energy and parameters (Ea, ΔH‡, ΔS‡, and ΔG‡) were determined for the reaction and a comparison between ΔH‡ and TΔS‡ values showed that the reaction is entropy-controlled. High values of the activation Gibbs free energy indicated that the reaction was chemically controlled. Also, the large negative value of ΔS‡ implied an associative mechanism.
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