TRIPHENYLARSINE AS AN EFFECTIVE CATALYST IN A MECHANISTIC INVESTIGATION OF TRANS-1, 2-DI (METHOXYCARBONYL)-6, 6- DIMETHYLSPIRO [2, 5] OCTANE-4, 8-DIONE FORMATION

The kinetics and mechanistic investigation of the reaction between dimethyl acetylendicarboxcylate (DMAD) and Dimedon in ethanol environment with triphenylarsine as a catalyst using UV/vis spectrophotometry was studied for generation of trans-1, 2-Di (methoxycarbonyl)-6, 6-dimethylspiro [2, 5] octane-4, 8-dione. Also, the effect of temperature and solvent on the rate of reaction were investigated. The reaction followed second-order kinetics and under pseudo-order conditions the partial order of DMAD and dimedon (CH) is one and one, respectively. Also, step 2 of the reaction mechanism was recognized as a rate determining step (RDS). Activation energy and parameters (Ea, ∆H‡, ∆S ‡ and ∆G‡) were determined and the comparison of ∆H‡ and T∆S‡ showed that the reaction is entropy-controlled. On the other hand, higher values of activation free energy from the Eyring equation indicated that the reaction was chemically controlled. Furthermore, the large negative value of ∆S‡ expressed that the reaction has an associated mechanism.