Abstract
The epoxidation mechanism of α,β-unsaturated acids catalyzed by Na 2WO 4 or Na 2MoO 4 in aqueous solvents has been studied by means of kinetic experiments, MS, 31P NMR and 13C NMR. The results show Na 2WO 4 or Na 2MoO 4 and H 2O 2 can rapidly form the diperoxocomplex irreversibly in aqueous solvent. 31P NMR and kinetics study reveal that –P O in cis-1-propenylphosphonic acid (CPPA) can fast coordinate to the metal center (Mo or W) of the diperoxocomplex irreversibly to form a stable complex. The subsequent direct oxygen transfer from peroxo bond to double bond is a monomolecular process, thus the epoxidation is zero-order on CPPA. However, 13C NMR shows the –C O in α,β-unsaturated carboxylic acids cannot coordinate to metal center of the diperoxocomplex. Therefore, the oxygen transfer is a bimolecular process and the epoxidation is a first-order reaction on the acids. In the mechanism, the nucleophilic attack of double bond towards the peroxo bond is regarded as through a spiro-transition structure.
Published Version
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