252874-22-9Relevant articles and documents
Competitive behavior of nitrogen based axial ligands in the oxovanadium(IV)-salen catalyzed sulfoxidation of phenylmercaptoacetic acid
Kavitha, C.,Subramaniam, P.
, (2020/08/10)
The sulfoxidation of twelve phenylmercaptoacetic acids (PMAA) by H2O2 catalyzed by three oxovanadium(IV)-salen complexes, having varied substituents on PMAA and salen with regard to their position, size and inductive effect, has been performed spectrophotometrically in 100percent acetonitrile medium. Three nitrogen bases (NB), pyridine (Py), imidazole (ImH) and 1-methylimidazole (MeIm), were used as axial ligands. It has been found that the rate of sulfoxidation is not only tuned by the substituents on PMAA and salen, but it is also varied by the addition of nitrogen bases. The observed order of retardation found among the different nitrogen bases is ImH > MeIm > Py. The rate of reaction decreases with the increase in concentration of the NB axial ligands. The strongly binding ImH shows the least reactivity. Hydroperoxovanadium(V)-salen has been proposed as the sole active oxidizing species. A detailed mechanistic study reveals that the low rate constant values in the presence of the nitrogen base is due to the existence of competition of NB with H2O2 and PMAA during the formation of active species and the coordination of PMAA with active species, respectively. Both electron donating and electron withdrawing substituents on PMAA retard the sulfoxidation rate significantly. The Hammett correlation between the rate constants and substituent constants shows a non-linear concave downward curve which is explained by the existence of two different rate determining steps within the same mechanism; coordination of PMAA with the active species for electron withdrawing substituents and transfer of oxygen to PMAA for electron donating substituents. All the experimental observations are explained by proposing a suitable mechanism.
