Hydrocarbon oxidation using molecular oxygen and hydrogen peroxide catalyzed by transition metal complexes.

摘要

The catalytic activity of coordination complex [Fe(4,7-diphenyl-1,10-phenanthroline) 3](SO3CF3)2 (1) has been investigated in the autoxidation of cumene in the presence of molecular oxygen. Reaction products include 2-phenyl-2-propanol, cumyl hydroperoxide, acetophenone, and traces of dicumyl peroxide. Parallel experiments were done comparing the catalytic activity of 1 to that of a fluorinated iron porphyrin (tetra-pentafluorophenylporphyrin iron(III) chloride (2), and the catalytic activities of 1 and 2 are comparable. Our detailed kinetic studies and UV-visible spectrophotometry support a radical autoxidation mechanism, in which the catalytic decomposition of alkyl hydroperoxides generates free-radical autoxidation chain carriers as described previously for halogenated porphyrin catalysts. The kinetics of the disproportionation of cumyl hydroperoxide were determined, and the catalytic rate constants for 1 and 2 were incorporated into a complete kinetic model that fits both autoxidation and peroxide-decomposition data. The inactivity of the Ru analog of 1 and other experiments suggest that ligand dissociation is crucial in the activation of 1. Related FeL 3X2, FeL2X2 (L=substituted 1,10-phenanthroline; X=anionic counter-ion), and FeLnXn (L=tetra,penta,hexa-dentate nitrogen donor ligands) were also investigated and their catalytic reactivity examined in the context of the metal catalyzed peroxide decomposition mechanism.; The advantages of using bicarbonate activated peroxide (BAP) versus H 2O2 alone as the oxidant in the presence of known epoxidation catalysts were investigated. The room-temperature epoxidation of sulfonated styrene in water was catalyzed by Mn(III)porphyrin/BAP, and resulted in formation of the epoxide with high conversion and selectivity. The rate of epoxidation catalyzed by Mn(III)porphyrin/BAP was found to be comparable to the free Mn2+/BAP system, suggesting catalyst decomposition. The MnTMPyP degraded quickly under the reaction conditions, releasing free Mn2+ into the solution. Presumably the resulting epoxide was formed though the well-known free manganese-catalyzed pathway.; Asymmetric epoxidation of styrene catalyzed by Jacobson's catalyst using BAP as an oxidant was also studied. Moderate enantioselectivity was achieved in a biphasic solvent system. Other anionic salts such as AcO- resulted in similar product enantioselectivity, suggesting that (unlike in the free Mn2+/BAP system), peroxymonocarbonate (peroxy acid formed in the BAP system) was not essential in forming the active catalytic species.