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https://hdl.handle.net/2142/70360
Description
Title
Shape Selective Oxidations of Hydrocarbons
Author(s)
Cook, Bruce Randall
Issue Date
1987
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Abstract
Tetrakis-5,10,15,20-(2',4',6'-triphenylphenyl)porphyrinate (TTPPP) manganese(III) and iron(III) acetate were both found to be shape selective alkane hydroxylation catalysts when iodosobenzene was used as oxidant. The selectivity observed was the same when these catalysts were used with metachloroperoxybenzoic acid, demonstrating the intermediacy of a common manganese porphyrin based oxidant. Primary selectivity was found to be diminished for FeTTPPP(OAc) relative to MnTTPPP(OAc), consistent with a greater amount of C-H bond breaking in the iron transition state. Shape selectivity was used as a sensitive probe for metalloporphyrin involvement in the hydroxylation transition state. Both tert-butylhydroperoxide and trifluoroethanol solubilized pentafluoroiodosobenzene were found not to be shape selective with manganese porphyrin catalysts indicating radical chain oxidation.
MnTTPPP(OAc) and FeTTPPP(OAc) were also found to be shape selective epoxidation catalysts for diene substrates using a wide variety of oxidants. Vastly diminished selectivities were observed when conjugated dienes are epoxidized by MnTTPPP using hypochlorite as oxidant. This indicates the presence of at least two different pathways for the manganese catalyzed epoxidations, and the latter pathway has a transition state with lessened steric constraint. Diminished selectivity was also observed for the iron catalyzed systems compared to manganese, indicating a different principle pathway for the iron porphyrin epoxidations. The selectivities observed for both iron and manganese were found to be insensitive to changes in oxidant or the addition of added imidazole. This indicates that the reactive species does not contain the oxidant (e.g. a metallo-iodosobenzene complex), and that imidazole does not affect the transition state.
Photolysis of 5,10,15,20-tetraphenylporphyrinate manganese(III) perchlorate (MnTPP(ClO(,4)) and CrTPP(ClO(,4)) in the porphyrin(p) to metal (e(,g)) charge transfer region leads to clean transformation to MnTPP(Cl) and Cr(IV)TPP(O) respectively. MnTPP(ClO(,4)) was found to photooxidze stoichiometrically cyclopentane, toluene, and cyclohexene. Photocatalytic oxidations of the same three hydrocarbon substrates were accomplished using MnTPP(OAc) and excess tetra-n-butylammonium periodate. Kinetics indicates a preequilibrium periodate displacement of acetate followed by photolysis to form the active Mn(V)TPP(O) species.
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