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Bismuth aryloxide reactivity: kinetics of thermal decomposition and resulting organic oxidation products
Brien, Kimberly A.
Brien, Kimberly A.
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[Fort Worth, Tex.] : Texas Christian University,
Date
2010
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Abstract
The Standard Oil of Ohio Company (SOHIO) process is an industrial method for the oxidation and ammoxidation of propene to produce acrolein and acrylonitrile. This process uses a bimetallic catalyst based on Bi2O3*MoO3. Bismuth has been shown to be necessary in the rate determining step as well as in later steps of the catalytic cycle. Our group was the first to describe a molecular bismuth model system with reactivity similar to the SOHIO catalysts using bismuth aryloxides as a model system. This represented the first experimental support that the fundamental step in SOHIO propene activation involves Bi(III)-O bond homolysis to form Bi(II). In an effort to obtain kinetic rates, we chose to study a phenoxy bismuth complex of intermediate steric bulk. We anticipated that 2-tert-butyl-6-isopropylphenol would give a corresponding bismuth aryloxide that would decompose at an intermediate rate.^A new synthesis of this phenol was developed.^In order to have authentic materials for comparative analysis in the decomposition of the Bi(III) aryloxide Bi(O-2-tBu-6-iPrC6H3)3, four potential decomposition products were synthesized; 2-tert-butyl-6-isopropylquinone, 2-tert-butyl-6-isopropylhydroquinone, 3,3'-di-tert-butyl-5,5'-diisopropyldiphenoquinone, and 3,3'-di-tert-butyl-4,4'-dihydroxy-5,5'-diisopropyldiphenyl. We observed during the isolation of 3,3'-di-tert-butyl-5,5'-diisopropyldiphenoquinone that only the E isomer crystallizes, and slowly equilibrates to a 51:49 E/Z mixture when in solution. We successfully obtained isomerization kinetics that favor a diradical isomerization mechanism. Computational studies in collaboration with the Borden research group at University of North Texas supported our experimental results but giving a smaller negative entropy value.^In an effort to obtain the Bi(OAr)3 product by reacting bismuth tert-butoxide with 2-tert-butyl-6-isopropylphenol, we obtained instead tBuOBi(OAr)2.^When this bismuth phenoxide was heated in C6D6, decomposition to the corresponding phenol and both E and Z isomers of 3,3'-di-tert-butyl-5,5'-diisopropyldiphenoquinone was observed by 1H NMR. Kinetic studies on this decomposition were initiated and will be discussed. The re-synthesis of a large number of bismuth aryloxides was also performed and their stabilities studied. Kinetic studies of the C-H activation of two bismuth complexes were also initiated. Both experimental and computational studies with the Janesko research group at TCU support a base catalyzed concerted pathway.
Contents
Subject
Subject(s)
Bismuth compounds.
Organometallic compounds.
Thermal analysis.
Chemical kinetics.
Organometallic compounds.
Thermal analysis.
Chemical kinetics.
Research Projects
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Dissertation
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Department
Chemistry and Biochemistry