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dc.contributor.advisor Engel, Paul S.
dc.creatorWu, Aiyin
dc.date.accessioned 2009-06-03T23:53:29Z
dc.date.available 2009-06-03T23:53:29Z
dc.date.issued 1994
dc.identifier.urihttps://hdl.handle.net/1911/16793
dc.description.abstract Peresters $\beta$ to azo or azoxy groups are potentially interesting bifunctional initiators. They decompose thermally at essentially the same rate as the analogous simple perester. It follows that decomposition occurs stepwise; that is, the observed rate constants are determined by the rate of oxygen-oxygen bond cleavage. Using 1,4-cyclohexadiene as a radical scavenger, we found that the lifetimes of $\beta$-azo radicals 59B and 59P and $\beta$-azoxy radicals 62B and 62P were 0.4 ns, 1.3 ns (110$\sp\circ$C), 2.4 ns and 6.6 ns (120$\sp\circ$C), respectively. The nature of the products generated on thermolysis of azoxyperesters depended on the position of oxygen and on the substituents on the azoxy group. tert-Butyl 3-tert-butylazoxy-NNO-3-methylperbutanoate (9B) afforded nitrous oxide in nearly 80% yield, showing that the bonds break in the same pattern as those of azo peresters. For tert-butyl 3-phenylazoxy-NNO-3-methylperbutanoate (9P), the NNO fragment appeared as nitrogen and water instead of nitrous oxide because the (phenylazo)oxyl $\pi$-radical (63P) is relatively stable to fragmentation. For tert-butyl 3-tert-butylazoxy-ONN-2-methylperbutanoate (8B) and tert-butyl 3-tert-butylazoxy-ONN-2,2-dimethylperpropanoate (28B), the $\beta$-azoxy radical is proposed to attack the azoxy group to form an aziridine substituted nitroxide (86). This unstable species undergoes ring opening to afford primary and tertiary $\beta$-azoxy radicals (82, 83) which were trapped with 1,4-cyclohexadiene. The rate constant of 82 going to 83 is 1.5 $\times$ 10$\sp7$ s$\sp{-1}$ and from 83 to 82, it is 1.5 $\times$ 10$\sp3$ s$\sp{-1}$ at 120$\sp\circ$C. Only trans to cis isomerization of the azo group could be observed upon 405 nm irradiation of tert-butyl 3-phenylazo-3-methyperbutanoate (2P) at room temperature. However, 366 nm irradiation of tert-butyl 3-tert-butylazo-3-methylperbutanoate (2B) at room temperature generated $\beta$ perester radicals, which might be trapped by a radical scavenger. In order to obtain the lifetime of the $\beta$-perester radical, tert-butyl 3-tert-butylazo-3-cyclopropylperbutanoate 43 was synthesized and by using the cyclopropylcarbinyl (CPC) rearrangement as a radical clock, the lifetime of 44 was determined as 200 ns at 25$\sp\circ$C.
dc.format.extent 198 p.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subjectOrganic chemistry
Physical chemistry
dc.title Thermolysis and photolysis of bifunctional initiators: Free radical centers beta to the azo, azoxy and perester groups
dc.type.genre Thesis
dc.type.material Text
thesis.degree.department Chemistry
thesis.degree.discipline Natural Sciences
thesis.degree.grantor Rice University
thesis.degree.level Doctoral
thesis.degree.name Doctor of Philosophy
dc.identifier.citation Wu, Aiyin. "Thermolysis and photolysis of bifunctional initiators: Free radical centers beta to the azo, azoxy and perester groups." (1994) Diss., Rice University. https://hdl.handle.net/1911/16793.


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