Detection of free radicals from low temperature ozone-olefin reactions by ESR spin trapping: evidence that the radical precursor is a trioxide
Free radicals are detected fom the low-temperature ozonation of a series of olefins by using an electron spin resonance (ESR) spin-trap method. The technique involves ozonation at -78/sup 0/C in Freon-11, blowing out the ozone with an inert gas, adding the spin trap at -78/sup 0/C, and then warming the solution while in the probe of the ESR spectrometer. A series of small olefins was examined, and tetramethylethylene (TME) and 2-methyl-2-pentene (2-MP) gave the highest yield of radicals. However, even thse two olefins give yields of radicals that are less than 1% on the basis of ozone consumed. Thus, our data indicate that while the nonradical Criegee ozonation process is the principal reaction for monoolefins, radical production is a significant side reaction. The temperature dependence of the appearance of spin adducts from both TME and 2-MP shows that the radical precursor in this case is a trioxidic species; specifically, we suggest that it is an alkyl hydrotroxide, ROOOH. We propose the ROOOH is formed by allylic hydride abstraction from the olefin by ozone to give a pair of caged ions that combine to form the trioxide. (Benson has proposed a similar hydride abstraction for alkanes and several other types of compounds.) The reaction may proceed through a charge-transfer complex of the olefin and ozone as an intermediate.
- Research Organization:
- Louisiana State Univ., Baton Rouge
- OSTI ID:
- 5304194
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 105:9; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKENES
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
ELECTRON SPIN RESONANCE
HYDROCARBONS
LOW TEMPERATURE
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
OZONE
OZONIZATION
RADICALS
RESONANCE
TRAPPING
YIELDS