Health & Environmental Research Online (HERO)


Print Feedback Export to File
8631828 
Journal Article 
Detection of Free Radicals from Low-Temperature Ozone-Olefin Reactions by ESR Spin Trapping: Evidence that the Radical Precursor is a Trioxide 
Pryor, WA; Prier, DG; Church, DF 
1983 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
105 
9 
2883-2888 
English 
Free radicals are detected from the low-temperature ozonation of a series of olefins by using an electron spin resonanee (ESR) spin-trap method. The technique involves ozonation at -78 °C in Freon-11, blowing out the ozone with an inert gas, adding the spin trap at -78 °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 these 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 hydrotrioxide, ROOOH. We propose that 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. © 1983, American Chemical Society. All rights reserved.