The kinetics of the interaction of peroxy radicals. I. The Tertiary Peroxy Radicals

✍ Scribed by Prakash S. Nangia; Sidney W. Benson

• Publisher: John Wiley and Sons
• Year: 1980
• Tongue: English
• Weight: 807 KB
• Volume: 12
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550120104

✦ Synopsis

Existing data on the self-reactions of tertiary peroxy radicals ROn has been reanalyzed and corrected to deduce Arrhenius parameters for both termination and nontermination paths.

For R = t-Rutyl, these are logk,(M-'sec-') = 7.1 -(7.0/8) and logknt(A4-'sec-') = 9.4 -(9.0/0), respectively, different from those recommended by other authors. The higher magnitudes observed for termination processes of tertiary peroxy radicals like those of cumyl and 1,1-diphenylethyl have been discussed in terms of a much greater cage recombination of'cumyloxy radicals as contrasted with t-butoxy radicals. It is shown that for benzyl peroxy radicals, the R-0; bond dissociation energy is sufficiently low (18-20 kcal) that reversible dissociation into ff. + 0 2 opens a competing second-order path to fast recombination R. + RO" -ROOR. This path is probably not important for cumyl peroxy radicals under usual experimental conditions but can become important for 1,l-diphenyl ethyl peroxy radicals a t (On) 5 10-3MM. At very low RO; concentrations (<10-5M), in the absence of added 0 2 , an apparent first-order disappearance of RO; can occur reflecting the rate determining breaking of the cumyl-oi bond GOnc + 0; followed by the second step above. The thermochemistry of RO, is used to show that the reaction of Rz04 -2 R 0 + 0 2 must be concerted and cannot proceed via RO;, which is too unstable and cannot form even from R O + 0 2 .