ISSN:
0009-2940
Keywords:
Oxyl radicals
;
Phosphonoyl peroxides
;
Laser flash photolysis
;
ESR-Spin trapping
;
Electron transfer
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The thermal and photochemical decomposition of the first bis(phenylphosphonoyl)peroxides, dioxybis[(n-butoxy)phenyl-phosphane oxide] (5), and dioxybis[(phenoxy)phenylphosphane oxide] (6) has been studied in various solvents by 1H-, 13C-, and 31P-NMR spectroscopy, laser flash photolysis (LFP), and ESR spin-trapping experiments. Kinetic studies reveal at 20°C a ca. 270 times slower thermal decay for 5 than for 6, which primarily results from a lower A factor rather than differences in the activation energies. The thermal decay of 5 occurs predominantly by a novel, presumably concerted polar rearrangement with formation of a thermally unstable, mixed phosphonoyl-phosphoryl anhydride. Photolysis of 5 induces homolytical cleavage of the peroxy bond with release of [(n-butoxy)phenylphosphonoyl]oxyl radicals 7. Radical 7 is characterized by a broad, transient UV/Vis absorption spectrum in the 400 to 〉700 nm range (λmax ca. 580 nm), as has been demonstrated by 248-nm LFP of 5 in acetonitrile solution. The short lifetime of this absorption indicates an extremely high reactivity (in hydrogen abstraction and addition) of this electrophilic radical. The thermal and photochemical decomposition of peroxide 6 leads to a virtually identical product distribution, suggesting O-O bond cleavage to be the major initial reaction under both conditions. LFP at 248 and 308 nm of a solution of 6 in acetonitrile initially produces a weak, broad absorption at ca. 500 nm and stronger bands at 280 and 400 nm. The highly transient 500-nm absorption is assigned to the [(phenoxy)phenylphosphonoyl]oxyl radical 8, the other bands are attributed to the phosphonoyloxy-substituted benzene radical cation 8Z. The formation of this species can be explained in terms of electron transfer in the first-formed oxyl radical 8 and/or the intact peroxide 6, followed by cleavage of the peroxy bond. The decay of 8Z is accompanied by the build-up of the absorption spectrum of a 1,4-dioxy-substituted biphenyl radical cation.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19921251114
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