Yields of Singlet Molecular Oxygen from Peroxyl Radical Termination

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The reaction, 2R1R2CHOO• → R1R2CHOH + R1R2CO + O2 with R1,R2 = H or simple alkyl, gave 3–14% (mean = 8%) 1O2 (1Δg) in tert-butylbenzene at 60–80 °C. The yields were lower in some peroxyls, with N or atoms in the α- or β-positions of R1 and R2, and were small-to-negligible when the precursor could give a peroxyl which lacked α-H atoms (cumene, t-BuOOH, Me2NCHO). Changes in temperature had little effect on the yield of 1O2 in the title reaction, and yields changed about 10-fold in different solvents. Peroxyls derived from Ph2CH2 and Ph2CD2 gave identical (11–12%) yields of singlet oxygen relative to benzophenone. Since the yield of 1O2 from the 9-fluorenylperoxyl self-reaction was only 6–10%, the intermediacy of triplet 9-fluorenone and 3O2 could apparently be ruled out, because the latter gave 80–90% 1O2 by photochemical approaches. A concerted decomposition of (R1R2CHOO)2 by the “Russell” scheme to give 1O2 (1Σg), which then partitions between 1Δg and 3Σg, is in accord with most, but not all, of our experimental results. © 1992, American Chemical Society. All rights reserved.

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Journal of the American Chemical Society