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Fenton Reagents (1:1 FeIILx/HOOH) React Via [LxFeIIOOH(BH+), 1] as Hydroxylases (RH → ROH); NOT as Generators of Free Hydroxyl Radicals (HO·)

  • Donald T. Sawyer
  • Chan Kang
  • Antoni Llobet
  • Chad Redman

Abstract

The one-to-one combination of hydrogen peroxide and FeII(PA)2 [PAH = picolinic acid (2-carboxyl-pyridine)], a Fenton reagent, forms an adduct \( \{ {\text{F}}{{\text{e}}^{{\text{II}}}}{({\text{PA}})_2} + {\text{HOOH}}\xrightarrow[{{{({\text{py}})}_2}{\text{HOAc}}}]{{{\text{k}},{\text{2}} \times {\text{1}}{{\text{0}}^3}{{\text{M}}^{ - 1}}{{\text{s}}^{ - 1}}}}[{({\text{PA}})_2}^ - {\text{F}}{{\text{e}}^{{\text{II}}}}{\text{OOH}} + {\text{py}}{{\text{H}}^ + }](1)\} \) that is (py)2HOAc the primary reactant with (a) excess FeII(PA)2 to give two (PA)2FeIIIOH, (b) excess HOOH to give O2 plus two H2O, and (c) excess cyclohexane (C-C6H12) to give (c-C6H11)py (or c-C6H11OH in the absence of pyridine). The presence of a carbon-radical trap (PhSeSePh) with the organic substrate yields c-C6H11SePh with an efficiency of >90% (relative to HOOH). This Fenton reagent has reactivity ratios (kA/kB) [in comparison with free HO·] with c-C6H12/c-C6D12 (KIE) of 1.7 [versus 1.0], with l°/2°/3° carbon centers (per C-H, normalized) of 0.07/0.44/1.0 [0.41/0.50/1.0], and with c-C6H12/PhCH2CH3 of 2.0 [0.6]. In the presence of O2 (1 atm, 3.4 mM) 1 forms an adduct [1(O2), 5], which reacts with c-C6H12 to give c-C6H10(O) (KIE, 2.1), cyclohexene (c-C6H10) to give c-C6H8(O), and PhCH2CH3 to give PhC(O)CH3 (reactivity ratio for c-C6H12/PhCH2CH3, 0.6). Similar chemistry results for HOOH/O2 with FeII(bpy)22+ [reactivity ratio for c-C6H12/PhCH2CH3 (0.4)], FeII(OPPh3)42+ (1.0), and CuI(bpy) 2 + (1.0)]. All of this is compelling evidence that Fenton reagents do not produce (a) free hydroxyl radicals (HO·) or (b) free carbon radicals (R·), but (c) can exhibit catalytic turnovers with respect to HOOH and O2.

Keywords

Physical Chemistry Hydrogen Peroxide Inorganic Chemistry Organic Chemistry Organic Substrate 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer Science+Business Media New York 1993

Authors and Affiliations

  • Donald T. Sawyer
    • 1
  • Chan Kang
    • 1
  • Antoni Llobet
    • 1
  • Chad Redman
    • 1
  1. 1.Department of ChemistryTexas A&M UniversityCollege StationUSA

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