Aromatic Hydroxylation
FULL PAPER
Determination of phenol yield using GCMS: Mixture of 1 with benzene
in CH3CN was prepared in a glove box. Hydrogen peroxide was prepared
aerobically and delivered at room temperature; the resulting solution
was stirred for 30 min for reaction to complete. Reaction mixtures were
acetylated (0.1 mL of 1-methylimidazole and 1 mL of acetic anhydride)
for 30 min followed by addition of 1m HCl (2 mL) and extraction with di-
chloromethane (1 mL). The organic layer was washed with saturated
aqueous NaHCO3 (2 mL), water (2 mL) and finally dried over MgSO4.
Internal standard (nitrobenzene or naphthalene) was added prior to the
extraction. Yields of hydroxylated products were established by GCMS
relative to the internal standard and converted to absolute yields using a
calibration curve with phenyl acetate and the corresponding standard, de-
termined prior to each run. All experiments were run at least in tripli-
cate, reported yields are average of these trials.
MPPH cleavage: O2 was bubbled through anaerobically prepared solu-
tion of 1 (2 mm) and benzene (280 equiv vs. iron) in acetonitrile (1 mL)
for 20 s followed by injection of MPPH (60 mL, 2 mmol, 1 equiv vs. iron)
at room temperature. After addition of MPPH, solutions were stirred for
ꢁ30 min and prepared for GCMS analysis as described above. When
looking at the effects of H+ on the reactivity, acetic acid (10 mL, 1 mmol,
0.5 equiv vs. iron) was added to 1/benzene mixture before purging it with
O2.
Blank solutions containing only pure acetonitrile (1 mL) were treated
same way as the 1/benzene mixtures. Control samples with pure bibenzyl,
benzyl alcohol acetate, benzaldehyde, 2-methyl-1-phenyl-2-propyl alcohol
acetate (MPPol), phenyl acetate and nitrobenzene were run to find de-
tector response for each product against nitrobenzene.
Determination of H/D KIE: An solution of 1 (5 mm) in acetonitrile and
a 1:1 mixture of toluene/[D8]toluene (150 equiv each; the ratio of protio/
deuterio isotopomers was analyzed by GCMS and adjusted to 1:1 if nec-
essary) was prepared in a glove box. H2O2 (3 equiv vs. 1) was added
dropwise at room temperature and the mixture was left to react for
30 min. Products were acetylated and subjected to GCMS analysis; the
amounts of the 2H and 1H products were quantified by integrating the
peaks of their corresponding ions. The o-, m-, and p-cresols were well
separated in the chromatogram; however, the GC peak from meta cresol
partially overlapped with benzyl alcohol. Therefore we used an ion
unique to benzyl alcohol (91 for protio and 98 for deutero) to determine
KIE for the hydroxylation of CH3 group; relatively low intensity of this
peak limits the accuracy of KIE for benzylic hydroxylation. Additional
details are provided in Supporting Information (Figure S24).
Acknowledgements
We thank Prof. Dr. L. Que, Jr. for fruitful discussion and Dr. Ivan V. Ko-
rendovych and Dr. Rubꢂn Mas-Ballestꢂ for critical reading of the manu-
script. This work was supported by the US Department of Energy (Grant
DE-FG02–06ER15799). The NMR facility, the ESI-MS spectrometer,
and rapid kinetic instrumentation at Tufts were supported by the NSF
(grants CHE-9723772, MRI CHE 0821508, MRI CHE 0320783, and
CHE 0639138).
Stopped-flow experiments: Kinetic measurements were performed in the
diode array mode using a stopped-flow instrument. Reactivity of 1 with
hydrogen peroxide in the presence of benzene was studied in acetonitrile
at 208C. In a single mixing experiment, an acetonitrile solution of 1 and
benzene was prepared in a glove box and mixed with H2O2 in the
stopped-flow. In a double mixing experiment 1 was mixed with H2O2, the
[2] O. V. Makhlynets, P. Das, S. Taktak, M. Flook, R. Mas-Balleste,
[3] J.-U. Rohde, J.-H. In, M. H. Lim, W. W. Brennessel, M. R. Bukow-
[4] J. England, Y. Guo, E. R. Farquhar, V. G. Young, Jr., E. Mꢃnck, L.
[5] E. J. Klinker, J. Kaizer, W. W. Brennessel, N. L. Woodrum, C. J.
reaction mixture was incubated to reach the highest yield of FeIII
ACTHNUTRGNE(NUG OOH)
(age time), followed by addition of benzene. The effect of acetic acid on
hydroxylation rate was studied in a double mixing experiment, in which
FeIII
ACHTUNGTRENNUNG(OOH) was pre-generated by mixing 1 and H2O2 at 208C followed
by addition of benzene with variable amounts of acetic acid (1–4 equiv
vs. 1). Concentrations of all reagents are reported in the figure captions
for the onset of the reaction (after mixing). Kinetic parameters were de-
termined in SPECFIT (global fitting), Kinetic Studio or IgorPro using
single-exponential (A!B) or double exponential (A!B!C) models.
[8] S. Taktak, M. Flook, B. M. Foxman, L. Que, Jr., E. V. Rybak-Aki-
[9] L. Que, Jr., J. Biol. Inorg. Chem. 2004, 9, 684.
[10] I. V. Korendovych, S. V. Kryatov, E. V. Rybak-Akimova, Acc. Chem.
Single-exponential fit was calculated to A=Ainf +DAexp
(ꢀkt), in which
Ainf is absorbance of the reaction mixture after reaction is complete,
DA=A0ꢀAinf ; A0 is initial absorbance. Similarly, double-exponential fit
was calculated using A=Ainf +DA1 exp
N
U
[12] R. Mas-Ballestꢂ, L. Que Jr. , J. Am. Chem. Soc. 2007, 129, 15964.
[13] Although blue species decays over time this process is not due to
overoxidation reaction, GCMS analysis showed that the blue solu-
tion (maximum accumulation of phenolate) and the yellow solution
(1 h after the onset of the reaction) contain the same amount of
phenol (Figure S2 in the Supporting Information).
[14] H. Marusawa, K. Ichikawa, N. Narita, H. Murakami, K. Ito, T.
[16] M. Lubben, A. Meetsma, E. C. Wilkinson, B. Ferinda, L. Que, Jr.,
[17] P. Mialane, A. Nivorojkine, G. Pratviel, L. Azema, M. Slany, F.
Godde, A. Simaan, F. Banse, T. Kargar-Grisel, G. Bouchoux, J. Sain-
ton, O. Horner, J. Guilhem, L. Tchertanova, B. Meunier, J.-J.
[18] B. Bernal, I. M. Jensen, K. B. Jensen, C. J. McKenzie, H. Toftlund,
[19] K. B. Jensen, C. J. McKenzie, N. P. Nielsen, J. Z. Pedersen, H. M.
ments were run in at least triplicate and averaged rate constants are re-
ported. The activation enthalpy and entropy for FeIII
(OOH) formation
were calculated from linear Arrhenius and Eyring plots.
AHCTUNGTRENNUNG
Isotope-labeling studies: A mixture of 1 (2 mm) and benzene (280 equiv
vs. 1) was prepared in a glove box. In experiments with labeled hydrogen
peroxide, H218O2 (11 mL, 0.53m, 3 equiv vs. 1) was added to the 1/benzene
mixture (1 mL) at room temperature. In an experiment with labeled
water, H218O (11 mL, 98%) was added to solution of the 1/benzene
(1 mL) prior to the addition of H2O2 (60 mL of 0.1m H2O2 diluted by
CH3CN from 70% stock solution). After 30 min the reaction mixture was
subjected to GCMS analysis as described above.
EPR studies: Purple species 2 was generated directly in the EPR tube by
mixing 1 (3 mm, 0.15 mL) with H2O2 (30 mm, 0.15 mL) in acetonitrile at
room temperature. The tube was frozen immediately after all hydrogen
peroxide was injected (5 s). Complex 2 decays fast when treated with
acetic acid: Complex 2 was pre-generated in the EPR tube as described
above and then acetic acid (1.5 mm, 0.11 mL, <0.5 equiv vs. iron) was in-
jected into the tube and reaction quenched in liquid nitrogen (reaction
time 5 s). All EPR spectra were acquired at 120 K. EPR spectra simula-
tion were done using SimFonia (Bruker).
Chem. Eur. J. 2010, 16, 13995 – 14006
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
14005