This proposition is in accord with the literature reports that 1
In summary the F TPPFe(III)Cl catalyzed selective and efficient
20
cannot epoxidize alkenes and hydroxylate alkanes that efficiently
hydroxylation of cyclohexene to 2-cyclohexen-1-ol has been
achieved by t-BuOOH at room temperature from aqueous
acetonitrile medium. The shifting of medium to CH Cl –MeOH
14–17
and that 2 is more reactive than 1.
is extremely crucial in achieving the hydroxylation reaction and
this step seems to be highly solvent sensitive. In CH CN–H
The formation of 2 (eqn (4))
2
2
3
2
O
has produced epoxide as the major product. The hydroxylation of
cyclohexane to cyclohexanol has also been achieved by the same
oxidizing system in 47% yields from the same aqueous acetonitrile
medium. Studies in this laboratory are focused understanding the
reason of this remarkable solvent effect and to further improve the
efficiency of hydroxylation of cyclohexane and its possible
industrial application.
neither component is that easily oxidizable, so in this solvent
system 2 abstracts a hydrogen atom from the substrate only (eqn
(5)). This could be the reason for theobserved hydroxylation in
CH CN–H O and not in CH Cl –MeOH. The final hydroxylation
3
2
2
2
step (eqn (6)) may be progressing by the rebound type mechanism
originally proposed by Groves. We believe that the PFe(III)–
t
OO Bu (3) is mainly responsible for the slow epoxidation of
We thank the Department of Science and Technology (Project
No. SR/S1/IC-11/2002) for funding and CSIR for the fellowship to
AA.
2 2
cyclohexene in CH Cl –MeOH (2 : 1). However its slow
transformation to 1 or 2 and their immediate reaction with
MeOH cannot be overruled. This probably explains the slow and
inefficient transformation of cyclohexene to the epoxide in
Notes and references
+
2
methanolic solvent. The H and t-BuO evolved from eqn (6)
and (4) respectively recombines to give t-BuOH (eqn 7) as the
reduced product of t-BuOOH consumedin eqn 2. The catalytic
cycle will thus start from eqn (1) and will proceed up to eqn (6)
where F TPPFe(III)–OH will be regenerated, so that the next
{
4
Experimental Section: In a typical reaction 50 mM of catalyst and 200–
00 mM of substrate were dissolved in 1.1 ml of argon saturated solvent
mixture of CH CN–H O in a small screw capped vial fitted with PTFE
3
2
septa. The oxidation reaction was initiated by adding 2 mM of t-BuOOH
and the contents were magnetically stirred for 10–30 min under argon. The
standard solution of C F I was added to this reaction mixture and an
6 5
20
cycle will start from eqn (2) and not from eqn (1). In order to get
the full utility of the oxo-iron(IV) porphyrin cation radical the most
obvious side reactions represented by eqn (8) to (10) are to be
suppressed. Increasing the substrate concentration was one of the
options, and this has been the case in the hydroxylation reactions
aliquot was injected into a capillary column (carbowax, 30 meter) of a
preheated GC. The identification and the quantitation of the products were
done from the response factors of standard product samples as usual.
1
J. T. Groves and Y.-Z. Han, in Cytochrome P450: Structure, Mechanism
and Biochemistry, ed. P. R. Ortiz de Montellano, Plenum Press, New
York, 2nd edn, 1995, p. 1.
of cyclohexene in CH
the importance of eqn (3), when we conducted hydroxylation of
cyclohexene in CH CN–H O but in the presence of O , the major
3 2
CN–H O medium (Fig. 3). In order to test
2 M. J. Gunter and P. Turner, Coord. Chem. Rev., 1991, 108, 115;
J. L. Mclain, J. Lee and J. T. Groves, in Biomimetic Oxidations by
Transition Metal Complexes, ed. B. Meunier, Imperial College Press,
London, 2000, p. 91.
3
2
2
product was 2-cyclohexen-1-one and the yield of 2-cyclohexen-1-ol
?
was dramatically reduced. This was expected because the t-BuO
3
M. W. Grinstaff, M. G. Hill, J. A. Labinger and H. B. Gray, Science,
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A. M. d’A. Rocha Gonsalves, R. A. W. Johnstone, M. M. Pereira,
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radical will initiate auto oxidation of cyclohexene, 2-cyclohexen-1-
one will be the major product and formation of 2 (eqn (4)) will be
disrupted.
4
5
z .
.
F20TPPFeðIVÞ~OztꢀBuO DCCA F20 T P PFeðIVÞ~O (4)
ꢀ
ꢀtBuO
6
7
1993, 115, 2775.
8
S. L. H. Rebelo, M. M. Pereira, M. M. Q. Simoes, M. Graca,
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ð5Þ
ð6Þ
9
10 T. G. Traylor, K. W. Hill, W.-P. Fann, S. Tsuchiya and B. E. Dunlap,
J. Am. Chem. Soc., 1992, 114, 1308.
1 J.-F. Bartoli, K. L. Barch, M. Palacio, P. Battioni and D. Mansuy,
1
Chem. Commun., 2001, 1718.
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+
H
+ t-BuO– = t-BuOH
(7)
(8)
9622.
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14 J. T. Groves, Z. Gross and M. K. Stern, Inorg. Chem., 1994, 33, 5065.
?
t-BuO + t-BuOOH = t-BuOO + t-BuOH
?
15 W. Nam, S.-E. Park, I. K. Lim, M. H. Lim, J. Hong and J. Kim, J. Am.
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16 D. H. Chin, G. N. La Mar and A. L. Balch, J. Am. Chem. Soc., 1980,
z
.
.
F20 TP PF eðIVÞ~OztꢀBuOOH~tꢀBuOO zF20TPPFeðIVÞꢀOH (9)
1
02, 5945.
7 E. Derat, D. Kumar, H. Hirao and S. Shaik, J. Am. Chem. Soc., 2006,
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1
?
t
t-BuO = t-BuOO Bu
2
(10)
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