Catir et al.
1
TABLE 1. Chemiluminescence Detection of O2 Generated from
PIFA (0.01 M) and Hydrogen Peroxide (0.2 mol L-1) in the Presence
of NaHCO3 (0.1 mol L-1) at 20 °C in Various Organic Solventsa
solvent
τ∆ (µs)15
Imax (mV)
∆t (min)
area (mV min)
CH3OH
MTBE
toluene
THF
CH2Cl2
CHCl3
CCl4
10
30
30
22
97
255
370
145
450
280
252
319
0.1
4
40
2
5
40
60
6
233
1250
200
370
1890
4632
230
1300
a Imax ) maximal intensity of the luminescence signal, ∆t ) time
corresponding to 5% of Imax, area ) area under the curve of the
1
FIGURE 3. IR luminescence signal of O2 generated by a solution
containing 0.01 M PIFA, 0.1 M NaHCO3, and 0.1 M rac-1-phenylethyl
hydroperoxide (7) in toluene at T ) 20 °C.
1
luminescence signal, τ∆ ) lifetime of O2 in the pure solvent.
TABLE 2. Influence of Base, Temperature, and Hydrogen
The temperature has no effect on the yield of 1O2, but
decreasing the temperature below 18 °C causes a slowing down
of the reaction by a factor 4. Concerning the H2O2 concentration,
the results indicate that 2 molar equiv compared to PIFA is
required to obtain maximum 1O2 production. In the presence of
a stoichiometric amount of H2O2, the signal is two times lower
1
Peroxide Concentration on Chemiluminescence Detection of O2
Generated from PIFA (0.01 M) and Hydrogen Peroxide under
Variable Conditions
T
[H2O2]
Imax
area
reaction media
[°C] (mol L-1
)
(mV) ∆t (min)
(mV min)
CHCl3 +
pyridine (0.1 M)
CHCl3
CHCl3 +
NaHCO3 (0.1 M)
THF
THF
toluene
toluene
toluene
20
0.2
180 a few
seconds
300 25
252 40
not
significant
880
1
in terms of both the rate of O2 generation and yield. Above 2
20
20
0.2
0.2
molar equiv, no improvement is observed, suggesting that the
excess of hydrogen peroxide has no influence on the reaction.
1890
1
This result indicates that the reaction of O2 production from
2
20
20
20
20
20
20
0.2
0.2
0.01
0.02
0.05
0.1
132
450
8
2
195
200
450
1170
1270
1400
1100
the H2O2/PIFA system is first-order compared to H2O2.
Mechanistic Aspects. Ligand exchange reactions of hyper-
valent iodine compounds with nucleophiles are widely used for
the synthesis of other hypervalent iodine compounds in which
the oxidation state of iodine does not change.16 Milas and
Plesnicar17a reported the reaction of [bis(acetoxy)iodo]benzene
with tert-butyl hydroperoxide and proposed the in situ generation
of labile peroxyiodane [bis(tert-butylperoxy)iodo]benzene (2),
which decomposes even at -80 °C to tert-butyl peroxy radical,
molecular oxygen, and iodobenzene (3).
40 50
80 60
80 60
80 60
100 50
toluene
toluene
0.3
Influence of the Solvent. The generation of singlet oxygen
from the PIFA/H2O2 system was also studied in seven other
typical solvents of different polarity. The solvents were com-
pared in terms of maximal signal intensity (Imax) and time
required to decompose a given amount of H2O2 (∆t). The results
are listed in Table 1. Among the studied solvents, methanol
1
does not allow significant production of O2 from the H2O2/
PIFA system. The initial chemiluminescence signal is relatively
high (255 mV) but disappears within a few seconds. On the
other hand, if we compare toluene, MTBE (methyl-tert-
This ready decomposition of [bis(tert-butylperoxy)iodo]ben-
zene (2) is rationalized in terms of the small dissociation energy
of the apical hypervalent peroxy-iodine(III) bond and is
facilitated by conjugative overlap of the breaking hypervalent
bond with π-orbitals of the benzene ring.17b,c In our preliminary
communication18 we reported the nucleophilic addition of
hydrogen peroxide to PIFA in THF at 10 °C, yielding molecular
1
butylether), and THF, in which the lifetimes of O2 are quite
1
similar, the highest O2 production is obtained in toluene even
if the other two produce the excited species faster as attested
from the Imax values. By comparing the area under each curve,
1
it can be deduced that the yield of O2 generated is about 5
times higher in toluene than in THF or in MTBE. Finally, it
1
appears that quite efficient generation of O2 also occurs in
(16) (a) HyperValent Iodine Chemistry: Modern DeVelopments in Organic
Synthesis; Topics in Current Chemistry Series 224; Wirth, T., Ed.; Springer:
Berlin-Tokyo, 2003. (b) Varvoglis, A. The Organic Chemistry of Polycoordinated
Iodine; VCH Publishers, Inc.: New York, 1992. (c) Varvoglis, A. HyperValent
Iodine in Organic Synthesis; Academic Press: London, 1997. (d) Moriarty, R. M.;
Prakash, O. HyperValent Iodine in Organic Chemistry: Chemical Transforma-
tions; Wiley-Interscience: New York, 2008. (e) Stang, P. J.; Zhdankin, V. V.
Chem. ReV. 1996, 96, 1123. (f) Zhdankin, V. V.; Stang, P. J. Chem. ReV. 2002,
102, 2523. (g) Wirth, T.; Hirt, U. H. Synthesis 1999, 1271. (h) Stang, P. J. J.
Org. Chem. 2003, 68, 2997. (i) Moriarty, R. M. J. Org. Chem. 2005, 70, 2893.
(k) Wirth, T. Angew. Chem., Int. Ed. 2005, 44, 3656. (l) Varvoglis, A.
Tetrahedron 1997, 53, 1179. (m) Zhdankin, V. V.; Stang, P. J. Chem. ReV. 2008,
108, 5299. (n) Moriarty, R. M.; Prakash, O. Acc. Chem. Res. 1986, 19, 244–
250. (o) Zhdankin, V. V. ArkiVoc 2009, 1–62.
(17) (a) Milas, N. A.; Plesnicar, B. J. Am. Chem. Soc. 1968, 90, 4450–4453.
(b) Ochiai, M.; Ito, T.; Takahashi, H.; Nakanishi, A.; Toyonari, M.; Sueda, T.;
Goto, S.; Shiro, M. J. Am. Chem. Soc. 1996, 118, 7716–7730. (c) Dolenc, D.;
Plesnicˇar, B. J. Am. Chem. Soc. 1997, 119, 2628–2632.
(18) (a) Catir, M.; Kilic, H. Synlett 2004, 2151. (b) Catir, M.; Kilic, H. Synlett
2003, 1180.
chlorinated solvents. It is noteworthy that in some solvents,
especially CCl4, there is a latent period that can be from 10 to
45 min before the production of O2.
1
Influence of Base, Temperature, and Hydrogen Per-
oxide Concentration. Other CL experiments have been per-
formed by varying either the base (no base, pyridine instead of
NaHCO3) and by changing the temperature. The results are listed
in Table 2. In the presence of pyridine, no singlet oxygen seems
to be formed. In the absence of NaHCO3, relatively good
production of 1O2 is observed, but this is doubled in the presence
of NaHCO3 0.1 mol L-1
.
(15) (a) Hurst, J. R.; McDonald, J. D.; Schuster, B. J. Am. Chem. Soc. 1982,
104, 2065–2067. (c) Okamoto, M.; Tanaka, F. J. Phys. Chem. 1993, 97, 177–
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4562 J. Org. Chem. Vol. 74, No. 12, 2009