The key intermediates that interact with the fluorophores in the peroxyoxalate chemiluminescence reaction of 2,4,6-trichlorophenyl N-aryl-N-tosyloxamates

Article abstract of DOI:10.1039/b300079f

A kinetic study of peroxyoxalate chemiluminescence reactions employing 2,4,6-trichlorophenyl N-aryl-N-tosyloxamates supports the 1,2-dioxetanones still bearing the eliminating group as the key intermediates that interact with the fluorophores rather than 1,2-dioxetanedione.

Full text of DOI:10.1039/b300079f

The key intermediates that interact with the fluorophores in the
peroxyoxalate chemiluminescence reaction of 2,4,6-trichlorophenyl
N-aryl-N-tosyloxamates
Ryu Koike, Jiro Motoyoshiya,* Yutaka Takaguchi and Hiromu Aoyama
Department of Chemistry, Faculty of Textile Science & Technology, Shinshu University, Ueda, Nagano
386-8567, Japan. E-mail: jmotoyo@giptc.shinshu-u.ac.jp
Received (in Cambridge, UK) 3rd January 2003, Accepted 11th February 2003
First published as an Advance Article on the web 25th February 2003
A kinetic study of peroxyoxalate chemiluminescence reac-
tions employing 2,4,6-trichlorophenyl N-aryl-N-tosyloxa-
mates supports the 1,2-dioxetanones still bearing the elim-
inating group as the key intermediates that interact with the
fluorophores rather than 1,2-dioxetanedione.
Peroxyoxalate chemiluminescence1 has received continuous
attention so far since its discovery,2 and it is being applied to
practical uses such as chemical lights or analytical reagents
because of its convenience and high emission efficiency. The
chemiluminescent reactions consist of the reaction of hydrogen
peroxide and the activated oxalates bearing the good eliminat-
ing groups,3 from which light emission with various wave-
lengths due to the fluorescence of the fluorophores is produced.
According to the relationship established between the emission
efficiencies and the oxidation potentials of the fluorophores, the
decompose into tosylanilides and CO2 via cyclic peroxides. In
CIEEL (Chemically Initiated Electron Exchange Lumines-
contrast, the reaction of ethyl 2,4,6-trichlorophenyl oxalate (2),
cence) process4 between the high-energy intermediates and the
EtOCOCOOTCP, with aq. H2O2 under the same conditions
fluorophores is applied to explain the high emission effi-
gave ethyl O-hydrogen monoxalate, EtOCOCOOH, with the
ciencies,5 or at least a contribution of a charge transfer
loss of an oxygen atom from the initially formed ethyl O,O-
interaction may be considered.6 In spite of accumulating
hydrogen monoperoxyoxalate, EtOCOCOOOH.13 In this reac-
knowledge of this chemiluminescence reaction,7 there still
tion, no light emission was detected in the presence of DPA.
remains a question of which is the key intermediate that
The kinetic NMR study, measuring the amount of liberated
interacts with the fluorophores. Of the key intermediates
tosylanilides, revealed that a Hammett relationship was estab-
proposed so far,8 the most probable peroxides are 1,2-dioxeta-
lished in the reactions of 1a–f but not for 1g12 under pseudo-first
nones (I)9 bearing eliminating groups and 1,2-dioxetanedione
order conditions, from which the r-value was estimated to be
(II),10 both of which are strained four-membered cyclic
+1.75 as shown in Fig. 1(a). In addition, a Hammett relationship
peroxides and tend to interact with fluorophores to provide
could be also applied to the correlation between the initial
chemiluminescence based on a structural similarity to the
chemiluminescence intensities (I0) enhanced by DPA and the
chemiluminescent a-peroxylactones and related dioxetanes.11
substituent constants, the s-values, as shown in Fig. 1(b) and
This study was undertaken to provide a more unambiguous
(c). As I0 is proportional to the rate of the interaction between
view of this subject by exploring the chemiluminescence of the
the high-energy intermediate and the fluorophore,14 it can also
newly prepared oxamates (1), the structural hybrids of oxalates
be regarded as a criterion for the generation rate of the high-
and oxamides.
energy intermediates. While the r-value was estimated to be
+2.66 under neutral conditions, it decreased to +1.20 under
basic conditions in the presence of sodium carbonate. These
results, no light emission from 2 and the Hammett relationship
for the light emission of 1, show that the crucial intermediate
interacting with DPA to generate its excited state is not a peracid
such as ArTsNCOCOOOH. The larger r-value for the light
emission than for the liberation of the tosylanilides suggests that
I is more favorable as the key intermediate than II, because the
proton transfer from the hydroxyl group of I to the nitrogen
atom should be involved in order to generate II by liberation of
the tosylanilides from I. Due to the essentially negative r-value
for the proton transfer to the nitrogen atoms, the r-value for the
emission must have been lower than that observed if II interacts
with the fluorophores to emit light. In other words, the
interaction of the crucial intermediate generating the excited
fluorophores takes place before the liberation of the tosylani-
lides. The difference between the r-values for the nucleophilic
addition of hydroxide ion to the amide carbonyl and the
liberation of the anilide groups was well documented by Bender
et al.15 for the alkaline hydrolysis of N-substituted acet-
anilides.
The sequential reactions of oxalyl chloride with substituted
N-tosylanilides and then with 2,4,6-trichlorophenol (TCPOH)
in the presence of triethylamine in benzene gave the 2,4,6-tri-
chlorophenyl N-tosyl-N-aryloxamates (1a–g), which displayed
chemiluminescence lasting several hours when reacted with
aqueous H2O2 in tetrahydrofuran (THF) in the presence of
fluorescent 9,10-diphenylanthracene (DPA).
The reactions of 1a–c, 1f and 1g with aqueous H2O2 in
deuterated THF were monitored by 1H and 13C NMR, in which
the signals of the starting oxamates gradually decreased and
completely disappeared after several hours along with an
increase in the signals of the liberated TCPOH and the
tosylanilides,12 but no signal corresponding to any intermediate
was detected. Since the reaction of PhNTsCOCONTsPh is
known to be almost unreactive against H2O2 under the same
conditions,5c the initial nucleophilic acyl substitution by H2O2
expels TCPOH to form labile hydroperacids which readily
Next, oxamate (3) having an N-2-naphthyl-N-tosylamide
group as a fluorescent residue was employed to obtain further
794
CHEM. COMMUN., 2003, 794–795
This journal is © The Royal Society of Chemistry 2003

Fig. 1 The Hammett relationship in the chemiluminescence reaction of oxamates (1). (a) Product formation. (b) Light emission under neutral conditions. (c)
Light emission under basic conditions.
can also be applicable to general peroxalate chemilumines-
cence.
This work was supported by a Grant-in-Aid for the 21st
Century COE Research (14B1-30) by the Ministry of Educa-
tion, Culture, Sports, Science and Technology of Japan.
Notes and references
1 C. L. R. Catherall, T. F. Palmer and R. B. Cundall, J. Biolumin.
Chemilumin., 1989, 3, 147.
2 (a) E. A. Chandross, Tetrahedron Lett., 1963, 12, 761–765; (b) M. M.
Ruahut, Acc. Chem. Res., 1969, 2, 80.
3 S. S. Tseng, A. G. Mohan, L. G. Haines, L. S. Vizcarra and M. M.
Rauhut, J. Org. Chem., 1979, 44, 4113.
4 G. B. Schuster, Acc. Chem. Res, 1797, 12, 366.
5 (a) K. W. Sigvardson, J. M. Kennish and J. W. Birks, Anal. Chem.,
Fig. 2 Double reciprocal plot of FCL of 3 vs. [4].
1984, 56, 1096; (b) C. V. Stevani, S. M. Silva and W. J. Baader, Eur. J.
Org. Chem., 2000, 4037; (c) J. Motoyoshiya, N. Sakai, M. Imai, Y.
Yamaguchi, R. Koike, Y. Takaguchi and H. Aoyama, J. Org. Chem.,
2002, 67, 7314–7318.
information about the intermediate. The reaction of 3 with aq.
H2O2 in THF showed only a feeble chemiluminescence, but the
addition of N-2-naphthyl-N-tosylamide (4) to the reaction
system led to enhanced chemiluminescence, and an emission
spectrum which was in good agreement with the fluorescence
spectrum of 4 having a fluorescence maximum at 402 nm. The
double reciprocal plot of the relative FCL vs. the concentration
of 4 was found to be linear as shown in Fig. 2, establishing a
bimolecular reaction process8 between 4 and the key inter-
mediate. This relation holds even when the concentration of 4 is
less than that of 3. Consequently, the light emission does not
arise from 4 liberated from 3 but from 4 externally added. If
1,2-dioxetanedione (II) is the crucial intermediate, the emission
should be observed without the addition of the external 4, and
the emission intensity should not depend on the concentration of
the added 4.
6 F. McCapra, Prog. Org. Chem., 1973, 8, 231–277.
7 Recent reports on the mechanism of peroxyoxalate chemiluminescence
(PO-CL) are as follows (and references cited therein): (a) S. M. Silva, F.
Casallanovo, Jr., K. H. Oyamaguchi, L. F. L. M. Ciscato, C. V. Stevani
and W. J. Baader, Luminescence, 2002, 17, 313; (b) J. H. Lee, J. C.
Rock, S. B. Park, M. A. Schlautman and E. R. Carraway, J. Chem. Soc.,
Perkin Trans. 2, 2002, 802.
8 Hydroperoxyoxalate esters and six-membered cyclic peroxides are
proposed for the likely high-energy intermediates in the PO-CL of
bis(2,4-dinitrophenyl) oxalate or photoinitiated PO-CL: (a) J. H. Lee, J.
C. Rock, M. A. Schautman and E. R. Carraway, J. Chem. Soc., Perkin
Trans. 2, 2002, 1653; (b) R. E. Milofsky and J. W. Birks, J. Am. Chem.
Soc., 1991, 113, 9715.
9 (a) C. L. R. Catherall, T. F. Palmer and R. B. Cundall, J. Chem. Soc.,
Faraday Trans. 2, 1984, 30, 823–837; (b) A. G. Hadd, A. L. Robinson,
K. L. Rowlen and J. W. Birks, J. Org. Chem., 1998, 63, 3023.
10 (a) C. V. Stevani, D. F. Lima, V. G. Toscano and W. J. Baader, J. Chem.
Soc., Perkin Trans. 2, 1996, 989; (b) C. V. Stevani and W. J. Baader, J.
Phys. Org. Chem., 1997, 10, 593; (c) C. V. Stevani and W. J. Baader, J.
Chem. Res. (S), 2002, 430.
11 W. Adam, Four-membered ring peroxides: 1,2-dioxetanes and a-
peroxylactones, , in The Chemistry of Peroxides, ed. S. Patai, John
Wiley & Sons Ltd., New York, 1983, ch. 24, pp. 829–920.
12 In the reaction of 1g the decomposition product from N-p-dimethylami-
nophenyltosylamide was detected.
13 This type of peroxyacid was isolated, see: (a) C. V. Stevani, D. F. Lima,
V. G. Toscano and W. J. Baader, J. Chem. Soc., Perkin Trans. 2, 1996,
989; (b) R. Hohman, R. S. Givens, R. G. Carlson and G. Orosz,
Tetrahedron Lett., 1996, 37, 8273.
14 W. Adam, C. Cadilla, O. Cueto and L. O. Rodriguez, J. Am. Chem. Soc.,
1980, 102, 4802.
In conclusion, the results presented here show that the most
likely key intermediates that interact with the fluorophores in
the present oxamate chemiluminescence system are 1,2-dioxe-
tanones (I) still bearing the eliminating group rather than
1,2-dioxetanedione (II). We believe that this mechanistic view
15 M. L. Bender and R. J. Thomas, J. Am. Chem. Soc., 1961, 83, 4183.
CHEM. COMMUN., 2003, 794–795
795