A two-color laser photolysis method for determining reaction rates of short-lived intermediates by product analysis: Application to the o-Quinodimethane problem

Article abstract of DOI:10.1021/ja027653v

A time-delayed, two-color pulse laser photolysis technique was used for a kinetic study of short-lived transient species through product analysis, the determination of the rate constant of the cycloaddition of o-quinodimethane (1) and maleic anhydride (2) in room-temperature solutions, o-Quinodimethane (1) was generated from 1,2-bis[(phenylseleno)methyl]benzene (3) by the irradiation of a pulse of a KrF excimer laser (248 nm) in the presence of excess 2, and a successive pulse of a XeCl excimer laser (308 nm) was irradiated to the reaction mixture after varied delay times from 0 to 0.1 s for the decomposition of the remaining 1 to quench the cycloaddition reaction. The rate constant of the cycloaddition of 1 and 2 was 2.1 × 10⁵ M^-1 s^-1, which was obtained by the analysis of the delay-time dependence of the product yields.

Full text of DOI:10.1021/ja027653v

Published on Web 12/31/2002
A Two-Color Laser Photolysis Method for Determining
Reaction Rates of Short-Lived Intermediates by Product
Analysis: Application to the o-Quinodimethane Problem
Akihiko Ouchi,*,† Zhong Li,†,§ Masako Sakuragi, and Tetsuro Majima
†
‡
Contribution from the Research Institute for Green Technology, National Institute of AdVanced
Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan, and The Institute of
Scientific and Industrial Research (SANKEN), Osaka UniVersity,
Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
Received July 11, 2002 ; E-mail: ouchi.akihiko@aist.go.jp
Abstract: A time-delayed, two-color pulse laser photolysis technique was used for a kinetic study of short-
lived transient species through product analysis, the determination of the rate constant of the cycloaddition
of o-quinodimethane (1) and maleic anhydride (2) in room-temperature solutions. o-Quinodimethane (1)
was generated from 1,2-bis[(phenylseleno)methyl]benzene (3) by the irradiation of a pulse of a KrF excimer
laser (248 nm) in the presence of excess 2, and a successive pulse of a XeCl excimer laser (308 nm) was
irradiated to the reaction mixture after varied delay times from 0 to 0.1 s for the decomposition of the
remaining 1 to quench the cycloaddition reaction. The rate constant of the cycloaddition of 1 and 2 was 2.1
5
-1 -1
×
10 M
s
, which was obtained by the analysis of the delay-time dependence of the product yields.
3
4
Introduction
intermediates, and many synthetic and physical works have
been reported. Cycloaddition of 1 with alkenes and alkynes is
Reactions of transient short-lived species have been studied
by using various spectroscopic techniques. Although spectro-
scopic methods are very effective tools for such studies, the
spectroscopic methods have some drawbacks such as (i) only
spectroscopically observable species can be detected, (ii) limited
applicability in the case of spectroscopic overlapping of different
transient species, and (iii) quantitative information on the
concentrations of the participating transient species is often
difficult to obtain. Therefore, the developments of other
experimental techniques that can avoid such spectroscopic
difficulties provide a new means for extending the research field
of transient short-lived species.
3,5
one of the well-investigated fields, but the reported kinetic
6
studies are mainly of some substituted o-quinodimethanes, and,
to the best of our knowledge, the rate constant of the cycload-
dition of parent 1 in room-temperature solutions has not been
reported so far.
The lack of such important and basic kinetic data seems to
be due to the difficulty for conducting the experiments by
spectroscopic means. In the cycloaddition reactions, it is possible
to observe the decay of 1 that is generated from conventional
precursors by the flash photolysis technique because in most
cases the absorption of 1 appears at a longer wavelength than
We report here an application of a time-delayed, two-color
pulse laser photolysis technique for the determination of a
kinetic constant of a transient species through product analysis.
(3) Reviews: (a) Sammes, P. G. Tetrahedron 1976, 32, 405-422. (b) Oppolzer,
W. Angew. Chem., Int. Ed. Engl. 1977, 16, 10-23. (c) Oppolzer, W.
Synthesis 1978, 793-802. (d) Funk, R. L.; Vollhardt, K. P. C. Chem. Soc.
ReV. 1980, 9, 41-61. (e) Kametani, T.; Nemoto, H. Tetrahedron 1981,
1
37, 3-16.
We have selected the cycloaddition reaction of o-quin-
(
4) (a) Flynn, C. R.; Michl, J. J. Am. Chem. Soc. 1973, 95, 5802-5803. (b)
Flynn, C. R.; Michl, J. J. Am. Chem. Soc. 1974, 96, 3280-3288. (c) Tseng,
K. L.; Michl, J. J. Am. Chem. Soc. 1977, 99, 4840-4842. (d) Roth, W. R.;
Biermann, M.; Dekker, H.; Jochems, R.; Mosselman, C.; Hermann, H.
Chem. Ber. 1978, 111, 3892-3903. (e) Roth, W. R.; Scholz, B. P. Chem.
Ber. 1981, 114, 3741-3750. (f) Chapman, O. L.; McMahon, R. J.; West,
P. R. J. Am. Chem. Soc. 1984, 106, 7973-7974. (g) Trahanovsky, W. S.;
Macias, J. R. J. Am. Chem. Soc. 1986, 108, 6820-6821. (h) Chapman, O.
L.; Johnson, J. W.; McMahon, R. J.; West, P. R. J. Am. Chem. Soc. 1988,
2
odimethane [1; 5,6-bis(methylene)cyclohexa-1,3-diene], a ther-
mally unstable short-lived intermediate, and maleic anhydride
2). o-Quinodimethane (1) is one of the extensively studied
(
†
National Institute of Advanced Industrial Science and Technology.
Osaka University.
On leave of absence from the Institute of Pesticides and Pharmaceu-
‡
1
10, 501-509. (i) Scaiano, J. C.; Wintgens, V.; Netto-Ferreira, J. C. Pure
§
Appl. Chem. 1990, 62, 1557-1564. (j) Miranda, M. A.; Font-Sanchis, E.;
Perez-Prieto, J.; Scaiano, J. C. Chem. Commun. 1998, 1541-1542. (k)
Catalani, L. H.; de Arruda Campos, I. P.; de Brito Rezende, D. J.
Photochem. Photobiol., A 2001, 140, 1-5.
ticals, East China University of Science and Technology.
(
1) (a) Netto-Ferreira, J. C.; Wintgens, V.; Scaiano, J. C. Tetrahedron Lett.
989, 30, 6851-6854. (b) Bendig, J.; Mitzner, R. Ber. Bunsen-Ges. Phys.
Chem. 1994, 98, 1004-1008. (c) Ouchi, A.; Koga, Y. Tetrahedron Lett.
1
(5) (a) Sato, H.; Isono, N.; Okamura, K.; Date, T.; Mori, M. Tetrahedron Lett.
1994, 35, 2035-2038. (b) de la Cruz, P.; de la Hoz, A.; Langa, F.; Illescas,
B.; Mart ´ı n, N.; Seoane, C. Synth. Met. 1997, 86, 2283-2284. (c) Jinno,
M.; Kitano, Y.; Tada, M.; Chiba, K. Org. Lett. 1999, 1, 435 and references
therein.
(6) Takahashi, Y.; Miyamoto, K.; Sakai, K.; Ikeda, H.; Miyashi, T.; Ito, T.;
Tabohashi, K. Tetrahedron Lett. 1996, 37, 5547-5550.
1
995, 36, 8999-9002. (d) Ouchi, A.; Koga, Y.; Adam, W. J. Am. Chem.
Soc. 1997, 119, 592-599 and references cited therein.
(
2) Reviews: (a) McCullough, J. J. Acc. Chem. Res. 1980, 13, 270-276. (b)
Charlton, J. L.; Alauddin, M. M. Tetrahedron 1987, 43, 2873-2889. (c)
Martin, N.; Seoane, C.; Hanack, M. Org. Prep. Proced. Int. 1991, 23, 237-
2
72. (d) Segura, J. L.; Mart ´ı n, N. Chem. ReV. 1999, 99, 3199-3246.
1104
9
J. AM. CHEM. SOC. 2003, 125, 1104-1108
10.1021/ja027653v CCC: $25.00 © 2003 American Chemical Society

Laser Photolysis in Determining Reaction Rates
A R T I C L E S
Scheme 1
Figure 1. Absorption spectra of 2 (a), 3 (b), 4 (c), and 5 (d). Concentration,
-
4
-3
10
M (3) and 10 M (2, 4, 5) in acetonitrile; optical path, 10 mm. The
wavelengths of the KrF and XeCl laser emissions are indicated in the figure.
discussion, we can obtain the rate constant of the cycloaddition
of 1 and 2.
To the best of our knowledge, this is the first report on the
determination of the rate constant of the cycloaddition of parent
1
with an alkene. The rate constant of the cycloaddition 1 + 2
5
-1 -1
f 4 was found to be 2.1 × 10 M s .
7
the precursors. However, the decay does not simply reflect the
Results
formation of the cycloadduct because 1 also gives other
8
products, such as its dimers, oligomers, and polymers. There
Precursor of 1. A necessary requirement for the precursor
of 1 in our experiments is the high efficiency for the formation
of 1 by a single laser pulse irradiation because detectable
amounts of cycloadduct 4 are necessary for the product analysis.
If the efficiency is low, several cycles of the time-delayed, two-
color pulse irradiations are necessary to obtain a detectable
amount of 4, and this causes complication in the analysis of
the reaction due to the secondary photochemical reactions
involved in the successive photolysis cycles. We have selected
are also difficulties for tracing the formation of the cycloadduct
spectroscopically because the absorption of the cycloadduct
appears at the same wavelength region as the precursors (a large
amount of the precursor remains intact even after the laser pulse
irradiation due to their low photochemical efficiency ) and the
above-mentioned dimers, oligomers, and polymers.
9
The strategy used in our experiment for the determination of
the rate constant of the cycloaddition of 1 and 2 in room-
temperature solutions was the fast and efficient generation of 1
by the first laser pulse irradiation and the quenching of the
reaction by the decomposition of remaining 1 by the second
laser pulse irradiation (Scheme 1).10 When 1 is generated by
the irradiation of the first KrF laser pulse in the presence of 2,
the cycloaddition with 2 gives cis-1,2,3,4-tetrahydro-2,3-naph-
thalenedicarboxylic anhydride (4) (path 1 with the rate constant
1
1
1
,2-bis[(phenylseleno)methyl]benzene (3) as the precursor in
the time-delayed, two-color experiments because the photo-
chemical efficiency of 3 for the formation of 1 by a single pulse
2
1
-2
-1
of a KrF excimer laser (1.25 × 10 photons m pulse ) was
very high (chemical yield: 48%) as compared with the low
efficiencies from the conventional precursors (chemical yield:
1
2,13
1
2
<
9.4%), which is not sufficient for our experiments.
Absorption Spectra. Figure 1 shows the absorption spectra
of 2, 3, 4, and 5. The molar absorption coefficients (ꢀ) of 2, 3,
8
of k1) together with thermal products of 1, which are formed
by second-order kinetics4g (path 2 with the bulk rate constant
of k2). The reaction is quenched by the second XeCl laser pulse
after a particular time in the course of the reaction to decompose
remaining 1, partly forming benzocyclobutene [5, bicyclo(4.2.0)-
octa-1,3,5-triene] as a photochemical product. By analyzing the
delay-time dependence of the yield of 4, as shown in the
-
1
-1
4
, and 5 at 248 nm were 16 800, 160, 140, and 640 M cm ,
-1
-1 10,12
and those at 308 nm were 1800, 10, 0, and 0 M cm .
4b,14
The absorption of 1 has been reported
absorption at <240 nm, an absorption minimum at ca. 300 nm
ꢀ 430), a maximum at 373 nm (ꢀ > 3000), and the absorption
edge at ca. 430 nm. The ratio of the ꢀ of 1 at 248 and 308 nm
to have strong
(
1
4
was reported to be 3.8:1.
(
7) The spectrum of 1 was measured in an EPA matrix at 77 K4b (1 was
generated by the photolysis of 1,4-dihydrophthalazine) and in an argon
matrix4c (1 was generated by a gas-phase reaction of R,R′-dibromo-o-xylene
with sodium or potassium vapor). In flash photolysis studies, the generation
and the decay of 1 were studied using 5,6-bis(methylene)bicyclo[2.2.1]-
hept-2-en-7-one4d and 2-indanone as precursors.
-4
One-Color Excimer Laser Photolyses. Photolyses of 10
M 3 in the presence of 10 M 2 in acetonitrile were conducted
-3
21
-2
-1
by KrF (248 nm, 1.25 × 10 photons m pulse ) and XeCl
4i
21
-2
-1
(308 nm, 1.88 × 10 photons m pulse ) excimer lasers. The
chemical yields of 4 and 5, and the consumption of 3 by a pulse
of the KrF laser, were 43, 4.1, and 91%, and those by the XeCl
(
8) For example: (a) Cava, M. P.; Deana, A. A. J. Am. Chem. Soc. 1959, 81,
4
266-4268. (b) Errede, L. A. J. Am. Chem. Soc. 1961, 83, 949-954. (c)
Sisido, K.; Kusano, N.; Noyori, R.; Nozaki, Y.; Simosaka, M.; Nozaki, H.
J. Polym. Sci., Part A: Polym. Chem. 1963, 1, 2101-2107.
1
3
laser were 11, 0.3, and 42%, respectively. o-Quinodimethane
spiro dimer [6, 3′,4′-dihydro-6-methylenespiro(2,4-cyclohexa-
(
9) The conventional precursors for the generation of 1 often used so far are
2d
4
a,b
4i
1
,4-dihydrophthalazine (8),
2-indanone (9), 3-isochromanone (10),
2d
sultine [11; 1,4-dihydro-2,3-benzoxathiin 3-oxide], and 1,3-dihydroisothion-
2
d
aphthene 2,2-dioxide (12). However, 8 is reported to be unstable at room
temperature and can be only handled at low temperature. Compounds 9-12
have absorptions at shorter wavelengths than 270 nm so that a KrF (248
nm) excimer laser was used for the generation of 1. It is revealed that the
(11) (a) Ouchi, A.; Koga, Y. Chem. Commun. 1996, 2075-2076. (b) Ouchi,
A.; Koga, Y. J. Org. Chem. 1997, 62, 7376-7383.
(12) Ouchi, A.; Sakuragi, M.; Kitahara, H.; Zandomeneghi, M. J. Org. Chem.
2000, 65, 2350-2357.
-4
consumption of 9-12 in 10 M acetonitrile solutions by the irradiation
of a single pulse of a KrF (1.25 × 10 photons m pulse ) excimer
2
1
-2
-1
(13) The yield is based on the starting material.
12
laser was <9.4%.
10) Ouchi, A.; Koga, Y. J. Org. Chem. 1998, 63, 6780-6781.
(14) Fujiwara, M.; Mishima, K.; Tamai, K.; Tanimoto, Y.; Mizuno, K.; Ishii,
Y. J. Phys. Chem. A 1997, 101, 4912-4915.
(
J. AM. CHEM. SOC.
9
VOL. 125, NO. 4, 2003 1105

A R T I C L E S
Ouchi et al.
Scheme 2
addition of 2. This indicates that 4 was the only product formed
by the reaction of 1 and 2. The absence of 6 and the presence
of unidentified by-products observed in the HPLC and TLC
analyses were similar to those in the one-color excimer laser
photolyses.
Photochemical Stability of 4 and 5. Photolyses of 4 in 10-
M acetonitrile showed no decomposition of 4 by a pulse of the
KrF or XeCl lasers under the same reaction conditions as those
in the one-color laser photolyses of 3. This indicates that the
delay-time dependence on the yield of 4 is only due to its
formation and not to its decomposition. It is also reported that
4
Figure 2. Chemical yields13 of 4 and 5 in the time-delayed, two-color
photolysis as a function of the delay time between the KrF and XeCl lasers.
Delay time: 0-0.1 s (a) and 0-0.003 s (b). b, 4; O, 5. Concentration:
-
4
-3
21
1
0
M 3 and 10 M 2 in acetonitrile. Laser fluence: 1.25 × 10 (KrF)
21 -2 -1
and 1.88 × 10 (XeCl) photons m pulse . Optical path: 1 mm. The
5
is stable under the same photolysis condition of the KrF or
jitter between the KrF and XeCl laser pulses was (3 ns.
1
2
XeCl lasers.
diene-1,2′(1′H)-naphthalene)] was not detected in the product
mixtures, although 6 was observed in the laser photolyses of 3
in the absence of 2.12 However, some unidentified peaks were
Discussion
To obtain the rate constant of cycloaddition 1 + 2 f 4, k1,
by the analysis of the delay-time dependence of the yield of 4,
we have to understand the reaction path of 1 and the time
profiles of 1, 4, and 5. Although some unidentified products
were observed in the two-color laser photolyses of 3 both in
the presence and in the absence of 2, it was found that 4 was
the only new product that appeared by the addition of 2. This
implies that the products other than 1 generated by the photolysis
of 3 do not affect successive reactions of 1. Therefore, we only
have to consider the thermal (with and without 2) and
photochemical reactions of 1.
observed in reverse phase HPLC analyses, and silica gel TLC
analyses also showed the existence of a significant amount of
unidentified compounds at the origin. These compounds are
8
expected to be oligomers and polymers generated from 1.
Time-Delayed, Two-Color Excimer Laser Photolyses. The
two-color photolyses were conducted by one pair of laser pulse
irradiations; the photolysis was conducted by one pulse of the
KrF excimer laser and one subsequent pulse of the XeCl excimer
laser that was flashed after various delay times (0-0.1 s).
Figures 2 shows the chemical yields13 of 4 and 5 as a function
Reaction Paths of 1. Scheme 2 shows the reaction paths of
of the delay time of the two laser pulses in the time-delayed,
two-color photolyses. The consumption of 3 in the two-color
photolyses (91-95%)13 was independent of the delay times and
1
in the time-delayed, two-color photolysis. Before the second
XeCl laser pulse, 1, which is generated by the first KrF laser
pulse, undergoes thermal processes that partly give 4 (100a%,
almost the same as that in the one-color KrF laser photolysis
0
e a e 1) by the cycloaddition with 2, and the rest forms
(91%). This indicates that the consumption of 3 proceeded
other thermal products of 1 [100(1 - a)%]. When the second
XeCl laser pulse is irradiated, a part of the remaining 1 (100b%,
mainly by the KrF laser. On the contrary, the yields of 4 and 5
were much dependent on the delay time of the second XeCl
laser pulse. A maximum for the yield of 5 and a minimum for
the yield of 4 were observed at the delay time of ca. 0.3 ms
0
e b e 1) undergoes photochemical processes, and the rest
[100(1 - b)%] proceeds by thermal processes.
(cf., Figure 2b). However, after the delay time of ca. 20 ms,
The decomposition of 4 by the second XeCl laser can be
the yields of 4 and 5 returned to the same level as those of the
one-color KrF laser photolysis (cf., Figure 2a). As seen in Figure
excluded because the control experiments showed no decom-
position of 4 by the XeCl laser irradiation.
2
, the time scale of the recovery of 4, 0.3-20 ms, was much
Time Profile of 1, 4, and 5. Scheme 3a shows schematically
the time profile of 1, 4, and 5 in the one-color KrF laser
photolysis, and Scheme 3b shows those in the time-delayed,
two-color photolysis. As shown in Scheme 3a, 1 and 5 are
longer than that of the decrease of 4, 0-0.3 ms.
The existence of the maximum for the chemical yield of 5
indicates that the highest concentration of 1 was reached at 0.3
ms delay time and the decrease of 1 by further reactions started
from this point.
generated by a pulse of the KrF laser (at t ) 0) from 3 with the
initial concentrations of [1]0 and [5]s, respectively.1
0,12
The
Comparison of the HPLC data on the photolysis of 3 in the
presence and absence of 2 showed that the peak corresponding
to 4 was practically the only new peak that appeared by the
concentration of 5 does not change in the course of the reaction
because 5 is stable in room-temperature solutions. On the
contrary, 1 undergoes cycloaddition with 2 to give 4. When
1106 J. AM. CHEM. SOC.
9
VOL. 125, NO. 4, 2003

Laser Photolysis in Determining Reaction Rates
A R T I C L E S
Scheme 3
the concentrations of 1 and 4 at time t are [1]t and [4]t,
b:(1 - b). From eqs 1′ and 4 at t ) 0, the value b is shown as
respectively, we obtain
L
∞ t
[
4] - [4]
∞
b )
(5)
[
4] ) a([1] - [1] )
(a: const.; 0 e a e 1) (1)
t
0
t
[4]∞
At t ) ∞, where the concentration of 4 is [4]∞, eq 1 becomes
eq 1′ because [1]∞ ) 0.
The concentration [4]∞L0 is related to the yield of 4 at the
delay time of 0 (in practice, at the delay time of 0.3 ms in Figure
2
where the concentration of 1 reached its maximum). The yield
[
4] ) a[1]0
(1′)
L
-5
∞
of 4 at t ) 0 was 10% so that [4]∞ 0 ) 1.0 × 10 M. By
L -5
substituting values [4]∞ 0 and [4]∞ ()4.3 × 10 M) into eq 5,
Scheme 3b shows the time profiles of 1, 4, and 5 in the time-
delayed, two-color photolysis. When the second XeCl laser is
irradiated at the delay time of t, the concentrations of 1 and 5
immediately change from [1]t to [1] t and from [5]s to [5] t,
respectively, by photochemical reactions. Thus, we obtain
we obtain
b ) 0.77
L
L
This value of b indicates that the ratio of the photochemical
to thermal processes of 1 by the irradiation of a pulse of the
XeCl laser was 77:23. This ratio is in good accord with that
obtained in the photolysis of 3 in the absence of 2, that is, 81:
L
[
1] ) (1 - b)[1]
(b: const.; 0 e b e 1) (2)
t
t
1
2
1
9.
Determination of the Rate Constant for the Cycloaddition
The final concentration of 4, [4]∞Lt, is shown as
of 1 and 2 in Room-Temperature Solution. We have shown
that 4 was the only product obtained by the reaction of 1 and
L
L
[
4]∞ t ) [4] + a[1]
(3)
(4)
t
t
2
. The decay of 1 in the absence of dienophiles follows second-
4d,g,i
Thus, eqs 1, 1′, 2, and 3 are reduced to
order kinetics, which is reported by spectroscopic
delayed, two-color photolysis experiments. Therefore, we
and time-
1
2
L
∞ t
obtain a kinetic equation on 1 as
[
4] - [4]
∞
[
1] )
t
ab
d[1]t
2
-
) k [2] [1] + k [1]
t
(6)
1
t
t
2
L
dt
Equation 4 indicates that the value ([4]∞ - [4]∞ t) is proportional
to [1]t, the concentration of 1 at delay time t.
Determination of Parameters a and b. The yield of 1
obtained from 10 M 3 in acetonitrile solution by the irradiation
of a pulse of the KrF excimer laser is reported to be 48%
under the same experimental conditions as those of the present
where [1]t and [2]t are the concentrations of 1 and 2 at time t,
k1 is the rate constant of the cycloaddition 1 + 2 f 4, and k2
is the rate constant of the second-order decay of 1 (cf., Scheme
-4
1
3
1
).
As we can approximate [2]t as a constant ([2]t ≈ [2]0), because
1
2
-5
experiments. Therefore, we obtain [1]0 ) 4.8 × 10 M. The
1
5
[
2]t . [1]t, eq 6 can be solved as
value [4]∞ can be calculated from the yield of 4 in the one-
-5
color KrF excimer laser photolysis, which is [4]∞ ) 4.3 × 10
1
1]t
k2
1
k2
M (43% yield from 10-4 M 3 and 10 M 2). From eq 1′ and
-3
)
+
exp(k [2] t) -
(7)
1
t
(
)
[
k1[2]t [1]0
k1[2]t
the values [1]0 and [4]∞ , we obtain
The second-order rate constant, k2, is reported to be 9.94 ×
[
4]∞
3
-1 -1
1
0 M
s
at 25 °C, which was obtained by a spectroscopic
By substituting the values k2, [2]t (≈[2]0 ) 10
a )
) 0.90
[
1]0
4g,16
-3
method.
(
15) When [2]
t
is a constant, eq 6 becomes a Bernoulli’s differential equation,
The result indicates that the selectivity of reaction 1 + 2 f 4
in the thermal reactions of 1 was 90%.
The ratio of photochemical to thermal processes by the
irradiation of the second XeCl laser pulse is indicated by
which can be easily solved. Derivation of eq 7 from eq 6 is shown in the
Supporting Information.
4
g
(
16) The reported second-order rate constant is thought to be dimerizations of
1
; however, we have revealed that other reactions are also involved in the
12
second-order decay of 1.
J. AM. CHEM. SOC.
9
VOL. 125, NO. 4, 2003 1107

A R T I C L E S
Ouchi et al.
to quench the cycloaddition reaction. The rate constant of the
cycloaddition of 1 and 2 was obtained by the analysis of the
delay-time dependence of the product yields; the rate constant
5
-1 -1
obtained was 2.1 × 10 M s .
Experimental Section
Compounds 3, 4, 5, and 6 were synthesized according to the reported
procedures.11b,12 Maleic anhydride (2) was purchased from Wako
Chemicals, and spectroscopic grade acetonitrile was from Cica-Merck/
Kanto Chemicals.
Figure 3. Plots of ([AD]∞ - [AD]∞Lt) as a function of t with curve fitting
according to eq 8.
Time-Delayed, Two-Color Photolyses. The reactions were con-
ducted in 0.05 mL of an acetonitrile solution of 10- M 3 and 10-3
4
M
Scheme 4
2
under a nitrogen atmosphere at room temperature by using a synthetic
quartz cuvette of 10 mm width and 1 mm optical path. The first laser
pulse was generated by a Lambda Physik EMG 201 MSC [KrF, 1.25
×
1021 photons m-2 pulse-1 (100 mJ cm-2 pulse-1), pulse width
(
fwhm): 30 ns], and the second pulse was generated by a Lambda
Physik EMG 102 MSC [XeCl, 1.88 × 10 photons m-2 pulse-1 (121
21
-2
-1
mJ cm pulse ), pulse width (fwhm): 14 ns] excimer laser. The pulse
energy was measured by a Gentec ED-500 joulemeter and a Tektronic
T912 10 MHz storage oscilloscope. The delay time was defined as the
time between two peaks of the KrF and XeCl laser pulses and varied
from 0 ns to 0.1 s. The delay times between the two laser pulses were
controlled by a Stanford Research Systems DG535 four-channel digital
delay/pulse generator. The delay times of the two laser pulses were
measured with a Hamamatsu Photonics R1193U-55 biplanar phototube
and an Iwatsu Electric TS-8123 storage scope. The consumption of 3
and the yields of 4, 5, and 6 were obtained from the average of two
independent runs.
-
5
M), [1]0 ()4.8 × 10 M), a ) 0.90, b ) 0.77, and eq 4 to eq
, we obtain
7
L
[
4] - [4]
)
∞ t
∞
0
.69
(8)
6
6
5
9
.94 × 10
10
-3
9.94 × 10
+
exp(10 k t) -
1
(
)
k
4.8
k
1
1
Figure 3 shows the plots of ([4]∞ - [4]∞Lt) as a function of
delay time, t, which was calculated from the values in Figure
. The solid curve in Figure 3 shows the result on the curve
fitting according to eq 8; the room-temperature rate constant
k1 obtained by the curve fitting was 2.1 × 10 M s .
The rate constant of the cycloaddition of substituted o-
quinodimethane 7 and 2 (Scheme 4) in acetonitrile has been
reported to be 2.2 × 10 M s , which is ca. 10-fold larger
than that of 1. However, this difference may be explained by
the acceleration of the cycloaddition reaction due to the
substituent effects.
One-Color Excimer Laser Photolyses and Decomposition of 4
2
and 5. The photolyses of 10 M 3 in the presence of 10-3 M 2, and
those of 10- M 4 and 5, were conducted with an excimer laser using
the same experimental setup and procedure as those of the time-delayed,
two-color laser photolysis. The fluence of the lasers was the same as
that in the two-color experiments. The results were obtained from the
average of three independent runs.
-4
17
4
5
-1 -1
6
-1 -1 6
Analyses of the Products. The yields of 4, 5, and 6, and the
consumption of 3, were determined by HPLC analysis (detection
wavelengths of UV detectors: 254 and 300 nm) on a Merck Super-
sphere 60 RP-8e column (244 mm × 4 mm i.d.), and their retention
times were compared with authentic samples.
Conclusion
A time-delayed, two-color pulse laser photolysis technique
was used for a kinetic study of short-lived transient species
through product analysis, the determination of the rate constant
of the cycloaddition of 1 and 2 in room-temperature solutions.
o-Quinodimethane (1) was generated from 3 by the irradiation
of a pulse of a KrF excimer laser (248 nm) in the presence of
excess 2, and a successive pulse of a XeCl excimer laser (308
nm) was irradiated to the reaction mixture after varied delay
times from 0 to 0.1 s for the decomposition of the remaining 1
Acknowledgment. We thank the Agency of Industrial Science
and Technology for financial support. Z.L. thanks the Agency
of Industrial Science and Technology for the ITIT and AIST
fellowships.
Supporting Information Available: Derivation of eq 4 from
eqs 1, 1′, 2, and 3, and derivation of eq 7 from eq 6 (PDF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
(
17) The Levenberg-Marquardt algorithm was used for the curve fitting, which
was conducted by using a computer program ORIGIN version 6.1J,
produced by MICROCAL Software, Inc.
JA027653V
1108 J. AM. CHEM. SOC.
9
VOL. 125, NO. 4, 2003