Synthesis and thermal decomposition of hydrotrioxide obtained by ozonization of exo-bicyclo[2.2.1]heptan-2-ol

Article abstract of DOI:10.1007/s11172-007-0044-x

Low-temperature (-70 °C) ozonization of exo-bicyclo[2.2.1]heptan-2-ol in CCl₃F led to a hydrotrioxide, which was identified by ¹H NMR spectroscopy. Kinetics of decomposition of given hydrotrioxide was studied by analysis of the chemiluminescence fading in the IR range of the spectrum and the activation parameters of the process were calculated. Singlet oxygen (¹Δ_g) served as an emitter of eradiation. Yields of ¹O₂ in a range of temperature from -31.0 to +12.5 °C were determined (at -31 °C the yield was 37.6%). Bicyclo[2.2.1]heptan-2-one was found to be the main product of decomposition of the hydrotrioxide (the yield was 98%).

Full text of DOI:10.1007/s11172-007-0044-x

Russian Chemical Bulletin, International Edition, Vol. 56, No. 2, pp. 271—275, February, 2007
271
Synthesis and thermal decomposition of hydrotrioxide
obtained by ozonization of exoꢀbicyclo[2.2.1]heptanꢀ2ꢀol
A. R. Abdrakhmanova, L. R. Khalitova, L. V. Spirikhin,
V. A. Dokichev, S. A. Grabovskiy,ꢀ and N. N. Kabal'nova
Institute of Organic Chemistry, Ufa Research Center of the Russian Academy of Sciences,
71 prosp. Oktyabrya, 450054 Ufa, Russian Federation.
Fax: +7 (347 2) 35 6066. Eꢀmail: stas_g@anrb.ru
Lowꢀtemperature (–70 °С) ozonization of exoꢀbicyclo[2.2.1]heptanꢀ2ꢀol in CCl3F led to
a hydrotrioxide, which was identified by 1H NMR spectroscopy. Kinetics of decomposition of
given hydrotrioxide was studied by analysis of the chemiluminescence fading in the IR range of
the spectrum and the activation parameters of the process were calculated. Singlet oxygen (1∆ )
g
served as an emitter of eradiation. Yields of 1O2 in a range of temperature from –31.0 to
+12.5 °C were determined (at –31 °C the yield was 37.6%). Bicyclo[2.2.1]heptanꢀ2ꢀone was
found to be the main product of decomposition of the hydrotrioxide (the yield was 98%).
Key words: hydrotrioxide, singlet oxygen, rate constants, ozonization.
Hydrotrioxides (HTO) are known as unstable interꢀ
mediates in the lowꢀtemperature ozonization of various
saturated organic compounds.1,2 The most important proꢀ
cess in decomposition of HTO is the generation of oxygen
in a singlet state. Analysis of the methods for determinaꢀ
tion of the yields of singlet oxygen shows that most methꢀ
ods, which use the 1O2 acceptors, are not effective.3 There
is always a way for the direct interaction of HTO with the
acceptors of singlet oxygen, which might give too high
Bagdasar'yan equation.10 It is suggested that formation of
1O2 takes place either as a result of molecular decomposiꢀ
tion of HTO or during disproportionation of the radical
pair |RO• •OOH| in the solvent cage. The authors9 gave
preference to the latter suggestion. However, this attitude
does not explain why the 1O2 yields change from 15
(–15 °C) to 11% (+18 °C)9 and why the radical channel
part in the decomposition is equal to zero11 for the therꢀ
molysis of MeCH(OH)OOOH, the very object of the
analysis.
In the present work we have studied by the chemiluꢀ
minescence method the decomposition of hydrotrioxide 1,
arising during the lowꢀtemperature ozonization of exoꢀbiꢀ
cyclo[2.2.1]heptanꢀ2ꢀol. The kinetic parameters were deꢀ
termined and the yield of singlet oxygen was calculated.
1
yields of O2. Unfortunately, the most data on the yields
of 1O2 in decomposition of HTO was obtained exactly
with the use of acceptors.2
By now, there are known eleven literature examples
for synthesis of HTO of alcohols with alkyl substituents
(Me, Et, Pr, CH2Cl, CH2OH, Me2COH and MeCHOH)
as well as HTO with phenyl substituent, namely,
1ꢀhydroxyethylꢀ1ꢀphenylꢀ1ꢀhydrotrioxide.4—7 The kinetic
regularities of decomposition were studied for most HTO,
however, the yields of singlet oxygen were reliably deterꢀ
mined only for three of them.2
Experimental
exoꢀBicyclo[2.2.1]heptanꢀ2ꢀol (Aldrich, 98%) was purified
by sublimation under low pressure. Dichloromethane was shaken
with concentrated sulfuric acid, washed with saturated NaHCO3
solution and water until the neutral reaction persists, dried with
MgSO4, and redistilled. Freon 11 (CCl3F) was saturated with
ozone until the blue color steadily persists. After the removal of
the excess of ozone, Freon was treated with Na2CO3 solution,
dried with MgSO4, and redistilled. All the solvents were kept
over molecular sieves 4 Å.
NMR spectra were recorded on a Bruker AMꢀ300 specꢀ
trometer (standard, Me4Si; solvents, acetoneꢀd6, tolueneꢀd8
and CCl3F). GLCꢀanalysis was carried out on a Hewlett
Packard 5890E SERIES II gas chromatograph with a capilꢀ
lary column HPꢀ5 (crossꢀlinked 5% PH ME Silicon,
30 m × 0.32 mm × 0.25 µm Film). nꢀDecane was used as the
1
The highest yield of O2 calculated based on the obꢀ
servation data of chemiluminescence (CL) in the IR range
of the spectrum8 was recorded in the decomposition of
MeCH(OH)OOOH and varied in a range from 0.9% in
MeNO2 to 18% in CFCl3 (+5 °C).9 Analysis of the solꢀ
1
vent effect on the O2 yields within the framework of the
Koppel—Palm equation shows the yields rise with the
increase of the solvent polarity, whereas, the increase in
specific solvation leads to the yields decrease. Lowering
of the yields of 1O2 with the temperature increase2 is
observed for Me2C(OH)OOOH and MeCH(OH)OOOH,
which can be described within the framework of the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 263—266, February, 2007.
1066ꢀ5285/07/5602ꢀ0271 © 2007 Springer Science+Business Media, Inc.

272
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 2, February, 2007
Abdrakhmanova et al.
In one of the last publications15, dealing with the
ozonization of acetals, the authors made a conclusion
about the ionic character of the reaction of ozone with
a C—H bond. According to this mechanism, compounds 1
and 2 might be formed through an ion pair (Scheme 1).
internal standard. Registration of the IRꢀchemiluminescence
(IRꢀCL) was performed on a highꢀsensible photometric instalꢀ
lation.12 The light flows were measured with the help of
a FEUꢀ83 photomultiplyer cooled down to –70 °С. When
using an IKSꢀ7 light filter, the range of the registration was
1000—1300 nm.
Synthesis of hydrotrioxide 1 from exoꢀbicyclo[2.2.1]heptanꢀ
2ꢀol. A preꢀcooled ozoneꢀoxygen mixture was bubbled through
the solution of exoꢀbicyclo[2.2.1]heptanꢀ2ꢀol in CCl3F
(0.22—0.30 mol L–1) kept at –70 °С. It was found by experiꢀ
ment that the optimal time of ozonization to obtain hydrotrioxide
in sufficient yield without its further transformation under the
action of O3 is 3 h. After this period, the remaining ozone was
removed by bubbling of preꢀcooled argon through the solution.
The concentration of hydrotrioxide was determined by its reacꢀ
tion with triphenylphosphine.13 The solutions after ozonization
contained 0.21—0.28 mol L–1 of the hydrotrioxide. Comꢀ
pound 1 was identified by NMR spectroscopy at –70 °С. In the
1H NMR spectrum of the hydrotrioxide obtained, there was a
characteristic signal of a proton of the O3H group at δ 13.55
(tolueneꢀd8—CCl3F), disappearing after heating up to ~20 °C.
Kinetics of decomposition of hydrotrioxide 1 was studied by
analysis of the fading of CL in the IR range of the spectrum. The
СH2Cl2 (2.5—2.8 mL) was placed into a 10ꢀmL glass reactor
kept at constant temperature, then a solution of hydrotrioxide 1
(0.2—0.5 mL, concentration 0.21—0.28 mol L–1) was added
with a preꢀcooled pipette, and CL was registered. The temperaꢀ
ture was varied in the range of –31.0—+12.5 °С. After complete
consumption of hydrotrioxide 1, the solvent was evaporated.
The residue, according to the GLC data, contained the starting
alcohol (1.5%) and bicyclo[2.2.1]heptanꢀ2ꢀone (2) (98%). The
product was identified by comparison with authentic samples
and by 13С NMR spectroscopy.
Scheme 1
Phenomenologically in a simplified form, the process
can be shown as follows (Scheme 2).
Scheme 2
Results and Discussion
Ozonization products of exoꢀbicyclo[2.2.1]heptanꢀ2ꢀol.
Bicyclo[2.2.1]heptanꢀ2ꢀone (2) is found to be a reaction
product of ozone with exoꢀbicyclo[2.2.1]heptanꢀ2ꢀol and
hydrotrioxide 1 was an intermediate in this process. The
yield of the ketone after the decomposition of 1 was 98%
and the conversion of the substrate was 98%. Compound 2
was formed via intermediate 1 by thermal decomposition
Reagents and conditions: i. O3, –70 °C.
3
of the latter with emission of oxygen (1O2, O2) or upon
Consumption of the substrate in the reaction with
ozone can take place by two competing ways leading to
the ketone or hydrotrioxide. Apart from that, the latter is
consumed in the reaction with ozone. All the foregoing
accounts for the deviation of stoichiometry of the reacꢀ
tion from the 1 : 1 ratio and the impossibility of obtaining
hydrotrioxide 1 in more than 35% yield.
1H NMR spectrum of hydrotrioxide 1. The spectrum in
acetoneꢀd6 has a set of signals in the range of δ 11.5—13.0
corresponding to the proton of the O3H group (Fig. 1),
whereas in tolueneꢀd8 there is the only signal at δ 13.55.
The dramatic difference in the shape of the signal of the
hydrotrioxide proton in these solvents is apparently reꢀ
lated to the specific solvation of hydrotrioxide 1 with
acetone to form more stable solvate shells, which stabilize
its reaction with ozone. Earlier,14 it was found that triꢀ
oxides react with ozone. The stoichiometry of the reacꢀ
tion is evidence of this: 1 mol of the substrate requires
1.2—2 mol of ozone. The control experiments showed
that there is no consumption of the trioxide and ozone
at –70 °С in the solvent used. It should be noted that,
when using CH2Cl2 as a solvent for ozonization, the conꢀ
version of the substrate does not exceed 15%, with a moꢀ
lar ratio of substrate : O3 being 1 : 7. The last fact shows
that it is unreasonable to use solvents with weak C—H
bonds for the lowꢀtemperature ozonization. It is due to
the formation of oxygenꢀcentered radicals in the reaction
of trioxide with ozone14 and with involvement of the solꢀ
vent into the process.

Hydrotrioxide: synthesis and thermolysis
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 2, February, 2007
273
I (rel. units)
–ln I
–1.8
120
1
2
–2.7
–3.6
–4.5
90
60
30
13.0
12.5
12.0
δ
Fig. 1. Signals of proton in the O3H group in 1H NMR spectrum
of hydrotrioxide 1 in a mixture CFCl3—acetoneꢀd6 (1 : 1)
at –70 °С.
0
10
20
30
40
50
t/s
Fig. 2. The typical kinetic curve of the IRꢀCL fading for decomꢀ
position of hydrotrioxide 1 in dichloromethane (1) and its semiꢀ
logarithmic anamorphose (2) (–20 °С; [1]0 = 0.1 mol L–1).
various types of associates of 1. Moreover, acetoneꢀd6 can
react with compound 1 to yield trioxide 3 (Scheme 3).16
Table 1. Dependence of the rate constant of decomposition of
hydrotrioxide 1 in CH2Cl2 (k) and the singlet oxygen yields from
Scheme 3
the temperature ([1]0 = 0.1 mol L–1
)
1
T/°С
k•10–2/s–1
Yield O2 (%)
–31.0
–20.5
–11.5
0
0.8 0.2
1.4 0.1
2.8 0.1
3.3 0.1
6.3 0.3
37.6
35.0
29.2
24.4
23.9
+12.5
The latter, due to the two OH groups present, can
form stable associates with hydrotrioxide 1 causing apꢀ
pearance of new signals of the О3H group in the specꢀ
trum. The presence of only one signal in tolueneꢀd8 soluꢀ
tion can be explained by formation of associates with
similar structures and/or by similar electron density on
the hydroperoxide proton. In addition, it should be stated
that we deal with the individual trioxide and not with the
mixture of exoꢀ and endoꢀisomers, since the chemical
shifts of protons in the O3H group significantly differ for
such isomers.17,18 It is known4,6,7 that ozonization of difꢀ
ferent isomers occurs with retention of configuration, that
is why formation of 2ꢀexoꢀhydroxybicyclo[2.2.1]heptylꢀ
2ꢀhydrotrioxide is only possible.
Thermolysis. Thermal decomposition of hydrotrioxide
1 is accompanied by CL in the IR range of the spectrum
with the maximum at 1270 20 nm. The change in the
solvent (tolueneꢀh8 to tolueneꢀd8) leads to the increase in
the luminescence intensity. These facts are evidence of
the formation in the system of oxygen in a singlet state 1∆g.3
All the kinetic experiments were carried out in СH2Cl2,
since CL is the most intensive in this solvent. After the
addition of the hydrotrioxide solution into the kept at
constant temperature reactor, CL is observed the intenꢀ
sity of which reaches the maximum and then exponenꢀ
tially decays. The curve of the IRꢀCL decay after passing
the maximum is well linearized in the coordinates of the
first order kinetic equation (Fig. 2).
The effective rate constants were calculated from the
semiꢀlogarithmic anamorphoses of the IRꢀCL decay
curves (Table 1). In addition, the activation parameters of
the process were calculated from the data obtained
logk = (2.1 0.1) – (6.5 0.6)/θ,
θ = 2.3RT (kcal mol–1).
The too low value of the preꢀexponential factor may
be connected with the highly ordered transition state of
the decomposition of 1 to yield 1O2 and/or with the solvaꢀ
tion of the transition state by a solvent due to its higher
polarity as compared with the starting HTO or its associꢀ
ates. The activation parameters of decomposition of alcoꢀ
hol hydrotrioxides vary within wide limits,2 and the values
for decomposition of compound 1 are near the lower
border. The hydrotrioxide 1 is the least stable in compariꢀ
son with the HTO obtained from alcohols with two alkyl
substituents. Thus the rate constant for decomposition of
Me2C(OH)OOOH (see Ref. 6) at –20 °C is equal to
2.8•10–3 s–1, whereas for hydrotrioxide 1 this is 5 times as
high, which may be connected with the strained structure
of the alkyl fragment in the trioxide under consideration.
The yield of singlet oxygen decreases with the increase
in the temperature (see Table 1), which can be explained
based on the following suggestions.

274
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 2, February, 2007
Abdrakhmanova et al.
1. Singlet oxygen is formed in the disproportionation
In conclusion, the synthesis of hydrotrioxide from
exoꢀbicyclo[2.2.1]heptanꢀ2ꢀol has been accomplished for
the first time and its decomposition has been studied by the
IRꢀCL method. In the decomposition of the hydrotriꢀ
of the radical pair |RO• •OOH| in the solvent cage, the
lifetime of which decreases with the temperature increase
and, consequently, the yield of 1O2 drops.9 However, this
assumption does not always completely explain all the
experimental facts.
1
oxide, the yield of O2 can be as high as 38%. The use of
ozone for the oxidation of exoꢀbicyclo[2.2.1]heptanꢀ2ꢀol
allows one to obtain the corresponding ketone with a
high yield (98%).
2. It cannot be ruled out that the part of the radical
processes increases with the increase in temperature, which
can lead to the decrease in the yield of singlet oxygen.
This work was financially supported by the Division of
Chemistry and Materials Sciences of the Russian Acadꢀ
emy of Sciences (Program for Basic Research "Theoretiꢀ
cal and Experimental Studies of the Nature of Chemical
Bond and Mechanisms of the Most Important Chemical
Reactions and Processes").
1
3. In the decomposition of HTO, the O2 turns out to
be in the solvent cage together with the extinguisher (ROH
and/or H2O). It may so happen that with the increase in
temperature the decay inside the cage occurs more effiꢀ
cient than in the solution. An example, when the exited
state of indole reveals the extraordinary temperature senꢀ
sitivity concerning its lifetime and quantum yield in aqueꢀ
ous solution,19,20 can be shown in favour of this sugꢀ
gestion.
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)
contribute to the consumption of singlet oxygen with the
increase in the temperature.

Hydrotrioxide: synthesis and thermolysis
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Received October 12, 2006;
in revised form January 16, 2007