Formation of Singlet Oxygen during Thermal Degradation of Hydrotrioxides of Triorganosilanes

Article abstract of DOI:10.1134/S0018143919060109

Abstract: The yield of singlet oxygen (¹O₂) due to the degradation of triethylsilane, dimethylphenylsilane, triphenylsilane, and dimethyl(trimethylsiloxy)silane hydrotrioxides has been determined for the first time using the IR chemi

Full text of DOI:10.1134/S0018143919060109

ISSN 0018-1439, High Energy Chemistry, 2019, Vol. 53, No. 6, pp. 435–437. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Khimiya Vysokikh Energii, 2019, Vol. 53, No. 6, pp. 438–440.
PHOTONICS
Formation of Singlet Oxygen during Thermal Degradation
of Hydrotrioxides of Triorganosilanes
L. R. Khalitovaa, S. A. Grabovskiia, *, and N. N. Kabal’novaa
aUfa Institute of Chemistry, Ufa Federal Research Center, Russian Academy of Sciences, Ufa, 450054 Russia
*e-mail: stas_g@anrb.ru
Received May 6, 2019; revised June 10, 2019; accepted June 19, 2019
Abstract—The yield of singlet oxygen (1O2) due to the degradation of triethylsilane, dimethylphenylsilane,
triphenylsilane, and dimethyl(trimethylsiloxy)silane hydrotrioxides has been determined for the first time
using the IR chemiluminescence technique. The most effective sources of singlet oxygen in this series are
1
triphenylsilyl hydrotrioxide and dimethyl(trimethylsiloxy)silyl hydrotrioxide. The yield of O2 upon their
degradation is 69 and 92%, respectively.
Keywords: silanes, hydrotrioxides, singlet oxygen
DOI: 10.1134/S0018143919060109
INTRODUCTION
EXPERIMENTAL
Commercial silanes (triethylsilane (1), dimethyl-
phenylsilane (2), triphenylsilane (3), dime-
thyl(trimethylsiloxy)silane (4)) available from
Fluka/Aldrich and having purity of >95% (by GLC)
were used without further purification. Dichloro-
methane was purified according to a standard proce-
dure and dried over molecular sieves 4 Å. Ozone was
obtained using an ozonizer of standard design [18].
The concentration of ozone in the gas phase was
~1.75 mmol/L. Triphenylphosphite ozonide was
obtained according to the procedure described in [19].
Triphenylphosphite ozonide was analyzed using the
31P NMR technique (H3PO4 standard).
Silane hydrotrioxides were prepared at a tempera-
ture of 183 K by passing a cooled ozone–oxygen mix-
ture through a 0.038–0.2 M solution of the corre-
sponding silane in CH2Cl2. The ozonation time was
3–14 min. The concentrations of hydrotrioxides and
triphenylphosphite ozonide were determined accord-
ing to the standard procedure with triphenylphosphine
[17]. NMR spectra were recorded on a Varian Mer-
cury-500 spectrometer, which allows recording spec-
tra at low temperatures down to 183 K.
The search for new sources of singlet oxygen and
their study has been of interest to researchers over the
years [1–6]. Chemical sources that make it possible to
generate singlet oxygen in organic media with suffi-
cient efficiency and, hence, are the most promising in
organic synthesis are few. First of all, these are phos-
phite ozonides and hydrotrioxides, which can be easily
synthesized by low-temperature ozonation. Triphen-
ylphosphite ozonide is one of the reference sources of
1O2, since its thermal degradation produces singlet
oxygen in quantitative yield [7]. The thermolysis of
hydrotrioxides containing germanium or silicon atoms
is also accompanied by the formation of singlet oxy-
gen, the yield of which is 25–70%, as determined by
the consumption of typical singlet oxygen scavengers
(1,3-diphenylisobenzofuran, tetraphenylcyclopenta-
dienone, 9,10-dimethylanthracene) [8–13]. It was
shown that the decomposition of triethylsilyl hydrotri-
oxide is accompanied by chemiluminescence in the IR
spectral region at λ = 1270–1277 nm [14], which is
characteristic of radiative deactivation of the 1∆g state
of singlet oxygen [15, 16], but the yield of 1O2 was not
determined.
Chemiluminescence in the IR region was recorded
Previously, we used the chemiluminescence tech- using a highly sensitive setup [17] with an FEU-83
nique to study the kinetics of thermal degradation of a photomultiplier tube cooled with a nitrogen flow to
number of organic hydrotrioxides and determine the 183 K. The emission region of singlet oxygen was iso-
yield of singlet oxygen upon their decomposition [17]. lated with an IKS-7 cutoff filter (λ > 900 nm). The
In this work, we use the IR chemiluminescence tech- chemiluminescence measurement setup was cali-
nique to determine the yield of singlet oxygen pro- brated using a source with a known yield of singlet
duced by degradation of a number of silyl hydrotriox- oxygen (Ф)—triphenylphosphite ozonide, for which
ides in dichloromethane.
Ф = 1.0 [7]. All experiments to determine the yield of
435

436
I, arb. units
KHALITOVA et al.
with a maximum at ~1270 nm. The chemilumines-
cence during the reaction of thermal decomposition of
hydrotrioxides 1a–4a was studied in dichloromethane
at 248 K. The hydrolysis of silane hydrotrioxides to
give silanol and hydrogen hydrotrioxide can be
neglected in this case. This is due to the long half-life
of hydrotrioxides in the hydrolysis reaction compared
to the duration of the experiment, which was 20 min,
while the half-life toward hydrolysis is about 10 h at
235 K according to 1H NMR data.
14
12
10
8
1а
4а
3а
6
The rate curves of IR chemiluminescence during
thermal degradation of silane hydrotrioxides are
shown in Fig. 1. The IR chemiluminescence decay
follows the first-order rate law; the calculated rate
constants are given in Table 1. Silane hydrotrioxides
are less stable than organic hydrotrioxides [22].
4
2а
2
0
50
100
t, s
150
200
1
The yield of O2 upon thermal degradation of
hydrotrioxides 1a–4a (Table 1) was determined using
the chemiluminescence method. For the hydrotriox-
ides studied, it ranges from 33% for phenyldimethylsi-
lane hydrotrioxide to 92% for dimethyl(trimethylsi-
loxy)silane hydrotrioxide. According to the data
obtained using 9,10-dimethylanthracene as a scaven-
Fig. 1. IR chemiluminescence curves during the degrada-
tion of hydrotrioxides 1a–4a (248 K, dichloromethane,
−2
−2
[1a] = 3.8 × 10 mol/L, [2a] = 5.8 × 10 mol/L,
0
0
0
−2
−2
[3a] = 6.9 × 10 mol/L, and [4a] = 3.3 × 10 mol/L).
0
singlet oxygen were performed with maintaining con-
stant parameters, such as geometry and volume of the
reactor, total volume of the reaction mixture, voltage
applied to the photomultiplier (1.6 kV), and its tem-
perature. The yield of singlet oxygen was calculated
according to the procedure described in [20].
1
ger of singlet oxygen, the O2 yield from 1a–3a was
70 10% [13], a value that is in good agreement with
our results, except for PhSi(Me2)OOOH. For the lat-
ter hydrotrioxide, the yield determined by chemilumi-
nescence measurements is two times less, which can
be explained by its lower steric hindrance and, hence,
higher reactivity leading to overestimation of the
results obtained by the scavenging technique, which is
due to the direct reaction of the scavenger with hydro-
trioxide. In the case of thermal degradation of hydro-
trioxides of hydrocarbons, the yield of singlet oxygen
does not exceed 15% (1,4-dimethylcyclohexyl hydro-
trioxide, 15°С, dichloromethane) [23, 24]. The
replacement of carbon with silicon in the hydrotriox-
ide moiety has a significant effect on the yield of sin-
glet oxygen produced by their degradation; this effect
is apparently due to enhanced stability of the radical
complex [R3SiO● HOO●], which increases the likeli-
hood of retaining the biradical pair in the singlet state,
in comparison with the carbon-containing analogue.
RESULTS AND DISCUSSION
The low-temperature (183 K) ozonation of trieth-
ylsilane (1), dimethylphenylsilane (2) triphenylsilane
(3), and dimethyl(trimethylsiloxy)silane (4) in
dichloromethane results in the corresponding hydro-
trioxides (1a–4a) identified by 1H NMR spectroscopy
according to a signal characteristic of hydrotrioxides at
δ 12–14 ppm, which corresponds to the proton of the
–OOOH group [13, 21] and disappears irreversibly
after heating to room temperature. For silane 4, syn-
thesized for the first time, the signal was observed at
δ 14.02 ppm (198 K, acetone-d6).
The thermal degradation of triorganosilane hydro-
trioxides is accompanied by IR chemiluminescence
CONCLUSIONS
The yield of singlet oxygen O2 (1∆g) during the deg-
radation of silane hydrotrioxides—triethylsilane,
dimethylphenylsilane, triphenylsilane, and dimethyl
(trimethylsiloxy) silane—has been determined using
the IR chemiluminescence technique. The 1O2 yield is
comparable to or higher than that for organic hydrotri-
Table 1. Yield of singlet oxygen during thermal degradation
of silane hydrotrioxides 1a–4a and effective rate constants
of chemiluminescence decay at 248 K in СН2Сl2
ϕ(1О2), %
k × 102, s–1
Hydrotrioxide
1a Et3SiOOOH
9.1 0.8
2.7 0.2
8.1 0.7
57
33
69
92
4
3
4
6
1
2a PhSi(Me2)OOOH
3a Ph3SiOOOH
oxides. The values for the O2 yield obtained previ-
ously for silyl hydrotrioxides are overestimated
because the direct reaction of scavengers with hydro-
trioxides was not taken into account.
4a Me3SiO–Si(Me2)OOOH
10
1
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FORMATION OF SINGLET OXYGEN DURING THERMAL DEGRADATION
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