Formation of stable carbonyl oxide by photooxidation of (phenyl)(2-thienyl)diazomethane

Article abstract of DOI:10.1007/s11172-008-0108-6

Formation of (phenyl)(2-thienyl)carbonyl oxide, which has the longest lifetime among known carbonyl oxides, has been registered by flash photolysis in acetonitrile at room temperature. It is consumed in the pseudomonomolecular reaction with the parent dia

Full text of DOI:10.1007/s11172-008-0108-6

Russian Chemical Bulletin, International Edition, Vol. 57, No. 3, pp. 679—681, March, 2008
679
Formation of stable carbonyl oxide
by photooxidation of (phenyl)(2ꢀthienyl)diazomethane

A. G. Mukhamadeeva, E. M. Chainikova, and R. L. Safiullin
Institute of Organic Chemistry,
Ufa Research Center of the Russian Academy of Sciences,
71 prosp. Oktyabrya, 450054 Ufa, Russian Federation.
Fax: +7 (347) 235 6066. Eꢀmail: kinetic@anrb.ru
Formation of (phenyl)(2ꢀthienyl)carbonyl oxide, which has the longest lifetime among known
carbonyl oxides, has been registered by flash photolysis in acetonitrile at room temperature. It is
consumed in the pseudomonomolecular reaction with the parent diazo compound.
Key words: kinetics, flash photolysis, carbonyl oxides, diazo compounds, oxygen.
Carbonyl oxides (R2COO) are key intermediates in
ozonolysis of olefins.1 Photooxidation of diazo comꢀ
pounds, so called the "triplet mechanism" of carbonyl
oxides generation, is a convenient method for the prepaꢀ
ration of carbonyl oxides2 (Scheme 1).
lecular termination is characteristic of most aromatic
carbonyl oxides.3,4 Secondly, such substituents as broꢀ
mo,4 methyl,3,8 tertꢀbutyl9 in orthoꢀposition relatively to
the carbonyl oxide group sharply increase the lifetime of
the carbonyl oxides. Thus, the halflife time of unsubstiꢀ
tuted diphenylcarbonyl oxide in acetonitrile at room temꢀ
perature is ~10–2 s, while for 2ꢀbromodiphenylcarbonyl
oxide it increases by two orders of magnitude.4 Sterically
hindered dimesitylcarbonyl oxide (the halflife time at
room temperature in acetonitrile is ~0.4 s 3 or ~4 s 8) and
(6ꢀtertꢀbutylꢀ2,3,4ꢀtrimethylphenyl)phenylcarbonyl oxꢀ
ide (the halflife time in CCl3F—(CBrF2)2 (1 : 1) at 267 K
is 4.5 min 9) are the most stable out of known by far
carbonyl oxides. Both these carbonyl oxide are consumed
according to the first order kinetic law.
In the present work, an absorption spectrum of (pheꢀ
nyl)(2ꢀthienyl)carbonyl oxide (1) in acetonitrile has been
obtained by the flash photolysis at room temperature and
kinetic features of its decay have been studied. It was
found that the pseudomonomolecular termination obꢀ
served for this carbonyl oxide turned out to be its reacꢀ
tion with the parent diazo compound, by the decrease in
concentration of which, the time of consumption of comꢀ
pound 1 can be prolonged to 20 min or more.
The flash photolysis of acetonitrile solution of (pheꢀ
nyl)(2ꢀthienyl)diazomethane (2) in the presence of oxyꢀ
gen results in the optical absorption in the wavelength
region 350—420 nm, which disappears with time. In the
absence of oxygen, the signal in the mentioned wave
region is also absent. This gives us a reason to suggest that
it corresponds to carbonyl oxide 1. A similar signal is
also registered during the flash photolysis of the diazo
compound 2—methylene blue system, which was menꢀ
tioned above as the singlet pathway for the generation of
carbonyl oxides. The absorption spectrum of carbonyl
Scheme 1
The "singlet mechanism" of generation of carbonyl
oxides suggests an interaction of the singlet oxygen with
a diazo compound.2 In this case, the use of a singlet
sensitizer, for example, methylene blue (MB), is necesꢀ
sary (Scheme 2).
Scheme 2
Aromatic carbonyl oxides in solution are characꢀ
terized by optical absorption in the visible range of
the spectrum, the maximum of which is in the region
390—450 nm.3,4 Kinetic regularities of consumption of
these species in the absence of oxidizing substrates rather
strongly depend on the nature of substituents at the carꢀ
bonyl oxide group. The influence of a substituent characꢀ
ter on the mechanism of termination of carbonyl oxides
can be of two main kinds. First, strong electronꢀdonating
groups (amino, methoxy) in the aromatic core decrease
an activation energy of the isomerization of carbonyl
oxides into dioxiranes.5—7 Such carbonyl oxides are conꢀ
sumed in the monomolecular process, whereas a bimoꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 666—668, March, 2008.
1066ꢀ5285/08/5703ꢀ679 © 2008 Springer Science+Business Media, Inc.

680
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 3, March, 2008
Mukhamadeeva et al.
oxide 1, recorded for the concentration of the parent
diazo compound 2 being 6•10–4 mol L–1, is not changing
in time (Fig. 1). This demonstrates that only one species
absorbs the light under these conditions. The absorption
maximum of carbonyl oxide 1 is at 375 nm. A decrease in
time of optical density by 90% and more can be well
described by the first order kinetic equation (Fig. 2,
graph 2):
tion of diazo compound 2 in the system and this value
varies from a few seconds to 20 min, while the [2]0 value
changes in the range from 1•10–3 to 5•10–7 mol L–1
(see Fig. 2). The keff value is linearly dependent from
the concentration of diazo compound 2 in the range
(1—100)•10–5 mol L–1 (Fig. 3). From the slope of this
relationship, we obtained the rate constant of the reacꢀ
tion of carbonyl oxide 1 with the parent diazo comꢀ
pound: k1+2 = (1.37 0.04)•103 L mol–1 s–1. At [2]0 beꢀ
ing < 1•10–5 mol L–1, the kinetic curves of consumption
of carbonyl oxide 1 no more can suffice to the equation
(1) (see Fig. 2, graph 1). This can be rationalized in view
of the starting concentration of carbonyl oxide 1 being
comparable with the concentration of diazo compound 2
and, along with consumption of carbonyl oxide 1 in
the reaction with the parent diazo compound 2, by
all appearances, another channel for the termination of
this species is involved. Obviously, this is a very slow
process.
A – A∞ = (A0 – A∞)exp(–kefft),
(1)
where А0 is the initial optical density of carbonyl oxide 1;
А∞ is the final optical density, caused by absorption of
the reaction products; keff is effective rate constant of
consumption of carbonyl oxide 1.
The time of complete consumption of carbonyl oxide
1 decreases with the increase in the initial concentraꢀ
A
It can be suggested that the obtained carbonyl oxide 1
is stabilized by the interaction of the terminal oxygen
atom of the carbonyl oxide group and the neighboring
sulfur atom.
1
0.30
0.25
2
0.20
3
0.15
4
0.10
0.05
This hypothesis will be verified in our further
research.
360
370
380
390
400
410
λ/nm
We studied the products of the decay reaction of carꢀ
bonyl oxide 1 using for this purpose the "singlet pathway"
for the generation of carbonyl oxide 1 under steadyꢀstate
photooxidation conditions of acetonitrile solution of
diazo compound 2 ([2]0 = 2•10–4 mol L–1, methylene
Fig. 1. Optical spectrum of carbonyl oxide 1 in acetonitrile, recordꢀ
ed with concentration of the starting diazo compound [2]0
=
6•10–4 mol L–1 immediately after the flash (1), after 0.5 (2), 1 (3),
and 1.5 s (4).
A
1
2
3
4
5
t/s
k
eff/s–1
0.15
0.10
0.05
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
2
1
5
10
15
20
t/min
Fig. 2. Kinetic curves of consumption of carbonyl oxide 1
in acetonitrile at [2]0 = 5•10–7 (1) and 1•10—3 mol L–1 (2)
(the solid line represents theoretical description of the curve by
the equation (1)).
2.0
4.0
6.0
8.0 [2]0•104/mol L–1
Fig. 3. The effective rate constant of consumption of 1 versus
the starting concentration of diazo compound 2.

Stable phenyl(2ꢀthienyl)carbonyl oxide
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 3, March, 2008
681
blue was the sensitizer (1•10–5 mol L–1), irradiation with
the light of λ > 540 nm). Analysis of the reaction mixture
by HPLC showed that (phenyl)(2ꢀthienyl)ketone (3) was
the only reaction product (it was identified by compariꢀ
son with the authentic sample). Proceeding from this and
taking into account the observed kinetic features, it can
be concluded that when diazo compound 2 is presented
in a large excess as compared with the concentration
of carbonyl oxide 1, the only reaction takes place in
the system, namely, the interaction of carbonyl oxide 1
with its precursor (Scheme 3).
emy of Sciences (Program "Theoretical and Experimenꢀ
tal Study of the Nature of Chemical Bond and Mechaꢀ
nisms of the Most Important Chemical Reactions and
Processes") and the Ministry of Education and Science
of Russian Federation (Analytical Department Specially
Purposed Program "Development of the Scientific Poꢀ
tential of the Higher School" (2006—2008)", Project
code RNP 2.2.1.1.6332).
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Scheme 3
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In the following study, we are going to clarify
the mechanism of termination of carbonyl oxide 1 under
conditions when diazo compound is absent in the system.
This work was financially supported by the Division
of Chemistry and Materials Science of the Russian Acadꢀ
Received November 30, 2007;
in revised form January 19, 2008