Kinetics of heat-induced and photochemical transformations of quinonimines and their derivatives

Article abstract of DOI:10.1134/S1070363214040070

Heat-induced transformations of N-[2,6-diisopropylphenyl]-3,5-di(tert- butyl)-, N-[2,6-diethylphenyl]-3,5-di(tert-butyl)-, and N-[2-methyl-6- ethylphenyl]-3,5-di(tert-butyl)-o-benzoquinonimines in nonane follow the first-order rate equation, whereas that

Full text of DOI:10.1134/S1070363214040070

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 4, pp. 642–646. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © O.G. Mishchenko, I.V. Spirina, S.V. Maslennikov, A. V. Piskunov, I.N. Meshcheryakova, S.V. Panteleev, R.V. Kroik, 2014,
published in Zhurnal Obshchei Khimii, 2014, Vol. 84, No. 4, pp. 562–566.
Kinetics of Heat-Induced and Photochemical Transformations
of Quinonimines and Their Derivatives
O. G. Mishchenkoa, I. V. Spirinaa, S. V. Maslennikova, A. V. Piskunovb,
I. N. Meshcheryakovab, S. V. Panteleeva, and R. V. Kroika
a Research Institute of Chemistry, Nizhni Novgorod Lobachevsky State University,
pr. Gagarina 23, kor. 3, Nizhni Novgorod, 603950 Russia
e-mail: spirina@ichem.unn.ru
b Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, Nizhni Novgorod, Russia
Received June 17, 2013
Abstract―Heat-induced transformations of N-[2,6-diisopropylphenyl]-3,5-di(tert-butyl)-, N-[2,6-diethyl-
phenyl]-3,5-di(tert-butyl)-, and N-[2-methyl-6-ethylphenyl]-3,5-di(tert-butyl)-o-benzoquinonimines in nonane
follow the first-order rate equation, whereas that of N-[2,5-di(tert-butyl)phenyl]-3,5-di(tert-butyl-o-benzo-
quinonimine obey the second-order rate equation. Kinetic parameters of these reactions have been determined.
4аН-Phenoxazine derivatives of quinonimines are intermediates of the heat-induced transformations following
the first-order kinetics; under the irradiation with 405 nm light they undergo the ring opening to give the
starting compounds with quantum yield close to unity.
Keywords: quinonimine, reaction rate order, activation energy, photolysis, 4аН-phenoxazine, reaction rate
DOI: 10.1134/S1070363214040070
N-Aryl-o-benzoquinonimines (A) suffer the Diels–
Alder reaction in hexane or methanol at room
temperature to give dimers (C). Initially, the
quinonimine undergoes the cyclization into the 4аН-
phenoxazine (B); the reaction is possible only in the
case of Z-isomer of the starting compound [1, 2]
(Scheme 1).
In this work, we studied reactivity and mechanism
of heat-induced and photochemical transformations of
Scheme 1.
O
O
N
O
N
N
E
Z
А
B
O
O
N
N
C
642

KINETICS OF HEAT-INDUCED AND PHOTOCHEMICAL TRANSFORMATIONS
643
Scheme 2.
O
O
N
O
N
O
N
N
I
II
III
IV
N-aryl-o-benzoquinonimines I–IV as well as of the
products of their thermal decomposition in hydro-
carbon medium (Scheme 2).
Therefore, in the cases of compounds I–III, the
rate-limiting stage was the formation of 4аН-
phenoxazine derivatives (Scheme 1). Kinetic curves of
the consumption of the starting compounds and those
of accumulation of final products confirmed the
suggested reaction scheme (Fig. 3).
Heating of compounds I–IV in nonane at 283–
373 K induced certain changes in their electron
absorption spectra, and the initially red-violet solutions
turn yellow-green (Fig. 1).
After keeping the solutions with с = 1 × 10–2 mol/L
during 2 h at 323 K [mixture (a)] or during 4 h at
373 K [mixture (b)], the solvent was removed from the
reaction mixtures under a reduced pressure. In the IR
spectra of solids isolated from mixture (a) and (b) the
Heat-induced transformation of quinonimines I–III
followed the first-order rate equation at conversion up
to 70–80% (Fig. 2). The reaction order with respect to
the quinonimines was also 1.
c × 10–4, mol/L
D
(a)
(b)
t, min
t, min
λ, nm
Fig. 2. Kinetics of heat-induced transformation of com-
pound I in nonane (a) and the same kinetic curve in the
coordinates of the first-order reaction (b) (с0 = 1.8 ×
10–3 mol/L, 313 K).
Fig. 1. Changes of electron absorption spectra of com-
pound I in nonane (с0 = 1.8 × 10–3 mol/L, 323 K, l =
0.8 cm), thermal transformation during 2000 min.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 4 2014

644
MISHCHENKO et al.
c × 10–4, mol/L
Scheme 3.
R
R
O
N
O
N
Δ
hν
R
R
quinonimine, the latter being reduced to aminophenol
thus explaining the observed kinetics.
From the rate constants of thermal transformation
of compounds I–IV measured over a range of
temperatures we calculated the activation energy of the
process (Table 1).
The studied quinonimines were weakly sensitive to
UV and visible light irradiation. The presence of
phenoxazine moiety in the molecule could lead to its
photochromism [3]. Indeed, under visible light
irradiation, yellow-green solutions of quinonimines I–
III, partially transformed at preliminary heating (and
thus containing their 4аН-phenoxazine derivatives)
turned into initial red-violet color. After 5–7 min of
irradiation, electron absorption spectra of the solutions
were identical to those of the starting quinonimines.
Heating of the irradiated solutions induced repeated
formation of the 4аН-phenoxazine derivatives and
restoration of yellow-green coloration. Hence, the
observed heat- and light-induced transformations of
compounds I–III in the solution were reversible. The
underlying mechanism was thermal ring closure of Z-
isomer of quinonimine to form 4аН-phenoxazine cycle
and subsequent photoinduced ring opening (Scheme 3).
t, min
Fig. 3. Kinetics of transformation of compound I in nonane
(с0 = 2.05 × 10–3 mol/L, 343 K). (1) is consumption of I,
(2) is accumulation of intermediate B, (3) is accumulation
of dimer C.
band assigned to carbonyl group of starting quinones
(1555 cm–1) disappeared. In mass spectra of mixture
(a) molecular ions and their fragments were observed
assigned to the 4аН-phenoxazine derivative. Mass
spectra of mixture (b) contained the molecular ions of
dimer as well.
Heat-induced transformation of compound IV
followed the second-order rate equation. As discussed
in [2], the Diels–Alder dimerization of 4аН-phen-
oxazine derivative of compound IV is impeded as both
the conjugated double bonds in the positions 1 and 3 of
IV are shielded by the bulky tert-butyl substituents. In
the absence of oxygen, the oxazine (B) formed from
compound IV could be oxidized with the initial
The loss of compounds I and III after 5 cycles of
thermal and phototransformations was 8.0 and 16.7%,
respectively.
Kinetics of photolysis of 4аН-phenoxazine deri-
vative of quinonimine was studied using compound
I as an example; the compound was exposed to
405 nm irradiation with the intensity of (5–113) ×
1017 quant L–1 s–1 (Fig. 4). The reaction order was close
to unity, and the quantum yield was 0.95
independently of irradiation intensity.
Table 1. Rate constant (313 K) and activation energy of
heat-induced reactions of quinonimines I–IV
Comp. no.
Rate constant
Activation energy, kJ/mol
Additionally, we performed quantum-chemical simula-
tion to access the ground state energy of E- and Z-
isomers of the studied compounds I–IV as well as of
the corresponding 4аН-phenoxazines. Data collected in
Table 2 show that the energy of Z-isomers of
quinonimines is significantly higher than that of their
E-isomers, however being lower than that of the 4аН-
I
kI = 4.1 × 10–4 s–1
kI = 3.6 × 10–4 s–1
kI = 3.4 × 10–4 s–1
kII = 0.38 L mol–1 s–1
75±4
76±4
87±5
47±2
II
III
IVа
a Т = 323 K.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 4 2014

KINETICS OF HEAT-INDUCED AND PHOTOCHEMICAL TRANSFORMATIONS
phenoxazines (products of heat-induced transforma-
645
tion). Disregarding the entropy factor, the energy
difference should result in the equilibrium constant of
E-quinonimine transformation into phenoxazines of
102–104 at room temperature; that was consistent with
the experimental findings. The reverse process is
possible only upon external energy supply (for
instance, under irradiation). Noteworthily, the energy
difference between tert-butyl derivative IV and the
corresponding phenoxazine was lower than in the
cases of I–III.
EXPERIMENTAL
Quinonimines I–IV were prepared as described in
[1, 4], and their structures were confirmed by IR and
NMR spectroscopy. The solvents of chemically pure
grade were purified and dried as described in [5]. Air
was removed from the reaction mixtures by repeated
freezing under a reduced pressure.
t, min
Fig. 4. Photolytic transformation of 4aН-phenoxazine
derivative B of compound I (с0 = 2.3 × 10–4 mol/L, λ =
405 nm, I0,sp = 1.23 × 1018 quant s–1 L–1; (1) is decay of the
starting compound, (2) is accumulation of quinonimine I.
Heat- and light-induced transformations were
studied in evacuated ampules equipped with Teflon
valves and quartz windows. Photolysis was performed
using the DRSh-500 mercury lamp equipped with
quartz lens and standard set of optical filters. Intensity
of the incident radiation was measured with the
actinometer based on potassium ferrioxalate [6].
Kinetics of the process was monitored by spectro-
photometry (the SF-2000 spectrophotometer, quartz
cell, optical path of 0.8 cm).
positions of the phenyl ring (two tert-butyl, two
isopropyl, two ethyl, or two methyl) as well as of their
4аН-phenoxazine derivatives were optimized by the
DFT method. Hybrid B3PW91 functional in the 6-31G
(d) basis set was used, accounting for d-polarization
functions. All simulations were performed for isolated
molecules.
Output files of GAUSSIAN package contained
electron energy of the molecules in Hartree units; that
information was used to compute energy difference
between Z- and E-isomers of quinonimines and their
4аН-phenoxazines in kJ/mol.
IR spectra of the products were registered with a
Shimadzu IRPrestige-21 instrument (KBr). The
specimens were prepared by washing the purified and
dry salt with the reaction mixture based on hexane,
followed by the solvent distillation under reduced
pressure and the cell filling with inert gas.
Table 2. Energy of ground states of quinonimines I–IV (E-
and Z-isomers) and of products of their heat-induced
transformations
Chromatomass spectrometry analysis was per-
formed using a DSQ II instrument equipped with
quadrupole mass analyzer and the MALDI Bruker
microflex LT spectrometer (ion source temperature
230°С, ionization energy 70 eV). Mass spectra of
cations were registered at the mass number range of
70–800.
Compound
I
II
III
IV
Energy difference between Z- 5.683 6.313 6.532 9.308
and E-isomers, kJ/mol [E(Z) >
E(E)]
Quantum-chemical simulation of ground state of
the quinonimines and their 4аН-phenoxazine deriva-
tives was performed using GAUSSIAN 09W software
package [7]. Starting geometry was set and the results
were presented in GaussView software [8]. The preset
geometry parameters of 4Z- and 4E-isomers of
quinonimines bearing various substituents in 2,6 or 2,5
Energy difference between the 20.78827.33625.48712.866
Z-isomer and the phenoxazine,
kJ/mol
Energy difference between the 15.10421.02318.955 3.558
E-isomer and the phenoxazine,
kJ/mol
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 4 2014

646
MISHCHENKO et al.
4. Poddel’sky, A.I., Kuskii, Y.A., Piskunov, A.V., So-
REFERENCES
mov, N.N., Cherkasov, V.K., and Abakumov, G.A.,
Appl. Organomet. Chem., 2011, vol. 25, no. 3, p. 180.
1. Abakumov, G.A., Druzhkov, N.O., Kurskiy, Yu.A., and
Shavyrin, A.S., Russ. Chem. Bull., 2003, vol. 52, no. 3,
p. 712.
2. Abakumov, G.A., Druzhkov, N.O., Kurskiy, Yu.A.,
Abakumova, L.G., Fukin, G.K., Poddelskiy, A.I.,
Cherkasov, V.K., and Okhlopkova, L.S., Russ. Chem.
Bull., 2005, vol. 54, no. 11, p. 2571.
5. Gordon, A.J. and Ford, R.A., The Chemist’s Com
panion. A Handbook of Practical Data, Techniques and
References, New York: Wiley, 1972.
6. Calvert, J.G. and Pitts, J.N., Photochemistry, Willey,
1966.
3. Traven, V.F., Manaev, A.V., Bochkov, A.Yu.,
Chibisova, T.A., and Ivanov, I.V., Russ. Chem. Bull.,
2012, no. 7, p. 1343.
7. http://gaussian.com.
8. gaussian.com/g_prod/gv5.htm.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 4 2014