Antiradical activity of dioxolane derivatives

Article abstract of DOI:10.1134/S1070428013030226

1,3-Benzodioxoles synthesized by condensation of 3,6-di-tert-butylbenzene- 1,2-diol with carbonyl compounds showed antiradical activity due to their ability to undergo one-electron oxidation with formation of stable radical cations. On this basis, the ant

Full text of DOI:10.1134/S1070428013030226

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 3, pp. 446–449. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © V.B. Vol’eva, I.S. Belostotskaya, N.L. Komissarova, A.V. Malkova, T.V. Pokholok, E.Ya. Davydov, 2013, published in Zhurnal
Organicheskoi Khimii, 2013, Vol. 49, No. 3, pp. 458–461.
Dedicated to Full Member of the Russian Academy of Sciences
I.P. Beletskaya on her jubilee
Antiradical Activity of Dioxolane Derivatives
V. B. Vol’eva, I. S. Belostotskaya, N. L. Komissarova, A. V. Malkova,
T. V. Pokholok, and E. Ya. Davydov†
Emanuel’Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119334 Russia
e-mail: komissarova@polymer.chph.ras.ru
Received May 25, 2012
Abstract—1,3-Benzodioxoles synthesized by condensation of 3,6-di-tert-butylbenzene-1,2-diol with carbonyl
compounds showed antiradical activity due to their ability to undergo one-electron oxidation with formation of
stable radical cations. On this basis, the antiknock effect of their structural analogs, 1,3-dioxolanes derived
from vicinal diols, was interpreted in terms of oxidation of these compounds with active radicals generated
from fuel hydrocarbons to produce more stable radical or radical ion species, depending on the fuel
composition. The formation of radical species was detected in model oxidation reactions of 2,2-dimethyl-1,3-
dioxolane and 2,2-dimethyl-1,3-dioxolan-4-ylmethanol with radicals generated by photolysis of iron(III)
chloride and benzoyl peroxide.
DOI: 10.1134/S1070428013030226
We previously showed that benzodioxoles obtained
by condensation of 3,6-di-tert-butylbenzene-1,2-diol
with aldehydes and ketones exhibit antiradical activity
despite the lack of free hydroxy groups in their mole-
cules [1, 2]. Naturally, the antiradical activity of ben-
zodioxoles is determined by the ability of the dioxole
ring to undergo one-electron oxidation to produce
radical cations which were detected by ESR spectros-
copy while studying the oxidation of 1,3-benzodi-
oxoles I–III with thallium trifluoroacetate or lead(IV)
oxide in trifluoroacetic acid or its mixture with methy-
lene chloride (Scheme 1).
The ESR spectra of radical cations derived from
compounds I–III indicated coupling of the unpaired
electron with two equivalent aromatic protons, as well
as with protons on C2 or in groups attached thereto
[CH2, CHPh, C(CH3)2]. The ESR spectra of radical
cations I+· and II+· and hyperfine coupling constants
(HCC) aH are given in Fig. 1 (see table).
The triplet signal from the ring protons with
an HCC of 4.2–4.8 G may be regarded as spectral
marker indicating formation of radical cations in the
oxidation of acyclic precursors, 3,6-di-tert-butyl-
benzene-1,2-diol monoethers. As shown by the ESR
data, the oxidation of 3,6-di-tert-butylbenzene-2-(tert-
butoxymethoxy)phenol (IV) with PbO2 in CF3CO2H–
CH2Cl2 gave a product which was spectrally identical
to the radical cation generated by oxidation of benzodi-
oxole I under analogous conditions. Obviously, ether
IV undergoes oxidative cyclization with elimination of
the tert-butoxy group (Scheme 2). Ether IV was iso-
lated instead of expected 1,3-benzodioxole (I) in the
condensation of 3,6-di-tert-butylbenzene-1,2-diol with
methylene iodide in the presence of potassium tert-
butoxide in t-BuOH [3]. Compound I was synthesized
in a different way, by reaction of 3,6-di-tert-butyl-1,2-
benzoquinone with diazomethane [4].
Scheme 1.
t-Bu
t-Bu
t-Bu
O
O
O
O
O
O
Me
Me
Ph
t-Bu
t-Bu
t-Bu
I
II
III
t-Bu
t-Bu
t-Bu
O
O
O
O
R'
R'
R
R
t-Bu
I
+·, II+·, III+·
I+·, R = R′ = H; II+·, R = H, R′ = Ph; III+·, R = R′ = Me.
†
Deceased.
446

ANTIRADICAL ACTIVITY OF DIOXOLANE DERIVATIVES
447
Scheme 2.
t-Bu
t-Bu
OH
OH
OH
t-BuOK–t-BuOH
PbO2, H+
+
CH2I2
–t-BuOH
Bu-t
t-Bu
t-Bu
O
O
t-Bu
t-Bu
t-Bu
t-Bu
O
O
CH+
IV
·
O
O
O
PbO2, H+
I+·
+
CH2N2
O
t-Bu
t-Bu
I
Radical cations were also formed in the oxidation
of 3,6-di-tert-butylbenzene-1,2-diol monopropionate V
with lead(IV) oxide (Scheme 3). The reaction direction
depended on the solvent. In aprotic medium (CH2Cl2),
o-carboxyphenoxyl radical VI was obtained, and it was
converted into radical cation VII upon addition of
an acid (CF3COOH). Correspondingly, the spectral
pattern changed (Fig. 2). In the ESR spectrum of VI
we observed a doublet of doublets due to coupling
etc.) with carbonyl compounds. Addition of dioxolanes
to fuel compositions is known to considerably improve
their octane number [5].
The effect of antiknock agents originates from their
ability to inhibit development of radical processes
leading to explosive combustion; they react with active
(a)
with two nonequivalent protons in the aromatic ring.
Addition of acid gave rise to paramagnetic species
whose spectra were typical of radical cations with
equivalent aromatic protons (triplets with aHarom = 4.7,
4.8 G). Identical spectra of radical cations VII were
obtained when monoester V was oxidized with PbO2
directly in trifluoroacetic acid. Presumably, the forma-
tion of dioxolane ring is a structural factor stabilizing
the radical species in protic medium.
aH
It seemed reasonable to use the above results as
model for interpretation of the antiknock activity of
structural analogs of benzodioxoles, 1,3-dioxolanes
that are cyclic ketals formed by condensation of vicinal
diols and polyols (such as ethylene glycol, glycerol,
5 G
aHCH
2
(b)
Scheme 3.
t-Bu
t-Bu
·
OH
O
O
O
PbO2–CH2Cl2
O
O
Et
Et
t-Bu
t-Bu
V
VI
aH
t-Bu
PbO2
CF3COOH
aHCH
CF3COOH
O
C
O
OH
·
5 G
Et
Fig. 1. ESR spectra of radical cations (a) I+ · and (b) II+ ·;
t-Bu
VII
20°C, CF3COOH.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

VOL’EVA et al.
448
Hyperfine coupling constants aH in the ESR spectra of
radical cations generated from compounds I–III
Scheme 4.
O
hν
aHarom
aH
O
Ph
·
2Ph
+
2CO2
Radical cation
Ph
O
I+·
II+·
III+·
4.25
4.50
4.50
20.8 (CH2)
21.0 (CH)2
0.45 (CH)2
O
FeCl3
FeCl4
(FeCl4
+
FeCl2)
hν
FeCl2
+
Cl–
Me
+ Cl
·
O
O
Me
Me
·
radicals generated by oxidation of hydrocarbons and
responsible for chain propagation to produce less
active radicals. Radicals generated by photolysis of
peroxides, as well as halogen atoms expulsed from
high-valence inorganic halides, may be regarded as
models of such active hydrocarbon radicals. We used
both these models, FeCl3 and benzoyl peroxide, to
assess the possibility for radical oxidation of dioxo-
lanes and examine the ESR parameters of the resulting
radical species. The formation of radicals from ketals
VIII and IX implies initial generation of active
chlorine atoms from FeCl3 or phenyl radicals from
benzoyl peroxide [7] and their subsequent reactions
(Scheme 4).
Cl
OH
Me
·
O
O
CHOH
VIII
X
O
O
O
Me
Me
Me
Me
·
Cl
·
O
IX
XI
40 G, which is consistent with published data [8]. The
spectrum of X was a doublet of doublets, and that of
XI, a doublet of triplets. The spectral parameters did
not change as the temperature rose up to disappearance
of radical species on melting (>180 K [9]).
The formation of carbon-centered radicals which
are sufficiently stable to be observed by ESR conforms
to the antiknock effect of compounds VIII and IX. The
strongest effect on the octane number was observed
when these compounds were added in combination
with lower alcohols, primarily with ethanol [5]. Direct
ESR study of the effect of the alcohol component is
experimentally difficult; however, by analogy with the
above examples demonstrating structural transforma-
tions of radical species in protic medium, we may
presume that alcohol as proton donor promotes trans-
formation of carbon-centered radical into more stable
cyclic radical cation (Scheme 5).
Figure 3 shows the ESR spectra of radicals X and
XI generated by abstraction of hydrogen atom from
2,2-dimethyl-1,3-dioxolane (VIII) and 2,2-dimethyl-
1,3-dioxolan-4-ylmethanol (IX), respectively. The
shape of the spectral curves and spectral parameters
did not depend on the way of radical generation. The
hyperfine coupling constants for radical X were aαΗ =
17.2, aβΗ = 30 G, and for radical XI, aαΗ = aΗβ1 = 20, aΗβ2 =
(a)
Scheme 5.
·
R
O
R
R
O
R
(b)
+
H+
O
O
CH
The interaction with proton donors could provide
an additional contribution to the antiknock effect of
ketals via formation of supramolecular structures
acting as surfactants. The rate of decomposition of
hydroperoxides in the shells surrounding surfactant
micelles is considerably lower, so that the combustion
process turns from the explosive mode to stationary
[10]. Presumably, this factor is responsible for the
synergistic effect of ketals upon addition to alcohol-
containing gasoline [5].
5 G
Fig. 2. ESR spectra of (a) phenoxyl radical VI and (b) radi-
cal cation VII; 20°C, CF3COOH.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

ANTIRADICAL ACTIVITY OF DIOXOLANE DERIVATIVES
(a)
449
(b)
aα = 17.2 G
aβ = 30 G
aαΗ = aβ1 = 20 G
aβ2 = 40 G
3260
3300
3340
3380
H, G
3260
3300
3340
3380
H, G
Fig. 3. ESR spectra of (a) radical X recorded at 136 K and (b) radical XI recorded at 94 K (modulation amplitude 2 G); radicals were
generated by photolysis in the presence of FeCl3, BS-6 filter, 40 min at 77 K.
2. Malysheva, N.N., Prokof’ev, A.I., Solodovnikov, S.P.,
Bubnov, N.N., Prokof’eva, T.I., Vol’eva, V.B., Er-
shov, V.V., and Kabachnik, M.I., Izv. Akad. Nauk SSSR,
Ser. Khim., 1988, p. 1040.
EXPERIMENTAL
The ESR spectra were recorded on Varian E-12 and
EPR-10 (SPIn Co. Ltd.) spectrometers (modulation
frequency 100 kHz, temperature range 77–295 K).
Radical cations were generated by oxidation of
1,3-benzodioxoles I–III and 3,6-di-tert-butylbenzene-
1,2-diol ether IV and ester V with thallium trifluoro-
acetate or lead(IV) oxide in trifluoroacetic acid or its
mixture with methylene chloride in evacuated
ampules. The synthesis of the initial compounds was
described in [11, 12].
3. Vol’eva, V.B., Belostotskaya, I.S., Novikova, I.A.,
Dzhuaryan, E.V., and Ershov, V.V., Izv. Akad. Nauk
SSSR, Ser. Khim., 1980, p. 2414.
4. Komissarova, N.L., Belostotskaya, I.S., Vol’eva, V.B.,
Dzhuaryan, E.V., Novikova, I.A., and Ershov, V.V., Izv.
Akad. Nauk SSSR, Ser. Khim., 1981, p. 2360.
5. Varfolomeev, S.D., Nikiforov, G.A., Vol’eva, V.B.,
Makarov, G.G., and Trusov, L.I., Russian Patent
no. 2365617, 2009; Byull. Izobret., 2009, no. 24.
Radicals X and XI were generated from ketals VIII
and IX by adding FeCl3 or benzoyl peroxide, followed
by irradiation of frozen solutions (77 K) with a DRSh-
1000 mercury lamp through a BS-6 filter (λ >300 nm).
The temperature was maintained with an accuracy of
±3° using liquid nitrogen. The scan time was 10–15 s.
A solution of ketal VIII or IX, ~0.5 ml, containing
FeCl3 or (PhCOO)2 was placed into a quartz cylin-
drical ESR ampule, and the ampule was irradiated for
40 min at 77 K in a quartz Dewar flask. Three series of
experiments were performed: (1) ketal VIII with ad-
dition of ~1 wt % of FeCl3; (2) ketal IX with addition
of 10 wt % of benzoyl peroxide; and (3) ketal IX with
addition of FeCl3. In all cases, radical species were
detected, whose ESR spectra are shown in Fig. 3.
6. Pokholok, T.V., Zaitseva, N.I., Pariysky, G.B., and Top-
tygin, D.Ya., Polym. Photochem., 1982, vol. 2, p. 429.
7. Pariiskii, G.B., Toptygin, D.Ya., Davydov, E.Ya., Led-
neva, O.A., Mikheev, Yu.A., and Karasev, V.M., Vysoko-
mol. Soedin., Ser. B, 1972, vol. 14, p. 511.
8. Pshezhetskii, S.Ya., Kotov, A.G., Milinchuk, V.K., Ro-
ginskii, V.A., and Tupikov, V.I., EPR svobodnykh radi-
kalov v radiatsionnoi khimii (ESR of Free Radicals in
Radiation Chemistry), Moscow: Khimiya, 1972, p. 52.
9. Dyment, O.N., Kazanskii, K.S., and Miroshnikov, A.M.,
Glikoli i drugie proizvodnye okisi etilena i propilena
(Glycols and Other Derivatives of Ethylene and
Propylene Oxides), Dyment, O.N., Ed., Moscow:
Khimiya, 1976, p. 121.
10. Kasaikina, O.T., Kartasheva, Z.S., and Pisarenko, L.M.,
Russ. J. Gen. Chem., 2008, vol. 78, p. 1533.
REFERENCES
11. Vol’eva, V.B., Novikova, I.A., Ostapets-Sveshniko-
va, G.D., Belostotskaya, I.S., and Ershov, V.V., Izv.
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