Oxidation of 2-acetoxytoluene with ozone in acetic anhydride

Article abstract of DOI:10.1134/S1070363208090089

Kinetics and mechanism of the reaction of ozone with 2-acetoxytoluene in acetic anhydride in the presence of sulfuric acid were studied. It was shown that the prevailing reaction route under these conditions is ozonolysis (89%), and the selectivity of the oxidation of the substrate by the methyl group is no higher 9%. However, in the presence of manganese(II) sulfate as a catalyst, the selectivity increases to 76%. The major reaction products were 2-acetoxybenzyl acetate (59%) and 2-acetoxybenzylidene diacetate (17%). In the presence of a manganese bromide catalyst, the oxidation depth increases, and the major reaction product is already 2-acetoxybenzylidene (66%), while the yield of 2-acetoxybenzyl acetate is 15%. The mechanism of the redox catalysis is considered, that explains the experimental results.

Full text of DOI:10.1134/S1070363208090089

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 9, pp. 1690–1694. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © A.G. Galstyan, 2008, published in Zhurnal Obshchei Khimii, 2008, Vol. 78, No. 9, pp. 1457–1462.
Oxidation of 2-Acetoxytoluene with Ozone in Acetic Anhydride
A. G. Galstyan
Institute of Chemical Technologies, Vladimir Dal East-Ukrainian National University,
ul. Lenina 31, Rubezhnoe, Lugansk oblast, 93000 Ukraine
e-mail: ozon@megabit.com.ua
Received March 18, 2008
Abstract―Kinetics and mechanism of the reaction of ozone with 2-acetoxytoluene in acetic anhydride in the
presence of sulfuric acid were studied. It was shown that the prevailing reaction route under these conditions is
ozonolysis (89%), and the selectivity of the oxidation of the substrate by the methyl group is no higher 9%.
However, in the presence of manganese(II) sulfate as a catalyst, the selectivity increases to 76%. The major
reaction products were 2-acetoxybenzyl acetate (59%) and 2-acetoxybenzylidene diacetate (17%). In the
presence of a manganese bromide catalyst, the oxidation depth increases, and the major reaction product is
already 2-acetoxybenzylidene (66%), while the yield of 2-acetoxybenzyl acetate is 15%. The mechanism of the
redox catalysis is considered, that explains the experimental results.
DOI: 10.1134/S1070363208090089
It is known that the reaction of toluene (I) with
ozone in acetic acid primarily involves double bonds
of the aromatic ring (83%) and, to a less extent, the
methyl group (16%) [1, 2]. Hydroxyl substitution of
the 2-H atom in I sharply enhances the reactivity of the
enhancement is most likely to be associated with a
changed site of the primary ozone attack. It is
suggested [3] that ozone attacks II by the weakest
bond HO to form the phenoxyl radical, after which
addition of the hydroxyl radical takes place, followed
by opening of the aromatic ring and formation of
unsaturated carbonyl compounds (Scheme 1). The
oxidation products by the methyl group could not be
isolated.
resulting 2-hydroxytoluene (II) (k
0.8 [1]; kII+О3
I+О3
2
–1 –1
9
.8×10 l mol
s
[2]). This fact is impossible to
explain in terms of π-conjugation exclusively.
According to commonly accepted concepts, this
Scheme 1.
H
OH
O
O
O
O
Me
Me
Me
Me
O
Me
O3
+
OH
+ O2
O
H
O
O
H
O O
O
O
O3
C
CH CH CH CH
C
C
C
CH CH CH
C
Me
Me
In the present work we showed that compound II
after having been acylated with acetic anhydride in the
presence of sulfuric acid to form 2-acetoxytoluene
coordinates log (k /k )–σ is observed for a series of
i t 0
electrophilic reactions with substituted toluenes (Fig. 1).
(
III) is no longer reactive: The reactivity of compound
Compound III in acetic anhydride in the presence
of sulfuric acid reacts with ozone similarly to
compound I, i.e. primarily by double bonds of the
–
1 –1
III toward ozone (kapp 0.47 l mol s is close to that of
methylbenzenes [1]). A fair correlation in the
1690

OXIDATION OF 2-ACETOXYTOLUENE WITH OZONE
1691
C, M
1
0
0
.2
.8
.4
0
p-Ме
m-Ме
0.4
2
m-OAc
H
1
o-OAc
0
.3
p-OAc
–
–
–
–
0.4
0.8
1.2
1.6
p-Br
m-Br
p-NO
2
0.2
m-NO
2
o-NO
2
–
0.2
0
0.2
0.4
0.6
0.8
0
.1
σ
0
Fig. 1. Plot of the apparent reaction rate constant of
substituted toluenes with ozone in acetic acid vs. σ
3
0
.
4
2
0
40
60
80
100
t, min
benzene ring to form hydroperoxides (89%) and, to a
less extent, by the methyl group to form 2-
acetoxybenzyl acetate (VII) (9%) and 2-aceto-
xybenzylidene diacetate (IX) in concentrations of no
Fig. 2. Oxidation kinetics of compound III with ozone in
acetic anhydride in the presence of sulfuric acid at 5°С.
1.2 M; specific
feeding rate of the ozone–air mixture 0.37 s . Compound:
1) III; (2) peroxides; (3) VII; and (4) IX. (С),
concentration, M; and (t), reaction time, min (the same for
–4
[
(III)]
0
0.4; [O
3
]
0
4.7×10 ; [Н
2
4
SO ]
0
–1
–3
(
higher than 10 M (Fig. 2).
The initial rate of the reaction of III with ozone is
first-order in reagents (Fig. 3): The consumption of
ozone per 1 mol of the substrate is 1.1 mol.
Fig. 4).
of ozone, but in its presence it occurs very fast after a
short inductive period. When product III is introduced
into the system in which manganese is present in an
oxidized form, Mn(III), oxidation develops without
any inductive period. Therefore, ozone should
continuously fed into the system; otherwise, oxidation
of III and accumulation of products fast cease, and
Mn(III) passes into Mn(II). Initially, the catalytic
Hydroperoxides formed in the reactions are tolerant
to ozone at temperatures of up to 20°С, actively react
with alkalis, and react with potassium iodide to liberate
iodine in a quantity equivalent to one hydroxyperoxy
group. The structure and mechanism of hydroperoxide
formation have not been studied, but, based on
published [3, 4] and our own data, we can suggest that
the structure of the peroxides and the mechanism of
their formation are similar to those with benzene
hydroperoxides (Scheme 2; route А).
log [O
3 0
]
–
3.0
–3.7 –3.5
–3.3
Route B in Scheme 2 describes the possible
mechanism of the oxidation by the methyl group, first
suggested by Pryor et al. [5] for ozonation of cumene.
According to this scheme, 2-acetoxybenzyl alcohol (V)
and 2-acetoxybenzaldehyde (VIII) in statu nascendi
can be acylated to 2-acetoxybenzyl acetate (VII) and
2
–
–
–
–
4.0
4.2
4.4
4.6
2
-acetoxybenzylidene diacetate (IX), respectively.
The selectivity of the oxidation of product III by
the methyl group in acetic anhydride increases in the
presence of manganese(III) sulfate. At 5°С and a 0.14 M
1
concentration of MnSO under conditions of sulfuric
4
–
0.6
–0.4
–0.2
0
acid catalysis (1.2 M) the total yield of oxidation by
the methyl group increases from 9 to 76%. The major
reaction products were compounds VII (59%) and IX
log [(III)]
0
Fig. 3. Plots of the oxidation rate of compound III vs.
concentration of (1) substrate and (2) ozone at 5°С. (W),
Reaction rate, mol l s .
(
17%) (Fig. 4). A characteristic feature of the catalytic
–
1 –1
reaction is that oxidation does not start in the absence
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 9 2008

1
692
GALSTYAN
Scheme 2.
Me
Me
AcO
AcO
O3
+ O3
III
A
B
_OH
_O2
Me
CH2
AcO
AcO
+
_
O
IV
O
O
OH
O2
X
CH OH
CH O2
2
2
AcO
AcO
Me
AcO
V
VI
O3
O
Ac O, H+
2
O
O
CH OAc
CHO
2
XI
AcO
AcO
Me
H
C
O
H
VII
VIII
H+
_
O3
+
C
C
CH
CH
C
C
CH
O
O
Ac O
2
CH(OAc)2
OAc
AcO
AcOH
Me
C
H
O
H
IX
C
CH
C
OOH
OAc
OAc
XIII
reaction is first-order in catalyst, compound III, and
ozone.
catalyst to give the active form Mn(III) [reaction (0)].
The oxidized form is reduced by reaction (1) with the
methyl group of the substrate, thus involving the latter
into oxidation (see table).
The fact that the aromatic ring undergoes no
destructive oxidation in the presence of the MnSO4
catalyst is explained by that ozone under these
conditions reacts not with the organic molecule
2+
+
3+
·
Mn + O
3
+ Н → Мn + HO + O
2
,
(0)
(1)
3+
2+
+
2
АсОArMe + Мn → АсОArĊH + Mn + H .
(
Scheme 2), but with the reduced form Mn(II) of the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 9 2008

OXIDATION OF 2-ACETOXYTOLUENE WITH OZONE
1693
The acetoxybenzyl radical formed by reaction (1)
C, M
.4
converts, in an oxygen atmosphere {[O ] /[O ]
2
g
3 g
2
6
.7×10 } into the peroxide radical [reaction (2)].
0
1
·
·
АсОArСH
2
+ O
2
→ АсОArCH
2
O
2
.
(2)
The latter radical can undergo the following
transformations [8, 9].
0.3
0.2
0.1
2
·
2 2
АсОArCH O + АсОArMe
4
→
АсОArCH
2
O
2
Н + АсОArĊH
2
,
(3)
·
2+
+
АсОArCH
2
O
2
+ Mn + H
3
→
АсОArCH
2
O
2
Н + Мn ,
(4)
(5)
3
·
·
АсОArCH
2
O
2
+ O
3
→ АсОArCH
2
O + 2O
2
,
·
2
2
АсОArCH
2
O
2
→ АсОArCH OН + АсОArCHО (6)
1
0
20
30
40
50
·
·
2
АсОArCH
2
O
2
→ 2АсОArCH
2
O + O
2
.
(7)
t, min
·
2+
–
3+
Fig. 4. Oxidation kinetics of compound III with ozone in
acetic anhydride in the presence of manganese(II) sulfate at
АсОArCH
АсОArCH
2
2
O + Mn → АсОArCH
2
O + Mn , (8)
+
–
O + CH
3
–C=О → АсОArCH
2
OАс. (9)
5
°С. [(III)] 0.4; [MnSO ] 0.18; [Н SO ] 1.2; [O ]
0 4 0 2 4 0 3 0
–4
3
+
2+
4.7×10 M. Compound: (1) III; (2) VII; (3) IX; and (4)
АсОArCH
2
OАс + Mn → АсОArĊHOАс + Mn , (10)
manganese(III) sulfate.
+
+
Ac
2
О + H → CH
3
C=О + AcОН.
(11)
As judged from the estimated initial kinetic
parameters of the above stages, when oxidation
products are still absent (see table), at high
2
+
–
2+
−
Мn + Br → Мn Br
,
(12)
2+
−
+
3+
−
2+
·
·
Мn Br + O
3
+ Н → Мn Br (Mn Br ) + НО + О
2
. (13)
concentrations of compound III and MnSO , low
concentrations of ozone, and 5°С, the rate constants of
4
Further oxidation occurs as a nonchain radical
reaction to form 66% of IX and 15% of VII.
initiation (W ) and decay (W ) of peroxyl radicals are
1
7
roughly close to the total rate of oxidation of
–
4
–1 –1
compound III [W 1×10 mol l s , Fig. 4]. Among
ox
Kinetic parameters of the catalytic reaction of ozone with 2-
acetoxytoluene (for conditions, see Fig. 4)
the possible chain propagation reactions (W , W , and
3
4
W ), the fastest has the rate W , but is lower by an
5
4
a
Reaction
no.
Rate constant (k) ,
Reaction rate (W),
order of magnitude than W and W . From this it
1
7
–
1
–1
–1 –1
l mol
s
mol l s
follows that at the chain length ν = W / i ≈ 1 the
ox W
catalytic reaction of ozone with compound III occurs
as a nonchain radical reaction, under which conditions
the decay of peroxide radicals can give rise to alkoxyl
radicals [reaction (7)]; the latter go into the bulk
solution [8], where they can be reduced [reaction (8)]
to form, finally, product VII. Reaction (6) is not
included into the scheme, since it suggests concurrent
formation of products VII and IX, which contradicts
the experimental data (Fig. 4). Compound IX is
probably formed by a similar scheme [reaction (10)
and further reactions (2) and (7)–(9)].
–3
–4
–7
–5
–8
–4
–4
–4
–4
–4
0
1
3
4
5
6
7
8
19.2
1.12×10
0.23
1.4×10
0.8×10
0.8×10
1.6×10
3.6×10
0.9×10
0.9×10
1.6×10
1.7×10
13.8×10
–3
2
10
2
10
8
10
8
10
3
10
–
4
1
1
0
4
2.3×10
–
2
3.46×10
a
k
k
k
0
6
5
, k
, and k
determined for the reaction СН
1 3 4
, k10, and k14 were calculated with the authors’ data; k , k ,
The selectivity of the oxidation of compound III
by the methyl group increases in the presence of
7
determined for toluene and Со(II) were taken from [6];
was taken from [2];
8
was taken from [7]. The concentration of peroxyl radicals
·
2
3
О
+ О
3
and k
MnSO and KBr. According to modern views [9], a
4
was estimated under the assumption of steady-state
manganese bromide catalyst which is more active than
Мn(III) is formed in the system [see table and
reactions (1) and (14).
3+
1
concentrations of reacting species: 2k [AcOArMe][Mn ] =
·
·
k
7
[АсОArCH
[AcOArMe][Mn ])/k
2 2 2 2 2 1
O ] , from where [АсОArCH O ] = {(2k ·
3+ 1/2 –6
7
}
= 0.9×10 M.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 9 2008

1
694
GALSTYAN
2
+
·
АсОArMe + Mn Br
of consumption of the reagents, taking into account
that the reaction rate is independent on the
concentration of Мn(II) under these conditions.
2
+
–
+
→
АсОArĊH
2
+ Mn Br + H ,
(14)
(15)
(16)
·
·
АсОArСH
2
+ O
2
→ АсОArCH
2
O
2
,
·
2
·
Compound III was prepared by the procedure in
11], compounds IX, VII, and VIII were prepared by
2
АсОArCH
2
O
→ 2АсОArCH
2
O + O
2
,
[
·
2+
–
–
2+
·
АсОArCH
2
O + Mn Br → АсОArCH
2
O + Mn Br , (17)
the procedure in [12], and compound V was prepared
by the procedure in [13]; all compounds were
chromatographically pure.
+
–
АсОArCH
2
O + CH
3
–C=О → АсОArCH
2
OАс, (18)
2
+
2
АсОArCH OАс + Mn Br
2
+
–
+
→
АсОArĊHОАс + Mn Br + H ,
(19)
REFERENCES
·
АсОArĊHОАс + O
2
→ АсОArCH(O)
2
OAc,
(20)
·
·
1. Galstyan, G.A., Zh. Fiz. Khim., 1992, vol. 66, no. 4,
p. 75.
2. Galstyan, G.A., Tyupalo, N.F., and Razumovskii, S.D.,
2
АсОArCH(O)
2
OAc → 2АсОArCH(O)OAc + 2O
2
, (21)
·
2
+
–
АсОArCH(O)OAc + Mn Br
2
+
·
Ozon i ego reaktsii s aromaticheskimi soedineniyami
→
АсОArCH(Ō)OAc + Mn Br
,
(22)
(23)
(
Ozone and Its Reactions with Aromatic Compounds),
+
АсОArCH(Ō)OAc + CH
AcOArCH(OAc)
3
–C=О
Lugansk: Vost. Ukr. Gos. Univ., 2004.
→
.
3
4
. Razumovskii, S.D. and Zaikov, G.E., Ozon i ego
reaktsii s organicheskimi soedineniyami (Ozone and Its
Reactions with Organic Compounds), Moscow: Nauka,
EXPERIMENTAL
Compound III was oxidized in a thermostated
column (volume 20 ml) with a microporous partition
for dispersing the gas mixture. The reactor was loaded
with acetic anhydride, compound II, sulfuric acid, and
manganese(II) sulfate. The components were mixed by
bubbling air for 10 min, the mixture was thermostated
at 5°С, and then an ozone–air mixture containing
1
974, p. 229.
. Bailey, P.S., Ozonation in Organic Chemistry, Vol. 2.
Nonolefinic Compounds, New York: Academic, 1982,
p. 19.
. Pryor, W.A., Norio, O., and Church, D.F., J. Am. Chem.
Soc., 1982, vol. 104, p. 5813.
. Zakharov, I.V. and Galetii, Yu.V., Neftehimiya, 1978,
vol. 18, no. 4, p. 615.
7. Denisov, E.T., Konstanty skorosti gomoliticheskih zhid
kofaznyh reaktsii (Rate Constants of Homolytic Liquid-
Phase Reactions), Moscow: Nauka, 1971.
. Emanuel’, N.M., Denisov, E.T., and Maizus, E.K.,
Tsepnye reaktsii okisleniya uglevodorodov v zhidkoi
faze (Chain Oxidation of Hydrocarbons in the Liquid
Phase), Moscow: Nauka, 1965.
. Kamiya, Y., J. Catal., 1974, vol. 33, no. 3, p. 480.
0. Galstyan, A.G, Sedikh, G.O, and Galstyan, G.A., Ukr.
Khim. Zh., 2007, vol. 73, nos. 5–6, p. 104.
5
6
–4
–1
4
.7×10 mol of ozone was fed at a rate of 30 l h . The
quantity of ozone in the gas mixture outgoing from the
reactor was measured by spectrophotometry by the
absorptivity at 254–290 nm, and the concentrations of
Mn(III) and hydroperoxides in the solute were
determined by iodometry. Compound III and its
acylated and nonacylated oxidation products were
analyzed by GLC on a 2-m column packed with
PNFS-6 on Chromaton N-AW; injector temperature
8
9
1
1
2
(
50°С; oven temperature 180°С; rates of carrier gas
nitrogen) 1.8, hydrogen 1.8, and air 18 l h ; internal
1. Agranomov, A.E. and Shabarov, Yu.S., Laboratornye
raboty v organicheskom praktikume (Laboratory Man
ual on Organic Chemistry), Moscow: Mosk. Gos. Univ.,
–
1
reference p-nitrochlorobenzene.
1
971.
The rate constants of the reactions of ozone with
compounds II and III were determined by the
procedure in [10].
1
2. Weygand–Hilgetag Organisch-chemische Experimen
tierkunst, Hilgetag, G. and Martini, A., Eds., Leipzig:
Barth, 1964, 3rd ed.
The rate constants of the reactions of compound
III and its oxidation products with Mn Br were
calculated by the initial portions of the kinetic curves
13. Becker, H. and Berger, W., Organikum, Berlin: Wis
sennschaften, 1976. Translated under the title Manual
on Organic Chemistry, Moscow: Mir, 1979, vol. 2.
2
+
·
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 9 2008