Study of reaction of isomeric acetoxytoluenes with ozone in liquid phase in the presence of manganese bromide catalyst

Article abstract of DOI:10.1134/S1070363210050154

The kinetics of the ozone reaction with isomeric acetoxytoluenes in acetic anhydride in the presence of sulfuric acid and mixed manganese bromide catalyst was studied. Under these conditions it is possible to stop the oxidation process at the stage of formation of hydroxybenzaldehydes in the form of the respective acetoxybenzylidendiacetates (63-70%). The reaction products contain also acetoxybenzyl acetate (16-18%) and a small amount of acetoxybenzyl bromide (2%). The mechanism of oxidation-reduction catalysis with manganese bromide complex explaining the experimental data was considered. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S1070363210050154

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 5, pp. 948–952. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.G. Galstyan, A.A. Sedykh, 2010, published in Zhurnal Obshchei Khimii, 2010, Vol. 80, No. 5, pp. 778–782.
Study of Reaction of Isomeric Acetoxytoluenes
with Ozone in Liquid Phase in the Presence
of Manganese Bromide Catalyst
A. G. Galstyan and A. A. Sedykh
Dal’ East Ukrainian National University, Institute for Chemical Technologies,
ul. Lenina 31, Rubezhnoe, Luganskaya Oblast, 93000 Ukraine
e-mail: ozon@megabit.com.ua
Received September 1, 2009
Abstract―The kinetics of the ozone reaction with isomeric acetoxytoluenes in acetic anhydride in the
presence of sulfuric acid and mixed manganese bromide catalyst was studied. Under these conditions it is
possible to stop the oxidation process at the stage of formation of hydroxybenzaldehydes in the form of the
respective acetoxybenzylidendiacetates (63–70%). The reaction products contain also acetoxybenzyl acetate
(16–18%) and a small amount of acetoxybenzyl bromide (2%). The mechanism of oxidation–reduction
catalysis with manganese bromide complex explaining the experimental data was considered.
DOI: 10.1134/S1070363210050154
It was shown earlier [1, 2] that the selective
oxidation of hydroxytoluenes with ozone proceeding
without destroying the aromatic ring could be carried
out in acetic anhydride solution, in the presence of
manganese acetate and sulfuric acid, the catalyst of
acylation. The main reaction products in the conditions
of catalysis are hydroxybenzyl alcohols in the form of
the acetoxybenzylacetates (II), formed in a yield
reaching 59–63%. Attempts to obtain in these
conditions hydroxybenzaldehyde in the form of
acetoxybenzylidendiacetate (III) as the main product
failed, the yield was less than 17–19%.
hydrocarbons with ozone [3]. The experimental
procedure and analysis technique were described in
[2].
At atmospheric pressure and 5ºC (Fig. 1) the
ozonization of 4-acetoxytoluene Ic in acetic anhydride
in the presence of a catalytic additive of sulfuric acid,
manganese acetate, and potassium bromide proceeds
with the formation of 4-acetoxybenzylidenediacetate
IIIc mainly (70%). In the reaction mixture there are
also present 4-acetoxybenzyl acetate IIc (18%) and 4-
acetoxybenzyl bromide (2%). At the exhaustive
oxidation of Ic, 4-acetoxybenzoic acid accumulates in
the system. Similar results were obtained at the
oxidation of 3-acetoxytoluene Ib. In the case of
ozonization of 2-isomer Ia the selectivity of oxidation
of methyl group is somewhat lower (see data in the end
of the article), which is probably due to the steric
effects of substituents.
To solve this problem, in the present study we
investigated the effect of potassium bromide additives
on the kinetics of the process and the product com-
position of catalytic oxidation of acetoxytoluenes (I)
with ozone, since the alkali metal bromides were
known to enhance the depth, selectivity, and the
reaction rate in the catalytic oxidation of alkylaromatic
CH3
o
CH
2
OAc
+
CH(OAc)2 CH
2
Br
COOH
O3, H SO t 5 C
2
4,
Mn(OAc)2, KBr
+
+
OAc
OAc
II
OAc
III
OAc
IV
OAc
V
I
9
48

STUDY OF REACTION OF ISOMERIC ACETOXYTOLUENES
949
–
3 0
log [O ]
0
0
.4
.3
3
0
.3
.9
3.5
1.1
3.7
3.9
2
–
log [KBr]
0
1.3
1.5
0
0
.2
.1
1
–
log W
3
3
3
3
.1
.3
.5
.7
4
6
3
2
4
5
3
1
5
30
t, min
45
Fig. 1. Kinetics of oxidation of Ic with ozone in acetic
1
1.6
anhydride in the presence of manganese bromide catalyst at
5
1
ºC. [I] = 0.1; [H
0
= 0.4; [Mn(OAc)
2
] = 0.1; [KBr]
0
0
2 4 0
SO ] =
–
4
–1
.2; [O ] = 4,2·10 mol l . Compounds: (1) I, (2) III,
3 0
1
.0
1.2
0.4
1.4
2
+
•
(
3) II, (4) V, (5) IV, and (6) [Mn Br ]; c is concentration,
–1
–
log [Mn(II)]
0
mol l ; t is reaction time, min.
0
.2
0.6
–
0.8
1.0
Quantitative composition of manganese bromide
catalyst affects significantly the selectivity and the
ratio of oxidation products (Table 1). Maximum yield
of III and higher selectivity of oxidation of compounds
I is reached at the molar ratio [Mn(OAc) ] :[KBr] =
3 0
log [AcOArCH ]
Fig. 2. Dependence of the rate of oxidation of Ib on the
concentration of: (1) manganese acetate, (2) substrate,
3) potassium bromide, and (4) ozone, at 5ºC; W is the
(
2
0
0
–1 –1
reaction rate, mol l s .
1
:1 (initial concentrations of manganese acetate and
–
1
potassium bromide is 0.1 mol l ), further increase in
the KBr concentration does not lead to significant
changes (Table 2). The linear relationship of log W–
However, kinetic studies of the ozone reaction with the
reaction products showed that the patterns obtained
can actually occur, since the dependence of oxidation
rate on temperature increases in the sequence: W17
W > W (E = 47.5, E = 40.5, E = 34.4 kJ mol ,
2
+
–
log [Mn ] vs. log [Br ] is found, the reaction order
with respect to the catalyst is close to 1 (Fig. 2). The
higher rate and selectivity of oxidation of the methyl
group in the presence of potassium bromide is due to
the fact that the rate of initiation of selective oxidation
>
–
1
1
6
5
17
16
5
Table 2).
In accordance with the obtained kinetic data, as
well as with the general concepts of the mechanism of
oxidation reactions catalyzed by metal-bromide
catalysts [3, 8–10], we consider the results of kinetic
2+
•
of I in reactions with Mn Br [Eq. (5)] is almost three
times higher than the rate of initiation of the oxidation
with manganese acetate [Eq. (4)] (Table 2). High
selectivity of the oxidation occurs therewith at a
decrease in the manganese concentration in the
manganese bromide catalyst by 40% (Table 2).
Table 1. Oxidation of Ia in the presence of manganese
bromide catalyst of varied composition
The rate and selectivity of oxidation I → III
depend on temperature: At the increased temperature
the overall rate of oxidation and selectivity of methyl
group oxidation grow with formation of III, and the
fraction of II is reduced (Table 3). At a first glance,
this dependence contradicts the experimental data:
according to the experiment, at the overall trend to
increase in the rate, the rate of selective oxidation
Yield, %
[
Mn(ОАс)
2
]
0
,
0
[KBr] ,
–
1
–1
mol l
mol l
IIIa
IIa
0.14
–
17.0
22.0
41.3
63.0
62.0
62.1
59.0
46.2
28.0
16.0
16.1
15.9
0
0
0
.10
.10
.10
0.04
0.08
0.10
0.12
0.14
[
Eq. (5)] grows faster than the rate of ozonolysis
0.10
0.10
–
1
[
Eq. (19)] (E = 34.4, E19 = 20.3 kJ mol , Table 2).
5
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 5 2010

9
50
GALSTYAN, SEDYKH
a
Table 2. Kinetic parameters of reactions of the catalytic cycle
b
–1 –1
K , l mol
s
5°С
E,
W
,
Reaction no.
Reaction
–
1
–1 –1
5
°С
30°С
kJ mol
mol l
s
2
+
–
–4
3
О
3
+ Мn Br
20.30±2.00
0.59±0.05
55.00±5.50
0.82±0.05
22.1±2.2
20.3±2.0
22.1±2.2
34.4±3.6
8.1×10
–
4
1
9
4
5
6
7
8
9
2
3
5
6
7
Ic + О
3
0.9×10
5.6×10
3
2
+
+
–3
–3
–4
–4
2
Ic + Мn
10.00×10
19.52×10
•
–2
–2
Ic + Мn Br
3.10×10
12.10×10
12.4×10
•
9
АсОАrСН
АсОАrСН
АсОАrСН
АсОАrСН
2
2
2
2
+ О
2
4.7×10
1.3×10
•
–6
О
О
О
2
+ АсОАrСН
3
2.3
3.2×10
3.5×10
1.4×10
12.4×10
3.5×10
12.4×10
3.7×10
2.0×10
•
2
2+
–
2
–5
–7
–4
–4
–4
–4
–4
+ Мn Br
10
•
2
2
+ О
3
10 (20°С)
•
8
1
1
1
1
1
2АсОАrСН
2
О
•
2
10
2+
–
3
АсОАrСН
2
О + Мn Br
10
•
2
8
2АсОАrСН
2
О
•
10
2
+
–3
–3
IIc + Мn Br
9.21×10
31.34×10
40.5±4.0
47.5±5.0
2
+
•
–3
–3
IIIc + Мn Br
4.92×10
13.28×10
a
–4
–1 –1
b
The reaction rate determined from Fig. 1 is 9.5×10 mol l s .
obtained in this study, the value of K is that for the methyl radical [4], K
for the reaction of toluene with cobalt [6] corrected for the redox potential of Mn [7], K13 = 10 K
reactivity of alkoxy radical [7]. Acetoxyperoxyde radical concentration in the calculations was estimated based on the conditions of
K
19, K
3
, K
4 5
and K , K16, K17 are calculated according to the data
•
6
9
for the reaction CH
3
O
2
+ O
3
[5], K
7 8
, K , K12 and K15 were taken
2
+
8
, taking into account the higher
2
+
•
•
•
steady-state concentrations of reacting species: K
5
[AcOArCH
3
][Mn Br ] = K12[AcOArCH
2
O
2
]
2
, hence [AcOArCH
2
O ] = (K
2
5
2
+
•
[
3
AcOArCH ][Mn Br ])/K12.
•
2+
–
+
studies in the framework of the classical scheme of
unbranched chain reaction:
АсОArCH
2
O
2
+ Mn Br + Н
2
+
•
→
АсОArCH
2
O
2
Н + Mn Br ,
(8)
(9)
•
2
•
2
+
–
2+
–
АсОArCH
АсОArCH
АсОArCH
2
O
+ O
3 2 2
→ АсОArCH O + 2О ,
Mn + Br → Mn Br ,
(1)
(2)
•
•
2+
+
3+
•
2
O
2
Н → АсОArCH
2
O + HO ,
(10)
Mn + O
3
+ Н → Мn + HO + O
2
,
2+
–
2+
–
+
3+
–
2
2
O Н + Mn Br
O + Mn Br + HO ,
Mn Br + O
3
+ Н → (Мn Br )
–
2+
•
•
→
АсОArCH
2
(11)
(12)
→
←
2+
•
•
Mn Br + НО + О
2
,
(3)
•
•
АсОArCH
2
O
2
→ 2 АсОArCH
2
O + O
2
,
3
+
•
2
2+
+
АсОArCH
3
+ Мn → АсОArСH
+ Mn + H , (4)
•
2+
–
2
АсОArCH O + Mn Br
2
+
•
АсОArCH
3
+ Mn Br
–
2+
•
→
АсОArCH
2
O + Mn Br ,
(13)
•
2+
–
+
→
АсОArСH
2
+ Mn Br + H ,
(5)
(6)
–
АсОArCH
2
O + CH
3
–C=О → АсОArCH
2
OАс, (14)
•
•
АсОArСH
2
+ O
2
→ АсОArCH
2
O
2
,
•
2
2
АсОArCH
OH + АсОArCHO + O
2
O
•
АсОArCH
АсОArCH
2 2
O + АсОArCH
3
→
АсОArCH
2
2
,
(15)
(16)
•
→
2
O
2
Н + АсОArСH
2
,
(7)
2+
•
АсОArCH
2
OАc + Mn Br
АсОArCH OAc + Mn Br + H ,
•
2
–
+
→
Table 3. Effect of temperature on the selectivity and rate of
oxidation of Ib
2+
•
2
АсОArCH(OАc) + Mn Br
•
2+
–
+
→
АсОArC (OАc)
2
+ Mn + Br + H ,
(17)
(18)
(19)
(20)
(21)
+
Reaction products,
Ас О + H → CH –C=О + АсОН,
4
2
3
W×10 ,
–1
Total
Т, °С
mol l
3 3
АсОArCH + O → ozonides,
–
1
–1
mol l
s
selectivity,%
–
+
•
•
ІІІb
ІІb
3 3
Br + O + Н → Br + HO ,
•
•
5
8.6
10.1
13.6
17.2
0.274
0.256
0.203
0.120
0.070
0.067
0.060
0.046
87.9
80.8
65.8
41.5
Br + Br → Br ,
2
•
•
1
2
3
5
0
0
АсОArСH
2 2 2
+ Br → АсОArСH Br + Br (22)
In the absence of bromide ions the active form of
the catalyst is the particle Mn [Eq. (2)], which
3
+
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 5 2010

STUDY OF REACTION OF ISOMERIC ACETOXYTOLUENES
951
involves in the oxidation the methyl group of
color of the reaction mixture is light brown). Upon
compound I with formation of acetoxybenzyl radical
consumption of I and formation of less reactive II and
2
+
•
[Eq. (4)]. Introduction to the system of bromide ions
III the rate of reduction of Mn Br falls, resulting in
an increase of its equilibrium concentration in the
system (at the end of the oxidation the solution
becomes of violet color). It is characteristic that at the
leads to the formation of more active manganese
bromide catalyst [Eqs. (1) and (3)]. At the ratio
–
[
Mn(II)]:[Br ] = 1:1, compound I is involved in the
2
+
•
oxidation reaction (5). When concentrations in the
initial time, when the concentration of Mn Br in
solution is low, the rate of oxidation of I is higher than
the rate of formation of III (Fig. 1). In these
conditions, I is oxidized by ozone mainly at the double
bonds of the aromatic ring [Eq. (19)] with the
formation of ozonides.
ozone–air mixture [O ] >> [O ] ≈ 22, the formed
2
3
acetoxybenzyl radicals are transformed into acetoxy-
peroxyde radicals [Eq. (6)]. Further transformation of
the latter in the framework of the considered scheme is
possible when W = W << W , i.e. when the chain
i
t
r
length ν = W /W >> 1. However, estimates show that
in the experimental conditions this dependence is not
exp
i
From the above follows that in the oxidation of I
with ozone in the presence of manganese bromide
catalyst the high selectivity of oxidation of the methyl
group is achieved at comparable concentrations of
catalyst and the substrate. Below are shown the data on
the oxidation of I by ozone-air mixture in acetic
observed: W (W ) = W (W ) >> W (W , W , W ), and
i
5
t
12
r
7
8
9
–
4
–4
the chain length ν = W /W = 3.5×10 /12.4×10
=
r
i
0
.28. Most likely, in the presence of manganese
bromide catalyst, the oxidation of I develops by the
ion-radical non-chain mechanism, whereby the
oxidation products are mainly formed as a result of
termination of acetoxyperoxy radicals.
anhydride in the presence of the manganese bromide
–4
catalyst at 5ºC: [O3]0 = 4.2×10 , [I] = 0.4,
0
[
Mn(OAc) ] = 0.1, [KBr]0 = 0.1, [H SO ]
=
2
0
2
4 0
–
1
Terminating of acetoxyperoxy radicals can proceed
predominantly by the reaction (12), since the reaction
1.2 mol l , V =0.01 l.
r
(
15) suggests a parallel formation of II and III, which
contradicts the experimental data. It seems that alkoxy
radicals formed in the solvent cell in the experimental
conditions go over into the bulk of solution (12) [7],
where they react with a high rate with the reduced
form of catalyst (13) forming the reaction products
Yield of the oxidation products, %
Comp. no.
III
II
IV
Iа
Ib
Ic
63.0
68.7
70.0
16.0
17.6
18.0
traces
1.6
(
K /K ≈ 10.0 [7]). The whole process development
3 8
2.0
obviously corresponds to the sequence of reactions (6–
2–13–14), but it does not stop at the stage of
1
formation of compound II and continues until the
formation of compounds III and V [Eqs. (16), (18) and
then similarly to the reaction scheme (6)–(12)–(13)–
The oxidation proceeds by the ion-radical non-
chain mechanism, comprising the following sequence
of reactions: (5)–(6)–(12)–(13)–(14)–(17). Material
balance of the process accounting for these reactions
leads to the final Eq. (23), which corresponds to the
experimentally observed first order with respect to the
initial components (Fig. 2) [Eq. (24)]:
(
14)]. Formation of compound IV is probably a result
of reactions (20)–(22).
It was noted (Fig. 1, curve 6) that the concentration
of active catalyst in solution at the initial time is close
to zero, but it continuously increases with the decrease
in the concentration of I and reaches maximum value
2+
–
3 3
АсОArCH + Mn Br + О
–
2+
•
•
–
1
→ АсОArCH
2
О + Mn Br + НО + 1/2О
2
,
(23)
(24)
(
0.08 mol l ) during exhaustive oxidation of the
2+
–
substrate. The reason is that initially the reaction rate
W = K [АсОАrСН ] [Mn Br ] [О ] .
eff
3 0
0
3 0
2
+
–
of oxidation of Mn Br with ozone (W ) slightly
3
exceeds the rate of its reduction in the reaction with the
REFERENCES
–4
substrate (W ) (at [AcOArCH ] = 0.4, [O ] =4.0×10 ;
5
3 0
3 0
2
+
–
2+
•
–1
1
2
.
.
Galstyan, A.G., Zh. Obshch. Khim., 2008, vol. 78, no. 9,
[
2
Mn Br ] = 0.07; [Mn Br ] = 0.03 mol l ; K =
0
3
–2
–1 –1
–4
p. 1457.
0.3, K = 3.1×10 l mol s , W = 5.7×10 , and
5 3
W = 3.7×10 mol l s ), so the concentration of
Mn Br in the system at the initial time is low (the
–
4
–1 –1
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2
+
•
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 5 2010