Oxidation of 2-methoxy-3,6-dichloropropenylbenzene with ozone

Article abstract of DOI:10.1134/S1070427207040180

Oxidation of 2-methoxy-3,6-dichloropropenylbenzene with ozone in acetic acid and carbon tetrachloride was studied.

Full text of DOI:10.1134/S1070427207040180

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 4, pp. 611 614.
Pleiades Publishing, Ltd., 2007.
Original Russian Text
R.L. Safiullin, L.R. Enikeeva, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 4, pp. 623 626.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Oxidation of 2-Methoxy-3,6-dichloropropenylbenzene
with Ozone
R. L. Safiullin and L. R. Enikeeva
Institute of Organic Chemistry, Ufa Scientific Center, Ufa, Bashkortostan, Russia
Received June 27, 2006
Abstract Oxidation of 2-methoxy-3,6-dichloropropenylbenzene with ozone in acetic acid and carbon
tetrachloride was studied.
DOI: 10.1134/S1070427207040180
1
Ozonolysis is one of the most promising methods
for oxidation of hydrocarbons containing double
bonds. In this study, we examined the formation of
2-methoxy-3,6-dichlorobenzaldehyde by ozonation
of 2-methoxy-3,6-dichloropropenylbenzene (DCPB).
2-Methoxy-3,6-dichlorobenzaldehyde can serve as
a starting compound for preparing 2-methoxy-3,6-di-
chlorobenzoic acid and its derivatives used in agri-
culture as herbicides [1 3]. It is known that the effi-
ciency of ozonolytic conversion of olefins is deter-
mined by the decomposition of intermediate ozono-
lysis products, ozonides. In this study, we examined
the thermal stability of ozonides formed by ozonation
of 2-methoxy-3,6-dichloropropenylbenzene and the ef-
fect of acidity on their decomposition.
95 l mol 1 cm ) [4]. After the breakthrough of ozone
through the reactor, the ozonation was stopped.
The intermediate compounds containing peroxy
groups were determined by spectrophotometric iodo-
metric titration [5]. The concentration of intermediates
containing peroxy groups ( O O ) was calculated by
the equation
[ O O ] = AVas /( lVs ),
The extinction coefficient of I3 at = 360 nm is
= 28 000 l mol 1 cm , the optical cell width is 1 cm,
1
the volume of the solution being analyzed Vas
2.5 3.0 ml, and the introduced sample volume Vs =
=
2 10 l.
EXPERIMENTAL
The decomposition products of ozonized com-
1
pounds were examined by H and 13C NMR, IR, and
UV spectroscopies, and also by GLC. The H and 13C
2-Methoxy-3,6-dichloropropenylbenzene was puri-
fied by vacuum distillation under argon. Carbon tetra-
chloride (CCl4) was successively treated with ozone,
dried over CaCl2, and distilled in argon. Methane-
sulfonic acid (CH3SO3H) and p-toluenesulfonic acid
(p-TolSO3H) of chemically pure grade were used with-
out purification. Ozone was prepared from oxygen in
a ozonizer with an output capacity of 0.5 g of ozone
1
NMR spectra were recorded in CDCl3 on a Bruker
AM-300 NMR spectrometer (300 and 75 MHz, re-
spectively).
Ozonation of the olefin in acetic acid solutions.
2-Methoxy-3,6-dichloropropenylbenzene (27.4 mol,
6.06 g) was dissolved in glacial acetic acid (50 ml)
and ozonized at 315 K. In the course of the ozonation,
the reaction mixture was sampled at regular intervals
and the samples were titrated iodometrically. The re-
action mixture was ozonized for 3 h . After the ozona-
tion was complete, the ozonide concentration in the re-
action mixture was 0.12 M.
1
per hour at an oxygen consumption of 4 l h .
The ozonation of DCPB and isolation of products
of its conversion were carried out as follows. A solu-
tion of the olefin in acetic acid or CCl4 was purged
with an ozone oxygen mixture fed into the lower
part of a reactor. The ozone content at the inlet and
outlet of the reactor was determined spectrophoto-
metrically at = 300 nm (ozone extinction coefficient
Ozonation of the olefin in acetic acid containing
water and p-toluenesulfonic acid. The initial mix-
611

612
SAFIULLIN, ENIKEEVA
tinued for 3 h. Under these conditions, the ozonide
content in the reaction mixture did not exceed 0.1 M.
The thermal stability of ozonides formed by ozona-
tion of the olefin was examined as follows. A portion
of the reaction mixture was taken from the reactor and
dissolved in acetic acid. This solution was placed in
a temperature-controlled reactor equipped with a wa-
ter-cooled reflux condenser and a stirrer. At certain
intervals, the reaction mixture was sampled drawn
and the concentration of the peroxy groups in was
determined iodometrically. This experiment was con-
tinued until the degree of decomposition of the ozon-
ide reached no less than 70%. To elucidate how
the acidity affects the kinetics of acid-catalyzed de-
composition of ozonides, weighed portions of the sul-
fonic acid were added to the reaction mixture.
Fig. 1. Kinetic curves of ozonide decomposition in
CH3COOH. ( ) Time. Temperature, K: (1) 298, (2) 326,
(3) 347, and (4) 347 in the presence of [CH SO H] =
3
3
2
1.1 10 M.
ture to be ozonized (50 ml) contained olefin (6.06 g)
dissolved in an acetic acid solution containing
p-TolSO3H (0.1 g) and H2O (3.2 g). The ozonation
was carried out at 315 K. After a lapse of 2 h
35 min, the ozonide concentration in the reaction
mixture reached 0.2 M.
Thermal stability of 2-methoxy-3,6-dichloropro-
penylbenzene ozonide. The thermal decomposition
of the ozonide was examined in acetic acid solutions
at 288 347 K. As can be seen from Fig. 1, 2-methoxy-
3,6-dichloropropenylbenzene ozonide is stable at room
temperature for several hours. We found that the ad-
dition of water (3.3 M) does not affect the kinetics of
degradation of the ozonide. With increasing tempera-
ture, the ozonide stability decreases. Noticeable de-
composition of the ozonide begins at 347 K. The ki-
netic curve of thermal decomposition of the ozonide
is linear in the coordinates of equation of a first-order
reaction, which allows calculation of the effective
rate constant keff of the ozonide decomposition (see
table). These data show that this rate constant is in-
dependent of both the initial ozonide concentration
and solvent type, and its value is close to that of de-
composition of 1-hexene ozonide [4].
Ozonation of the olefin in CCl4. In these experi-
ments, solutions of the olefin in CCl4 (50 ml) con-
taining 6.06 g of the olefin were ozonized at 295 K.
Although the ozone breakthrough occurred 40 min
after the start of the reaction, the ozonation was con-
Rate constant of ozonide decomposition in an acetic acid
solution at various temperatures and sulfonic acid con-
centrations
[Ozonide]0,
M
1
T, K
[RSO3H], M
keff, s
7
7
5
290
298
347
0.03*
0.01
0.04
(5 0.2) 10
(7.5 2.1) 10
(2.3 0.4) 10
Acid-catalyzed decomposition of ozonide. We
found that addition of methane and p-toluenesul-
fonic acids (RSO3H) accelerates the decomposition
of the ozonide. Acetic acid used as the solvent (pKa
4.75) [6] is weaker than methane- and p-toluenesul-
fonic acids (pKa 0 and 0.7, respectively) [7]. The table
shows that the ozonide decomposition is noticeably
accelerated in the presence of methanesulfonic acid.
The kinetic curve of ozonide decomposition in the
presence of methanesulfonic acid is linear in the co-
ordinates of equation of a first-order reaction, which
allows calculation of the effective rate constant keff
of ozonide decomposition. The effective rate constants
keff of ozonide decomposition in the presence of sul-
fonic acids at varied temperature are listed in the table.
Thus, with the content of sulfonic acid in acetic acid
solutions increasing within the entire concentration
[Methanesul-
fonic acid]:
2
5
5
5
5
5
347
0.5 10
0.9 10
3.1 10
5.0 10
0.12
0.16
0.07
0.14
0.14
(4.0 0.5) 10
(4.2 0.5) 10
(7.3 0.5) 10
(11.4 1.5) 10
(12.9 1.6) 10
2
2
2
2
7.0 10
[p-Toluenesul-
fonic acid]:
2
5
5
5
5
347
0.6 10
1.8 10
2.9 10
6.8 10
0.03
0.07
0.06
0.07
(4.6 0.7) 10
(7.5 0.7) 10
(8.1 0.7) 10
(14.7 0.8) 10
2
2
2
*
In CCl .
4
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 4 2007

OXIDATION OF 2-METHOXY-3,6-DICHLOROPROPENYLBENZENE WITH OZONE
range, the stability of ozonides decreases, with keff
613
weakly dependent on the initial ozonide concentration.
Figure 2 shows that keff linearly depends on the sul-
fonic acid concentration. These correlations suggest
that the rate of ozonide decomposition is described
by the linear equation
W = keff[ozonide] = (k0 + kc[RSO3])[ozonide]0,
where k0 is the rate constant of ozonide decomposi
tion in the absence of sulfonic acid, and kc , the rate
constant of ozonide decomposition catalyzed by sul-
fonic acid.
Fig. 2. Plot of k
vs. RSO H concentration at 347 K.
3
eff
(1) CH SO H and (2) p-TolSO H.
3
3
3
isolated by two different methods. In the first method,
water was added to the reaction mixture and the re-
sulting yellow oily precipitate was treated with satu-
rated aqueous Na2SO4 and cooled to 273 K. A grayish
precipitate formed under these conditions was filtered
The rate constants of ozonide decomposition in
acetic acid containing a sulfonic acid were calculated
from our experimental data for [ozonide]0 = 0.16
0.03 M and are as follows: in the presence of p-tol-
5
1
uenesulfonic acid, k0 = (3.5 1.5) 10 s , kc =
1
off, washed with benzene, and dried. The H and 13C
3
1
(1.5 0.3) 10 l mol 1 s ; and in the presence of
5
1
NMR spectra of this product formed in a yield of 98%
were found to be identical to those of 2-methoxy-3,6-
dichlorobenzaldehyde.
methanesulfonic acid, k0 = (2.8 1,5) 10
s
and
kc = (1.5 1.3) 10 l mol 1 s .
3
1
It should be noted that the rate constant of acid-
catalyzed decomposition of 2-methoxy-3,6-dichloro-
propenylbenzene ozonide determined in this study
reasonably agrees with the rate constant of decompos-
ition of 1-hexene ozonide catalyzed by p-toluenesul-
fonic acid in the presence of the accumulated alde-
In the second method, acetic acid was distilled
off from the reaction mixture, and the resulting pre-
cipitate was dissolved in CCl4. This solution was fil-
1
tered and CCl4 was distilled off. The H NMR spec-
trum of the resulting product formed in 96% yield
contains a signal at 10.4 ppm belonging to the alde-
hyde group. The 13C NMR spectra show that the prod-
uct of oxidation of DCPB is 2-methoxy-3,6-dichloro-
benzaldehyde.
4
1
hyde, 7.4 10
s
[8].
After the completion of the ozonide decomposition,
the products of oxidative conversion of DCPB were
1H NMR spectrum of 2-methoxy-3,6-dichlorobenzaldehyde
Proton
, ppm:
OCH3
C(O)H
CH
CH
calculation
experiment
3.84
3.8 395
10.57
10.2 10.4
7.32
7.3 7.5
7.23
7.1 7.2
12C NMR spectrum of 2-methoxy-3,6-dichlorobenzaldehyde
C atom
, ppm:
OCH3
H C
H C
C Cl
C Cl
C OR
CH=O
calculation
experiment
62.49
62.84
127.0
127.1
134.6
134.9
122.8
121.1
137.3
134.9
156.05
156.12
190.4
188.5
Our experimental results can be adequately
described within the framework of the known
mechanism of ozonation of unsaturated compounds
[4]:
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 4 2007

614
SAFIULLIN, ENIKEEVA
Cl
Cl
Cl
Cl
Cl
OCH3
OCH3
OCH3
+
O O
H
+ O3
+ CH3C
H
C
CH CH CH3
CH CH CH3
O
Cl
O
O
O
I
II
III
ROH
Cl
Cl
Cl
OOH
+ CH3 CH
OCH3
O
CH CH
OCH3
C(O)H
OR
Cl
O
O
IV
Chemical scheme of ozonation.
In this scheme, molozonide I formed by the reac-
tion of ozone with the double bond is very unstable
and decomposes to yield aldehyde II and carbonyl
oxide III. Owing to the cell effect, some portion of
carbonyl oxide has no time to escape into the bulk and
reacts with the aldehyde to form more stable ozonide
IV. This is evident from the fact that, if the compo-
nents of the reaction mixture containing active oxygen
are not decomposed, the aldehyde yield does not ex-
ceed 70%. At the same time, the yield of the product
containing the O O group increases in the course
of ozonation and, after the reaction is complete, it is
approximately 20% of the initial olefin amount.
(2) Strong acids catalyze the ozonide decomposi-
tion.
(3) The main ozonation product in acetic acid,
formed in 98% yield after completion of decomposi-
tion of the ozonide, is 2-methoxy-3,6-dichlorobenz-
aldehyde.
REFERENCES
1. Mel’nikov, N.N., Novozhilov, K.V., and Belan, S.R.,
Pestitsidy i regulyatory rosta rastenii: Spravochnik
(Pesticides and Plant Growth Regulators: Handbook),
Moscow: Khimiya, 1995.
2. RF Patent 2106782.
3. RF Patent 2070877.
4. Razumovskii, S.D. and Zaikov, G.E., Ozon i ego re-
aktsii s organicheskimi soedineniyami (Ozone and Its
Reactions with Organic Compounds), Moscow: Nauka,
1974.
Thus, the main part of aldehyde is formed by direct
ozonation of 2-methoxy-3,6-dichlorobenzene. A small
portion of the aldehyde (up to 20% of the initial ole-
fin) is converted to ozonide by the reaction with the
simultaneously formed carbonyl oxide. After decom-
position of the ozonide in the presence of p-toluene-
sulfonic acid, 2-methoxy-3,6-dichlorobenzaldehyde is
formed in a yield of up to 98%.
5. Safiullin, R.L., Enikeeva, L.R., and Komissarov, V.D.,
Kinet. Katal., 1989, vol. 30, no. 5, pp.1040 1044.
6. Spravochnik khimika (Chemist’s Handbook), Nikol’-
skii, B.P., Ed., Moscow: Khimiya, 1964, vol. 3.
CONCLUSIONS
7. Organic Chemistry of Sulfur, Oae, S., Ed., New York:
Plenum, 1977.
(1) The ozonation of 2-methoxy-3,6-dichloropro-
penylbenzene yields 2-methoxy-3,6-dichlorobenzal-
dehyde (up to 70%) and the corresponding ozonide.
8. Yur’ev, Yu.N., Razumovskii, S.D., Berezova, L.D.,
and Zelikman, E.S., Zh. Org. Khim., 1975, vol. 11,
no. 1, pp. 7 11.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 4 2007