METHOD OF REDUCING RING CHLORINATION IN THE MANUFACTURE OF A TRICHLOROMETHOXYBENZENE

PROCEDE PERMETTANT DE REDUIRE LA CHLORATION D'UN NOYAU DANS LA FABRICATION D'UN TRICHLOROMETHOXYBENZENE

English Abstract

Disclosed is a method of making a trichloromethoxybenzene from a
methoxybenzene or partially chlorinated methoxybenzene, such as anisole or p-
chloroanisole, that contains at least 20 ppm phenol. The phenol concentration
is reduced to less than 20 ppm and a mixture is prepared of the methoxybenzene
and a source of chlorine free radicals, such as chlorine or sulfuryl chloride.
The reaction is performed in a solvent, which can be either benzotrifluoride,
orthochlorobenzotrifluoride, metachlorobenzotrifluoride,
parachlorobenzotrifluoride, or a dichlorobenzotrifluoride. The mixture is
exposed to actinic radiation, such as ultraviolet light, which generates the
chlorine free radicals.

French Abstract

L'invention concerne un procédé de fabrication d'un trichlorométhoxybenzène à partir d'un méthoxybenzène ou d'un méthoxybenzène partiellement chloré, tel que l'anisole ou le p-chloro-anisole, renfermant au moins 20 ppm de phénol. La concentration en phénol est réduite à moins de 20 ppm et on prépare un mélange dudit méthoxybenzène et d'une source de radicaux libres de chlore, tels que le chlore ou le chlorure de sulfuryle. La réaction s'effectue dans un solvant qui peut être du benzotrifluorure, de l'orthochlorobenzotrifluorure, du métachlorobenzotrifluorure, du parachlorobenzotrifluorure ou du dichlorobenzotrifluorure. Le mélange est exposé à un rayonnement actinique, tel qu'un rayonnement ultraviolet, générant les radicaux libres de chlore.

Claims

WE CLAIM:
1. A method of making a trichloromethoxybenzene selected from the group
consisting of .alpha.,.alpha.,.alpha.-trichloromethoxybenezene,
.alpha.,.alpha.,.alpha.-trichloromethoxcy-p-
chlorobenzene, or a mixture thereof comprising
(A) taking a methoxybenzene having the general formula
<IMG>
where m is 0 or 1 and n is 1, 2, or 3, that contains more than 20 ppm phenol
and removing sufficient phenol to reduce the phenol concentration therein to
less than 20 ppm; (B)preparing a mixture of said methoxybenezene from
step A and a source of chlorine free radicals in a solvent selected from the
group consisting of benzotrifluoride, orthochlorobenzotrifluoride,
metachlorobenzotrifluoride, parachlorobenzotrifluoride, and
dichlorobenzotrifluoride;
(C) heating said mixture; and
(D) generating said chlorine free radicals in said mixture.
2. A method according to Claim 1 wherein said mixture is heated to the reflux
14

temperature of said solvent.
3. A method according to Claim 1 or 2 wherein said source of chlorine free
radicals is chlorine gas.
4. A method according to Claim 1, 2 or 3 wherein said solvent is
benzotrifluoride.
5. A method according to Claim 1, 2 or 3 wherein said solvent is
parachlorobenzotrifluoride.
6. A method according to any one of the preceding Claims wherein
methoxybenzene is anisole.
7. A method according to any one of the preceding Claims including the
additional last step of reacting said trichloromethoxybenzene with hydrogen
fluoride to produce a trifluoromethoxybenzene.
8. A method according to any one of the preceding Claims wherein said source
of chlorine free radicals is added to a mixture of said methoxybenzene and
said solvent.
15

9. A method according to any one of Claims 1 to 7 wherein said
methoxybenezene and said source of chlorine free radicals are added
separately to said solvent.
10. A method according to Claim 9 wherein a small amount of said
methoxybenzene is first mixed with said solvent.
11. A method according to any one of the preceding Claims wherein the amount
of said methoxybenzene is about 10 to about 60 wt% of the total weight of
methoxybenzene and solvent.
12. A method according to any one of the preceding Claims wherein said process
is performed in contact with metal and about 5 to about 500 ppm of a metal
scavenger is added to said mixture.
13. A method according to any one of the preceding Claims comprising the step
of irradiating said mixture with actinic radiation of an energy sufficient to
form
chlorine free radicals.
14. A method of making .alpha.,.alpha.,.alpha.-trichloromethoxybenzene
comprising
(A) removing sufficient phenol from anisole that contains more than 1000
ppm phenol to reduce the phenol concentration therein to less than 5
16

ppm;
(B) preparing a mixture of
(1) about 30 to about 50 wt% of said anisole from step A;
(2) about 50 to about 70 wt% benzotrifluoride or
parachlorobenzotrifluoride; and
(3) at least a stoichiometric amount of chlorine gas;
(C) heating said mixture to reflux; and
(D) irradiating said mixture with actinic radiation of an energy sufficient to
form chlorine free radicals.
15. A method according to Claim 13 or Claim 14 wherein the actinic radiation
is
ultraviolet light.
16. A method according to Claim 14 or Claim 15 dependent thereon wherein said
solvent is benzotrifluoride.
17. A method according to Claim 14 or Claim 15 dependent thereon wherein said
solvent is parachlorobenzotrifluoride.
18. A method according to Claim 14, 15 as dependent thereon 16 or 17 wherein
said anisole and said chlorine gas are added separately to said solvent.
17

19. A method according to Claim 18 wherein a small amount of said solvent is
first mixed with said anisole.
20. A method of making .alpha.,.alpha.,.alpha.-trichloromethoxybenzene
comprising
(A) removing sufficient phenol from anisole that contains more than 1000
ppm phenol to reduce the phenol concentration therein to less than 5
ppm;
(B) continuously separately adding anisole and chlorine gas to a moving
stream of benzotrifluoride or parachlorobenzotrifluoride heated to
reflux, where the concentration of anisole in said stream is about 30 to
about 50 wt% and said chlorine gas is about 1 to about 5 mole% in
excess of stoichiometric;
(C) exposing said moving stream to ultraviolet light.
21. A method according to Claim 20 wherein said solvent is benzotrifluoride.
22. A method according to Claim 20 wherein said solvent is
parachlorobenzotrifluoride.
18

Description

CA 02341539 2001-02-23
14-09-2000 PCT/G 899/02156
EpO, ~
~~'.S ~~ U~zioh
. .
METHOD OF REDUCING RING CHLORINATION IN THE
MANUFACTURE OF A TRICHLOROMETHOXYBENZENE
This invention relates to a method of making a trichloromethoxybenzene
by reacting a methoxybenzene, selected from anisole or p-chloroanisole, with
chlorine free radicals in a benzotrifluoride {BTF) solvent to produce a
trichloromethoxybenzene, selected from a,a,a trichloromethoxybenzene (TCMB)
or a,a,a-trichloromethoxy-p-chlorobenzene {TCMCB), respectively, or a mixture
thereof. In particular, it relates to the use of a trichloromethoxybenzene
that
contains phenol as an impurity and to the removal of that phenol prior to this
reaction.
U.S. Patent No. 5,773,668 discloses a process for making TCMB by
reacting anisole with gaseous chlorine in the presence of ultraviolet light in
a
BTF based solvent. While that reaction works well, the product can sometimes
contain small quantities of ring chlorinated TCMB, chlorinated phenols,
dioxins,
and furans.
We have discovered that the presence of a small amount of phenol in a
methoxybenzene results in ring ch(orination and dioxin formation, and that
ring
chlorination and dioxin formation can be very significantly reduced if the
phenol
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is removed first. While we do not wish to be bound by any theories, we believe
that the phenol is chlorinated first, and that the chlorinated phenol then
ring
chlorinates the methoxybenzene. We have found that a methoxybenzene can be
photochlorinated in a BTF based solvent without significant chlorination of
the
aromatic ring and without the formation of significant amounts of dioxin if a
methoxybenzene that contains phenol is first purified to reduce the amount of
phenol to below 20 ppm.
While in the prior process it was preferable to use 20% anisole and meter
in the anisole in order to avoid ring chlorination, we have found that if the
anisole
is first purred of phenol, ring chlorination is avoided even when the anisole
is
not metered in and is used at 50 wt%. As a result, throughput is substantially
higher and the process is more efficient and economical. Capital costs are
also
lower.
Thus according to one aspect of this invention there is provided a method
of making a trichloromethoxybenzene selected from the group consisting of
a,a,a-trichloromethoxybenezene, a,a,a-trichloromethoxy-p-chlorobenzene, or a
mixture thereof comprising
(A) taking a methoxybenzene having the genera! formula
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Hn~3 - n
Cl m
where m is 0 or 1 and n is 1, 2, or 3, that contains more than 20 ppm phenol
and
removing sufficient phenol to reduce the phenol concentration therein to less
than 20 ppm;
(B) preparing a mixture of said methoxybenezene from step A and a
source of chlorine free radicals in a solvent selected from the group
consisting of
benzotrifluoride, orthochlorobenzotrifluoride, metachlorobenzotrifluoride,
parachlorobenzotrifluoride, and dichlorobenzotrifluoride;
(C) heating said mixture; and
(D) generating said chlorine free radicals in said mixture.
- Preferably said mixture is heated to the reflex temperature of said solvent.
Conveniently said source of chlorine free radicals is chlorine gas.
The solvent may be benzotrifluoride and preferably is
parachlorobenzotrifluoride. Conveniently the methoxybenzene is anisole.
3
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Preferably the method includes the additional last step of reacting said
trichloromethoxybenzene with hydrogen fluoride to produce a
trifluoromethoxybenzxene.
Advantageously said source of chlorine free radicals is added to a mixture
of said methoxybenzene and said solvent.
In an alternative method said methoxybenezene and said source of
chlorine free radicals are added separately to said solvent.
Conveniently a small amount of said methoxybenzene is first mixed with
said solvent.
Preferably the amount of said methoxybenzene is about 10 to about fi0
wt% of the total weight of methoxybenzene and solvent.
Conveniently said process is pertormed in contact with metal and about 5
to about 500 ppm of a metal scavenger is added to said mixture.
Advantageously the method comprises the step of irradiating said mixture
with actinic radiation of an energy sufficient to form chlorine free radicals.
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The invention also provides A method of making a,a,a
trichloromethoxybenzene comprising
(A) removing sufficient phenol from anisole that contains more than
1000 ppm phenol to reduce the phenol concentration therein to
less than 5 ppm;
(B) preparing a mixture of
(1 ) about 30 to about 50 wt% of said anisole from step A;
(2) about 50 to about 70 wt% benzotrifluoride or
parachlorobenzotrifluoride; and
{3) at least a stoichiometric amount of chlorine gas;
(C) heating said mixture to reflux; and
{D) irradiating said mixture with actinic radiation of an energy sufficient
to form chlorine free radicals.
Conveniently the actinic radiation is ultraviolet light. Again the solvent
may be benzotrifluoride, preferably parachlorobenzotrifluoride. Advantageously
said anisole and said chlorine gas are added separately to said solvent.
Preferably a small amount of said solvent is first mixed with said anisole.
The invention also provides A method of making a,a,a-
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trichioromethoxybenzene comprising
(A) removing sufficient phenol from anisole that contains more than
1000 ppm phenol to reduce the phenol concentration therein to
less than 5 ppm;
(B) continuously separately adding anisole and chlorine gas to a
moving stream of benzotrifluoride or parachlorobenzotrifluoride
heated to reflux, where the concentration of anisole in said stream
is about 30 to about 50 wt% and said chlorine gas is about 1 to
about 5 mole% in excess of stoichiometric;
(C) exposing said moving stream to ultraviolet light.
The solvent may be benzotrifluoride or parachlorobenzotrifluoride.
Anisole can be made by reacting phenol with dimethyl sulfate or with a
base and methyl chloride. When anisole is made by either process, some
unreacted phenol remains in the product. Other methods of making anisole and
p-chloroanisole also result in a product that contains some phenol. This
invention applies to methoxybenzenes (i.e., anisole, p-chloroanisole, and
mixtures thereof), including partially a-chlorinated methoxybenzenes (e.g., a-
chloromethoxybenzene), that contain at least 20 ppm of phenol. Preferably, the
methoxybenzene contains at least 1000 ppm of phenol as those grades are less
expensive and work as well.
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In the first step of the process of this invention, the phenol content of the
methoxybenzene feed is reduced to less than 20 ppm and preferably to less than
ppm. Methods that can be used for accomplishing this are known iri the art.
For example, the methoxybenzene can be passed through a bed of basic
alumina, clay, or zeolite. Purification can also be accomplished by
distillation.
in the second step of the method of this invention, the methoxybenzene is
reacted with chlorine free radicals in a BTF based solvent to produce a
trichloromethoxybenzene. If chlorine is used, the reaction with anisole is:
OCH~ OCCh
+ 3Ch -~-~ s ~ + 3HC1
BTF Solvent
Anisole TCMB
The methoxybenzenes are liquids which can be mixed with the BTF based
solvent in order to control undesireable side reactions. At least about 10 wt%
methoxybenzene (based on total solvent plus methoxybenzene weight) should
be used for an economical process, and if the weight °~ of
methoxybenzene is
greater than about 60, ring chlorination may begin to occur. Preferably, the
concentration of methoxybenzene is about 30 to about 50 wt%.
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Examples of BTF based solvents that can be used in this invention
include BTF, orthochlorobenzotrifluoride, metachlorobenzotrifluoride,
parachlorobenzotrifluoride (PCBTF), and dichlorobenzotrifluoride. BTF and
PCBTF are preferred. The use of these solvents is essential to reducing ring
chlorination.
The source of chlorine free radicals can be, for example, elemental
gaseous or liquefied chlorine or liquid sulfuryl chloride (S02C12). Gaseous
chlorine is preferred as it results in fewer byproducts, it is inexpensive,
and it
works well. At least a stoichiometric amount of the source of chlorine free
radicals is needed (i.e., 3 moles C12 per mole of the methoxybenzene), but a
slight (1 to 5 mole°~) excess is preferred to insure a complete
reaction and
reduce ring chlorination.
The methoxybenzene, solvent, and chlorine free radical source can be
mixed together in any fashion such as, for example, adding the chlorine free
radical source to a mixture of the methoxybenezene and the solvent, adding the
methoxybenezene and the chlorine free radical source separately to the
solvent,
or mixing some of the solvent with the methoxybenezene first, then adding that
mixture and the chlorine free radical source separately to a solvent. It has
been
found that if the methoxybenezene and the chlorine free radical source are
kept
apart until they are mixed with the solvent, ring chlorination is reduced.
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It has also been found that ring chlorination increases at lower
temperatures and therefore it is preferable to perform the reaction at as high
a
temperature as is practical. Generally, therefore, it is preferable to reflux
the
solvent during the reaction; this reduces ring chlorination by removing
hydrogen
chloride.
Chlorine tree radicals can be produced by exposing the source of chlorine
free radicals to actinic radiation of an energy sufficient to form chlorine
free
radicals, such as by the reaction
C12 h~ 2C1~
Examples of actinic radiation include, for example, ultraviolet light, radio
frequency, or x-rays. Free radical initiators can also be used to generate
chlorine free radicals, but ultraviolet light is preferred as it is convenient
and
easy to use. An ultraviolet wavelength of about 320 to about 340 nm is
preferred. Since the light does not penetrate deeply into the mixture, the
light
source should be placed as close to the mixture as possible. This can be
accomplished, for example, by placing the light in a well which is inside the
reactor. The mixture should be stirred to expose all portions of the mixture
to the
light to ensure continuous generation of chlorine free radicals.
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If the reaction mixture is in contact with a metal, it may be desirable to add
about 5 to about 500 ppm (based on mixture weight) of a metal scavenger to the
mixture to prevent the metal ions from catalyzing the production of
byproducts.
Examples of suitable metal scavengers include N,N-dialkyl amides (sold as
"Hallcomid" by the C.P. Hall company) and ethylenediaminetetraacetic acid
(EDTA).
The reaction can be pertormed as a batch, continuous, or semi-
continuous process, but a continuous process is preferred as it is more
efficient
and is more likely to result in less ring chlorination. It is also possible to
partially
chlorinate the methoxybenzene to a mixture of mono-, di- and
trichloromethoxybenzenes in a continuous process, and then transfer the
mixture
to a batch reactor to finish off the chlorination. In a preferred continuous
process, the methoxybenezene and the chlorinating agent are added separately
to a stream moving past a source of ultraviolet light. The rate of addition to
the
stream in a continuous process should be selected to optimize the reaction.
The TCMB product is useful as a chemical intermediate. For example, it
can be reacted with hydrogen fluoride to make trifluoromethoxybenzene, which
can be used to make herbicides and pesticides. The TCMCB product is useful
as an agricultural intermediate.
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The following examples further illustrate this invention.
Example 1 - Comparative
Into a 500 ml photochlorination vessel equipped with a 100 watt medium
pressure Hanovia light (air cooled), a reflex condenser, and an inlet for
chlorine was
placed 81 g of anisole and 325 g of BTF. The anisole contained 1200 ppm of
phenol as a by-product of the manufacturing process. The UV light was turned
on,
and the unit was heated to reflex (108°C) by means of a heat tape
wrapped around
the vessel. Once the unit was at reflex, chlorine flow was started at a rate
of 250
cclmin for 140 minutes, then decreased to 225 cGmin for the remainder of the
reaction. Chlorine flow was stopped when approximately 2.9 equivalents of
chlorine
had been added to the unit. A total of 460 g of solvent and chlorinated
anisoles
were recovered. Analysis by gas chromatography {GC) showed 23.6 wt% a,a-
dichloromethoxybenzene, 44.9 wt% TCMB, and 29.2 wt% of various ring
chlorinated
methoxybenzenes.
Example 2
Example 1 was repeated with 326 g of benzotrifluoride and 81 g of anisole
made by a process that resulted in the anisole containing less than 20 ppm of
phenol. The UV light was turned on, and the unit was heated to reflex
(108°C)
before chlorine flow was started. Chlorine was added at a rate of 275 cdmin
for
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approximately 3 hours. Chlorine flow was stopped when approximately 3.1
equivalents of chlorine had been added to the unit. A total of 457 g of
solvent and
chlorinated anisoles were recovered. Analysis by GC showed 87.8 wt% TCMB and
5.4 wt°~ of various ring chlorinated methoxybenzenes.
Examale 3 - Comparative
Example 2 was repeated with 82 g of the anisole that contained less than 20
ppm of phenol, 328 g BTF, and 0.101 g of added phenol for a total phenol
content of
1200 ppm. The UV light was turned on, and the unit was heated to reflux
(109°C),
before chlorine flow was started. Chlorine was added at a rate of 275 cc/min
for
approximately 3 hours. Chlorine flow was stopped when approximately 2.9
equivalents of chlorine had been added to the unit. A total of 461 g of
solvent and
chlorinated anisoles were recovered. Analysis by GC showed 24.8 wt% a,a-
dichloromethoxybenzene, 48.3 wt% TCMB, and 26.2 wt% of various ring
chlorinated
methoxybenzenes.
Examt~le 4 - Comparative
Example 2 was repeated with 82 g of the anisole that contained less than 20
ppm of phenol, 324 g BTF, and 0.097 g of added phenol for a total phenol
content of
1180 ppm. The UV light was turned on, and the unit was heated to reflux
(109°C)
before the chlorine flow was started. Chlorine was added at a rate of 275
cclmin for
approximately 3 hours. Chlorine flow was stopped when approximately 2.9
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equivalents of chlorine had been added to the unit. A total of 434 g of
solvent and
chlorinated anisoles were recovered. Analysis by GC showed 26.2 wt% a,a-
dichloromethoxybenzene, 47.5 wt% TCMB, and 25.2 wt% of various ring
chlorinated
methoxybenzenes.
Example 5
Anisole containing 1200 ppm phenol, which was used in Example 1, was
passed through a column containing 80 to 325 mesh activated basic alumina.
Analysis after treatment indicated less than 20 ppm phenol. As in Example 1,
82 g
of the purified anisole was charged to the reactor along with 328 g of BTF.
The UV
light was turned on, and the unit was heated to reflux (109°C) before
chlorine flow
was started. Chlorine was added at a rate of 275 cc/min for approximately 3
hours.
Chlorine flow was stopped when approximately 2.9 equivalents of chlorine had
been added to the unit. A total of 464 g of solvent and chlorinated anisoles
were
recovered. Analysis by GC showed 11.6 wt% a,a-dichloromethoxybenzene, 80.3
wt% TCMB, and 5.7 wt% of various ring chlorinated methoxybenzenes.
13