PROCESS FOR PREPARING 2,3,4,5-TETRACHLORO-6- (TRICHLOROMETHYL) PYRIDINE

PROCEDE DE PREPARATION DE 2,3,4,5-TETRACHLORO-6-(TRICHLOROMETHYL)PYRIDINE

English Abstract

ABSTRACT
Heptachloropicoline is prepared by continuously reacting chlorine
in the gas phase at an elevated temperature with one or more
lower-chlorinated 6-trichloromethyl pyridines in the presence of an
effective amount of ferric chloride.

Claims

72427-1
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparing heptachloropicoline which
comprises continuously reacting chlorine with one or more
lower-chlorinated picolines chosen from
<IMG>
where n = 1-3,
characterized in that the reaction is conducted at an elevated
temperature in the gas phase in the presence of gaseous ferric
chloride, and separating the heptachloropicoline formed.
2. A process in accordance with Claim 1, wherein a
mixture of tetrapenta, and hexachloropicolines containing an
average of five chlorine atoms are used.
3. A process in accordance with Claim 1 wherein the
reaction temperature is in the range of from 250°C to 500°C.
4. A process in accordance with Claim 3 wherein the
reaction temperature is in the range of from 300°C to 400°C.
5. A process in accordance with Claim 1 wherein the
reaction is run over a filler.
-9-

72427-1
6. A process in accordance with Claim 5 wherein the
filler is chosen from the group consisting of silica,
carborundum, and alumina.
7. A process in accordance with Claim 6 wherein the
filler is chosen from the group consisting of carborundum and
alumina.
-9a-

8. A process in accordance with Claim 1 wherein the ferric chloride
is continuously regenerated during the reaction.
9. A process in accordance with Claim 8 wherein the regeneration
of ferric chloride is carried out by passing ferric chloride
vapors through the reactor.
10. A process in accordance with Claim 1 wherein the mole ratio of
chlorine to lower-chlorinated picolines is in the ratio of from
2:1 to 20:1.
11. A process in accordance with Claim 10 wherein the mole ratio of
chlorine to lower-chlorinated picolines is in the ratio of from
4:1 to 15:1.
12. A process for preparing heptachloropicoline which comprises
continuously reacting chlorine with one or more lower-chlorinated
picolines chosen from
<IMG>
where n = 1-3,
characterized in that the reaction is conducted in the gas phase
at a temperature between 300°C and 400°C in the presence of con-
tinuously formed gaseous ferric chloride and separating the
heptachloropicoline formed.
13. A process in accordance with Claim 12 wherein a mixture of tetra-,
penta-, and hexachloropicolines containing an average of five
chlorine atoms are used.
- 10 -

14. A process in accordance with Claim 12 wherein the reaction is
run over a filler.
15. A process in accordance with Claim 14 wherein the filler is
chosen from the group consisting of silica, carborundum, and
alumina.
16. A process in accordance with Claim 15 wherein the filler is
chosen from the group consisting of carborundum and alumina.
17. A process in accordance with Claim 12 wherein the regeneration of
ferric chloride is carried out by passing ferric chloride vapors
through the reactor.
18. A process in accordance with Claim 12 wherein the mole ratio of
chlorine to lower-chlorinated picolines is in the ratio of from
2:1 to 20:1.
19. A process in accordance with Claim 18 wherein the mole ratio of
chlorine to lower-chlorinated picolines is in the ratio of from
4:1 to 15:1.
20. A process for preparing heptachloropicoline which comprises con-
tinuously reacting chlorine with a mixture of tetra-, penta-, and
hexachloropicolines containing an average of five chlorine atoms
chosen from:
<IMG>
where n = 1-3
- 11 -

characterized in that the reaction is conducted in the gas
phase at a temperature between 300°C and 400°C in the presence
of a filler chosen from the group consisting of carborundum
and alumina, and in the presence of continuously formed gaseous
ferric chloride and separating the heptachloropicoline formed.
21. A process in accordance with Claim 20 wherein the regeneration
of ferric chloride is carried out by passing ferric chloride
vapors through the reactor.
22. A process in accordance with Claim 20 wherein the mole ratio
of chlorine to lower-chlorinated picolines is in the ratio of
from 2:1 to 20:1.
23. A process in accordance with Claim 22 wherein the mole ratio of
chlorine to lower-chlorinated picolines is in the ratio of from
4:1 to 15:1.
12

Description

~3Q~O~
BACKGROUND OF THE INVENT ION
The present invention concerns the improved process for the preparationof 2,3,4,5-tetrachloro-6-(trichloromethyl)pyridine, hereinafter referred
to as heptachloropicoline.
Heptachloropicoline is a known compound having been previously prepared
by a number of processes. This compound has uses as a pesticide; and
is also employed as a chemical intermediate in the preparation of other
highly desired pesticide products. Previous methods for preparing this
lo compound include those described in the following patents as well as
the prior art noted therein. United States patent numbers~ 3~256~167;
3,420,833; 3,732,230; 4,227,001; and 4,256,894.
Thus, U.S. 3,256,167 describes the continuous liquid-phase reaction of
alpha-picoline hydrochloride with chlorine preferably in the presence of
a Lewis catalyst or under UV radiation. However, this process requires
a large excess of chlorine and a long reaction time.
U.S. 3,420,833 describPs a process for preparing polychlorinated aromatic
heterocyclic nitrogen compounds whereby alpha-picoline is reacted in the
gas phase with gaseous chlorine at a temperature of from 400C to 700C.
A large excess of chlorine is required; but heptachloropicoline is neither
mentioned nor exemplified.
U.S. 3,732,230 describes the reaction of liquid alpha-pico1ine hydro-
chloride with chlorine under a pressure of hydrogen chloride. However,
this reaction must be run under pressure as well as requiring a reaction
time of from 6 to 18 hours.
-- 2

~3~
U.S. 4,227,001 describPs the liquid phase reaction of 2,4-dichloro-6-
(trichloromethyl) pyridine with chlorine at a temperature up to 220C in
the presence of a Lewis acid catalyst and at superatmospheric pressure.
Here too, reaction times of about eight hours are required.
U.S. 4,256,894 describes the reaction of a chloro-substituted 6-(tri-
chloromethyl)pyridine in the liquid state with chlorine in the presence
of a Lewis acid catalyst. However, here too long reaction times are
required, and the heptachloropicoline is obtained in very low yield in
a mixture of other chlorinated pyridines.
OBJECTIVES OF`THE INVENTION
It is the objective of the present invention to provide a new and improved
method for the production of heptachloropicoline. It is a further
objective of the present invention to provide a method more economical
than known methods for the production of this compound substantially free
of pentachloropyridine in yields far in exsess of those previously obtained
in known methods.
SUM~ARY OF THE INVENTION
~t has unexpectedly been discovered that heptachloropicoline can be pre
pared by continuously reacting chlorine with one or more lower chlorinated
picolines chosen from:
Clx~
~ CC13
where n = 1-3,
comprising running the reaction at an elevated temperature in the gas phase
in the presence of ferric chloride and separating th~heptachloropicoline
formed.

~L3~0~3~
DETAILED DESCRIPTION OF THE INVENTION
-
The process of the present invention may be run using as a reactant
one of the lower-chlorinated picolines or using a mixture containing
two or more of the lower-chlorinated picolines. The lower-chlorinated
picolines can be prepared by standard methods. Since the product from
these standard methods is usually in the form of a mixture of lower-
chlorinated picolines, it Ts more convenient to use such a mixture as
a reactant in the process of the present invention.
In carrying out the process of ~he present invention, one or more of
the lower-chlorinated picolines is added to an evaporator kept at a
temperature of 300 C. The vapors leaving the evaporator are directed
into a reactor containing chlorine, gaseous ferric chloride, and optionally
a filler. A gas such as nitrogen, chlorine, or a mixture of these two
and/or an inert solvent such as gaseous carbon tetrachloride may be
optionally used to assist in the evaporation of the reactants in the
evaporator.
The reaction of the present invention requires the use of a catalyst
such as ferric chloride. However, simple coating or impregnating of
the filler of the reactor is insufficient. Under the conditions of
the reaction, the ferric chloride very quickly evaporates off. The
result being that very little if any heptachloropicoline is formed.
It is one of the surprising and novel aspects of the present invention
that the chlorination of lower-chlorinated picolines affords high
yields of heptachloropicoline when the ferric chloride is continuously
regenerated preferably by passing gaseous ferric chloride through the
reactor during the reaction . The gaseous ferric chloride can be formed
by heating of the solid -ferric chloricle at 300C in the presence of a
carrier gas such as nitrogen or chlorine. Alternatively, the ferric
chloride may be continuously regenerated by passing chlorine gas or ~
mixture of chlorine and nitrogen gas over iron filings kept at a temper-
ature of 300C.
- 4 -

~3~1 39
The gaseous ferric chloride and the gaseous lower-chlorinated picoline or
mixture of these are directed into a reactor- optionally containing a -filler.
The reactor can be made from any material which s-tands up to the condit-
ions of the present reaction. The filler serves the purpose oF increasing
the rate of the reaction. Thus, any inert granular or powdered material
may be used, such as silica, carborundum or alumina. A preferred filler is
carborundum or alumina.
While a lower limit of about 250C is required for the present invention,
the temperature of the reaction will naturally depend upon the mole ratio
of chlorine to chlorinated piColines and the residence time of the reactants.
As a general rule, temperatures of from about 200 C to about 500C have
been found suitable for the reaction of the present invention, with a pre-
ferred temperature range of from 300 C to 400C, and a most pre-ferred
temperature of 350C.
The reaction of the present invention is run in a continuous manner. The
residence time will naturally depend upon the temperature, rate of adding
the reactants, and type of filler used. However, residence times of
from 0.1 to 5 seconds and preferably from 0.6 to 1.0 seconds are usually
employed.
The reaction may be run at atmospheric :pressure or at superatmospheric
pressure. However, the use of superatmospheric pressure does not
afford any advanta3e.
The process of the present invention requires the reacting of one to three
moles of chlorine per mole of lower-chlorinated picolines, depending
upon the type of reactant used.
- 5
!

~3~40~
For economic reasons i-t is preferred to use an excess of chlorine. A
mole ratio of chlorine to lower-chlorinated picolines of from Z:l to 20:1
has been found suitable; with a mole ratio of 4:1 to 15:1 most preferred.
Chlorine gas alone or in mixture with an inert gas or solvent(such as
nitrogen or carbon tetrachloride~are passed simultaneously into the reactor.
After passing through the reactor the product and unreacted reactants are
collected by cooling and condensation in a collector kept at O C. The
unreacted chlorine is removed by scrubbing in caustic. Alternatively
it may be optionally separated by known methods and recycled into the
reactor. The resulting product is worked up and separated by standard
methods to afford~ yields of 80-85% with conversions of 50-60% The
unreacted lower chlorinated picolines may be recycled in the reaction to
afford-in a very short period of time- an almost complete conversion of the
lower-chlorinated picolines into the desired heptachloropicoline.
Thus, the present invention unexpectedly aFfords an inexpensive method
of preparing heptachloropicoline in high yield and high conversion in a
very short time, without the need for running the reaction under pressure.
The process of the present invention is also advantageous in that there
is a very low degradation of the product to -the undesireable pentachloro-
pyridine.
While the invention will now be described in connection with certain pre-
ferred embodiments in the following examples it will be understood that
it is not intended to limit the invention to these particular embod;ments.
On the contrary it is intended to cover all alternatives, modifications
and equivalents as may be included within the scope of the invention as
defined by tlle appended claims.

~L3Q4~9
EXAMPLES 1-4
The process of the present invention involves the use of three sections:
an evaporator, a ferric chloride generator, and the main reactor as follows:
(a) The lcwer chlorinated picolines are vaporized in an avaporator kept
at 300C and the resul ting gas swept out with carrier gases such as 309
nitrogen per hour; 509 chlorine per hour; or with a mixture of 17g nitrogen
and 25g chlorine per hour. (b) The ferric chloride ls formed during the
reaction using a generator. This generator is conveniently made out of
a glass tube having a diameter of 30mm and a length of 150 mm filled with
iron filings. While heating at 300C, 49 per hour of chlorine gas and
139 per hour of nitrogen gas are passed through the tube to afford 0.03
moles of ferric~chloride per hour. (c) The main reactor is conveniently
a tube 67cm in length with a diameter of 30 mm, Filled with either carbor-
undum or alumina~ preferably precoated wi-th ferric chloride.
Using the above described sections, the gaseous lower-chlorinated picolines,
the sirrultaneously formed gaseous ferric chloride, and additional chlorine
gas alone or together wi-th nitrogen or carbon tetrachloride are passed into
the main reactor kept at 350C using a residence time of o.6 sec. to obtain
the results summarized and shown in Table 1.
EXAMPLE 5
Following the method of Examples 1-4 a mixture of pentachloropicolines
was reacted at 350C over carborundum coated with ferric chloride. After
a few minutes practically no heptachloropicoline is formed, as the ferric
chloricle evaporates off the carborundum under the conditions o-F the reaction.

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