Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
It is known that p-xylene can be reacted with chlorine in the presence
of a catalyst to produce a mixture of various ring-chlorinated compounds and
isomers including 2,5-dichloro-p-xylene, a compound useful as an intermediate
in the preparation of pesticides and polymeric materials. Such reactions may
be effected in solution, in suspension or in the absence of a solvent. Thus,
~or example, in U.S. Patent 2,412,389, it is disclosed that p-xylene may be
chlorinated in the presence of a catalyst such as iron fi,ings or ferric
chloride, to produce mixtures of nuclear chlorinated materialc which may then
be separated by a series of steps to isolate some components of the mixture. '
However, the various compounds and isomers which may be produced in this ';~
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manner are not of equa'l commercial importance or value. Although such a
procedure may be of value in the production of mixtures of variously ring-
chlorinated mate`rials it provides little advantage as a direct chlorination
process for the production of specific ring-chlorinated products.
A more spèc1fic process for the ring-chlorination of p-xylene, util~
izing acetic ac~d~as a solvent and carried out in the presence of catalytic
amounts of ferric chloride or iodine is disclosed in U.5. :pdten~ ~3~,002,027.
The process limits the ring-chlorination~to the formation of mono-iand di~
~ chlorination derivatives. The~2,5-dichloro-p-xylene isomer may be separated '` '
from the~crude reactloo product by pouring into water followed by~'re crystal- ' '
l1zation of thè precipitate from~a~suitable solvent such dS an organic alcohol
or acet~c acid.
;It l~s~further~known ~rom U.S~ Patent 3,035,103, that~p-xylene may be
~ chlorinated,~in a solYent,~such~as~carbon tetrachloride, in the prèsence of ~'~
~ ~ a catalyst such a~ ferric chloride to yield a mixture of mono-, di-, tr~
; and tetra-~ring-ch1'or1nated p-xy1anes;~wh1ch~may then be~dist111ed ànd~the ~ ~ -
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dichloro-para-xylene fraction treated with a lower alkanol to recover
the commercially desirable 2,~-dichloro-p-xylene.
Although the processes of the prior art are useful in the preparation
of chlorinated xylenes and, with subsequent separation, the isolation of
2,5-dichloro-p-xylene, it will be apprec;ated that further improvements
in the efficiency, economy of preparation and yield of the desired product,
2,5-dichloro-p-xylene, are nevertheless desirable.
Accordingly, it is an object of the present invention to provide a
simple, direct process for the preparation of 2,5-dichlor~-p-xylene of hiah
purity whereby the number of processing and handling steps is minimized. It
is a further object to provide a process for the catalytic chlorination
of p-xylene that maximizes the yield of 2,5-dichloro-p-xylene while mini- , :-:
mizing the yield of the unwanted 2,3-dichloro-p-xylene isomer and over-
and under-chlorinated products.
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~ ` SUMMARY OF THE INVENTION
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It has now been found that hiqh yieids of 2,5-dichloro-p-xylene are
obtained when p-xylene is reacted with chlorine in the presence of~a cat-
alyst selected from the group consisting of sulfides of iron, sulfides of
antimony, and mixtures thereof. Sulfides of iron and/or antimony which may
be employed in accordance with this invention include, for example, FeS,
FeS2, Fe354,~Fe253,~ Sb2S3, Sb2S5, and the like, as well as~mixtures thereoF.
The chlorination process of this invention may be carried out in the
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presence of a suitable solvent, such as carbon tetrachloride, chloroform,
polychloro and perchloroalkanes and the like which is inert to reaction
with chlorine under conditions of the chlorination. However, it ;s an ad-
vantage of the process of the present invention, that it may be efficiently
carried out in the absence of a solvent, thus eliminating the need for an
additional separation step in the isolation of the desired product. The
amount of catalyst employed may vary considerably, for example from about
0.01 percent by weight or less to about 10.0 percent by weight or higher,
based on the weight of p-xylene. Preferably, between abclt 0.1 and 1.0
percent by weight o~ catalyst based on the weight of p-xylent, is employed.
To caximize the yield of 2,5-dichloro-p-xylene as well as to minimize
the formation of higher chlorinated products, it is advantageous to employ
a nearly stoichiometric quantity of chlorine, for example about 1.8 to 2.1
moles of chlor~n~ per mole of p-xylene although other ratios can be used.
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The reaction temperature may vary considerably but is preferably in '
the range of about 0 to about 100 Celsius, and most preferably in the '
range of about ~5 to about 70 Celsius. It has been found expedient to
initiate the reaction at about room temperature, such as 25 Celsius and
; . . .
gradually increase the reaction temperature to about 50 to 70 Celsius
during the reac~'ion.~ Although~the process of this invention is~preferab~y
carried out at atmospheric pressure, sub-atmospheric or super-atmospheric
pressures may be;employed, if desired.~ Upon completion of the reaction, '';`
any rema~ning by-product hydrogen chloride formed d~ring the reac~ion, and
any residual chlori~ne~gàs. may bè conveniently removed,~n a known~manner,
~ by blowing air oP nitrogen through the mixture.
pically,''the;~crude chlorination product obtained in accordance with
the process o~"this invention contains, after~removal'of~HCl,~about~0 to
6 percent by wéight of 2-chloro-p-xylene, about 65 to 80 percent by weight
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of 2,5-dichloro-p-xylene, about 10 to 20 percent by weight of 2,3-dichloro- '
p-xylene, about 0 to 8 percent by weight 2,3,5-trichloro-p-xylene and trace ''
amounts, generally less than one percent of 2,3,5,6-tetrachloro-p-xylene.
This crude product is readily succeptible to simple purification steps to
yield a 2,5-dichloro-p-xylene product having a purity in excess of about 90
percent. i'"
If the reaction is run in a solvent, the solvent may be conveniently
removed in a known manner, for example, by distillation. Alternately, the
2,5-dichloro-p-xylene may be obtained directly by filtrat'on of the reaction '
mixture. If the reaction is run in the absence of a solvent, the solvent ~
separation step is omitted. The crude reaction product is then treated by ~ ;
crystall~zation from suitable solvent in which the 2,5-dichloro-p-xylene is
substantially insoluble while the major portion of the remain~ng chlorinated
products is soluble. Solvents suitable for this purpose include for example,
alkanols, especially the lower alkanols such as methanolg ethanol, n-propanol, '
isopropanol and the various isomeric butanols. The preferred solvent for this
purpose i~s isopropanol. Generally the amount of solvent will range from about
0.25 parts to about 10.0 parts by weight and preferably from about 0.5 to
about 5.0 parts by weight of solvent~per part of crude reaction product. The
solid portion of'the resulting mixture is then filtered, preferably at about
room temperature (such as 25 Celsius~ and dried.~' The resulting sol~d will,
typically, exhibit a melting point in the range of 64.5 to-66.5 Celsius
which corresponds closely to that of 2,5-dichloro-p-xylene of high purity.
Gas chromatograph1c analysis'of the product thus obtained typ~cally discloses
a composition of approxlmately 94 percent 2,5-dichloro-p-xylene, approximately '4 percent of 2,3-clichloro-p-xylene and approximately 2 percent of 2,3,5-tr~-~
chloro-p-xylene. ~ ~ '
: ~ ; Thè fo110wing~examples will serve to further 111ustrate~the present
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invention and manner in which it may be practiced. It is to be understood,
however, that such examples are illustrative of the way in which the inven-
tion may be carried out and are not to be construed as limitative thereof.
In the examples, as well as elsewhere in the specification and claims ap-
pended thereto~ parts and percentages are by weight and temperatures are
in degrees Celsi~s unless otherwise stated.
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Example I -
A. A mixture of 955.8 parts of p-xylene and l.9 pa ts of ferrous
sulfide (0.2 percent by weight) wa~ charged to a reaction vessel and
heated to about 55C. The temperature of the reaction mixture ~as main-
tained at about 55 to 60C with agitation while l325 parts of chlorine
gas was introduced slowly over a period of approximately fourteen hours.
The react~on product was purged with nitrogen to remove hydrogen chloride
and any residuat chlorine. Analysis of this crude reaction product by
gas chromatographic methods is set forth in Table I.
B. Approximately 788 parts of isopropanol was added and mixed with
the crude reaction product, at a temperature of about 60C. The mixture
was cooled to roc~temperature and the solid portion thereof was removed
by filtration and dried to yield l006~parts of a solid material hàving a
~ melting range of 64.5 to 66.5C. and a composition as established by gas
chromatographic analysis of 93.5 percent 2,5-dichloro-p-xylene; 4.2~per-
cent 2.3-dichloro-p-xylene:~dnd 2.3 percent 2,3,5-trichloro-p-xylene.
Example I I
The procedure of Example IA was repeated except that ferrous sulf~de
was employed in the amount of about 0.5 percent by weight-based on the
weight of P-xYl~en~- ~Analys~s of the crude reaction product thus obtained is
set forth in Table I.
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Treatment of the crude reaction product with isopropanol as in Example
IB, yields 2,5-dichloro-p-xylene having a purity greater than 90 percent.
Example III
To a solution of 1062 parts p-xylene ;n 100 parts of carbon tetrachloride
was added 3.2 parts of ferrous sulfide. The solution was charged to a react~on
vessel at an lnitial temperature of about 25C. The temperature was gradually
increased from about 25C to about 55C to maintain the reaction product in
solution while 1448 parts of chlorine gas was introduced ~ith agitation over
a period of approximately 18 hours. ~ -
The reaction mixture was purged with nitrogen to remove hydrogen chloride
and residual chlorine and then slowly cooled to 25C. The resultant precip-
itated solid was separated by filtration and dried to yield 969 parts of
product having the following assay by gas chromatographic analysis:
2,5-dichloro-p-xylene 95.9 percent-
2,3-dichloro-p-xylene 2.7 percent
2,3,5-trichloro-p-xylene 1.3 percent ~ ~
The filtrate was;distilled free of carbon tetrachloride and the residu~ -
(785 parts) was crystallized from about 393 parts of isopropanol.~The re-
crystallization from lsopropanol yielded an add;tional 266 parts of product
having the~following assay~by ga~s~chromatographlc analysis~
2,5-dichloro-p-xylene 98.3 percent
2,3-dichloro-p-xylene 1.6 percent
2l3,5-trichloro-p-xylenè 0.1 percent
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~ Exam~
A mixture o~f 106.2 parts of p-xylene and 0.32 parts of ant;imony~sul-
fide (about 0.3 percent) was charged to a reaction vessel and heated to
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about 25C. The temperature of the reaction mixture was maintained at
about 25C with agitation while approximately 152 parts of chlorine gas was
introduced slowly over a period of about 5 hours. The reaction product was
purged with nitrogen to remove hydrogen chloride and any residual chlorine.
Analysis of the remaining crude reaction product, by gas chromatoyraphic
technique is set forth in Table I.
Treatment of the crude reaction product with isopropanol, as in Example
IB y;elds 2,5-dichloro-p-xylene having a purity of greater than 90 percent.
Example V
For purposes of comparison, a known prior art catalyst, Fe~13, was
employed as a catalyst in the chlorination of p-xylene following a procedure
similar to that of Examples I, II and IV. Thus, a mixture of 106.2 parts of
p-xylene and 0.53 parts (about 0.5 percent) of ferric chloride was charged
to a reaction vessel and heated to about 55C. The temperature of the re-
action mixture was maintained at about 55 to 60C, with agitation, while
142 parts of chlorine was introduced slowly over a period~of about 3 hours.
The reaction product was purged with nitrogen to remove hydrogen chloride
and any residu~l`chlorine. Analysis of the remaining crude product, by
gas chromatographic tmchnique is set forth in Table I.
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