Note: Descriptions are shown in the official language in which they were submitted.
?~
PROCESS FOR PREPARING 1-CHLORO-2,6-DINITRO-4-(TRIFLUORO-
METHYL) BENZENE FREE FROM NITROSATING AGENTS
This invention relates -to a process for preparing
1-chloro-2,6-dinitro-4-(trifluoromethyl)benzene free from
nitrosating agents, from which it is possible to prepare
technical TRIFLURALIN with a par-ticularly low nitrosoamine
conten-t (specifically NDPA).
It is well known that certain agricultural products
can contain nitrosoamines, and the danger of these sub-
stances is equally well known.
In particular, it has been public knowledge since 1976that nitrosoamines are present in formulations of agricultu-
ral products such as TRIFLURALIN
~ 2
F3C ~ N(CH2CH2CH3)2
N02
which is a very important selective herbicide, and is
prepared by the following reaction
~ 2
F3C ~ ( 3 2 2)2
N02
~N02
F C ~ O ~ N(CH2CH2cH3)2+ NaCl + H2
N02
This compound contains N-nitrosodipropylamine (NDPA),
i.e. (CH3 CH2CH2)2N-NO as impurity, this forming during the
herbicide synthesis.
This is because 1-chloro-2,6-dinitro-4-(trifluoro-
methyl) benzene (DINITRO-PCBT), which is prepared by dini-
tra-ting 1-chloro-4-(trifluoromethyl)benzene (PCBT), and
which is the starting substance for synthesising TRIFLURA-
LIN, contains dissolved nitrogen oxides of various compo-
sition, which are responsible for the formation of nitroso
-- 1 --
amines in accordance with the reaction (CH3CH2CH2)2NH ~
(N0)x ~ (CH3CH2CH2)N - N0 which takes place in a basic
environment.
As stated, the danger of nitrosoamines is well known.
They exercise an acute hepatotoxic action, and in particu-
lar are carcinogenic~ mutagenic and teratogenic. It is
therefore essential that the quantity of NDPA in the TRIFLU-
RALIN is as low as possible, and legislation in the more
advanc~ed countries considers that an NDPA content in the
technical product of less than 1 ppm is acceptable.
From research carried out up to the present time, it
has emerged that if the DINITR0-PCBT is synthesised without
special purification processes, the quantity of dissolved
nitrogen oxîdes is such as to generate an NDPA content of
15 between 150 and 500 ppm in the technical TRIFLURALIN subse-
quently produced. If purification processes are introduced
(for example those indicated in USA patent No. 4,120l905),
the nitrosating agents contained in the DINITR0-PCBT are
reduced, but the results obtained are not constant and it
is not possible to obtain technical TRIFLURALIN with an
NDPA content of less than 1 ppm.
Research has therefore been directed towards methods
which provide for eliminating the formed nitrosoamines from
the final product.
Even if they allow a final product of satisfactory
characteristics to be obtained, processes which comprise
the destruction of preformed nitrosoamines have the very
serious drawback of being dangerous because of the presence
of nitrosoamines in certain stages of the process during
which contact, including accidental contact, is always pos-
sible with the environment and with the process operators.
It has therefore appeared very desirable to discover
processes which exclude the formation of nitrosoamines in
D3~;~
order to use them in place of processes which destroy the
already formed nitrosoamines, and the research of the ap-
plicant has developed in this direction.
This research has been successful, and the present
invention relates to the original purification process for
obtaining DINITR0-PCBT practically free from nitrosating
agents, to which said research has led. As will be apparent
hereinafter, using the DINITR0-PCBT obtained by this pro-
cess it is p~ssible to prepare technical TRIFLURALIN with
an NDPA content which is always less than 1 ppm. Thus the
sta-ted object is completely attained.
The present invention therefore relates to a process
for preparing l~chloro-2,6-dinitro-4-(trifluoromethyl)-
benzene (DINITR0-PCBT) free from nitrosating agents, charac-
terised in that DINITR0-PCBT is treated with an aqueous
bisulphite solution having an S02 concentration of between
1% and 5% at a pH of between 1 and 3, at a temperature of
between 50 and 100C for a time of between 1 and 3 hours,
and in that the organic layer is separated from the aqueous
layer, and the acidity and last traces of the bisulphite
solution are eliminated from the organic layer by an aque-
ous alkaline solution.
The bisulphite used is preferably sodium bisulphite,
but analogous results can be obtained by using other bisul-
phites such as potassium bisulphite or ammonium bisulphite.Alternatively, the bisulphite can be prepared directly in
the reactor by reacting S02 with the necessary quantity of
alkali. As stated, the S02 concentration of the bisulphite
solution is between 1% and 5%. Preferably, a concentration
of 1.6% is used. Concentrations higher than 5% should be
avoided, because they decrease the yield without increasing
purity.
The pH is preferably kept at around 2, and must not
3~
exceed 3 in order not to reduce the yield (as occurs for
example if sodium sulphite is used instead of the bisul-
phite) because high pH values favour substitution of the
mobile Cl of the 1-chloro-2,6-dinitro-4-(trifluoromethyl)-
benzene. Whereas pH values which are too low favour S02elimination, and thus make the treatment ineffective. In
this respect, the initial DINITR0-PCBT must not contain
mineral acids (such as H2S04 or HN03), which can be elimina-
ted by neutralisation.
The temperature is preferably kept at 70-75C. In
this respect it is important not to fall below the melting
point of the DINITR0-PCBT whereas too high temperatures
favour yield reduction.
The reaction time is preferably 2 hours. Very long
reaction times favour yield reduction.
The choice of the alkali for eliminating the acidity
and last traces of the bisulphite-contaminated solution
contained in the treated organic DINIT~0-PCBT layer is not
very important. Na2S03 is preferably used for economical
reasons and because the pH of the aqueous solution is not
too high, so that there is no appreciable yield reduction.
Some examples of how the process according to the
invention can be carried out in practice are given herein-
after. These are obviously purely indicative, and in no way
limit the invention.
EXAMPLE 1
200 ml of ~2 and 100 g of 1-chloro-2,6-dinitro-4-(tri-
fluoromethyl)benzene (DINITR0-PCBT) are fed into a reactor.
The mass is heated to 70-75C under strong stirring in
order to obtain perfect mixing of the organic layer with
the aqueous layer, after which 13.3 g of a sodium bisul-
phite solution containing 25.5% of S02 (corresponding to an
overall concentration of 1.59% if the H20 present in the
mass is taken into account) are dripped in over about 20
minutes.
The mass is kept at 70-75C for 2 hours under conti~
nuous vigorous stirring. The stirring is stopped, and the
mass allowed to decant. The lower organic layer is separa-
ted, and is added to a solution containing 200 ml of H20
and 5 g of Na2C03 which has previously been heated to
70-75C. The mass is stirred vigorously for 30-60 minutes,
after which stirring is stopped.
The lower organic layer is separated~ to give 96 g of
purified DINITR0-PCBT.
The following results are obtained on converting sam-
ples of the initial DINITR0-PCBT and of the purified DINI-
TR0-PCBT into TRIFLURALIN and analysing the products obtai~
15 ned for nitrosoamine:
using the initial DINITR0-PCBT 156 ppm NDPA present in
the TRIFLURALIN produced
using purified DINITR0-PCBT 0.5 ppm NDPA present in
the TRIFLURALIN produced
As can be seen, the NDPA content of the TRIFLURALIN
produced using the DINITR0-PCBT prepared by the process
according to the present invention is extremely low, and
equal to one half the maximum allowable value under the
most severe present legislation.
EXAMPLE 2
The procedure of example 1 is followed, but using 26.6
g of a sodium bisulphite solution containing 25.5% of S02.
In this manner, 93 g of purified DINITR0-PCBT are
obtained.
1`he NDPA content of the TRIFLURALIN produced is 0.45
ppm in this case.
EXAMPLE 3
The procedure of example 1 is followed, but using 6.4
-- 5 --
g of potassium metabisulphite containing 53% of ~2 dissol-
ved in 10 ml of H20.
95 g of purified DINITRO-PCBT are obtained.
The NDPA content of the TRIFLURALIN produced is 0.7
ppm.
EXAMPLE ~
The procedure of example 1 is followed, but 3.3 g of
sodium sulphite dissolved in 10 ml of H20 are used.
87 g of purified DINITRO-PCBT are obtained.
In this case, the too high pH value leads to an
unacceptable yield reduction.
E_AMPLE 5
The procedure of example 1 is followed, but using 6.1
g of a sodium bisulphite solution containing 25.5% of S02.
97 g of purified DINITRO-PCBT are obtained.
The NDPA content of the TRIFLURALIN produced is 0.9
ppm.
EXAMPLE 6
The procedure of example 1 is followed, but using 8 g
of 30% NaOH for the alkalising stage.
88 g of DINITRO-PCBT are obtained.
Again, the too high pH value leads to an unacceptable
yield reduction.
