CA1180352A - Process for preparing 1-chloro-2,6-dinitro-4- (trifluoromethyl) - benzene free from nitrosating agents - Google Patents
Process for preparing 1-chloro-2,6-dinitro-4- (trifluoromethyl) - benzene free from nitrosating agentsInfo
- Publication number
- CA1180352A CA1180352A CA000401460A CA401460A CA1180352A CA 1180352 A CA1180352 A CA 1180352A CA 000401460 A CA000401460 A CA 000401460A CA 401460 A CA401460 A CA 401460A CA 1180352 A CA1180352 A CA 1180352A
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- Prior art keywords
- dinitro
- pcbt
- bisulphite
- solution
- aqueous
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
To produce technical TRIFLURALIN with a nitrosoamine content not exceeding 1 ppm, for use as a herbicide, DINITRO-PCBT free from nitrosating agents is prepared by a process in which DINITRO-PCBT is treated with an aqueous bisulphite solution having a S02 concentration of between 1% and 5% at a pH of between 1 and 3, at a temperature of between 50° and 100°C for a time of between 1 and 3 hours.
The organic layer is then separated from the aqueous layer, and the acidity and last traces of the bisulphite solution are eliminated from the organic layer by means of an aqueous alkaline solution.
To produce technical TRIFLURALIN with a nitrosoamine content not exceeding 1 ppm, for use as a herbicide, DINITRO-PCBT free from nitrosating agents is prepared by a process in which DINITRO-PCBT is treated with an aqueous bisulphite solution having a S02 concentration of between 1% and 5% at a pH of between 1 and 3, at a temperature of between 50° and 100°C for a time of between 1 and 3 hours.
The organic layer is then separated from the aqueous layer, and the acidity and last traces of the bisulphite solution are eliminated from the organic layer by means of an aqueous alkaline solution.
Description
?~
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 which is a very important selective herbicide, and is prepared by the following reaction ~ 2 F3C ~ ( 3 2 2)2 ~N02 F C ~ O ~ N(CH2CH2cH3)2+ NaCl + H2 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 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.
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.
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.
The procedure of example 1 is followed, but using 6.4 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.
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.
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 which is a very important selective herbicide, and is prepared by the following reaction ~ 2 F3C ~ ( 3 2 2)2 ~N02 F C ~ O ~ N(CH2CH2cH3)2+ NaCl + H2 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 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.
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.
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.
The procedure of example 1 is followed, but using 6.4 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.
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.
Claims (14)
1. A process for preparing l-chloro-2,6-dinitro-4-(trifluoromethyl) benzene (DINITRO-PCBT) free from nitrosating agents, characterised in that DINITRO-PCBT is treated with an aqueous bisulphite solution having an SO2 concentration of between 1% and 5% at a pH of between 1 and 3, at a temperature of between 50°C and lOO°C 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 aqueous alkaline solution.
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 aqueous alkaline solution.
2. A process as defined in claim 1, wherein sodium bisulphite is used for the DINITRO-PCBT treatment solution.
3. A process as defined in claim 1, wherein potassium or ammonium bisulphite are used for the DINITRO-PCBT treat-ment solution.
4. A process as defined in claim 1, wherein the bisulphite for treating the DINITRO-PCBT is prepared directly in the reactor by reacting SO2 with alkali.
5. A process as defined in anyone of claims 1 to 3, wherein the aqueous bisulphite solution has an SO2 concentration of 1.6%.
6. A process as defined in claim 4, wherein the aqueous bisulphite solution has an SO2 concentration of 1.6%.
7. A process as defined in anyone of claims 1 to 3, wherein the pH is kept at around 2.
8. A process as defined in claim 6, wherein the pH
is kept at around 2.
is kept at around 2.
9. A process as defined in anyone of claims 1 to 3, wherein the temperature is kept between 70°C and 75°C.
10. A process as defined in claim 8, wherein the temperature is kept between 70°C and 75°C.
11. A process as defined in anyone of claims 1 to 3, wherein the reaction time is kept equal to about 2 hours.
12. A process as defined in claim 10, wherein the reaction time is kept equal to about 2 hours.
13. A process as defined in anyone claims 1 to 3, wherein sodium carbonate is used to form the alkaline solution for neutralising the organic layer.
14. A process as defined in claim 12, wherein sodium carbonate is used to form the alkaline solution for neutral-ising the organic layer.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000401460A CA1180352A (en) | 1982-04-22 | 1982-04-22 | Process for preparing 1-chloro-2,6-dinitro-4- (trifluoromethyl) - benzene free from nitrosating agents |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000401460A CA1180352A (en) | 1982-04-22 | 1982-04-22 | Process for preparing 1-chloro-2,6-dinitro-4- (trifluoromethyl) - benzene free from nitrosating agents |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1180352A true CA1180352A (en) | 1985-01-02 |
Family
ID=4122630
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000401460A Expired CA1180352A (en) | 1982-04-22 | 1982-04-22 | Process for preparing 1-chloro-2,6-dinitro-4- (trifluoromethyl) - benzene free from nitrosating agents |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1180352A (en) |
-
1982
- 1982-04-22 CA CA000401460A patent/CA1180352A/en not_active Expired
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