DK152039B - Process for preparing 1-chloro-2,6-dinitro-4- (trifluoromethyl)benzene which does not contain nitrozating agents - Google Patents

Description

DK 152039 B

The invention relates to a process for the preparation of 1-chloro-2,6-dinitro-4- (trifluoromethyl) benzene (DINITRO-PCBT) which does not contain nitrosating agents.

It is possible from the DINITRO-PCBT produced hereby to make technical "TRIFLURALIN" with a particularly low nitrosamine content (especially NDPA).

It is well known that certain products for use in agriculture may contain nitrosamines and the dangerousness of these substances is also well known.

10 It has been known, in particular, since 1976 that nitros amines are present in products for agricultural use, such as "TRIFLURALIN" 15 f3c-0- ^ n (ch2ch2ch3) 2

NO

2 which is ten. very important selective herbicide, which is produced by the following reaction: 20 / P ^ N ° 2 F3C \ Q / -C1 + (CH3CH2CtV2NH + NaOH -

NO

2 25 -►-N (CH 2 CH 2 CH 3) 2+ NaCl + H2 O

NO

2

This compound contains an impurity in the form of N-nitroso-dipropylamine (NDPA), ie. (CH 3 CH 2 CH 2) 2N-NO, forming this compound during herbicide synthesis.

This is because 1-chloro-2,6-dinitro-4- (trifluoromethyl) benzene (DINITRO-PCBT), which is produced by the dinitration of 1-chloro-4- (trifluoromethyl) benzene (PCBT), which is the starting material for the synthesis of "TRIFLURALIN", dissolved nitric oxides of different composition responsible for the formation of 35 nitrosamines according to the reaction contain: (ch3ch2ch2) 2nh + (no) x - * (ch3ch2ch2) n-no which reaction proceeds in a basic environment.

As mentioned, the danger of nitrosamines is well known. They exert an acute hepatotoxic effect and are especially carcinogenic, mutagenic and DK 152039 B j in z teratogenic. It is therefore important that the amount of NDPA in "TRI-FLURALiN" is as low as possible, and legislation in more developed countries considers an NDPA content of the technical product of less than 1 ppm as acceptable.

5 The research conducted so far shows that if: DINITRO-PCBT is synthesized without special purification processes, there is such an amount of dissolved nitrogen oxides that an NDPA content of between 150 and 500 ppm is developed in the technical TRIFLURALIN subsequently produced . If purification processes are introduced (e.g., the processes disclosed in U.S. Patent No. 4,120,905), the content of nitrosating agents in DINITRO-PCBT is reduced, but the results obtained are not constant and it is not possible to obtain technical TRIFLURALIN with an NDPA-j content pi below 1 ppm.

Therefore, attempts have been made to find methods by which the nitrosamines formed can be eliminated from the final product.

Although an end product with satisfactory properties is obtained, processes involving destruction of formed nitrosamines have the very serious disadvantage of being dangerous due to the presence of nitrosamines at certain stages of the process. where there will always be the possibility of contact, including in the event of an accident, ”with the surroundings and operating personnel.

Therefore, it has been desirable to find methods which preclude the formation of nitrosamines in order to use these processes in place of methods by which already formed nitrosamines are destroyed and the applicant's research is

gone in this direction. IN

The object of the invention is to provide a process for the preparation of 1-chloro-2,6-dinitro-4- (trifluoromethyl) benzene (DINITRO-30 PCBT) containing no nitrosating agents.

This object is achieved with the process according to the invention, which is characterized in that DINITRO-PCBT is treated with an aqueous bisulfite solution having a final SOg concentration of between 1 and 5% by weight at a pH between 1 35 and 3 and at temperature between 50 and 100 ° C for from 1 to 3 hours, separating the organic phase from the aqueous phase and removing the acidity and last traces of the bisulfite solution from the organic phase with an aqueous alkaline solution.

As will be seen from the following, using j I '3

DK 152039 B

the DINITRO-PCBT obtained by the process according to the invention can be made technically "TRIFLURALIN" with an NDPA content which is always less than 1 ppm.

The bisulfite used is preferably sodium bisulfite, but similar results can be obtained using other bisulfites such as potassium bisulfite or ammonium bisulfite. Alternatively, bisulfite can be prepared directly in the tank by reacting SOg with the required amount of alkali. As stated, the SO2 concentration is between 1 and 5% by weight. Preferably, a concentration of 1.6% is used.

10 Concentrations above 5% by weight are avoided because the yield is thereby reduced without increasing the purity.

The pH value is preferably kept in the vicinity of 2 and must not exceed 3 so as not to decrease the yield (which occurs, for example, if sodium sulfite is used instead of bisulfite), because higher pH values favor substitution of the mobile Cl 1-chloro-2,6-dinitro-4- (trifluoromethyl) benzene. Too low pHs favor SOg elimination and thus render the treatment ineffective. In this regard, the original DINITRO-PCBT must not contain mineral acids (such as H2SO4 or HNOg); these can be eliminated by neutralization.

The temperature is preferably maintained at 70-75 ° C. In this connection, it is important that the temperature does not fall below the melting point of DINITRO-PCBT, while the yield falls at too high temperatures.

The reaction time is preferably 2 hours. Very long reaction times result in poor yields.

The choice of the alkali solution used to neutralize and remove the last traces of bisulfite solution in the treated organic DINITRO-PCBT phase is not important. The NagCO2 is preferably used for economic reasons and because the pH of the aqueous phase is not too high, so that no significant reduction of the yield occurs.

Following are some examples of embodiments of the method of the invention.

EXAMPLE 1 200 ml of HgO and 100 g of 1-chloro-2,6-dinitro-4- (trifluoromethyl) benzene (DINITRO-PCBT) were transferred to a container. The mixture was heated to 70-75 ° C with vigorous stirring to obtain a complete mixture of the organic phase with the aqueous phase, after which 13.3 g of a sodium bisulfite solution containing 25.5% SO 2 (corresponding to 4

DK 152039 B

a total final concentration of 1.59% by weight, taking into account the water in the mixture) was added over a period of approx. 20 minutes.

The mixture was kept at 70-75 ° C for 2 hours under continuous, stirring vigorously. Stirring was stopped and the mixture was allowed to decant. The lower organic phase was separated and added to a solution containing 200 ml of H 2 O and 5 g of Na 2 CO 3, which had previously been heated to 70-75 ° C. The mass was stirred vigorously for 30-60 j minutes, after which the stirring was stopped. The lower organic phase was separated to give j 96g of purified DINITRO-PCBT. j

The subsequent results were obtained by converting samples of! the original DINITRO-PCBT and the purified DINITRO-PCBT for j "TRIFLURALIN" and analyze the obtained products for nitrosamine :! i 15 i

Using the 156 ppm NDPA present in the original DINITRO PCBT: produced "TRIFLURALIN" 20 Using 0.5 ppm NDPA present in the purified DINITRO PCBT: produced "TRIFLURALIN"

As can be seen, the NDPA content of TRIFLURALIN is produced using the DINITRO-PCBT produced by the process of the invention 25 extremely low and equal to half the maximum permitted value under the most stringent current legislation.

EXAMPLE 2

The procedure of Example 1 was repeated, but using 26.6 g of a sodium bisulfite solution containing 25.5% of SO 2.

This yielded 93 g of purified DINITRO-PCBT.

The NDPA content of the "TRIFLURALIN" produced is 0.45 ppm in this case.

EXAMPLE 3

The procedure of Example 1 was repeated, but using 6.4 g of potassium metabisulphite containing 53% SO2 dissolved in 10 ml of H 2 O, corresponding to a final concentration of SO9 of 1.59% by weight.

DK 152039 B

5

95 g of purified DINITRO-PCBT were obtained.

The content of the "TRIFLURALIN" produced is 0.7 ppm.

Example 4 (Comparative Example 5) The procedure of Example 1 was repeated, but 3.3 g of sodium sulfite dissolved in 10 ml of HgO was used, corresponding to a final SOg concentration of 0.67% by weight.

87 g of purified DINITRO-PCBT were obtained.

In this case, the too high pH value led to an unacceptable reduction in yield.

EXAMPLE 5 (Comparative Example)

The procedure of Example 1 was repeated, but 8 g of 30% NaOH Ϊ alkali treatment step was used.

88 g of DINITRO-PCBT were obtained.

Again, the excessive pH led to an unacceptable reduction in yield.

20 25 30 35

Claims (9)

A process for the preparation of 1-chloro-2,6-dinitro-4- (trifluoromethyl) benzene (DINITRO-PCBT), which does not contain 5 nitrosating agents, characterized in that DINITRO-PCBT an aqueous bisulfite solution having a final SO 2 concentration of between 1 and 5% by weight at a pH of between 1 and 3 and at a temperature between 50 and 100 C for from 1 to 3 hours separating the organic phase from the aqueous phase, and that the acidity 10 and the last traces of the bisulfite solution are removed from the organic phase with an aqueous alkaline solution. Process according to claim 1, characterized in that sodium bisulfite is used to treat the DINITRO-PCBT. j Process according to claim 1, characterized in that potassium or ammonium bisulfite is used for the treatment of the DINITRO-PCBT. in Process according to claim 1, characterized in that the bisulfite for treating the DINITRO-PCBT is prepared directly in the reactor by reacting SO 2 with alkali. in Process according to claims 1-4, characterized in that the aqueous bisulfite solution has a final SOg concentration of 1.6% by weight. Process according to claims 1-5, characterized in that the pH is maintained at about 2. · Process according to claims 1-6, characterized in that the temperature is maintained between 70 and 75 ° C. Process according to claims 1-7, characterized in that the reaction time is approx. 2 hours. Process according to claims 1-8, characterized in that sodium carbonate is used to produce the alkaline solution which is used to neutralize the organic phase. 35