JPH0129784B2 - - Google Patents

Description

[Detailed description of the invention]

"Nitrated aromatic compounds" hereinafter refer to aromatic compounds obtained by nitration of the corresponding aromatic starting compounds with concentrated nitric acid or nitric acid (concentrated nitric acid/sulfuric acid) and by common after-treatments. It is a nitro compound. Aromatic nitro compounds reacted further in a reaction step after nitration are not understood here as "nitrated aromatic compounds". Nitrated aromatic compounds are objective and intermediate products in various fields, in particular in the field of explosives, medicine and plant protection. Nitrated aromatic compounds, which are important as intermediates in the field of plant protection, are, for example, 4-chloro-
3,5-dinitrobenzotrifluoride,
This produces the herbicide trifluralin (=4-di-n-propylamino-3,5-dinitrobenzotrifluoride), especially in reaction with di-n-propylamine. This synthesis can be explained by the following reaction equation: However, modern analytical methods have found small amounts of nitrosamines in the trifluralin produced in this way; these nitrosamines are highly undesirable as they can act as carcinogens, at least in animals (e.g. Showa 54-41826
(see publication). The production of this nitrosamine is
The nitrosative substances from the nitration reaction, which may be present in small amounts in the precursor of trifluralin, i.e., 4-chloro-3,5-dinitrobenzotrifluoride, were used in the last reaction step. It is recognized that this is the result of nitrosation of di-n-propylamine. Therefore, various methods have already been developed to remove nitrosamines from trifluralin as completely as possible again. For example, German patent application publication no.
According to the method of publication No. 2831119, this is 20 to 38
% hydrochloric acid or in the liquid phase with gaseous hydrogen chloride at 140 °C
This is done by processing at temperatures up to Similarly, treatment with bromine, chlorine, N-bromosuccinimide, N-chlorosuccinimide, bromochloride, pyridine perbromide and/or pyridinium bromide-perbromide to reduce nitrosamine concentrations has been reported in German Patent Application No.
2835530 and phosphorus or sulfur halides and -oxyhalides or
Treatment with TiCl ₄ was published in German Patent Application No. 2837529
It is stated in the specification of the No. Although these methods initially reduce the nitrosamine value satisfactorily, this value is said to rise again in the case of relatively long reaction times. If the reaction time is not precisely optimized, cases may therefore inevitably arise in which the possible low nitrosamine values are not achieved with these methods. Furthermore, these methods include additional reaction steps that require work-up and optionally recovery of used reagents. Attempts have also been made to avoid the formation of nitrosamines by removing as much as possible the nitrosative substances contained therein as by-products from the nitrated precursor of trifluralin, namely 4-chloro-3,5-dinitrobenzotrifluoride. (Refer to Japanese Patent Application Laid-Open No. 54-55527). This means that the precursor described above is (a) treated with an aqueous solution of an inorganic base at a temperature of from 50°C to 100°C, optionally separated from the product thus treated, and (b) exposed to an inert gas, e.g. air. and (c) optionally repeating steps (a) and/or (b) any number of times in any order. By this treatment, the content of single or multiple nitrosatable substances in 4-chloro-3,5-dinitrobenzotrifluoride can be reduced to nitrosamine directly from trifluralin by trifluralin obtained in the subsequent reaction with di-n-propylamine. The content of nitrosamines is clearly reduced to the extent that the nitrosamine content is almost as low as that obtained by known methods except for nitrosamines. 4
- If chloro-3,5-dinitrobenzotrifluoride is treated with water alone, i.e. without an inorganic base, at elevated temperature and passing an inert gas, the nitrosamine content of trifluralin is not or hardly reduced. (See table of test results on page 16 of DE 2840551). German Patent Application Publication No. 2840551
The method of removing nitrosatable substances from the precursor of trifluralin according to the specification of the above specification hardly causes a re-increase in the nitrosamine content of trifluralin. Although it appears to be more preferable than the method of publication No. 41826, it is again a disadvantage here, in particular that several steps are required in each case. The problem was therefore to avoid the drawbacks of the known processes and to develop a simple method which would allow the production of nitrosamine-free trifluralin by avoiding the formation of this nitrosamine and which could be used not only in this particular case but quite generally. However, it was necessary to develop an economical method. This problem has been solved by the present invention with 4-chloro-3,5-
The problem was simply and satisfactorily solved by treating dinitrobenzotrifluoride with water at ambient or elevated temperature and removing the used water at least partially in the form of steam. This method can be used not only for this special case but also for other nitrated aromatic compounds to remove the nitrosative substances still contained therein from the nitration. It was very surprising that in the treatment of nitrated aromatic compounds with water, the nitrosatable substances could be removed by removing the water used at least partially in the form of steam, since German patent application No. 2840551
In view of the results summarized in the table on page 16 of the specification, it appears that the nitrosative substances still present in the nitrated aromatic compound from nitration can be replaced by the addition of other substances (e.g. basic substances). This is because it could hardly be expected that it could be removed by treatment with water. Therefore, the present invention provides a method for removing a nitrosatable substance from a nitrated aromatic compound, which comprises: (a) introducing water vapor into the nitrated aromatic compound; or (b) introducing water into the nitrated aromatic compound. and subjecting the mixture to vacuum distillation, in both cases removing an amount of water in the form of steam of at least 10%, based on the weight of the nitrated aromatic compound. Nitrated aromatic compounds suitable for the process of the invention are in principle all possible nitrated aromatic compounds as defined above, such as nitrobenzene, nitronaphthalene and their derivatives. However, particularly preferred is the general formula [In the formula, the groups R are independently hydrogen, (C ₁
~ _C4 )-alkyl, _CF3 , _{SO2NH2 , SO2CH3} , and Hal represents F, Cl, Br, I especially Cl, Br _] . Specific compounds of this type are, for example:

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The method according to the invention is particularly suitable for treating 4-chloro-3,5-dinitrobenzotrifluoride, a precursor of trifluralin. In one particularly preferred embodiment according to the invention, the treatment with water, which simultaneously or subsequently removes at least a portion of the water in the form of steam, is carried out at a temperature of approximately 80° C. to 120° C.
In particular, it is carried out at temperatures of approximately 95 to 100°C. The amount of water used can generally be arbitrary, but is generally between 10 and 50, calculated from the nitrated aromatic starting compound.
Particular preference is given to % by weight, in particular approximately 20 to 40 % by weight. The treatment with water according to the invention is carried out in this embodiment by passing steam through the nitrated aromatic starting compound (as in steam distillation, for example) or by passing the nitrated aromatic starting compound together with water. After heating the water to a temperature in the above range, at least a portion of the water - preferably under a weak vacuum to approximately 95°C
Particularly preferred is removal by distillation at a temperature of from 100°C to 100°C. The nitrated aromatic compound should preferably be present in liquid or molten form in this case. Preferably, the duration of this water treatment, which removes at least a portion of the water in steam, is approximately from 10 to 60 minutes. Depending on the amount to be treated and the individual treatment conditions (temperature and rate at which water vapor is passed or temperature and rate at which water is removed by distillation, etc.), the treatment time may be short or long;
There are generally no special benefits. In another particularly preferred embodiment, which is carried out under relatively mild conditions, the treatment with water is carried out in the form of crystallization from an aqueous solution or emulsion under reduced pressure and also at temperatures down to room temperature. . The aqueous crystal suspension obtained by crystallization under reduced pressure from an aqueous solution or emulsion is then preferably further freed of at least a portion of the water, also under reduced pressure. In contrast to the first described embodiments and reactions according to the invention (which are carried out virtually exclusively with liquid or molten nitrated aromatic compounds), the latter embodiments are preferred in the crystallization region of the respective nitrated aromatic compounds, i.e. It takes place in the region where there is a transition from the liquid state to the solid state and in which the compound is already solid. In this latter embodiment, it is important to reduce the pressure during crystallization from the aqueous solution or emulsion so that the water can be distilled off. Therefore, the pressure must be less than or equal to the vapor pressure of water at each temperature. If a relatively large amount of water is still present, the vacuum applied is preferably not too lower than the water vapor pressure at the respective temperature to avoid undesirable boiling delays and the like. The same holds true for the vacuum applied and for the removal of water from the corresponding aqueous crystal suspension. Considering the standards listed here, the pressure is approximately 10 m
Can be lowered to bar. It is only necessary that sufficient water evaporation rate and unhindered evaporation be guaranteed. This embodiment of the process of the invention is not suitable for nitrated aromatic compounds which exhibit a higher vapor pressure than water at the respective temperature. The temperature in the latter embodiment is the same as in the first described embodiment, approximately room temperature (approximately 20
℃), thus roughly ranging from 20℃ to 120℃. This temperature, of course, depends in each case on the melting point of the respective nitrated compound and is close to and below this melting point. Therefore, in this case,
The temperatures for processing one and the same nitrated aromatic compound are lower than in the first described embodiment, in which the nitrated compound is virtually always present only in liquid state. Temperatures below approximately 20° C. are generally amenable to water treatment according to the invention, but without any benefit. By the treatment with water according to the invention, in which the water is removed at least partially in the form of steam, the nitrosatable substances present as by-products from the nitration in the nitrated aromatic starting compound are likely to be cleaved and decomposed. and/or removed along with water vapor. When the nitrated aromatic compounds treated in this way are further reacted, for example with amines, virtually no nitrosamines can be detected in the reaction product. The process according to the invention has the advantage, inter alia, of the fact that it can be carried out very simply and without the use of additional chemicals and without additional steps for removing nitrosamines from the corresponding reaction products and for nitrating aromatic products. This method differs from known methods for removing nitrosative substances from family compounds. Since the nitration is in any case generally followed by a neutral wash for purification of the nitrated aromatic compound, the removal of nitrosatable substances according to the invention can be carried out in virtually the same step. The second described embodiment of the method can be carried out under much milder conditions than the first described embodiment due to the lower temperatures at which it can be carried out. The invention therefore represents a significant advance. Hereinafter, the present invention will be explained in more detail by giving examples. The concentration of nitrosamines was determined, for example, by the method described in German Patent Application No. 2831119. Example 1 (a) Preparation of trifluralin by conventional methods: 2 moles of p-chlorobenzotrifluoride are mononitrated in a known manner and then
Dinitration was carried out at 125°C. After diluting the final acid to approximately 70% by weight sulfuric acid, the liquid nitro product is
It was separated at 80°C and washed repeatedly with water and a small amount of sodium hydroxide solution until neutral.
432 g of 4-chloro-3,5 melting at 54.8°C
-Dinitrobenzotrifluoride was obtained. A conventional reaction with di-n-propylamine gives trifluralin (yield almost quantitative, mp 46.2
The reaction product was found to contain 29 ppm nitros-di-n-propylamine. (b) Removal of the precursor 4-chloro-3,5-dinitrobenzotrifluoride with a nitrosating substance according to a first preferred embodiment of the invention: 500 g of 4-chloro-3,5-dinitrobenzo Steam was introduced into the trifluoride (prepared according to Example 1a) at approximately 100° C. for 10 minutes. Approximately 220 g of condensate was obtained, which is approximately equal to the water used.
It was equivalent to 30%. This was converted into trifluralin using a normal reaction. The product is nitrosodi-n
-The content of propylamine was 1 ppm. (c) Removal of the nitrosating agent from the same precursor according to another preferred embodiment of the invention: 500 g of 4-chloro-3,5-dinitrobenzotrifluoride (prepared as described in Example 1a) is Emulsify in 500 ml of water at 70°C with stirring, partially evaporate the water under reduced pressure and bring to 50°C.
and crystallization occurred at this temperature. After further cooling to about 40℃, the total amount is about 100ml.
The mixture was heated to 40-50°C under reduced pressure until 50% of water was distilled out. After melting and separation of the water (eg by decantation), the product is reacted as usual with di-n-propylamine. The nitroso-di-n-propylamine content of the trifluralin obtained was 1 ppm. Example 2 500 g of 4-chloro-3,5-dinitrobenzotrifluoride (prepared according to Example 1a) and 200 g
of water was heated to 98 to 100°C. A slight vacuum was then applied to distill off all the water. Then,
It was converted into trifluralin by a conventional reaction. Nitrosodi-n-propylamine content is
It was 2ppm.

Claims (1)

[Claims] 1. A method for removing a nitrosative substance from a nitrated aromatic compound, which includes: (a) introducing water vapor into the nitrated aromatic compound; or (b) introducing water vapor into the nitrated aromatic compound. and subjecting the mixture to distillation under reduced pressure, in which case an amount of water of at least 10%, based on the weight of the nitrated aromatic compound, is removed in the form of steam. 2 General formula () as a nitrated aromatic compound [In the formula, the groups R are independently hydrogen, (C ₁
~ _C4 )-alkyl, _CF3 , _{SO2NH2 , SO2CH3 ,} and Hal represents F, Cl, Br, I, in particular Cl, Br] Range 1
The method described in section. 3 4-chloro- as a nitrated aromatic compound
3. A method according to claim 1 or 2, wherein 3,5-dinitrobenzotrifluoride is used. 4 From about 80℃ to 120℃, especially about 95 to 100℃
The method according to any one of claims 1 to 3, which is carried out at a temperature of . 5. Process according to any one of claims 1 to 4, characterized in that about 10 to 50% by weight, in particular about 20 to 40% by weight, of water, calculated from the nitrated aromatic compound, is used. 6. The method according to any one of claims 1 to 5, which is carried out by introducing water vapor into the nitrated aromatic compound. 7 Heating the nitrated aromatic compound with water,
6. A process according to claim 1, wherein the water is distilled off at a temperature of about 95 DEG C. to 100 DEG C., optionally under slight vacuum. 8. The method according to any one of claims 1 to 7, which is carried out for about 10 to 60 minutes. 9. The method according to any one of claims 1 to 3, which is carried out by crystallization from an aqueous solution or emulsion under reduced pressure. 10. Process according to claim 9, further comprising removing at least a portion of the water from the crystal suspension obtained by crystallization under reduced pressure from an aqueous solution, also under reduced pressure.