CH620418A5 - Process for the preparation of m-nitrobenzoic acid - Google Patents

Description

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PATENT CLAIMS

1. A process for the preparation of m-nitrobenzoic acid by nitrating benzoic acid, characterized in that the nitriding is carried out by means of a mixture of concentrated nitric acid, concentrated sulfuric acid, sulfur trioxide and reaction medium, the amount of sulfur trioxide being more than 20% by weight and less than 90 % By weight, based on the total amount of sulfuric acid and sulfur trioxide, the reaction temperature is kept below 20 ° C. and the process is carried out in such a way that the sulfonating and decomposing action of the sulfur trioxide is substantially avoided.

2. The method according to claim 1, characterized in that the reaction temperature is kept below 0 ° C.

3. The method according to claim 1, characterized in that the amount of sulfur trioxide is more than 40%.

4. The method according to claim 3, characterized in that the amount of sulfur trioxide is more than 60%.

5. The method according to claim 1, characterized in that the total amount of sulfuric acid and sulfur trioxide is at least 300% by weight, based on the amount of benzoic acid.

6. The method according to claim 1, characterized in that the reaction is carried out with vigorous stirring of the reaction mixture.

7. The method according to claim 1, characterized in that the amount of nitric acid is at least 10% by weight more than the theoretical amount.

8. The method according to claim 1, characterized in that benzoic acid is added to a mixture of nitric acid, sulfuric acid and sulfur trioxide.

9. The method according to claim 1, characterized in that nitric acid and benzoic acid are added to a mixture of sulfuric acid and sulfur trioxide alternately or in parallel with one another, continuously or discontinuously, for at least 30 minutes, preferably for at least 1 hour.

It is known to produce m-nitrobenzoic acid by nitrating benzoic acid using a mixture of nitric acid and sulfuric acid at temperatures above room temperature. This forms a product (crude product) that contains a large amount, sometimes up to 20 percent, of o-nitro-benzoic acid and a smaller amount, at least about 2 percent, of p-nitrobenzoic acid. With such a high content of o-isomers as the above, not only the content of m-isomers in the crude product is low, but also the yield of m-isomers in a later cleaning, e.g. B. by recrystallization in water, is far from the one that corresponds to the content in the crude product, since part of the m-nitrobenzoic acid remains in the recrystallization mother liquor. Since the more solvent the recrystallization has to be used, the higher the o-isomer content, the greater the loss of the m-isomer is. The loss of the m-isomer during recrystallization is thus essentially proportional to the o-isomer content in the crude product. The yield of recrystallized m-nitrobenzoic acid therefore becomes rather low. According to a Japanese study, which is referenced in Chemical Abstracts 49, 2363 g (1955), a yield of 24.5 g of recrystallized m-nitrobenzoic acid from 30.5 g of benzoic acid is obtained, which is only 59% of the theoretically possible. Although part of the dissolved m-isomer can be obtained from the recrystallization mother liquor as an isomer mixture together with the o- and p-isomers, this mixture has no particular value as such and the division into isomers is expensive. It can be added that although p-nitrobenzoic acid forms in a relatively small amount when nitrating benzoic acid, it is difficult to remove during recrystallization, since a not a small part of it follows with m-nitrobenzoic acid when the latter crystallizes out. It has been shown that if the p-isomer content in the crude product clearly exceeds 1 percent, it is difficult to obtain an m-nitrobenzoic acid by a single recrystallization which is sufficiently free of the p-isomer for certain purposes.

It is clear from the above that it is highly desirable that the m-isomer content be as high as possible and the o-and p-isomer contents as low as possible when nitrating benzoic acid.

Swedish patent application 1441/67 (Example 1) describes a process for nitrating benzoic acid, according to which the reaction is carried out in liquid sulfur dioxide as a medium and with a mixture of nitric acid and sulfur trioxide as the nitrating reagent. This gave a product with an isomer distribution of 93% m-, 6% o- and approx. 1% p-nitrobenzoic acid. However, the use of sulfur dioxide as a reaction medium poses difficult problems both from the point of view of industrial hygiene and that of environmental protection. This applies in particular to the water mother liquor containing sulfur dioxide. The use and recovery of sulfur dioxide also means an economic burden. In addition, the transport and storage of sulfur dioxide pressure vessels with very strict safety regulations. One such chemical which is difficult to handle is the sulfur trioxide used in the process mentioned above, which is very difficult to store and transport in the pure state and which is also relatively difficult to obtain as a commodity.

It has now been shown in accordance with the present process according to the invention that an isomer distribution which is particularly favorable for the preparation of m-nitrobenzoic acid is obtained in the nitration of benzoic acid, the process according to the invention being characterized in that the nitriding is carried out using a mixture of concentrated Nitric acid, concentrated sulfuric acid, sulfur trioxide and reaction medium is carried out, the amount of sulfur trioxide being more than 20% by weight and less than 90% by weight, based on the total amount of sulfuric acid and sulfur trioxide, the reaction temperature being kept below 20 ° C. and that The method is carried out in such a way that the sulfonating and decomposing action of the sulfur trioxide is substantially avoided.

The temperature during nitriding is expediently z. B. kept below 10 ° C, and particularly good results are obtained at reaction temperatures below 0 ° C. The amount of sulfur trioxide in the oleum mixture should be greater than 20% by weight, suitably greater than 40 and preferably greater than 60% by weight. The total amount of sulfuric acid, calculated as H2S04, and sulfur trioxide should generally be at least 200 and expediently at least 300% by weight, based on the amount of benzoic acid. The amount of nitric acid can usually be equal to or slightly greater than the theoretical amount. However, in certain cases one can advantageously use a larger excess of nitric acid, e.g. B. at least 10% excess beyond the theoretical amount, work. When carrying out the process according to the invention, it can often be expedient to add a mixture of sulfuric acid and sulfur trioxide, nitric acid and benzoic acid alternately or in parallel with one another, continuously or batchwise, for at least 30 minutes, preferably for at least 1 hour.

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When carrying out the process according to the invention, the sulfonating and also the generally decomposing effect of sulfur trioxide on organic substances should be taken into account. In weak oleum - this is a common name for sulfuric acid and sulfur trioxide - these dangers are low. They are particularly large in such strong oleum, such as. B. the usual commercially available, which is 65% (65% S03 + 35% H2S04). The unfavorable effect of sulfur trioxide can, however, be almost completely prevented by one or some of the following measures:

1. Addition of benzoic acid to a mixture of nitric acid and oleum.

2. Stir effectively during the reaction, which is desirable and sometimes necessary for a good result to be obtained.

3. Carrying out the reaction at low temperature, especially when using strong oleum. However, in oleum with a composition corresponding to 1 mole of S03 + 1 mole of H2S04 and of similar composition, as well as in weaker oleum, nitriding could be carried out at room temperature and slightly higher temperature. Low nitriding temperature is also advantageous because the o- and p-isomer contents are lower than at higher temperatures.

In certain cases, part of the o-isomers can be decomposed during nitration, which can be seen from the fact that the reaction mixture is colored dark. If the nitration is carried out in accordance with the above, however, this has little or no effect on the quality of the recrystallized m-nitrobenzoic acid or on the yield thereof.

To reduce the time and cooling requirements for the nitriding process itself can in advance and z. B. with water cooling, a mixture of nitric acid and a certain proportion of the required amount of oleum. When carrying out the nitriding process, the sentence nitric acid can then be brought about by taking from this so-called nitrating acid, which together with further oleum forms the nitrating and reacting agent for the process.

Nitriding is carried out using essentially only a mixture of nitric acid and oleum, but smaller amounts of substances which are essentially inert during nitriding may also be present in the reaction mixture.

The water mother liquor containing sulfuric acid, which is produced when the m-nitrobenzoic acid (the crude product) is obtained from the nitration mixture, does not have to be an environmental problem, since the sulfuric acid can easily be recovered as concentrated sulfuric acid by distilling off water from the mother liquor.

example 1

50 ml of concentrated sulfuric acid (96%), 38 ml of 99% nitric acid and 125 ml of 65% oleum were mixed in the order mentioned with cooling. The nitric acid is mixed here with 340 g of 45% oleum. To the mixture, 100 g of benzoic acid was added in small amounts with stirring over the course of 2 hours while the temperature was kept at 25-30 ° C. A short time later, 300 ml of water was added and the mixture was cooled. The crystallized product was filtered out, washed and dried. It weighed 137 g and contained 2.9% H2S04 and 2.2% H20. The isomer distribution was 91% m-, 8% o- and <1% p-nitrobenzoic acid. After recrystallization in water, an m-nitrobenzoic acid of very high quality was obtained and a yield of 83% of the theoretical, based on the benzoic acid.

Example 2

To a mixture of 38 ml of 99% nitric acid and 150 ml of 65% oleum, 100 g of benzoic acid was added in small amounts over 2 hours while the temperature was kept at 10-15 ° C by cooling and effective stirring. After heating to a temperature slightly above room temperature, 300 ml of water was added and the mixture was cooled. The crystallized product was filtered out, washed with water and dried. It weighed 135 g and contained 2.5% H2SO4 and 1.2% H2O. The isomer distribution was 95% m-, 4% o- and less than 1% p-nitrobenzoic acid. After recrystallization in water, a very high quality m-nitrobenzoic acid was obtained with a yield of 88 percent of the theoretical, calculated on the benzoic acid.

Example 3

100 ml of 96% sulfuric acid, 40 ml of 99% nitric acid and 150 ml of 65% oleum were mixed with cooling. The nitric acid is mixed here with 480 g of 34% oleum. 100 g of benzoic acid were added to the mixture in small portions with stirring over a period of about 1 hour while the temperature was kept between 2 and 10 ° C. After about V2 hours the mixture was warmed to a temperature above room temperature, whereupon 350 ml of water were added and the mixture was cooled. The crystallized product was filtered out, washed and dried. It weighed 140 g and contained 4.2% H2S04 and 1.9% H20. The isomer distribution was 92.5% m-, 6.5% o- and less than 1% p-nitrobenzoic acid.

Example 4

To a mixture of 40 ml of 99% nitric acid and 150 ml of 65% oleum, 100 g of benzoic acid were added in small amounts with vigorous stirring over a period of 2 hours while the temperature was kept between 0 and -5 ° C. After some time, the mixture was warmed to about 30 ° C., after which 300 ml of water were added and the mixture was cooled. The crystallized product weighed 133 g and contained 1.1% H2SO4 and 0.5% H2O. The isomer distribution was 96% m-, 3.5% o- and approx. 0.5% p-nitrobenzoic acid. After recrystallization in water, an m-nitrobenzoic acid of very high quality was obtained with a yield of 90 percent of the theoretical, based on the benzoic acid.

Example 5

80 ml of 95% sulfuric acid, 38 ml of 99% nitric acid and 200 ml of 65% oleum were mixed in the order mentioned with cooling. The nitric acid is mixed here with 545 g 45% oleum. The mixture was added with stirring 100 g of benzoic acid in small amounts over 2 hours while the temperature was kept between 0 and -5 ° C. After 1/2 to 1 hour the mixture was warmed to room temperature. 350 ml of water were then added and the mixture was cooled. The crystallized product was filtered out, washed and dried. It weighed 133 g and contained 2.4% H2SO4 and 1.3% H2O. The isomer distribution was 97% m-, 2.5% o- and 0.5% p-nitrobenzoic acid. After recrystallization in water, an m-nitrobenzoic acid of very high quality was obtained with a yield of 90% of the theoretical, based on the benzoic acid.

Example 6

To a mixture of 40 ml of 99% nitric acid and 200 ml of 65% oleum were added 100 g of benzoic acid in small quantities with stirring over 2 hours,

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while the temperature was kept between 0 and -5 ° C. After a while, the temperature was raised to slightly above room temperature. 350 ml of water were then added and the mixture was cooled. The crystallized product was filtered out, washed and dried. It weighed 133 g and contained 1.8% H2S04 and 0.5% H20. The isomer distribution was 97.5% m-, 2% o- and 0.5% p-nitrobenzoic acid. After recrystallization in water, an m-nitrobenzoic acid of very high quality was obtained with a yield of 90% of the theoretical, based on the benzoic acid.

Example 7

To a mixture of 45 ml of 99% nitric acid and 250 ml of 65% oleum, 10 g of benzoic acid was added in small amounts with stirring over a period of about 15 minutes while the temperature was kept between -5 and -10 ° C. 5 ml of 99% nitric acid and then a further 90 g of benzoic acid were added in portions over the course of about 2 hours at the same temperature as for the first 10 g of benzoic acid. After about V2 hours, the mixture was warmed to room temperature, whereupon 400 ml of water were added and the mixture was cooled. The crystallized product was filtered out, washed and dried. It weighed 129 g and contained 0.5% H2S04 and 0.25% H20. The isomer distribution was 98.5% m-, less than 1% o- and less than 0.5% p-nitrobenzoic acid. After recrystallization in (a small amount) 5 water, an m-nitrobenzoic acid of very high quality was obtained with a yield of almost 92% of the theoretical, based on the benzoic acid.

Example 8

To a mixture of 40 ml of 99% nitric acid and 280 ml of 65% oleum, 100 g of benzoic acid was added in small quantities with stirring over a period of about 2 hours while the temperature was kept between 0 and -5 ° C. After half an hour the mixture was warmed to room temperature 15, 400 ml of water were added and the mixture was cooled. The crystallized product was filtered out, washed and dried. It weighed 125 g and contained 2.0% H2S04 and 0.7% H20. The isomer distribution was more than 99% m-, less than 0.5% o- and less than 0.5% p-nitro-20 benzoic acid. This m-nitrobenzoic acid can be recrystallized for certain purposes, e.g. B. Reduction to m-aminobenzoic acid can be applied.

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