ON THE NITRATION OF BENZOIC AND SALICYLIC ACIDS

A. N. Novikov

(Presented by Prof. B. V. Tronov, Doctor of Chemical Sciences)

The m-nitrobenzoic and 5-nitrosalicylic acids obtained in the nitration of benzoic and salicylic acids are used for the production of pharmaceuticals and dyes [1, 2].

According to the most widely recommended method, m-nitrobenzoic acid is prepared by nitrating benzoic acid with a mixture of an alkali-metal nitrate and concentrated sulfuric acid [3, 4, 5, 6]. The yield of m-nitrobenzoic acid is 50–55% (m.p. 141°). The disadvantages of this method include isolation and purification of the acid through the barium salt and a relatively high consumption of nitrate and sulfuric acid.

m-Nitrobenzoic acid can be obtained by nitrating the methyl ester of benzoic acid or benzotrichloride, followed by saponification [7].

One of the previously proposed methods for obtaining m-nitrobenzoic acid consists in the action of nitric acid or a mixed nitric–sulfuric acid on benzoic acid [8]. In this case, m-nitrobenzoic acid is obtained in low yield and with a low melting point. Varma and Kulkarni [9], nitrating benzoic acid with a sulfuric–nitric acid mixture obtained by passing sulfuric anhydride into nitric acid (d 1.502), obtained m-nitrobenzoic acid in 65% yield (m.p. 138°, reference value—141°).

We nitrated benzoic acid with a mixture consisting of sulfuric (d 1.84) and nitric (d 1.4) acids. As a result, m-nitrobenzoic acid was obtained, which was isolated and purified by crystallization from water.

This eliminated the need to purify it through the barium salt. For comparison, m-nitrobenzoic acid was obtained by nitrating benzoic acid with a mixture of potassium nitrate and concentrated sulfuric acid [5], with purification through the barium salt. The product had m.p. 141°. Yield 52%. In determining the melting point of a mixed sample of the two m-nitrobenzoic acids obtained by the indicated methods, no depression was observed. Consequently, the products are identical and pure.

Salicylic acid was also investigated. Since the nitrating mixture acts very vigorously on salicylic acid, we limited ourselves to the use of nitric acid alone. From the reaction products, 5-nitrosalicylic acid was isolated. Yield 35%. M.p. 235°. The yield of product with m.p. 226–228° was 60%. In reference books

[10, 11, 12] give melting points for 5-nitrosalicylic acid of 228°, 230°.

5-Nitrosalicylic acid can be prepared by treating salicylic acid with: 1) sodium nitrite and sulfuric acid [11] (m.p. 220°, yield 60%); 2) a sulfuric–nitric acid mixture [13] (yield 40%, m.p. 228°); 3) dilute nitric acid in the presence of mercury salts [14].

A. A. Goldberg [15, 16] prepared 5-nitrosalicylic acid from 2-chloro-5-nitrobenzoic acid, replacing chlorine with a hydroxy group (m.p. 234°, yield 70%), and from 2-carboxydiphenyl ether by nitration followed by saponification.

Experimental Part

Nitration of Benzoic Acid

In a 100 ml round-bottom flask, benzoic acid (6.1 g) and sulfuric acid (10 ml, d 1.84) are mixed. The mixture is heated for 10 minutes on a water bath at a temperature of 75–80°. Then, over the course of 5 minutes, with vigorous stirring, 5 ml of nitric acid (d 1.4) is added. The temperature of the mixture must not exceed 80° (cooling). When all the nitric acid has been introduced, the flask is heated with stirring on a water bath (bath temperature not above 85°) for 45 minutes. After cooling, water (50–75 ml) is added to the crude m-nitrobenzoic acid obtained; the acid is filtered off, washed with water, and recrystallized from an excess of water (200 ml). The product obtained has m.p. 139.5°. Yield 55% (4.6 g). After a second crystallization from 125 ml of water, m-nitrobenzoic acid with m.p. 141° is obtained.

Yield 50% (4.2 g). A third crystallization did not change the melting point of the acid.

Nitration of Salicylic Acid

In a 100 ml flask, salicylic acid (3.45 g) and nitric acid (5.4 ml, d 1.4) were mixed. After 10 minutes, a vigorous process was observed: the mass foamed up, and nitrogen oxides were evolved abundantly. After 3–5 minutes the process ceased. The reaction mixture was yellowish in color. The reaction product was then washed with water and crystallized twice from water. After the first crystallization, 2.8 g of substance with a melting point of 226–228° was obtained (60%); after the second, 1.55 g, m.p. 235° (yield 35%). A third crystallization did not change the melting point of the substance.

After reduction of the product obtained with ferrous sulfate in ammonia solution, a compound with m.p. 280° was isolated, which corresponds to 5-aminosalicylic acid. Consequently, 5-nitrosalicylic acid was obtained.

Conclusions

1. The procedure for preparing m-nitrobenzoic acid is simplified. It is recommended that it be obtained by nitrating benzoic acid with a sulfuric–nitric acid mixture, followed by crystallization from water.

2. The preparation of 5-nitrosalicylic acid by nitration of salicylic acid with nitric acid of specific gravity 1.4 is described.

References

1. N. N. Vorozhtsov. Fundamentals of the Synthesis of Intermediates and Dyes. Goskhimizdat, 274, 596, 296, 1950.

2. I. M. Kogan. Chemistry of Dyes (Synthetic). ONTI, Moscow, 68, 217, 753, 1938.

3. I. Guben. Methods of Organic Chemistry. Goskhimizdat, vol. IV, book 1, 265, 1949.

4. A. P. Kreshkov, I. N. Kurbatov. Laboratory Work on the Synthesis and Analysis of Organic Compounds. Goskhimizdat, Moscow, 317, 1940.

5. V. M. Rodionov, V. M. Bogoslovskii, A. M. Fedorova. Laboratory Manual on the Chemistry of Intermediates and Dyes. Goskhimizdat, 26, 1948.

6. A. Ortner, D. Reikhel. Practicum in Organic Chemistry. GONTI, 50, 1931.

7. Syntheses of Organic Preparations. IL, collection 1, 296, 1949.

8. Beilstein, 9 main vol., 376, 1926.

9. P. S. Varma, A. Kulkarni, J. Am. Chem. Soc., 47, 143, 1925.

10. Beilstein, 10 main vol., 116, 1938.

11. I. Guben. Methods of Organic Chemistry. Goskhimizdat, vol. IV, book 1, 296, 1949.

12. Dictionary of Organic Compounds. IL, 3, 245, 1949.

13. A. N. Meldrum, N. W. Hirve, Chem. Abstr., 22, 4515, 1, 2, 1928.

14. A. I. Zakharov, Zh. Kh. P., 8, 30, 1931.

15. A. A. Goldberg, J. Chem. Soc., 1368, 1952.

16. A. A. Goldberg, H. A. Walner, J. Chem. Soc., 2049, 1952.