2 4 6-Trinitrobenzoic Acid Synthesis Essay

1Department of Chemistry and Engineering Chemistry, Malek Ashtar University of Technology, P.O. Box 16765-3454, Tehran, Iran
2Department of Chemistry, Ayatollah Amoli Branch, Islamic Azad University, P.O. Box 678, Amol, Iran

Copyright © 2013 Mohammad Ali Zarei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The oxidation of 2,4,6-trinitrotoluene (TNT) to 1,3,5-trinitrobenzene (TNB) in one step, 2,4,6-trinitrobenzoic acid (TNBA), and 2,4,6-trinitrobenzaldehyde (TNBAl) with an ozone-oxygen mixture in different solvents, catalysts, and temperatures has been investigated. Reducing the number of steps in the oxidation of TNT to TNB is the major advantage of this procedure with respect to conventional processes such as chromic acid and potassium permanganate. The oxidation of TNT to TNB was completed in one step as compared to two steps in the conventional approach. The products were obtained with relatively good yield.

1. Introduction

1,3,5-Trinitrobenzene (TNB) is an explosive compound with slightly greater explosive force than 2,4,6-trinitrotoluene (TNT) [1]. TNB is used primarily as a high explosive for commercial mining and military use. Also, it has been employed as an agent to vulcanize natural rubber [2] and as a mediating agent to mediate the synthesis of other explosive compounds [3].

So far, the different methods for preparation of TNB were reported [4–8]. The most common method is the oxidation of TNT to TNB using oxidants such as chromic acid, potassium permanganate in acid, basic, and neutral solutions, nitric acid, and silver oxide in which these methods are not attractive because they produce the large amounts of toxic and difficultly utilizable wastes. On the other hand, direct nitration of benzene requires such harsh conditions whose yields are poor, and purification of TNB is very difficult. Even the use of modern catalysts such as lanthanide nitrates does not alleviate this problem [9].

In this paper, we investigated the one-step oxidation of TNT with an ozone-oxygen mixture in presence of the different conditions such as catalyst, temperature, and oxidative agents (Table 1). In addition, this method can be used to develop a low-waste process for TNB production. Also, this reaction is carried out with 2,4-dinitrotoluene (DNT) to prove the generality of this procedure (Table 2). The obtained results approximately were similar to each other. Synthesis route of the reactions is shown in Figure 1.

Table 1: The conditions and results of the oxidation of TNT.

Table 2: The conditions and results of the oxidation of DNT.

Figure 1: Synthesis route of DNT and TNT oxidation. Only the major product is shown.

2. Experimental

Materials were purchased from Merck and Fluka companies. 1HNMR spectra were recorded with a Bruker DRX-300 Avance instrument using CDCl3 as the deuterated solvent containing tetramethylsilane as internal standard, at 300, δ in parts per million, and J in hertz. The experiments were carried out with a Compact Ozone Generator (OZONEUF, model: COG 10 S). Elemental analyses (C, H, and N) were obtained with a Heraeus CHN–O– Rapid analyzer.

2.1. Typical Procedure without Hydrogen Peroxide

TNT or DNT was oxidized in a round-bottom flask (100 mL) with a fine-pore barrier for dispersion of the gas mixture. The reactor was charged with TNT or DNT (4 mmol), catalyst (1 mmol), KBr (0.1 g), and 40 mL of glacial acetic acid or formic acid. Then it was stirred and heated to the required temperature, and an ozone-oxygen mixture was fed for 6 h. Afterwards, the mixture of reaction is mixed with 500 g of crushed ice. Then the produced precipitation was purified by column chromatography (SiO2; n-hexane/AcOEt = 5/1) to afford the pure adducts.

2.2. Typical Procedure with Hydrogen Peroxide

TNT or DNT was oxidized in a round-bottom flask (100 mL) with a fine-pore barrier for dispersion of the gas mixture. The reactor was charged with TNT or DNT (4 mmol), catalyst (1 mmol), KBr (0.1 g), 40 mL of glacial acetic or formic acid, and 10 mL (H2O2 %30). Then it was stirred and heated to the required temperature, and an ozone-oxygen mixture was fed. After 2 h ozonolysis, 10 mL H2O2 again was added to the mixture of reaction. Afterwards, the mixture of reaction is mixed with 500 g of crushed ice. Then the produced precipitation was purified by column chromatography (SiO2; n-hexane/AcOEt = 5/1) to afford the pure adducts.

3. Data

2,4,6-Trinitrobenzaldehyde. Yield: 68%, yellow powder, mp 119°C [lit. [10] mp 119°C]. IR (KBr) (): 3092 (CH), 2859 (CH aldehyde), 1696 (C=O), 1587 (C=C), 1529 and 1349 (NO2). Anal. Calcd. for C7H3N3O7 (241.00): C, 34.87; H, 1.25; N, 17.43; Found: C, 34.6; H, 1.2; N, 17.5. 1H NMR (300 MHz, CDCl3): 8.85 (s, 2H), 10.33 (s, 1H).

2,4,6-Trinitrobenzoic   Acid. Yield: 36%, yellow powder, mp 229°C. IR (KBr) (): 3110 (OH), 3086 (CH), 1712 (C=O), 1609 (C=C), 1549 and 1369 (NO2). Anal. Calcd. for C7H3N3O7 (256.99): C, 32.70; H, 1.18; N, 16.34; Found: C, 32.8; H, 1.1; N, 16.6. 1H NMR (300 MHz, CDCl3): 9.13 (s, 2H), 11.1 (s, 1H).

1,3,5-Trinitrobenzene. Yield: 74%, yellow sludgy powder, mp 123°C [lit. [4, 11, 12] mp 121-122°C]. IR (KBr) (): 3107 (CH), 1623 (C=C), 1544 and 1345 (NO2). Anal. Calcd. for C6H3N3O6 (213.00): C, 33.82; H, 1.42; N, 19.72; Found: C, 33.6; H, 1.5; N, 19.9. 1H NMR (300 MHz, CD3COCD3): 9.33 (s, 3H).

2,4-Dinitrobenzaldehyde. Yield: 73%, yellow crystal, mp 73°C [lit. [10, 13] mp 69–72°C]. IR (KBr) (): 3111 (CH), 2877 (CH aldehyde), 1701 (C=O), 1601 (C=C), 1537 and 1360 (NO2). Anal. Calcd. for C7H4N2O5 (196.12): C, 42.87; H, 2.06; N, 14.28; Found: C, 42.6; H, 2.02; N 14.15. 1H NMR (300 MHz, CDCl3): 8.34 (s, 1H), 8.14 (d,1H), 8.03 (d,1H), 10.32 (s, 1H).

2,4-Dinitrobenzoic   Acid. Yield: 57%, yellow crystals, mp 181°C [lit. [14] mp 182-183°C]. IR (KBr) (): 3122 (OH), 3084 (CH), 1724 (C=O), 1620 (C=C), 1544 and 1356 (NO2). Anal. Calcd. for C7H4N2O6 (212.12): C, 39.64; H, 1.90; N, 13.21; Found: C, 39.5; H, 1.8; N, 13.4. 1H NMR (300 MHz, CDCl3): 8.65 (d, 1H), 8.48 (dd), 8.06 (d, 1H), 10.8 (s, 1H).

1,3-Dinitrobenzene. Yield: 86%, yellow powder, mp 91°C [lit. [12] mp 89-90°C]. IR (KBr) (): 3110 (CH), 1615 (C=C), 1538 and 1364 (NO2). Anal. Calcd. for C6H4N2O4 (168.11): C, 42.87; H, 2.40; N, 16.66; Found: C, 42.7; H, 2.3; N, 16.4. 1H NMR (300 MHz, CDCl3): 8.79 (t, 1H), 8.62 (dd, 2H), 7.96 (t,1H).

4. Results and Discussion

According to Table 1, the reaction of ozone with TNT in different conditions leads to the diverse products such as TNBAl, TNBA, and TNB. As it is observed, the temperature plays an important role in the ozonolysis reaction. At 40°C, the reaction of ozone with TNT in presence of Co(OAc)2 was slow, and the conversion reached 10% after 6 hours (entry 1). At 100°C, TNBAl yield based on the reacted substrate reaches 60% (entry 2). Also, it is characterized that if the time and temperature of ozonolysis increase (12 h, 100°C), the reaction yield reaches 0%. This shows that the reaction with cleavage of aromatic ring forwarded which could be degraded gradually into final products such as aliphatic organic acids, water, and carbon dioxide [15, 16]. The addition of hydrogen peroxide to pervious reactions causes acceleration of the oxidation and the increase of yield at 100°C (TNBAl 68% and TNBA 23%). When the reaction is carried out in formic acid and hydrogen peroxide, the obtained results were remarkable. At 100°C, TNB as the major product (%74) obtained which it is the favorable method for synthesis this compound. Also, according to Table 1, the obtained results with Co(NO3)2 almost were similar to Co(OAc)2 (entries 9–16). On the other hand, the oxidation of DNT is carried out to prove the generality of this method. According to Table 2, it could be found that the results approximately are the same to TNT oxidation which confirms this efficient procedure for other substituted toluenes.

Only, the mechanism which we have suggested to correlate all the results of this work involves the presence of the free radicals of hydroxyl and perhydroxyl as intermediates in these homogeneous reactions. A plausible mechanism for the formation of products is shown in Figure 2. Under the experimental conditions, ozone oxidizes mainly Co2+ to reactive Co3+ species (1) which rapidly and selectively oxidize the methyl group of aryl (2). In the presence of H2O2, after the ozone undergoes a catalytic decomposition by Co+2, the mixture of Co+3 and ozone is added to hydrogen peroxide in which the reaction between Co+3 and hydrogen peroxide induces a decomposition of ozone by reactions (4) and (5). The produced free radicals, hydroxyl and perhydroxyl ones, will start a chain decomposition by reactions (4) and (5). The presence of these radicals previously has been reported [17, 18]. Then, the produced benzyl radical (2, 6) is attacked by O2 to produce peroxide and aldehyde. Also, the subsequent reaction with ozone or hydrogen peroxide results in TNBA or TNB.

Figure 2: Plausible mechanism for the formation of products.

Introduction of potassium bromide into the reaction mixture substantially accelerates the oxidation with an ozone-oxygen mixture [19]. The suggested mechanism is that potassium bromide reacts with cobalt (II) to form in which this complex is more reactive than Co3+ and oxidizes TNT by the reaction shown in Figure 3.

Figure 3

5. Conclusion

The yields of TNB and DNB in this procedure were obtained as 74% and 86%, respectively. Also, this method can be used to produce TNB and DNB for applied future.

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