2.4.6- trinitrobenzoic acid, decarboxylation

Trinitrobenzene is present in crude TNT manufactured by mixed acid nitration and results from methyl group oxidation followed by decarboxylation." In fact, a convenient method for the synthesis of 1,3,5-trinitrobenzene involves oxidation of 2,4,6-trinitrotoluene with a solution of sodium dichromate in sulfuric acid, followed by decarboxylation of the resulting 2,4,6-trinitrobenzoic acid in boiling water." 1,3,5-Trinitrobenzene is prepared from 2,4,6-trinitro-m-xylene by a similar route." 2,4,6-Trinitroanisole can be prepared from the... 

TNB has also been produced from TNT by removing a methyl group (Sax and Lewis 1987). Trinitrobenzoic acid, the result of oxidation of TNT, has also been decarboxylated to yield 1,3,5-TNB (Merck 1989). 

Preparation from a- trinitrotoluene. In 1893 a patent was granted to the Chemische Fabrik Griesheim [47a] for the manufacture of sym-trinitrobenzene from trinitrotoluene. The method was based on the fact observed by Tiemann [48] Mid by Claus and Becker [49], that trinitrotoluene can be oxidized with nitric acid to trinitrobenzoic acid, the latter being readily decarboxylated to form sym-trinitrobenzene ... 

Like other aromatic nitro compounds, trinitrotoluene is resistant to the action of acids. Only concentrated nitric acid at a temperature over 110°C can oxidize it to 2,4,6-trinitrobenzoic acid, and at 200°C trinitrobenzene is formed, as a result of decarboxylation (p. 254). 

During the trinitration the methyl group is oxidized to the carboxyl group. The trinitrobenzoic acids behave in different ways in the course of hot washing of crude TNT. Thus 2,4,6-trinitrobenzoic acid is readily decarboxylated and... 

Hydroxynitro acids (I), (II) and (III) are (according to Schmidt) washed from the crude TNT and are present in the wash-waters. Trinitrobenzoic acids remain in TNT as impurities. The trinitrobenzoic acids formed are readily decarboxylated. C02 is evolved and only trinitrobenzenes remain in TNT as its impurities. 

Trinitrobenzene is formed by of decarboxylation of trinitrobenzoic acid. It can also be prepared from trinitrochlorobenzene by reduction with copper in alcohol. Further nitration of dinitrobenzene also yields trinitrobenzene, but the reaction must be carried out under very severe conditions (high S03-concentration in the mixed acid, high nitration temperature), and the yields are low. 

Benzoic acid and most mono-substituted benzoic acids are stable with respect to decarboxylation in aqueous solution, even at a temperature of 100 °C. However, decarboxylation may occur with a measurable rate if either strong electron-withdrawing or strong electron-releasing substituents are present in the aromatic acid. The decarboxylation rate of 2,4,6-trinitrobenzoic acid is increased by addition of base to the aqueous solution, and it attains a maximum value when the substrate is completely transformed to the anion [236]. A carbon-13 isotope effect of ft, 2/ft, 3 = 1.036 (50 °C) has been observed [237]. There is no D20 solvent isotope effect [238]. These findings indicate that the mechanism of decarboxylation of 2,4,6-trinitrobenzoic acid is a unimolecular electrophilic substitution (SE1), viz. 

Other decarboxylations are noteworthy. Thermal decomposition of 2,4,6-trinitrobenzoic acid furnishes 1,3,5-trinitrobenzene in 46% yield. In an adaptation of a procedure for the decarboxylation of halogenated furoic acids with boiling quinoline and powdered copper, 2- and 3-nitro-benzofuran are prepared from nitro acids and 5-nitrothionaphthene is formed from the corresponding 2-carboxylic acid. ... 

TNT that resides in aerobic environments at the surface of the soil is often degraded by photocatalyzed oxidation of the methyl carbon. This oxidation is probably a multistep process by which the methyl group is initially oxidized to an alcohol, then to an aldehyde, and finally to a carboxylic acid. Decarboxylation of the resultant product yields trinitrobenzene. Evidence for this pathway was supplied by Spanggord et al. [29], who reported formation of trinitrobenzaldehyde and trinitrobenzoic acid during the degradation of TNT to trinitrobenzene. It has been reported that oxidation of the methyl group of TNT is mediated by surface catalysis on soil minerals [30], by ozonation [31], and by the action of sunlight [29], At sites where the TNT contamination is localized to the soil surface, the concentration of trinitrobenzene may often exceed that of TNT [32],... 

While no new synthetic methods for this group have appeared improvements in the synthesis of phloroglucinol and that of some of its derivatives have attracted attention. The classic route by way of trinitrotoluene, trinitrobenzoic acid, triaminobenzoic acid and its hydrolysis and decarboxylation has been challenged by methods based on the use of acyclic precursors. 

Johnston and Moelwyn-Hughes (80) find dEaldT values of —20, —20, and —45 cal deg for the decarboxylation of trichloroacetic, tribromoacetic, and trinitrobenzoic acids, and give a detailed analysis in terms of molecular vibrations. 

Trinitrobenzaldehyde, an oxidation product of TNT, and TNB (formed by further oxidation to 2,4,6-trinitrobenzoic acid followed by decarboxylation) were also found. 3,5-Dinitroaniline, the reduction product of TNB was also identified. 2,4-Dinitrotoluene and 2,6-DNT were found in relatively large amounts. Their presence was attributed to disposal of propellants in the studied locations, rather than to the disposal of TNT. 

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