Trinitrotoluene mechanism, thermal decomposition

In the coordinate system shown in Fig. 5, the set of polynitro arenes studied falls into several classes. Classes A and C contain compounds characterised by the trinitrotoluene mechanism of primary fission in their thermal decomposition. Class B represents unsubstituted polynitro arenes (TNB, HNB and NONA) with primary homolysis of C-NO2 bond in their thermal decomposition. Correlation of HNS data with this Class may be a coincidence but it may also be a result of intermolecular interaction in its crystals. Class D contains dipicryl derivatives in which the intermolecular interaction should dominate the influence on their reactivity (primary fission by heat in NONA is different from that in DIPS). The said influence occurs occasionally in larger molecules with strong intermolecular interactions and was observed in some cases of decomposition initiated by impact [36,75], electric spark [35,36] and (depending on the measurement method applied) also heat [102]. 

Scheme 2. Presumed mechanism of electron shifts at the beginning of low-temperature thermal decomposition of 3,3 -dimethyl-2,2, 4,4, 6,6 -hexanitrodiphenylsulfide with participation of nitro group at 2-position in the reaction center (typical trinitrotoluene mechanism - left formula) and with participation of nitro group at 6-position in the reaction center (right formula - real pathway of the fission).

Current processes for the manufacture of trinitrotoluene (TNT) produce atmospheric and water pollution that is only partly relieved by mechanical clean-up methods. TNT is currently produced from toluene by successive mono-, di-, and trinitrations with mixed aqueous nitric and sulfuric acids in the first two steps and anhydrous mixed acid in the last. Each stage in the current process is conducted at elevated temperatures, and side reactions in the overall process directly produce thousands of pounds of oxides of nitrogen, sulfuric acid aerosols, and volatile nitro organic products (such as tetranitromethane and nitroaro-matics). These pollutants derive from the thermal decomposition of the aqueous nitric acid solutions, from oxidative side reactions that produce as many as 40 by-product compounds, and from formation of unsymmetrlcal "meta" Isomers. Since symmetrical TNT is inevitably accompanied by meta isomers as well as oxidation products, the crude material is treated with sodium sulfite solutions to remove the undesirable Isomers and nitroaromatics by derivatization. The spent sulfite solution, known as "red water, is then disposed of by combustion to an inorganic ash. Itself a disposal problem. 

Scheme 2 Trinitrotoluene mechanism of thermal decomposition of polynitro arenes with a hydrogen atom in the y-position towards the nitro group - here X can be CH, CH2, O, N, or S in the case of TNT, the last fragment forms 4,6-dinitro-2,l-benzoisoxazole and other decomposition products [11] in the case of amino derivatives (X = NH2) derivatives of 4,6-dinitrobenzofurazans and furoxans result...

Schemes a Theoretical, less probable mechanism of electron shifts at the beginning of the low-temperature thermal decomposition of 2,4,6-trinitro-3-[(3-methyl-2,4,6-trinitrophenyl)thio] toluene (DMDIPS) with participation of the nitro group at the 2-position in the reaction centre (typical trinitrotoluene mechanism ) [6,148). b Presumed...

E. Neal, Jr et al, Effects of Thermal Cycling on Trinitrotoluene (TNT) and Tritonal Explosive Compositions , AFATL-TR-79-15, Rept WQEC/C 79-111 (1979) (limited dis-trib) 109) Di7. McMillen et al, Kinetics and Mechanisms of the Gas-Phase Decomposition of Nitroaromatics , ACS mtg, Honolulu (April 1979) 110) S. Bulusu, JOrgMassSpec... 

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