Polynitro arenes

Tab.40 Polynitro-arene durch Oxidation von Polynitro-anilinen mit Peroxodischwefel-...

Polynitro-anilm Schwefel- saure [%] Polynitro-aren Aus- beute [%] Schmp. [ C]... 

There is, unfortunately, no obvious correlation between the impact sensitivity of a compound, its thermal behavior, and its structure. Thus, most polynitro arenes can explode on mechanical shock or rapid heating [96], but the shock sensitivity and thermal stability varies widely. TNT, for instance, is rather insensitive toward mechanical shocks or heating, and even pentanitrotoluene and hexanitrobenzene have been prepared, and their melting points (240 °C and 260 °C, respectively) could be determined [97]. The potassium salt of the radical anion of nitrobenzene, on the other hand, is highly shock sensitive, and detonates on simple agitation [92], Similarly, whereas nitromethane can be handled safely the dry sodium salt of deprotonated nitromethane is potentially explosive [98]. 

There are three groups of substrates for which SNH reactions are especially characteristic (i) neutral azines and azoles (ii) azinium and azolium salts and (iii) nitro-arenes. Their electron-deficiency and, thus, their ability to react with nucleophiles strongly differ from each other. Azinium salts are the more electrophilic and are able to add even neutral nucleophiles very easily. Triazines,. v-tetrazines and polynitro-arenes also possess high electrophilicity. At the same time substrates such as pyridine (82JHC1285, 72JA682) and cinnoline (03CHE87), at a low temperature (e.g. in liquid ammonia as a solvent), do not react even with sodium amide. It should also be... 

The same shape of relationship as shown in Fig. 3 is valid for polynitro arenes in Fig. 5 here the impact sensitivity detected by sound correlates with C NMR chemical shifts of the bearers of the most reactive nitro groups in the molecule. According to this diagram, nitro groups in 2-positions of the... 

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]. 

An application of such approach to studies of detonation mechanism of the arenes studied is hindered by a serious problem the unavailability of NMR spectra of most of them. An analogous application of the easily available C NMR chemical shifts of the bearers of the most reactive nitro groups in their molecules is limited. In the case of unsubstituted polynitro arenes this application does not provide any useful relationships (the primary fission should consist in the homolysis of C-NO2 bond). However, for derivatives of the said compounds it is possible to find reliable relationships if the nitro group in the reaction centre of molecule stands in perfect mesomeric interaction with the 7t-electron system of nucleus at the moment of formation of the transition state (see Scheme 2). This means that this group participates in the primary fission by one of its oxygen atoms (the trinitrotoluene mechanism of thermal... 

Fig. 7. Relationship between squares of detonation velocity, and C NMR chemical shifts, 6c, of the carbons atom of aromatic system carrying the most reactive nitro groups (the numbers in brackets denote the positions in molecule) in polynitro arenes containing amino, hydroxy, and alkyl substituents or sulphur bridge atom.

Due to the unavailability of N NMR spectra of the majority of polynitro arenes studied, an analogous specification was made using the x NMR chemical shifts, of the bearers of the most reactive nitro groups in their molecules. In contrast to the initiation of detonation, in this case it was possible to find relationships between the Ees values and Sc chemical shifts even for the polynitro arenes whose decomposition should start by homolysis of the C-NO2 bond. From Fig. 9 follows that these relationships are not too close for the given type of compounds nor too clear-cut fi om the point of view of mechanism of primary fragmentation (e.g. the presumed 7-membered transition state in decomposition of 1,5-DNN). Never eless, in the case of BTX they signalise the... 

The chemical micro-mechanisms of primary fission processes in molecules of polynitro compounds during initiation by mechanical stimuli (inclusive of the detonation course) and electric spark should be the same as in the case of their low-temperature thermal decomposition. In the case of initiation of nitramines by impact and shock, an excellent agreement in this respect was also found with the results of molecular-dynamic simulation by Kohno et al. [27]. The more complex molecular structure of polynitro arenes makes the problem of their primary fission somewhat complicated, too. If a molecule of these compounds contains several types of substituents, it can contain several potential reaction centres (e.g. the TMPM and PYX molecules). The initiation proper can then be realised by the molecule simultaneously participating by... 

The values of detonation velocity, D, of the polynitro arenes studied were calculated using the known relationships of Kamlet Jacobs [72] for the maximum theoretical densities of crystals (i. e. for monocrystal). When the heat of formation of the substance was not available, the D values were obtained by using the relationship of Rothstein Petersen [73]. For compounds with sulphur heteroatom in molecule the D values were taken from Ref. [40]. The D values used are summarised in Table 1. 

Survey of the studied polynitro arenes and their derivatives, their code designations, C NMR chemical shifts and some sensitivity data. 

Zeman, S. Krupka, M. New aspects of impact reactivity of polynitro compounds, part II. Impact sensitivity as the first reaction of polynitro arenes. PrvpeUants, Explosives, Pyrotechnics 2003, 28, 249-255. 

Zeman S, Friedl Z, Huczala R (2002) Study of the impact reactivity of polynitro compounds part III. Relationship between electronic charges at nitrogen atoms of primarily split off nitro groups and impact sensitivity of some polynitro arenes. In Vagenknecht J (ed) New Trends in Research of Energetic Materials, Proceedings of the Seminar, 5th, Pardubice, Czech Republic, Apr. 24-25, 2002. University of Pardubice, Pardubice, p 426... 

Comparison of Splitting of Polynitro Arenes by Heat and by Shock. 256... 

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...

Also polarographic half-wave potentials, 1/2, of 24 polynitro arenes were apphed these potentials were determined in aqueous medium buffered at pH 7, the final concentration of their solutions being 0.5 x 10 M [159]. 

Figure 1 shows that in the case of HMX the effect of the liquid phase on its thermolysis should be absent even if the thermolysis is reahzed within a temperature range above 553 K (see discussion in [10]). An analogous dependence for polynitro arenes is presented in Fig. 2 [151]. 

On the basis of relationship between electron charges, q, at the nitrogen atoms of the first-reacting nitro groups and DTA onsets, Tp, of exothermic decomposition of polynitro arenes in Fig. 5, a set of these substances are di-... 

Fig.2 Graphical representation of the relationship between activation energies, E, of low-temperature thermal decomposition and NMR chemical shifts of polynitro arenes (the numbers in parenthesis denote the position in the molecule) a general scheme of the primary step of chemical decomposition is presented with each line [150]...

Fig. 4 Relationship between the slopes of the Kissinger relation Eq. 7, EaR, and MuUiken B3LYP/6-31G charges, q, at the nitrogen atoms of the primarily reacting nitro groups in molecules of high-thermostable polynitro arenes (decomposition of TNB and HNB in the liquid state given in parenthesis are the f positions in the molecule). Taken from [ 160]...

Fig. 5 Relationship between the values of the nitrogen atoms of the primarily reacting groups and onsets, Td, of exothermic decomposition. Codes of the genuine polynitro arenes are written in boldface type. Taken from [161]...

Likewise, for nitramines a relationship exists between values and NMR chemical shifts, 5c, of the most reactive nitro group bearers (i.e. carbon atoms in the reaction centres of the molecule) in polynitro arenes [148]. 

As shown in Figs. 8a and 8b the relationship has once, again, the same form as that for nitramines. The more complex molecular structure of polynitro arenes (particularly the mesomeric and steric effects) and the two presumed basic mechanisms of primary spUtting, as compared with nitramines, result in a more varied assortment of shapes of this relation-... 

The relationships between impact sensitivity in the sense of the first reaction of polynitro arenes and their heats of fusion on the one hand (Fig. 9), and the NMR chemical shifts at the reaction centres of their molecules (Figs. 8a,b) on the other hand, are of the same types as those found for nitramines. 

Fig. 9 Semilogarithmic relationships between the impact sensitivity (drop energy of the first reaction, Bdr) and heat of fusion (AHm tr) of polynitro arenes [148]...

The dependences given for polynitro arenes in Fig. 13 are analogous to those given for nitramines in Fig. 10. They are discussed in [147] we should... 

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