ReviewStudies on energetic compounds: Part XI: Preparation and thermolysis of polynitro organic compounds
Introduction
The chemistry of polynitro compounds have been described in a good number of publications 1, 2, 3. Kamlet [4], Kamlet and Adolph [5] and Bliss et al. [6] have investigated the relationship between structure of organic compounds with impact sensitivity. The early thermal decomposition reactions are very important from the view point of understanding the mechanism of explosion. Thus, the thermolysis of polynitro compounds have been undertaken using TG/DTA/DTG/DSC techniques in the last decade and most of the work is scattered and, hence, it was thought to review these studies. Further, the data on density, oxygen balance (OB), velocity of detonation (VOD) and impact sensitivity (h50% cm applying 2 kg weight) are also available in literature for some cases and this has also been included in the manuscript. The preparation and mechanistic aspects of thermolysis of polynitro compounds have been described critically in the present review.
Section snippets
Aliphatic nitro compounds
Aliphatic nitro compounds with nearly zero or even positive OB having high melting points are desirable explosives and useful oxidizers for solid propellants. New processes have been discovered to prepare polynitro aliphatic derivatives, in which an additional electronegative moiety has been incorporated into the molecule at the methyl group. This class of compounds have the general formula: RC(NO2)2X, where X=NO2 (trinitromethyl), F (fluorodinitromethyl, Ref. [7]), CN (cyanodinitromethyl) and N
Aromatic nitro compounds
Aromatic nitro compounds are obtained mostly either by the nitration of corresponding aromatic compound or by the oxidation of corresponding amines. Presence of even one nitro group is sufficient to increase the thermal decomposition of aromatic compounds. Nevertheless, aromatic compounds which have two or more nitro groups, exhibit distinctly marked explosive properties. Zeman et al. [15] and Zeman [16] have correlated the thermal decomposition kinetics of polynitro aromatic explosives at
Homocyclic nitro compounds
There is a considerable current interest in the synthesis 43, 44, 45, 46, 47 and thermolysis of polynitrohomocyclic (“cage”) compounds [48]. These are relatively highly strained molecules, that contain several –NO2 substituents, and emerging as high-density energetic materials [49]. Recently, Eaton et al. [50] have developed a systematic methodology for the syntheses of 1,3,5-trinitrocubane and 1,3,5,7-tetranitrocubane as superior high energy shock insensitive explosives. The thermal behaviour
Heterocyclic nitro compounds
Heterocyclic nitro compounds may be aliphatic or aromatic in character, depending upon the electronic constitution. These compounds represent explosives of higher performance compared with analogous aromatic systems, regarding their elemental composition, OB, density, standard heat of formation and VOD. Reactions of a polyatomic substituents with an ortho –NO2 group in an aromatic ring are now widely used to synthesise many heterobicyclic molecules 55, 56, 57. In general, the reactions between
Metal salts of nitro compounds
Metal salts of nitro compounds have long been of interest as energetic additives and/or as burning rate modifiers in composite solid rocket propellants and in explosive compositions. Recently, Rao et al. [139] have prepared Cu(II), Ag(I), Pb(II) salts of 2,4,N-trinitroanilinoacetic acid (2,4,N-TNAAA) and 2,4,6-trinitroanilino acetic acid (2,4,6-TNAAA). The order of thermal stability of salts of 2,4,N-TNAAA is reported to be Ag>Pb>Cu, while for salts of 2,4,6-TNAAA, it is Cu>Ag>Pb.
Metal salts of
Concluding remarks
The thermolysis of energetic compounds is a very complex process. The thermal decomposition of several polynitro organic compounds involve simple bond scission prior to explosion. A notable feature of these reactions is the fact that the aromatic ring remains intact. The next stage of thermolysis involves propagation reaction which involve exothermic oxidation/reduction reactions leading to the formation of low molecular weight and thermodynamically stable gaseous products. It has also been
Acknowledgements
Thanks are due to the Head of Chemistry Department, D.D.U. Gorakhpur University, Gorakhpur for library facilities. The financial assistance by ISRO and DST is also acknowledged.
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