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ABSTRACT
Hexamethylene tetramine (HMTA) is used as the starting material for the synthesis of well known explosives RDX and HMX. The present study postulates series of reactions to rationalize the formation of these explosives from HMTA, based on density functional theory calculations at the level of B3LYP/6-31G(d,p).
Keywords: Hexamine, hexaminedinitrate, RDX, HMX, DFT calculations.
1. INTRODUCTION
Cyclotrimethylene trinitramine or 1,3,5-trinitrohexahydro-sym-triazine (RDX) and cyclotetramethylene tetranitramine or 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX, Her Majesties' explosive) [1] are important explosives which have been in use for long. RDX is mainly obtained in the industry by direct nitrolysis process (Woolwich) in which hexamethylene tetramine is directly treated with a large excess of strong HNO3 at a temperature of 20-25 °C [1-4]. On the other hand, in the Bachman (Combination Process) process, which is also an industrial process for RDX, the reaction mixture contains HNO3, NH4NO3, acetic anhydride and acetic acid in addition to hexamine [1,2,4]. The product, RDX, of the Bachman process is higher in yield compared to the previous one, produces RDX (B) which contains 10 % HMX.
HMX/octogen is a superior explosive than RDX/cyclonite because of its higher chemical stability, higher density, higher velocity of detonation and higher ignition temperature, however its cost and sensitivity are higher than RDX [1,2].
Hexamine (hexamethylene tetramine, HMTA) is a heterocyclic organic compound having highly symmetrical cage-like structure. It is prepared from ammonia and formaldehyde [5]. Although it is feebly basic, protonates in strongly acidic media, to form salts. The reaction of hexamine with nitric acid has prime importance because of energetic properties of nitramine type products such as RDX and HMX.
Hexamethylene dinitrate (HDN) can be used as a precursor for manufacturing of RDX and its industrial method of preparation is described in the literature [6]. HDN shows weak explosive character, heating or ignition causes violet deflagration. Its hygroscopic nature prevents its usage in explosive formulations.
Besides the experimental studies on RDX, there are some computational studies on its reaction mechanism [7], conformations and bond dissociation energies [8, 9] and gas-phase structure [10]. RDX formation mechanism has been studied either experimentally [11] or computationally [12].
The present study considers series of reactions to rationalize the formation of RDX and HMX from HMTA, based on density functional theory calculations.
2. METHOD
The...