Organic Chemistry of Explosives

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SelectiveO-nitration 361

in methylene chloride is an interesting application of this chemistry.^68 NHTPB with∼10 %

of double bonds converted to dinitrate ester groups is an attractive energetic polymer with

potential use as a binder in propellant/explosive formulations. The synthesis of NHTPB via

this route has undergone scale-up and further evaluation.

N

N

N

N

N N

N

N

N

N

NN

NO 2

O 2 NOCH 2 CH 2 CH 2 CH 2 ONO 2

O 2 N

O 2 N

N

CH 2 CH 2 CH 2 CH 3

47

NO 2

N

CHCl 3 , 0 °C, 69 % CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 ONO 2

CHCl 3 , 96 %

N 2 O 5 (3 eq),

N 2 O 5 (1 eq)

45 46

(Tris-X)

48

(Bu-NENA)

CH 2 CH 2 ONO 2

Figure 9.21

The reaction of aziridines^69 ,^70 and azetidine^70 ,^71 heterocycles with dinitrogen pentoxide in

chlorinated solvents yields 1,2-nitramine nitrates and 1,3-nitramine nitrates respectively. In

most cases yields are good to excellent, but, reactions are not as general as with the oxygen

heterocycles; the outcome of reactions is heavily dependent on the nature of the substituent

on the exocyclic nitrogen. Some of the products from these reactions find use as melt-castable

explosives i.e. Tris-X (46)^72 and energetic plasticizers e.g. Bu-NENA (48);^73 the latter is a

component of some LOVA (low vulnerability ammunition) propellant formulations.

9.10 SELECTIVEO-NITRATION

Chemists at DERA found that dinitrogen pentoxide in aprotic solvents, specifically chlorinated

hydrocarbons, can be used for the selectiveO-nitration of substrates containing other poten-

tially reactive functionality. This is only possible because such reagents are mild and nonacidic

nitrating agents. TheO-nitration of alcohols under these conditions is exceptionally fast and

is complete, in many cases, within a matter of seconds. Other reactions like the ring-opening

nitration of epoxides and oxetane heterocycles are much slower in comparison. This enables

the synthesis of a class of interesting compounds containing the energetic nitrate ester func-

tionality with a reactive strained ring heterocycle. Such compounds are precursors to energetic

polymers and binders.

The success of these selective nitrations relies on the application on recent nitration technol-

ogy – the use of flow reactors. The following is a discussion of some important work conducted

at DERA and illustrates the research and development transition from laboratory to pilot plant

scale synthesis of energetic materials.^19