Organic Chemistry of Explosives

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JWBK121-09 October 11, 2006 21:24 Char Count= 0

362 Dinitrogen Pentoxide – An Eco-Friendly Nitrating Agent

9.10.1 Glycidyl nitrate and NIMMO – batch reactor verses flow reactor^19

O

H 3 C CH 2 ONO 2

ONO 2

O

OH

O

O

3 C CH 2 OHH

49

(GLYN)

50

(NIMMO)

37

41

(HMMO)

N 2 O 5 , CH 2 Cl 2

N 2 O 5 , CH 2 Cl 2

15–19 °C, 92.0–99.8 %

0.85–40.5 mole scale

12–23 °C, 96.3–99.8 %

0.95–43.2 mole scale

purity: 99.5–99.9 %

purity: 99.5–99.9 %

Figure 9.22

The potential of dinitrogen pentoxide for selective nitration is illustrated during the semi-

industrial synthesis of glycidyl nitrate (GLYN) (49) from glycidol (37) and 3-nitratomethyl-

3-methyloxetane (NIMMO) (50) from 3-hydroxymethyl-3-methyloxetane (HMMO) (41).

Glycidyl nitrate (49) and NIMMO (50) are precursors to the energetic plasticizers and binders

known as poly[GLYN] and poly[NIMMO].

The nitrations of glycidol (37) and HMMO (41) have been conducted in flow reactors. The

flow reactor consists of two reservoirs filled with the reactant and a solution of dinitrogen

pentoxide in methylene chloride, respectively. These can be pumped at specific rates into the

flow reactor – a packed column of glass beads surrounded by a cooling jacket and fitted with

a temperature probe. The reactants are continuously fed through the packed column where

they mix and react. The product stream is mixed with a continuous stream of aqueous alkali

solution and run into a stirred vessel to neutralize excess dinitrogen pentoxide and nitric acid

formed in the reaction. The product remains in the methylene chloride layer and is separated

from the aqueous phase in a continuous separator. This is a continuous process but at any one

time only a relatively small amount of reacting species and product are present in the reactor.

This is clearly a very attractive manufacturing route for energetic materials because of the

reduced hazards compared to batch reactors where all the materials are present in one pot

until the completion of the reaction. This has other advantages relating to safety – exothermic

reactions are easier to control because of the low reaction volume and reactions can be stopped

immediately by ceasing to pump reactants from the reservoir.

Flow reactors are ideal for the synthesis of large amounts of material where the primary

reaction is very fast and the secondary competing reaction is relatively slow. TheO-nitration of

glycidol (37) and HMMO (41) are therefore ideal reactions. Both of these compounds contain

two potential reaction centres – the hydroxy groups and the strained heterocyclic rings. Initial

O-nitration of these substrates is known to be extremely fast. The competing ring cleavage is

suppressed in the flow reactor by immediately quenching the reaction stream as it leaves the

reactor.

Reaction optimization was achieved by varying flow rate, concentration and the reaction

exotherm temperature. In this way glycidol nitration reactions were scaled-up from 0.85 moles

up to 40.5 moles. In a single run 4.64 kg of glycidyl nitrate (99.8 % yield) of 99.9 % purity

was produced. Similar optimization for HMMO nitration produced 5.5 kg of NIMMO (99.1 %

yield) of 99.6 % purity in a single run.