Organic Chemistry of Explosives

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O-Nitration 359

methylenediamines has been reported^59 with dinitrogen pentoxide in methylene chloride–

acetonitrile, although yields are generally low.

R'

N

R

Si

R''

R''

R''

R'

N

R

NO 2 + R'' 3 SiONO 2

N 2 O 5 , CH 2 Cl 2

33 34

R, R', R'' = alkyl

Figure 9.16

Millar and Philbin^60 reported using dinitrogen pentoxide in methylene chloride at subambi-

ent temperatures for the nitrodesilylation of silylamines (33) and silylamides. The methodology,

which results in nitramines (34), nitramides and nitroureas in excellent yields, is well suited

for the synthesis of energetic materials and we believe it will find wide use in the future.

9.8 O-nitration

Solutions of dinitrogen pentoxide in anhydrous nitric acid are unlikely to find wide use for the

industrial synthesis of nitrate esters – synthesis from the parent alcohol is relatively straight-

forward and so this reagent, which is more expensive than mixed acid, holds few advantages.

In contrast, theO-nitration of alcohols and polyols with a solution of dinitrogen pentoxide

in chlorinated solvent has many advantages over conventional nitrating agents.^3 ,^61 It is par-

ticularly useful for easily oxidized substrates and cases where the nitrate ester shows some

solubility in mixed acid or water e.g. ethylene glycol dinitrate (0.5 g/100 ml of water). Aqueous

liquors from such processes are hazardous and need treatment before disposal or acid recovery.

O-Nitration with dinitrogen pentoxide enables the isolation of the nitrate ester as a solution in

an organic solvent and, hence, greatly reduces the risk of accidental explosion.O-Nitrations

with dinitrogen pentoxide in chlorinated solvents are much less exothermic and more con-

trollable that those with mixed acid. Reactions are also very rapid and many are complete in

seconds. Polyols which are only sparingly soluble in the reaction solvent are readily converted

to the corresponding nitrate ester; mannitol (35) is converted to mannitol hexanitrate (36) in

near quantitative yield.^62

HO

OH

OH

OH

OH

OH

O 2 NO

ONO 2

ONO 2

ONO 2

ONO 2

ONO 2

N 2 O 5 , CCl 4

0 °C, 98–100 %

(^3536)
Figure 9.17
Nitric acid is formed during these reactions and in some cases the addition of sodium fluoride
as a base can be advantageous.^63 This is the case with higher carbohydrates like cellulose and
starch.^63 ,^64