Organic Chemistry of Explosives

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

354 Dinitrogen Pentoxide – An Eco-Friendly Nitrating Agent

Nitrations with dinitrogen pentoxide in organic solvents are limited to activated and moder-

ately deactivated aromatic substrates. Solutions of dinitrogen pentoxide in acetonitrile convert

resorcinol to 2,4,6-trinitroresorcinol (styphnic acid) in quantitative yield;^24 the heavy metal

salts of the latter finding use in ignition and pyrotechnic delay compositions. Phenol is quanti-

tatively converted to 2,4,6-trinitrophenol (picric acid) with a solution of dinitrogen pentoxide

in carbon tetrachloride.^3 The same reagent can be used to convert benzene to nitrobenzene;

further reaction generates 1,3-dinitrobenzene but no 1,3,5-trinitrobenzene, even at tempera-

tures up to 76◦C.^33 The formation of by-products is not uncommon during slow nitrations, or

those conducted above room temperature, and may result from the decomposition of dinitrogen

pentoxide.^34

NOH

1

O 2 NNO 2

NO 2 NO 2

O 2 NNO 2

NO 2 NO 2

O 2 N NO 2

N 2 O 5 , CH 2 Cl 2

13 mins, 20 °C

98 %

2

Figure 9.5

The use of dinitrogen pentoxide in the Ponzio reaction for the oxidation–nitration of oximes

togem-dinitro groups has been reported by Russian chemists.^35 Millar and co-workers^36 exten-

sively investigated these reactions and reported the synthesis of 2,4,5,7,9,9-hexanitrofluorene

(2), a thermally stable explosive with an oxygen balance better than TNT. Other energetic mate-

rials containinggem-dinitro functionality were synthesized from the oximes of acetophenone,

4-nitroacetophenone,α-nitroacetophenone and 2-hydroxyacetophenone.

CH 3

NO 2

NO 2

3

CH 3

NO 2

NO 2

4

(TNT)

N 2 O 5 , HNO 3 O 2 N

32 °C, 100 %

Figure 9.6

Dinitrogen pentoxide in nitric acid is suitable for the synthesis of deactivated polyni-

troarylenes. This reagent has been used to convert 2,4-dinitrotoluene (3) to 2,4,6-trinitrotoluene

(TNT) (4) in quantitative yield at a temperature of only 32◦C.^37 The fast rate of nitrations com-

pared to those using conventional nitrating agents is notable. Moodie and co-workers^38 noted

that at high concentrations of dinitrogen pentoxide in nitric acid i.e. 2.5–5 mol/L, the rate of ni-

tration can increase some 15–30 times faster than nitrations at low concentrations of dinitrogen

pentoxide and those using mixed acid of similar concentration.

CH 2 CH 3 CH 2 CH 3

NO 2

NO 2

7

CH 2 CH 3

NO 2

6

N 2 O 5 , HNO 3

5 °C

N 2 O 5 , HNO 3

25 °C

5

Figure 9.7