Organic Chemistry of Explosives

100 Synthetic Routes to Nitrate Esters

3.4.1.2 Vicinal dinitrate esters from the reaction of epoxides with dinitrogen pentoxide

Millar and co-workers^75 found that treating epoxides with dinitrogen pentoxide in inert chlo-

rinated solvents between 0 and 20◦C leads to nitrative ring opening and the formation of

vic-dinitrate esters. These reactions are very chemically efficient, resulting in complete utiliza-

tion of nitrogen by incorporating the whole molecule of N 2 O 5 into the dinitrate ester product.

No nitric acid is formed and if conditions are kept anhydrous the process constitutes a nonacidic

nitrating method. Reactions are much less exothermic and easier to control compared to con-

ventional nitrations with mixed acid.

In many cases almost quantitative yields are reported for the formation ofvic-dinitrate esters

from the reaction of simple alkyl and dialkyl epoxides with dinitrogen pentoxide (Table 3.2).

Some of the products formed include: ethylene glycol dinitrate (2) (96 %), 1,2-propanediol

dinitrate (8) (96 %), 2,3-butanediol dinitrate (94 %) and 1,2-butanediol dinitrate (96 %). Reac-

tion times are of the order of 5–15 minutes.

Some functionalized epoxides react much slower with dinitrogen pentoxide, especially

substrates containing oxygen functionality near to the epoxide group. This effect is seen during

the reaction of glycidol with dinitrogen pentoxide, which undergoes rapidO-nitration to give

glycidyl nitrate, followed by a much slower reaction to open the epoxide ring. Slow epoxide

ring-opening allows polymer formation to compete withO-nitration. Consequently, Millar and

O

R R^2

1

CH 2 Cl 2 R

1 R^2

ONO 2

ONO 2

O

OH

O

O O

O

O

O

O 2 NO

O 2 NO

O 2 NO

O 2 NO

O 2 NO

O 2 NO

ONO 2

CH 3

ONO 2

ONO 2

ONO 2

ONO 2

ONO 2

ONO 2 ONO 2

ONO 2

ONO 2

ONO 2

Cl

O

Cl

O

H CH 3

O

HH

N 2 O 5

Table 3.2

Synthesis of vicinal dinitrate esters from the ring opening nitration of epoxides

with dinitrogen pentoxide (Ref. 75)

Mole ratio

N 2 O 5 : epoxide

Yield (%)

2

3

4

5

6

1.1 : 1.0

1.1 : 1.0

1.1 : 1.0

3.0 : 1.0a

3.0 : 1.0a

2.15 : 1.0

96

96

73

85

55

31

(2)

(8)

(35)

(1)

(9)

(38)

a1 mole equivalent of aluminium chloride added.

(30)

(33)

(34)

(18)

(36)

(37)

Entry

1

Epoxide Nitrate ester