Organic Chemistry of Explosives

Additions to alkenes 105

3.6.2 Nitrogen oxides

N 2 O 4 , O 2

51

+ +

R

R

R

R

C

R

R

R

R

O 2 N

Et 2 O, 0 °C

C NO 2

52

C

R

R

R

R

O 2 N C ONO 2

53

C

R

R

R

R

O 2 N C ONO

Figure 3.30

Alkenes react with dinitrogen tetroxide in ether at 0◦C in the presence of oxygen to form

a mixture ofvic-dinitroalkane (51),β-nitro-nitrate (52) andβ-nitro-nitrite (53) compounds,

the nitrite being oxidized to the nitrate ester in the presence of excess dinitrogen tetroxide.^96

A stream of oxygen gas is normally bubbled through the reaction mixture to expel nitrous

oxide formed during the reaction. Nitrous oxide can add to alkenes to form nitroso compounds

and so its presence can lead to even more complex mixtures being formed.β-Nitroso-nitrates

have been observed in some cases.^97 Detailed discussions of these reactions have been given

by Olah4d, Topchiev^23 , and in numerous reviews^98 and mechanistic studies.^99 Additions of

dinitrogen tetroxide across C–C double bonds are selective – theβ-nitro-nitrate formed has

the nitrate ester group situated on the carbon bearing the least hydrogens i.e. the most substituted

carbon.^96 In general, difficulties in separation of such mixtures limit their synthetic value in

relation to nitrate ester synthesis. However, such reactions have found preparative value for

the synthesis of some dinitroalkanes^100 and nitroalkenes^101 (Section 1.4).

Alkenes react with dinitrogen pentoxide in chlorinated solvents at 0–25◦C to give a mix-

ture ofvic-dinitrate ester,vic-dinitroalkane andβ-nitro-nitrate ester compounds.^102 Propylene

reacts with dinitrogen pentoxide in the gas phase to give 1,2-propanediol dinitrate as one of

the products.^103 Dinitrate ester products are also observed during the reactions of ethylene and

cis-2-butene with dinitrogen pentoxide.^104 The same reactions at lower temperatures (−10 to

− 30 ◦C) produce the expected product of N 2 O 5 addition, theβ-nitro-nitrate ester, as the main

product, along with some nitroalkene from elimination of nitric acid from the latter.^105 The

reaction of hydroxy-terminated polybutadiene (HTPB) with dinitrogen pentoxide in methylene

chloride yields an energetic oligomer containingβ-nitro-nitrate ester functionality.^76 The in-

herent instability ofβ-nitro-nitrate esters limits their use for practical application as energetic

materials.

NF 2

F 2 N F 2 N

F 2 N

NF 2

ONO 2

ONO 2 ONO 2

ONO 2

ONO 2

ONO 2

F 2 NCH 2 CH CHCH 2 NF 2

54

55

N 2 O 5 , CHCl 3

-60 °C to -10 °C

30 %

56 57

Figure 3.31