Organic Chemistry of Explosives

Addition of nitric acid, nitrogen oxides 5

1,2-Dinitroethane and 1,2-dinitrocyclohexane can be formed in this way from the correspond-

ing alkenes in 42 % and 37 % yield respectively.36a

The addition of dinitrogen tetroxide across the double bonds of electron deficient fluorinated

alkenes is a particularly useful route tovic-dinitro compounds where yields are frequently

high;^8 ,^37 tetrafluoroethylene gives a 53 % yield of 1,2-dinitro-1,1,2,2-tetrafluoroethane.^38

6

7

N 2 O 4 , 85 °C

sealed tube

25 %

CH 3 CC

NO 2 NO 2

NO 2 NO 2

CH 3

H 3 C CH 3

O 2 NNO 2

Figure 1.5

The reaction ofα-nitroalkenes with nitrogen dioxide or its dimer, dinitrogen tetroxide, has

been used to synthesize polynitroalkanes. Thus, the reaction of dinitrogen tetroxide with 2,3-

dinitro-2-butene (6) and 3,4-dinitro-3-hexene is reported to yield 2,2,3,3-tetranitrobutane (7,

25 %) and 3,3,4,4-tetranitrohexane (32 %) respectively.^39

Additions of dinitrogen tetroxide across C–C double bonds are selective. Theβ-nitro-

nitrates formed from terminal alkenes have the nitro group situated on the carbon bearing

the most hydrogen and this is irrespective of neighbouring group polarity.^36 Altering reac-

tion conditions and stoichiometry enables the preferential formation ofβ-nitro-nitrates over

vic-dinitroalkanes, which, although inherently unstable, provide a synthetically useful route to

α-nitroalkenes via base-catalyzed elimination.^40 β-Nitro-nitrates are reduced to the nitroalkane

on treatment with sodium borohydride in ethanol.^41 β-Nitro-nitrates also undergo facile hydrol-

ysis to theβ-nitroalcohol, and conversion of the latter to the methanesulfonate^42 or acetate,^5

followed by reaction with triethylamine or potassium bicarbonate respectively, yields the

α-nitroalkene. The reaction of alkenes with dinitrogen tetroxide in the presence of iodine yields

β-nitroalkyl iodides, which on treatment with sodium acetate also yieldα-nitroalkenes. 1,4-

dinitro-2-butene has been prepared in this way from butadiene.^5 The synthesis ofα-nitroalkene

has been recently reviewed by Ono.^2

The reaction of alkenes with nitrogen oxides and other nitrating agents have been extensively

discussed by Olah,^3 Topchiev,^21 and in numerous reviews.^43

The reaction of alkynes with dinitrogen tetroxide is less synthetically useful as a route to

nitro compounds. The reaction of 3-hexyne with dinitrogen tetroxide yields a mixture of

cis- andtrans-3,4-dinitro-3-hexene (4.5 % and 13 % respectively), 4,4-dinitro-3-hexanone

(8 %), 3,4-hexanedione (16 %) and propanoic acid (6 %).^44 2-Butyne forms a mixture con-

taining bothcis- andtrans-2,3-dinitro-2-butene (7 % and 34 % respectively).^44

1.4.3 Dinitrogen pentoxide

Alkenes react with dinitrogen pentoxide in chlorinated solvents to give a mixture ofβ-nitro-

nitrate,vic-dinitro,vic-dinitrate ester and nitroalkene compounds.45a,bAt temperatures between

–30◦C and –10◦C theβ-nitro-nitrate is often the main product. Theβ-nitro-nitrates are in-

herently unstable and readily form the corresponding nitroalkenes.^40 Propylene reacts with

dinitrogen pentoxide in methylene chloride between –10◦C and 0◦C to form a mixture of

1-nitro-2-propanol nitrate (27 %) and isomeric nitropropenes (12 %). The same reaction with

cyclohexene is more complicated.45a