Organic Chemistry of Explosives

Nitration of compounds containing acidic hydrogen 27

ferricyanide oxidant in the presence of sodium nitrite. The process was later optimized and

its scope expanded by Kornblum and co-workers.^202 In a further modification to this proce-

dure Grakauskas and co-workers^203 showed that a catalytic amount of ferricyanide can be

used in conjunction with a stoichiometric amount of persulfate anion as co-oxidant. These

modifications often lead to improved yields compared to the original method. The inexpensive

reagents used in these reactions, and the high yields frequently obtained, makes this method a

very valuable route togem-dinitroaliphatic compounds. The importance of oxidative nitration

as a route togem-dinitroaliphatic compounds is reflected in its widespread use for the synthesis

of numerous energetic compounds, like those illustrated in Table 1.9. Oxidative nitration has

been used in the reported^204 synthesis of a powerful melt-castable explosive, TNAZ (89).

N

H NO 2

N

O 2 N NO 2

N

O 2 N NO 2

tBu tBu NO 2

87 88

or

K 3 Fe(CN) 6 ,

Na 2 S 2 O 8 , NaNO 2

60 %

NaNO 2 , AgNO 3

39 %

89

(TNAZ)

nitrolysis

(see Chapters 5/6)

Figure 1.37

1.8 Nitration of compounds containing acidic hydrogen

1.8.1 Alkaline nitration

The alkaline nitration of compounds containing acidic hydrogen is a valuable route to aliphatic

nitro compounds. In these reactions a base is used to remove an acidic proton from the substrate,

which is then treated with a source of –NO 2. Substrates used in these reactions usually have

an electron-withdrawing or resonance-stabilizing group positionedαto a proton(s), and these

include: aliphatic and alicyclic ketones, nitriles, carboxylic acid esters, sulfonate esters,N,N-

dialkylamides etc. Proton removal from these substrates may be reversible or irreversible

depending on the pKaof the base compared to the acidity of the substrates proton(s). Bases

used for these reactions include: alkali metal alkoxides, sodium hydride, alkali metal amides,

lithium bases etc. The nitrating agents range from alkyl nitrate esters to nitrogen oxides.

1.8.1.1 Alkaline nitration with nitrate esters

Alkaline nitration with alkoxide bases and nitrate esters was first explored by Endres and

Wislicenus^205 who synthesized phenylnitromethane by treating ethyl phenylacetate with potas-

sium ethoxide in ethanol, followed by addition of ethyl nitrate and hydrolysis–decarboxylation

of the resultingα-nitroester with aqueous acid. Phenylnitromethane is synthesized in a similar

way via alkaline nitration of benzyl cyanide, followed by treatment of the resultingα-nitronitrile

with aqueous base.^206 Wieland and co-workers^207 used alkali metal alkoxides and nitrate esters

for the nitration of cyclic ketones but the yields and purity of product are often poor.^208