Organic Chemistry of Explosives

12 Synthetic Routes to AliphaticC-Nitro

in aqueous potassium carbonate forms the potassium salt of 1,1-dinitroethane (24), which on

acidification, followed byin situreaction with formaldehyde, yields 2,2-dinitropropanol (25).

Note, while dinitromethane is unstable at room temperature other terminalgem-dinitroalkanes,

like 1,1-dinitroethane (26) and 1,1-dinitropropane, are perfectly stable.

O 2 NCH 2 CH 2 CH 2 CH 2 NO 2

27

Br(NO 2 )CHCH 2 CH 2 CH(NO 2 )Br

28

(NO 2 ) 2 CHCH 2 CH 2 CH(NO 2 ) 2

30

CCH 2 CH 2 C

NO 2

2 N NO 2 KKO

O 2 N

1. NaOMe,
   MeOH, Et 2 O
   2. Br 2
   96 % (2 steps)

KOH, KNO 2

HCl, Et 2 O

28 % (2 steps)

29

Figure 1.12

The Ter Meer reaction has been used to synthesizeα,α,ω,ω-tetranitroalkanes from the corre-

spondingα,ω-dihalo-α,ω-dinitroalkanes.^108 Thus, treatment of 1,4-dibromo-1,4-dinitrobutane

(28) under the Ter Meer conditions yields the dinitronate salt of 1,1,4,4-tetranitrobutane (29);

acidification of the latter yields 1,1,4,4-tetranitrobutane (30).^108

The Ter Meer reaction has not been widely exploited for the synthesis ofgem-dinitroaliphatic

compounds. This is partly because the Kaplan–Shechter oxidative nitration (Section 1.7) is

more convenient, but also because of some more serious limitations. The first is the inabil-

ity to synthesize internalgem-dinitroaliphatic compounds; functionality which shows high

chemical stability and is found in many cyclic and caged energetic materials. Secondly, the

gem-nitronitronate salts formed in the Ter Meer reactions often need to be isolated to improve

the yield and purity of the product. Drygem-nitronitronate salts are hazardous to handle and

those from nitroalkanes like 1,1,4,4-tetranitrobutane are primary explosives which can explode

even when wet. Even so, it is common to use conditions that lead to the precipitation ofgem-

nitronitronate salts from solution, a process that both drives the reaction to completion and

also provides isolation and purification of the product salt by simple filtration. Purification

ofgem-nitronitronate salts by filtration from the reaction liquors, followed by washing with

methanol or ethanol to remove occluded impurities, has been used, although these salts should

never be allowed to completely dry.

The choice of base used in the Ter Meer reaction is important for two reasons. First,

studies have found that strong bases, such as alkali metal hydroxides, inhibit the reaction

and promote side-reactions, whereas the weaker alkali metal carbonates generally give higher

yields.^107 Secondly, if thegem-nitronitronate salt needs to be purified by filtration it should be

sparingly soluble in the reaction solvent and both the reaction solvent and the counterion of

thegem-nitronitronate salt affect this solubility.^107 Use of the potassium salt is advantageous

for aqueous systems where thegem-nitronitronate salts are usually only sparingly soluble,

whereas the sodium salt can be used for nonaqueous reactions.^107

It must be emphasized thatgem-nitronitronate salts should never be stored on safety grounds.

These salts readily react with formaldehyde to give the methylol derivatives which are more

stable and less hazardous to handle. The latter are often used directly in condensation reactions

where treatment with aqueous base forms thegem-nitronitronate saltin situ.