Organic Chemistry of Explosives

Addition and condensation reactions 33

1.10 ADDITION AND CONDENSATION REACTIONS

Primary and secondary nitroalkanes, and substrates containing terminalgem-dinitroaliphatic

functionality, have one or more acidicα-protons, a consequence of inductive and resonance

effects imposed by the nitro group. As a result, such compounds can behave like carbanions and

participate in a number of addition and condensation reactions which are typical of substrates

like ketones, aldehydes, andβ-ketoesters. Such reactions are extremely useful for the syn-

thesis of functionalized polynitroaliphatic compounds which find potential use as explosives,

energetic oligomers and plasticizers.

Addition and condensation reactions employing nitroform or its methylol derivative, 2,2,2-

trinitroethanol, have been used to synthesize a huge number of compounds containing the

trinitromethyl group. Such compounds often have a very favourable oxygen balance which con-

tributes to explosive performance. However, compounds containing the trinitromethyl group

often exhibit an unacceptably high sensitivity to shock and impact. Kamlet^235 proposed that this

high sensitivity was due to the restricted rotation of the C–NO 2 groups. This theory proposes

that if rotation is restricted, energy normally dissipated through a combination of bond rotation

and bonded atom vibrational modes is more likely to result in bond breaking. In any energetic

material the sensitivity to impact is related to the weakest bond(s) in that molecule, and so, in

many energetic compounds, the trinitromethyl is the trigger for decomposition. It is not surpris-

ing that research in this area rapidly slumped after these findings. The chemistry and synthesis of

trinitromethyl containing compounds has been the subject of several excellent reviews.^9 ,^114 ,^115

2-Fluoro-2,2-dinitroethanol, the methylol derivative of fluorodinitromethane, has been used

extensively for the synthesis of fluorodinitromethyl compounds. The fluorine atom is similar

in size to that of a proton and so rotation in the fluorodinitromethyl group is much less hindered

compared to the trinitromethyl group. Consequently, these compounds are far less sensitive to

impact than trinitromethyl compounds but only slightly less energetic. The explosive perfor-

mance of fluorodinitromethyl compounds has been reviewed.^236

2-Fluoro-2,2-dinitroethanol is synthesized on a large scale^237 from nitroform in a reaction

involving fluorination^238 followed byin situreduction with alkaline hydrogen peroxide^239

in the presence of formaldehyde. The intermediate in this reaction, fluorotrinitromethane, is

also synthesized by treating tetranitromethane with potassium fluoride in DMF.^240 Fluorodini-

tromethane has been synthesized by treating 2,2-dinitro-1,3-propanediol with sodium hydrox-

ide followed by fluorination,^238 or from the direct fluorination of potassium dinitromethane.^233

The salts of fluorodinitromethane are dangerous, and so, itsin situformation in addition re-

actions is greatly preferred. Fluorodinitromethyl compounds have also been synthesized from

the fluorination ofgem-nitronitronate salts.239aThe synthesis of energetic fluorodinitromethyl

compounds has been reviewed.^37 ,^241 ,^242

1.10.1 1,2-Addition reactions

H 2 C CHOR + HC(NO 2 ) 3

OR

C

H

CH 3 C(NO 2 ) 3

113, R = Et, 68 %

114, R = iPr, 73 %

(^112) 115, R = THP, 81 %
dioxane
Figure 1.49
The 1,2-addition of nitroform across the double bonds of vinyl ethers has been used to syn-
thesize a large number ofα-trinitromethyl ethers; (113–115) have been synthesized from