Organic Chemistry of Explosives

Addition and condensation reactions 35

HC COEt

NO 2

NO 2

119

Hg(OAc) 2

H 3 C OEt

OCH 2 CF(NO 2 ) 2

OCH 2 CF(NO 2 ) 2

126

125 CH 2 Cl 2 , 95 %

+ 2 F CCH 2 OH C

Figure 1.53

The acetylenic bond of propargyl ethers can react with polynitroaliphatic alcohols, as in the

case of ethoxyacetylene (125), which reacts with two equivalents of 2-fluoro-2,2-dinitroethanol

(119) to give the orthoester (126).^248

1.10.2 1,4-Addition reactions

1.10.2.1 Michael reaction

Conjugate 1,4-addition of a nucleophile to the double bond of an electron deficientα,β-

unsaturated compound is known as the Michael reaction and ranks as one of the most important

carbon–carbon bond forming reactions in synthetic organic chemistry. The species undergoing

addition to the double bond is known as a Michael donor and includes substrates which are

capable of forming carbanions i.e. those with acidic protons. Nitroalkanes are good Michael

donors and literature examples of their use in the synthesis of functionalized polynitroaliphatic

compounds are extensive.^249 −^262 These include nitronate anions generated from nitroform,

fluorodinitromethane, primary nitroalkanes, secondary nitroalkanes and compounds containing

terminalgem-dinitroaliphatic functionality. The electron deficient alkene in these reactions is

known as the Michael acceptor and includesα,β-unsaturated ketones, aldehydes, carboxylic

acids, esters, amides, cyanides etc. Nitroalkenes are excellent Michael acceptors and important

from the view of energetic materials synthesis and so these reactions are discussed separately

in Section 1.10.2.2.

Michael reactions are base catalyzed and reversible, and so it is common to use either

the nitronate salt of the nitroalkane substrate or the nitroalkane in the presence of a catalytic

amount of alkali metal hydroxide, alkoxide or amine base.

O O

(O 2 N) 3 C C(NO 2 ) 3

OO H+, H 2 O

MeOH (aq)

70 %

HC(NO 2 ) 3

Figure 1.54

The product of a Michael addition depends on the number of acidic protons present in

the nitroalkane substrate. Nitroform, which has one acidic proton, can only react with one

equivalent of Michael acceptor.^252 −^258 Nitroform is a strong acid and sufficiently dissociated

in solution so that it can be used in addition reactions without a base catalyst. The reaction of

nitroform with unsaturated ketones has been investigated by Gilligan and Graff^256 and used to

synthesize a number of trinitromethyl-based explosives.

Frankel^258 reported the reaction of nitroform with acrylic acid and its esters. Methyl 4,4,4-

trinitrobutyrate (127), the product obtained from nitroform and methyl acrylate, has been used