Organic Chemistry of Explosives

46 Synthetic Routes to AliphaticC-Nitro

derivatives are much safer to store than the parent nitronate salts and are readily converted

back to the nitronate on treatment with base. Thus, treatment of the potassium salt of dini-

tromethane (18) with an excess of formaldehyde in the presence of acetic acid yields the

bis-methylol derivative, 2,2-dinitro-1,3-propanediol (19).^104 ,^106 Treatment of 2,2-dinitro-1,3-

propanediol (19) with one equivalent of potassium hydroxide leads to demethylolation and

yields the potassium salt of 2,2-dinitroethanol (20).^104 Further demethylolation of potassium

2,2-dinitroethanol (20) to potassium dinitromethane (18) is only affected with an excess of

base or with hot alkaline hydrogen peroxide solution.^104

The use of polynitroaliphatic alcohols as sources of the corresponding nitronate anions

is common in addition reactions. However, polynitroaliphatic alcohols are useful in their

own right. The hydroxy functionalities of 2,2-dinitroethanol, 2,2-dinitro-1,3-propanediol and

2,2-dinitropropanol^107 ,^306 are very versatile and have been extensively used for the synthesis

of energetic plasticizers, polymers, explosives and oxidizers in propellants (Section 1.11).

Diols obtained from the reactions of α,α,ω,ω-tetranitroalkanes with formaldehyde are

particularly useful for the synthesis of energetic polymers based on ester and carbamate

linkages.^108 ,^250 ,^259 ,^281 α, ω-Dinitroalkanes can react with either two or four equivalents of

formaldehyde to form diols or tetrols respectively; good yields can be obtained in both cases

by varying reaction conditions and the base used.^307

C

CH 2 ONO 2

O 2 N CH 2 ONO 2 O 2 N C

CH 2 ONO 2

166

CH 2 ONO 2

167

CH 3

CH 2 ONO 2

Figure 1.83

Henry reactions have been extensively exploited for the synthesis of nitrate ester explosives.

The condensation of nitroalkanes with aldehydes, followed by esterification of the hydroxy

groups with nitric acid, leads to a number of nitrate ester explosives (see Chapter 3). The

two examples given above (166 and 167) are synthesized from theO-nitration of the polyols

obtained from the condensation of formaldehyde with nitromethane^308 and nitroethane^309

respectively.

1.11 Derivatives of polynitroaliphatic alcohols

Polynitroaliphatic alcohols containing nitro groups on the carbonβto the hydroxy functionality

are less basic than their alkyl counterparts. This decreased basicity of the hydroxy group makes

reactions such as esterification, acetal formation and alkylation much slower than usual, and in

some cases, these reactions may not proceed without catalysts. To add to the problem, normal

base catalysts cannot be used in conjunction with 2,2-dinitroalkanols and 1,1,1-trinitro-2-

alkanols because of their facile dissociation in alkaline solution.

The weak nucleophilic nature of polynitroaliphatic alcohols means that reactions often need

to be catalyzed by Brønsted acids or Lewis acids. The following methods are commonly used

for the esterification of polynitroaliphatic alcohols: (1) heating a solution of the alcohol and acid

in the presence of sulfuric acid with Dean–Stark removal of water;^310 (2) using the acid chloride

or anhydride in the presence of aluminium chloride;^311 ,^312 (3) reacting the acid and alcohol