Organic Chemistry of Explosives

Oxidation and nitration of C N bonds 23

1.6.4 Oxidation of pseudonitroles

KOH (aq)

(CH 3 ) 2 CHNO 2 CH 3 C

CH 3

NO 2 K

(CH 3 ) 2 C

NO 2

NO

C NNC

H 3 C

H 3 C

CH 3

CH 3

O 2 N NO 2

O

O

76

78a 78b

1. KNO 2


2. H+

77

Figure 1.31

The tautomeric nitronic acids of secondary nitroalkanes or their nitronate salts react with

nitrous acid or alkali metal nitrites to yield pseudonitroles.^182 −^184 These pseudonitroles are

often isolated as their colourless dimers (78b) but are deep blue in monomeric form (78a).

Primary nitroalkanes also form pseudonitroles (80b) but these rapidly isomerise to the nitrolic

acid (80a).^182 ,^183 Reactions are commonly conducted by slowly acidifying a mixture containing

the nitronate salt and the metal nitrite, during which, the nitronic acid reacts with the nitrite

anion. These reactions, first discovered by Meyer,^182 have been used to prepare 2-nitroso-2-

nitropropane (78a) and acetonitrolic acid (80a) from 2-nitropropane (76) and nitroethane (22)

respectively.^182

CH 3 CH 2 NO 2

NaOH (aq)

22

80a 80b

1. NaNO 2


2. H+

NO

C

NO 2

CH 3 C CH 3 H

NO 2

NOH

CH 3 C

H

NO 2 Na

79

Figure 1.32

Pseudonitrole or nitrolic acid formation can be a side-reaction during the acidification of

nitronate salts, particularly if the acid addition is slow. This process has been studied, optimized,

and patented as a route to these compounds.^184

Nitrolic acids undergo oxidation–nitration on treatment with dinitrogen tetroxide to

the corresponding trinitromethyl compounds. Dinitroalkanes are obtained on oxidation of

pseudonitroles and nitrolic acids with reagents such as chromium trioxide in acetic acid,

dichromate, hydrogen peroxide, nitric acid, oxygen, and peroxyacids. Dinitrogen pentoxide

in chlorinated solvents has been used for the oxidation of pseudonitroles to internalgem-

dinitroalkanes.^185 The oxidation of acetonitrolic acid and 2-nitroso-2-nitropropane has been

used to synthesize 1,1-dinitroethane^186 and 2,2-dinitropropane^187 ,^188 respectively.

1.6.5 Oxidation of isocyanates

OCN O 2 N

81 69

O

(CH 3 ) 2 CO, H 2 O

85 %

NCO O NO 2

Figure 1.33

Dimethyldioxirane is a powerful oxidant prepared by reacting acetone with KHSO 5 ;^168 the lat-

ter is commercially available as a triple salt under the trade name ofoxone. 1,4-Dinitrocubane