52 Synthetic Routes to AliphaticC-Nitro
Table 1.11 Reactions of nitroalkanes and polynitroalkanes with mineral acid
Nitroalkane Hydrolysis product
RCH 2 NO 2 RCOOH
R^1 R^2 CHNO 2 No reaction
R^1 R^2 C NO 2 HR^1 R^2 C O
R^1 R^2 C(NO 2 ) 2 No reaction
RCH(NO 2 ) 2 RCOOH
R^1 R^2 CHC(NO 2 ) 3 , C-H not activated No reaction
R^1 R^2 CHC(NO 2 ) 3 , C-H activated R^1 R^2 C O
Source:Reprinted with permission from J. C. Dacons, M. J. Kamlet and L. A. Kaplan,J. Org. Chem.,
1961, 26 , 4371; Copyright 1961 American Chemical Society.
1.13.1 Reactions with mineral acids
Polynitroalkanes are generally stable to mineral acids, although hydrolysis can occur with
prolonged heating, depending on the arrangement of the nitro groups within the compound. On
treatment with mineral acid primary aliphatic nitro groups are hydrolyzed to the corresponding
carboxylic acid via an intermediate hydroxamic acid, whereas secondary nitro groups are
unaffected.^352 The presence of an acidic proton in relation to compound stability is illustrated
by the inertness of the internalgem-dinitroaliphatic group towards hot mineral acids, whereas a
terminalgem-dinitroaliphatic group is converted to the corresponding carboxylic acid.^352 The
same resistance to mineral acid hydrolysis is shown by tertiary nitroalkanes. Trinitromethyl
groups are also stable to acid hydrolysis with the exception that an electron-withdrawing group
or resonance-stabilizing group is not present on theβ-carbon atom. In such cases an acidic
protonβto the trinitromethyl group allows acid hydrolysis to lead to the formation of a carbonyl
group with the degradation of one carbon atom from the compounds skeleton. A summary of
the reactions of nitroalkanes and polynitroalkanes with mineral acid is given in Table 1.11.^352
Acidification of the nitronate salts of polynitroalkanes can be complicated by the fact that
some polynitroaliphatic compounds are unstable, as in the case of dinitromethane and 1,1,2,2-
tetranitroethane, where both decompose readily at ambient temperature. The nitronate salts of
both primary and secondary aliphatic nitro groups are decomposed to carbonyl compounds
on acidification with mineral acid, a synthetic process known as the Nef reaction.^353 gem-
Nitronitronate salts form thegem-dinitroaliphatic compound on acidification with mineral acid.
1.13.2 Reactions with base and nucleophiles
Both primary and secondary aliphatic nitro groups form nitronate salts on reaction with base.
Terminalgem-dinitroaliphatic groups form the corresponding nitronitronate salts. Internal
gem-dinitroaliphatic groups lack an acidic proton and cannot form nitronate salts. The nitro
groups in compounds containing trinitromethyl groups are especially electron deficient and
susceptible to attack by both bases and nucleophiles. The reaction of trinitromethyl compounds
with base generates the correspondinggem-nitronitronate salt.
The effect of having multiple, powerful electron-withdrawing groups on the same carbon
is seen in the extreme case of tetranitromethane with its readiness to lose a nitro group on