Organic Chemistry of Explosives

148 Synthetic Routes to AromaticC-Nitro Compounds

4.6 Reaction of diazonium salts with nitrite anion

Sandmeyer-type reactions are a useful route to polynitroarylenes with unusual substitution

patterns. In these reactions an arylamine is treated with a source of nitrous acid to form an

intermediate diazonium salt which is readily displaced on reaction with a suitable nucleophile.

Many substituents can be incorporated into the aromatic ring via this method, including the

nitro group.

NH 2

H 2 N

NO 2

O 2 N

51 52

1. H 2 SO 4 ,
   AcOH,


2. CuSO 3 /Cu 2 SO 3 ,

S

O

O

HO ONO

NaNO 2 (aq)

43 %

Figure 4.21

A number of different experimental procedures have been used to effect the conversion of a

diazonium group to a nitro group. The most common of these treats the preformed diazonium

salt with a cupric/cuprous sulfite catalyst in the presence of sodium nitrite; copper bronze or

precipitated copper has also been used. These reactions only occur in neutral or basic solution.

This can be achieved by first isolating the diazonium salt as the sulfate,^62 tetrafluoroborate,^146

or cobaltinitrite,^63 and washing the solid salt free from acid, or alternatively, adding calcium

carbonate^64 or sodium hydrogen carbonate^65 to the reaction mixture to neutralize excess acid

present. Chatt and Wynne^66 synthesized 2,6-dinitronaphthalene (52) by adding solid nitrosyl-

sulfuric acid to a solution of 2,6-diaminonaphthalene (51) in sulfuric and acetic acids, followed

by isolation of the intermediate diazonium salt as its solid sulfate salt and treatment with sodium

nitrite in the presence of copper sulfite. The isolation of diazonium salts, especially those con-

taining two or more nitro groups, must be considered hazardous and confined to a small scale.

Experimentally, the most convenient method adds a solution of the diazonium sulfate to an

aqueous solution of sodium hydrogen carbonate and excess sodium nitrite in the presence of a

copper catalyst.^65 This method is only useful on a laboratory scale because of the large excess

of reagents needed. It is not uncommon in these reactions to use up to 6000 mole % excess of

sodium nitrite and up to 400 mole % excess of the copper salt.^72

NH 2 NO 2

NO 2

NO 2 NO 2

O 2 N NO 2 O 2 N

53 54

1. NaNO 2 , dil. HNO 3


2. CuSO 3 /Cu 2 SO 3 ,
   NaNO 2 (aq)
   69 % (2 steps)

Figure 4.22

Nitration via diazotisation has been extensively used for the synthesis of isomeric

dinitronaphthalenes.^61 –^66 Ward and co-workers^62 used nitration via diazotisation to prepare

3,3′,4,4′-tetranitrobiphenyl from 3,3′-dinitrobenzidine, and 3,4,5-trinitrotoluene from 3,5-

dinitro-4-toluidine. Ward and Hardy^147 prepared 1,4,6-trinitronaphthalene from 4,7-dinitro-

1-naphthylamine. K ̈orner and Contardi used the nitrate salts of aryldiazonium compounds

for the synthesis of polynitro derivatives of benzene^148 and toluene.^149 –^151 Accordingly,