Organic Chemistry of Explosives

Nitramine rearrangement 147

attempted isolation of numerous nitramines from the nitration of aromatic amines has led to the

isolation of the diazophenol as the sole product; the bis-nitramine (44) is found to decompose

spontaneously at 25◦C in the solid state and in solution to give the diazophenol (45).^142

NO 2 NO 2

NO 2 NO 2

NHNO 2

O 2 NHN

O

NO 2 O

NO 2

N 2

N 2

25 °C

44 45

Figure 4.19

Diazophenol formation is most competitive when a nitramine substrate contains an electron-

withdrawing nitro grouporthoto the nitro group being displaced and hencemetato the

nitramine functionality, assumedly because that site is then activated towards nucleophilic aro-

matic substitution.^144 Heating nitramines in inert chlorinated solvents also favours diazophenol

formation but this is suppressed by using urea or sulfamic acid as additives.

The course of a reaction involvingN-nitration of an aromatic amine is very dependent on

both the substrate and the reaction conditions, i.e. nitrating agent, temperature, work-up etc. The

nitration of 3-amino-2,5-dinitrotoluene with mixed acid in glacial acetic acid at 0◦C yields the

corresponding diazophenol with no trace of the intermediate nitramine.^145 In contrast, nitration

of the same substrate at ambient temperature with mixed acid composed of 90 % nitric acid

and 96 % sulfuric acid yields the corresponding nitramine.^145

CH 3

NO 2

NH 2

46

O 2 N

CH 3

CH 3

NHNO 2

47

NHNO 2

49

NO 2

NO 2

NO 2

O 2 N NO 2

O 2 N

O 2 N

CH 3

NH 2

50

NO 2

O 2 N NO 2

O 2 N

CH 3

N 2

48

O

O 2 N NO 2

HNO 3 , H 2 SO 4

in AcOH, 0 °C

78 %

HNO 3 ,

H 2 SO 4 , 20 °C

100 %

CH 2 Cl 2 , reflux

81 %

H 2 SO 4 , 0 °C

35 %

H 2 SO 4 , 20 °C

78 %

PhOMe,

Figure 4.20

In some cases the Bamberger rearrangement of an arylnitramine can be low yielding and

may not be the best route to a product. For example, 4-amino-2,3,5,6-tetranitrotoluene (50)

is prepared in low yield via the acid-catalyzed rearrangement of the nitramine (47), the latter

formed from the controlled nitration of 4-amino-2,6-dinitrotoluene (46) with mixed acid in

glacial acid or with nitronium tetrafluoroborate in methylene chloride.^145 Alternatively, the

same starting material, 4-amino-2,6-dinitrotoluene (46), can be fully nitrated to 4-amino-

N,2,3,5,6-pentanitrotoluene (49), again with mixed acid, and the nitramino group subsequently

cleaved with sulfuric acid in anisole.^145 This latter route provides the product, 4-amino-2,3,5,6-

tetranitrotoluene (50), in a significantly higher overall yield.