Organic Chemistry of Explosives

Other methods 233

Davis studied the dehydration of urea nitrates as a route toN-nitroureas.^144 The nitrate

salt ofN-methylurea undergoes dehydration–rearrangement on treatment with concentrated

sulfuric acid to giveN-nitro-N-methylurea in 42 % yield. In this compound the nitro and

methyl groups are attached to the same nitrogen and so its hydrolysis can provide a route to

methylnitramine. In contrast, the nitrate salts of ethyl,n-propyl,n-butyl andn-amyl ureas, give

N-nitro-N′-ethylurea (49 %),N-nitro-N′-propylurea (60 %),N-nitro-N′-butylurea (67 %) and

N-nitro-N′-amylurea (67 %), respectively, on treatment with concentrated sulfuric acid.

178 179

or

Ac 2 O, 100 °C

H 2 SO 4 , - 5 °C

. 2 HNO 3

H

N

N

H

NHNO 2

H

N

N

H

NH 2

O 2 NHN

O

O

H 2 N

O

O

Figure 5.74

Bachman and co-workers^70 reported the synthesis of 3,3′-dinitro-1,1′-ethylenebisurea (179)

by treating the dinitrate salt of ethylenebisurea (178) with cold concentrated sulfuric acid or

by heating with acetic anhydride.

O

H 2 N NH 2. HNO 3 H 2 N NHNO 2

O

180 12

0 °C, 70–87 %

H 2 SO 4

Figure 5.75

H 2 NH 2 N

NH N

NO 2

H 2 SO 4 , 0 °C

181 15

NH2. HNO 3 73–75 % NH 2

Figure 5.76

A standard method for the synthesis of nitrourea (12) involves treating urea nitrate (180)

with 90 % sulfuric acid.^145 On a laboratory and industrial scale, nitroguanidine (15) is con-

veniently prepared from the dehydration–rearrangement of guanidine nitrate (181), a process

accomplished by stirring the latter as a suspension in concentrated sulfuric acid at subambient

temperature; note that nitroguanidine is actually a nitrimine and not a monobasic acid like

nitrourea.^146 The guanidine nitrate used for this synthesis is conveniently prepared on a lab-

oratory scale by fusing a mixture of dicyandiamide with two mole equivalents of ammonium

nitrate at 160◦C for 2 hours.^147 However, this preparation of guanidine nitrate has quite rightly

aroused concern due to the potentially explosive nature of this mixture.

5.12 Other methods

The oxidation of aryl diazoates with oxidants like hypochlorite, permanganate and ferri-

cyanide anion has seen some limited use for the synthesis of nitramines.^148 This method

finds use for the synthesis of arylnitramines where aromatic ring nitration is not required

and so excludes the use of standard nitrating agents.