Organic Chemistry of Explosives

216 Synthetic Routes toN-Nitro

The high performance nitramine explosive known as CL-20 (5) has been synthesized via a

two-stage nitrolysis starting from the key intermediate (83).^98 ,^99 The first stage uses dinitrogen

tetroxide or nitrosonium tetrafluoroborate for nitrosolysis.^98 The second step, involving ni-

trolysis of the acetamide and nitrosamine bonds, is achieved with nitronium tetrafluoroborate

(>90 %)^98 or mixed acid at 75◦Cto80◦C (93 %).^99 The synthesis of CL-20 is discussed in

more detail in Chapter 6.

NNNs

F 2 N NF 2

F 2 N NF 2

Ns

85

Ns = p-NO 2 C 6 H 4 SO 2

2 N NNO

F 2 N NF 2

F 2 N NF 2

NO 2

86

(HNFX)

HNO 3 , H 2 SO 4 , 70 °C

6 weeks, 16 %

or

HNO 3 , CF 3 SO 3 H, 55 °C

40 hours, 65 %

Figure 5.45

Inductive effects can have very pronounced effects on the reactivity of amides and similar

substrates towards nitrolysis. Chemists at the Naval Air Warfare Center (NAWC) have reported

an extreme case encountered during the synthesis of the energetic 1,5-diazocine known as

HNFX (86).^100 A key step in this synthesis involves a very difficult nitrolysis of the electron

deficient N-nosyl (4-nitrobenzenesulfonyl) bonds of (85). Nitrolysis with strong mixed acid

requires a temperature of 70◦C for 6 weeks to achieve a yield of 16 %. The same reaction with

nitric acid–triflic acid requires a temperature of 55◦C for 40 hours to achieve a 65 % yield of

HNFX. The same chemists reported a similar case of N-nosyl bond nitrolysis which needed a

nitrating agent composed of nitric acid–triflic acid–antimony pentafluoride.^101

5.6.1.2 Nitrolysis with nonacidic reagents

R^1 NR 2

O

+NO 2 BF 4 R 2 NNO 2 +R^1 CO BF 4 (Eq. 5.14)

Figure 5.46

Secondary nitramines are conveniently prepared from the nitrolysis ofN, N-dialkylamides with

nitronium salts in acetonitrile or ethyl acetate at 20◦C where the acyl group is converted into an

acylium tetrafluoroborate (Equation 5.14).^102 Problems can occur if commercial nitronium salts

like the tetrafluoroborate are used without purification. The presence of nitrosonium salts can

then lead to nitrosamines via nitrosolysis. Yields of secondary nitramine up to 90 % have been

reported^102 with solutions of nitronium tetrafluoroborate in acetonitrile; di-n-butylnitramine is

obtained in 82 % yield from the nitrolysis of corresponding acetamide.^46

NN

CH 3 OC COCH 3 NO 2 BF 4 COCH 3

87

NN

O 2 NNO 2

88

NN

O 2 N

89

+

Figure 5.47