Nitrolysis of amides and their derivatives

Substrates containing A,A-disubstimted amide functionality (76) can undergo niholysis by two pathways leading to different products - a secondary nitramine (77) can be formed from 

The nitrolysis of A,A-disubstituted amides is one of the key tools for the synthesis of nitramine containing energetic materials. The present synthesis of the high performance explosive HMX is via the nitrolysis of hexamine (Section 5.15). This is an inefficient reaction requiring large amounts of expensive acetic anhydride. An alternative route to HMX (4) is via the nitrolysis of either l,3,5,7-tetraacetyl-l,3,5,7-tetraazacyclooctane (79) (79%) or 1,5-dinitro-3,7-diacetyl-l,3,5,7-tetraazacyclooctane (80) (98 %) with dinitrogen pentoxide in absolute nitric acid. These reactions are discussed in more detail in Section 5.15. 

Nitrolysis reactions employing l,3,5-trisubstituted-l,3,5-triazacyclohexanes have been explored as alternative routes to RDX. Some of the results are illustrated in Table 5.4 and show the difference in the efficiency of the three nitrolysis agents used, namely, absolute nitric acid, phosphorus pentoxide-nitric acid and trifluoroacetic anhydride-nitric acid. The acetamide derivative (81) (TRAT) undergoes incomplete nitrolysis on treatment with absolute nitric acid and trifluoroacetic anhydride-nitric acid to give a crude product containing some l-acetyl-3,5-dinitro-1,3,5-triazacyclohexane (TAX) (82) (Table 5.4, Entry 1) the latter can be preferentially formed in 93 % by suitably modifying the reaction conditions. Interestingly, the nitrolysis of 

The high performance nitramine explosive known as CL-20 (5) has been synthesized via a two-stage nitrolysis starting from the key intermediate (83). The first stage uses dinitrogen tetroxide or nitrosonium tetrafluoroborate for nitrosolysis. The second step, involving nitrolysis of the acetamide and nitrosamine bonds, is achieved with nitronium tetrafluoroborate ( 90 %) or mixed acid at 75 °C to 80 °C (93 %). The synthesis of CL-20 is discussed in more detail in Chapter 6. 

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). 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.  

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